X-Git-Url: http://repo.macrolet.net/gitweb/?a=blobdiff_plain;f=src%2Fcode%2Ftarget-hash-table.lisp;h=ba5f7d88e06336e2cccbc661d1a601b5d881d48d;hb=82cd148d729c241e79c8df04b700beec1b7c55de;hp=c28e640a305ed8220cf8665f39da84c1875babe1;hpb=084168e1524a6493bc0f9d1697753d31239b158d;p=sbcl.git

diff --git a/src/code/target-hash-table.lisp b/src/code/target-hash-table.lisp
index c28e640..ba5f7d8 100644
--- a/src/code/target-hash-table.lisp
+++ b/src/code/target-hash-table.lisp
@@ -14,32 +14,82 @@
 
 ;;;; utilities
 
-(eval-when (:compile-toplevel :load-toplevel :execute)
-  (defconstant max-hash sb!xc:most-positive-fixnum))
-
-(deftype hash ()
-  `(integer 0 ,max-hash))
-
-;;; FIXME: Does this always make a nonnegative FIXNUM? If so, then
-;;; explain why. If not (or if the reason it always makes a
-;;; nonnegative FIXNUM is only the accident that pointers in supported
-;;; architectures happen to be in the lower half of the address
-;;; space), then fix it.
-#!-sb-fluid (declaim (inline pointer-hash))
-(defun pointer-hash (key)
-  (declare (values hash))
-  (truly-the hash (%primitive sb!c:make-fixnum key)))
+;;; Code for detecting concurrent accesses to the same table from
+;;; multiple threads. Only compiled in when the :SB-HASH-TABLE-DEBUG
+;;; feature is enabled. The main reason for the existence of this code
+;;; is to detect thread-unsafe uses of hash-tables in sbcl itself,
+;;; where debugging anythign can be impossible after an important
+;;; internal hash-table has been corrupted. It's plausible that this
+;;; could be useful for some user code too, but the runtime cost is
+;;; really too high to enable it by default.
+(defmacro with-concurrent-access-check (hash-table operation &body body)
+  (declare (ignorable hash-table operation)
+           (type (member :read :write) operation))
+  #!-sb-hash-table-debug
+  `(progn ,@body)
+  #!+sb-hash-table-debug
+  (let ((thread-slot-accessor (if (eq operation :read)
+                                  'hash-table-reading-thread
+                                  'hash-table-writing-thread)))
+    (once-only ((hash-table hash-table))
+      `(progn
+         (flet ((body-fun ()
+                  ,@body)
+                (error-fun ()
+                  ;; Don't signal more errors for this table.
+                  (setf (hash-table-signal-concurrent-access ,hash-table) nil)
+                  (cerror "Ignore the concurrent access"
+                          "Concurrent access to ~A" ,hash-table)))
+           (declare (inline body-fun))
+           (if (hash-table-signal-concurrent-access ,hash-table)
+               (unwind-protect
+                    (progn
+                      (unless (and (null (hash-table-writing-thread
+                                          ,hash-table))
+                                   ,@(when (eq operation :write)
+                                           `((null (hash-table-reading-thread
+                                                    ,hash-table)))))
+                        (error-fun))
+                      (setf (,thread-slot-accessor ,hash-table)
+                            sb!thread::*current-thread*)
+                      (body-fun))
+                 (unless (and ,@(when (eq operation :read)
+                                  `((null (hash-table-writing-thread
+                                           ,hash-table))))
+                              ,@(when (eq operation :write)
+                                  ;; no readers are allowed while writing
+                                  `((null (hash-table-reading-thread
+                                           ,hash-table))
+                                    (eq (hash-table-writing-thread
+                                         ,hash-table)
+                                        sb!thread::*current-thread*))))
+                   (error-fun))
+                 (when (eq (,thread-slot-accessor ,hash-table)
+                           sb!thread::*current-thread*)
+                   ;; this is not 100% correct here and may hide
+                   ;; concurrent access in rare circumstances.
+                   (setf (,thread-slot-accessor ,hash-table) nil)))
+               (body-fun)))))))
 
 #!-sb-fluid (declaim (inline eq-hash))
 (defun eq-hash (key)
   (declare (values hash (member t nil)))
   (values (pointer-hash key)
-	  (oddp (get-lisp-obj-address key))))
+          (oddp (get-lisp-obj-address key))))
 
 #!-sb-fluid (declaim (inline equal-hash))
 (defun equal-hash (key)
   (declare (values hash (member t nil)))
-  (values (sxhash key) nil))
+  (typecase key
+    ;; For some types the definition of EQUAL implies a special hash
+    ((or string cons number bit-vector pathname)
+     (values (sxhash key) nil))
+    ;; Otherwise use an EQ hash, rather than SXHASH, since the values
+    ;; of SXHASH will be extremely badly distributed due to the
+    ;; requirements of the spec fitting badly with our implementation
+    ;; strategy.
+    (t
+     (eq-hash key))))
 
 #!-sb-fluid (declaim (inline eql-hash))
 (defun eql-hash (key)
@@ -50,102 +100,255 @@
 
 (defun equalp-hash (key)
   (declare (values hash (member t nil)))
-  (values (psxhash key) nil))
+  (typecase key
+    ;; Types requiring special treatment. Note that PATHNAME and
+    ;; HASH-TABLE are caught by the STRUCTURE-OBJECT test.
+    ((or array cons number character structure-object)
+     (values (psxhash key) nil))
+    (t
+     (eq-hash key))))
+
+(declaim (inline index-for-hashing))
+(defun index-for-hashing (hash length)
+  (declare (type hash hash length))
+  ;; We're using power of two tables which obviously are very
+  ;; sensitive to the exact values of the low bits in the hash
+  ;; value. Do a little shuffling of the value to mix the high bits in
+  ;; there too.
+  (truly-the index
+             (logand (1- length)
+                     (+ (logxor #b11100101010001011010100111
+                                hash)
+                        (ash hash -3)
+                        (ash hash -12)
+                        (ash hash -20)))))
 
-(defun almost-primify (num)
-  (declare (type index num))
-  #!+sb-doc
-  "Return an almost prime number greater than or equal to NUM."
-  (if (= (rem num 2) 0)
-      (setq num (+ 1 num)))
-  (if (= (rem num 3) 0)
-      (setq num (+ 2 num)))
-  (if (= (rem num 7) 0)
-      (setq num (+ 4 num)))
-  num)
 
 ;;;; user-defined hash table tests
 
-(defvar *hash-table-tests* nil)
+(defvar *user-hash-table-tests* nil)
 
-(defun define-hash-table-test (name test-fun hash-fun)
-  #!+sb-doc
-  "Define a new kind of hash table test."
-  (declare (type symbol name)
-	   (type function test-fun hash-fun))
-  (setf *hash-table-tests*
-	(cons (list name test-fun hash-fun)
-	      (remove name *hash-table-tests* :test #'eq :key #'car)))
+(defun register-hash-table-test (name hash-fun)
+  (declare (symbol name) (function hash-fun))
+  (unless (fboundp name)
+    (error "Cannot register ~S has a hash table test: undefined function."
+           name))
+  (with-single-package-locked-error
+      (:symbol name "defining ~S as a hash table test")
+    (let* ((test-fun (fdefinition name))
+           (this (list name test-fun hash-fun))
+           (spec (assoc name *user-hash-table-tests*)))
+      (cond (spec
+             (unless (and (eq (second spec) test-fun)
+                          (eq (third spec) hash-fun))
+               (style-warn "Redefining hash table test ~S." name)
+               (setf (cdr spec) (cdr this))))
+            (t
+             (push this *user-hash-table-tests*)))))
   name)
+
+(defmacro define-hash-table-test (name hash-function)
+  #!+sb-doc
+  "Defines NAME as a new kind of hash table test for use with the :TEST
+argument to MAKE-HASH-TABLE, and associates a default HASH-FUNCTION with it.
+
+NAME must be a symbol naming a global two argument equivalence predicate.
+Afterwards both 'NAME and #'NAME can be used with :TEST argument. In both
+cases HASH-TABLE-TEST will return the symbol NAME.
+
+HASH-FUNCTION must be a symbol naming a global hash function consistent with
+the predicate, or be a LAMBDA form implementing one in the current lexical
+environment. The hash function must compute the same hash code for any two
+objects for which NAME returns true, and subsequent calls with already hashed
+objects must always return the same hash code.
+
+Note: The :HASH-FUNCTION keyword argument to MAKE-HASH-TABLE can be used to
+override the specified default hash-function.
+
+Attempting to define NAME in a locked package as hash-table test causes a
+package lock violation.
+
+Examples:
+
+  ;;; 1.
+
+  ;; We want to use objects of type FOO as keys (by their
+  ;; names.) EQUALP would work, but would make the names
+  ;; case-insensitive -- which we don't want.
+  (defstruct foo (name nil :type (or null string)))
+
+  ;; Define an equivalence test function and a hash function.
+  (defun foo-name= (f1 f2) (equal (foo-name f1) (foo-name f2)))
+  (defun sxhash-foo-name (f) (sxhash (foo-name f)))
+
+  (define-hash-table-test foo-name= sxhash-foo-name)
+
+  ;; #'foo-name would work too.
+  (defun make-foo-table () (make-hash-table :test 'foo-name=))
+
+  ;;; 2.
+
+  (defun == (x y) (= x y))
+
+  (define-hash-table-test ==
+    (lambda (x)
+      ;; Hash codes must be consistent with test, so
+      ;; not (SXHASH X), since
+      ;;   (= 1 1.0)                   => T
+      ;;   (= (SXHASH 1) (SXHASH 1.0)) => NIL
+      ;; Note: this doesn't deal with complex numbers or
+      ;; bignums too large to represent as double floats.
+      (sxhash (coerce x 'double-float))))
+
+  ;; #'== would work too
+  (defun make-number-table () (make-hash-table :test '==))
+"
+  (check-type name symbol)
+  (if (member name '(eq eql equal equalp))
+      (error "Cannot redefine standard hash table test ~S." name)
+      (cond ((symbolp hash-function)
+             `(register-hash-table-test ',name (symbol-function ',hash-function)))
+            ((and (consp hash-function) (eq 'lambda (car hash-function)))
+             `(register-hash-table-test ',name #',hash-function))
+            (t
+             (error "Malformed HASH-FUNCTION: ~S" hash-function)))))
 
 ;;;; construction and simple accessors
 
 (defconstant +min-hash-table-size+ 16)
 (defconstant +min-hash-table-rehash-threshold+ (float 1/16 1.0))
-;; as explained by pmai on openprojects #lisp IRC 2002-07-30: #x80000000
-;; is bigger than any possible nonEQ hash value, and thus indicates an
-;; empty slot; and EQ hash tables don't use HASH-TABLE-HASH-VECTOR
-(defconstant +magic-hash-vector-value+ #x80000000)
-
-(defun make-hash-table (&key (test 'eql)
-			     (size +min-hash-table-size+)
-			     (rehash-size 1.5)
-			     (rehash-threshold 1)
-			     (weak-p nil))
+
+(defun make-hash-table (&key
+                        (test 'eql)
+                        (size +min-hash-table-size+)
+                        (rehash-size 1.5)
+                        (rehash-threshold 1)
+                        (hash-function nil)
+                        (weakness nil)
+                        (synchronized))
   #!+sb-doc
   "Create and return a new hash table. The keywords are as follows:
-     :TEST -- Indicates what kind of test to use.
-     :SIZE -- A hint as to how many elements will be put in this hash
-       table.
-     :REHASH-SIZE -- Indicates how to expand the table when it fills up.
-       If an integer, add space for that many elements. If a floating
-       point number (which must be greater than 1.0), multiply the size
-       by that amount.
-     :REHASH-THRESHOLD -- Indicates how dense the table can become before
-       forcing a rehash. Can be any positive number <=1, with density
-       approaching zero as the threshold approaches 0. Density 1 means an
-       average of one entry per bucket.
-     :WEAK-P -- (This is an extension from CMU CL, not currently supported
-       in SBCL 0.6.6, but perhaps supported in a future version.) If T,
-       don't keep entries if the key would otherwise be garbage."
+
+  :TEST
+    Determines how keys are compared. Must a designator for one of the
+    standard hash table tests, or a hash table test defined using
+    SB-EXT:DEFINE-HASH-TABLE-TEST. Additionally, when an explicit
+    HASH-FUNCTION is provided (see below), any two argument equivalence
+    predicate can be used as the TEST.
+
+  :SIZE
+    A hint as to how many elements will be put in this hash table.
+
+  :REHASH-SIZE
+    Indicates how to expand the table when it fills up. If an integer, add
+    space for that many elements. If a floating point number (which must be
+    greater than 1.0), multiply the size by that amount.
+
+  :REHASH-THRESHOLD
+    Indicates how dense the table can become before forcing a rehash. Can be
+    any positive number <=1, with density approaching zero as the threshold
+    approaches 0. Density 1 means an average of one entry per bucket.
+
+  :HASH-FUNCTION
+    If NIL (the default), a hash function based on the TEST argument is used,
+    which then must be one of the standardized hash table test functions, or
+    one for which a default hash function has been defined using
+    SB-EXT:DEFINE-HASH-TABLE-TEST. If HASH-FUNCTION is specified, the TEST
+    argument can be any two argument predicate consistent with it. The
+    HASH-FUNCTION is expected to return a non-negative fixnum hash code.
+
+  :WEAKNESS
+    When :WEAKNESS is not NIL, garbage collection may remove entries from the
+    hash table. The value of :WEAKNESS specifies how the presence of a key or
+    value in the hash table preserves their entries from garbage collection.
+
+    Valid values are:
+
+      :KEY means that the key of an entry must be live to guarantee that the
+        entry is preserved.
+
+      :VALUE means that the value of an entry must be live to guarantee that
+        the entry is preserved.
+
+      :KEY-AND-VALUE means that both the key and the value must be live to
+        guarantee that the entry is preserved.
+
+      :KEY-OR-VALUE means that either the key or the value must be live to
+        guarantee that the entry is preserved.
+
+      NIL (the default) means that entries are always preserved.
+
+  :SYNCHRONIZED
+    If NIL (the default), the hash-table may have multiple concurrent readers,
+    but results are undefined if a thread writes to the hash-table
+    concurrently with another reader or writer. If T, all concurrent accesses
+    are safe, but note that CLHS 3.6 (Traversal Rules and Side Effects)
+    remains in force. See also: SB-EXT:WITH-LOCKED-HASH-TABLE. This keyword
+    argument is experimental, and may change incompatibly or be removed in the
+    future."
   (declare (type (or function symbol) test))
   (declare (type unsigned-byte size))
-  (when weak-p
-    (error "stub: unsupported WEAK-P option"))
   (multiple-value-bind (test test-fun hash-fun)
       (cond ((or (eq test #'eq) (eq test 'eq))
-	     (values 'eq #'eq #'eq-hash))
-	    ((or (eq test #'eql) (eq test 'eql))
-	     (values 'eql #'eql #'eql-hash))
-	    ((or (eq test #'equal) (eq test 'equal))
-	     (values 'equal #'equal #'equal-hash))
-	    ((or (eq test #'equalp) (eq test 'equalp))
-	     (values 'equalp #'equalp #'equalp-hash))
-	    (t
-	     ;; FIXME: I'd like to remove *HASH-TABLE-TESTS* stuff.
-	     ;; Failing that, I'd like to rename it to
-	     ;; *USER-HASH-TABLE-TESTS*.
-	     (dolist (info *hash-table-tests*
-			   (error "unknown :TEST for MAKE-HASH-TABLE: ~S"
-				  test))
-	       (destructuring-bind (test-name test-fun hash-fun) info
-		 (when (or (eq test test-name) (eq test test-fun))
-		   (return (values test-name test-fun hash-fun)))))))
+             (values 'eq #'eq #'eq-hash))
+            ((or (eq test #'eql) (eq test 'eql))
+             (values 'eql #'eql #'eql-hash))
+            ((or (eq test #'equal) (eq test 'equal))
+             (values 'equal #'equal #'equal-hash))
+            ((or (eq test #'equalp) (eq test 'equalp))
+             (values 'equalp #'equalp #'equalp-hash))
+            (t
+             ;; FIXME: It would be nice to have a compiler-macro
+             ;; that resolved this at compile time: we could grab
+             ;; the alist cell in a LOAD-TIME-VALUE, etc.
+             (dolist (info *user-hash-table-tests*
+                      (if hash-function
+                          (if (functionp test)
+                              (values (%fun-name test) test nil)
+                              (values test (%coerce-callable-to-fun test) nil))
+                       (error "Unknown :TEST for MAKE-HASH-TABLE: ~S"
+                              test)))
+               (destructuring-bind (test-name test-fun hash-fun) info
+                 (when (or (eq test test-name) (eq test test-fun))
+                   (return (values test-name test-fun hash-fun)))))))
+    (when hash-function
+      (setf hash-fun
+            ;; Quickly check if the function has return return type which
+            ;; guarantees that the secondary return value is always NIL:
+            ;; (VALUES * &OPTIONAL), (VALUES * NULL ...) or (VALUES *
+            ;; &OPTIONAL NULL ...)
+            (let* ((actual (%coerce-callable-to-fun hash-function))
+                   (type-spec (%fun-type actual))
+                   (return-spec (when (consp type-spec)
+                                  (caddr type-spec)))
+                   (extra-vals (when (consp return-spec)
+                                 (cddr return-spec))))
+              (if (and (consp extra-vals)
+                       (or (eq 'null (car extra-vals))
+                           (and (eq '&optional (car extra-vals))
+                                (or (not (cdr extra-vals))
+                                    (eq 'null (cadr extra-vals))))))
+                  actual
+                  ;; If there is a potential secondary value, make sure we
+                  ;; don't accidentally claim EQ based hashing...
+                  (lambda (object)
+                    (declare (optimize (safety 0) (speed 3)))
+                    (values (funcall actual object) nil))))))
     (let* ((size (max +min-hash-table-size+
-		      (min size
-			   ;; SIZE is just a hint, so if the user asks
-			   ;; for a SIZE which'd be too big for us to
- 			   ;; easily implement, we bump it down.
-			   (floor array-dimension-limit 1024))))
-	   (rehash-size (if (integerp rehash-size)
-			    rehash-size
-			    (float rehash-size 1.0)))
-	   ;; FIXME: Original REHASH-THRESHOLD default should be 1.0,
-	   ;; not 1, to make it easier for the compiler to avoid
-	   ;; boxing.
-	   (rehash-threshold (max +min-hash-table-rehash-threshold+
-				  (float rehash-threshold 1.0)))
-	   (size+1 (1+ size))		; The first element is not usable.
+                      (min size
+                           ;; SIZE is just a hint, so if the user asks
+                           ;; for a SIZE which'd be too big for us to
+                           ;; easily implement, we bump it down.
+                           (floor array-dimension-limit 1024))))
+           (rehash-size (if (integerp rehash-size)
+                            rehash-size
+                            (float rehash-size 1.0)))
+           ;; FIXME: Original REHASH-THRESHOLD default should be 1.0,
+           ;; not 1, to make it easier for the compiler to avoid
+           ;; boxing.
+           (rehash-threshold (max +min-hash-table-rehash-threshold+
+                                  (float rehash-threshold 1.0)))
+           (size+1 (1+ size))       ; The first element is not usable.
            ;; KLUDGE: The most natural way of expressing the below is
            ;; (round (/ (float size+1) rehash-threshold)), and indeed
            ;; it was expressed like that until 0.7.0. However,
@@ -154,44 +357,49 @@
            ;; but only for truncating; therefore, we fudge this issue
            ;; a little. The other uses of truncate, below, similarly
            ;; used to be round. -- CSR, 2002-10-01
-	   ;;
-	   ;; Note that this has not yet been audited for
-	   ;; correctness. It just seems to work. -- CSR, 2002-11-02
-	   (scaled-size (truncate (/ (float size+1) rehash-threshold)))
-	   (length (almost-primify (max scaled-size
-					(1+ +min-hash-table-size+))))
-	   (index-vector (make-array length
-				     :element-type '(unsigned-byte 32)
-				     :initial-element 0))
-	   ;; needs to be the same length as the KV vector
-           ;; (FIXME: really?  why doesn't the code agree?)
-	   (next-vector (make-array size+1
-				    :element-type '(unsigned-byte 32)))
-	   (kv-vector (make-array (* 2 size+1)
-				  :initial-element +empty-ht-slot+))
-	   (table (%make-hash-table
-		   :test test
-		   :test-fun test-fun
-		   :hash-fun hash-fun
-		   :rehash-size rehash-size
-		   :rehash-threshold rehash-threshold
-		   :rehash-trigger size
-		   :table kv-vector
-		   :weak-p weak-p
-		   :index-vector index-vector
-		   :next-vector next-vector
-		   :hash-vector (unless (eq test 'eq)
-				  (make-array size+1
-					      :element-type '(unsigned-byte 32)
-					      :initial-element +magic-hash-vector-value+)))))
+           ;;
+           ;; Note that this has not yet been audited for
+           ;; correctness. It just seems to work. -- CSR, 2002-11-02
+           (scaled-size (truncate (/ (float size+1) rehash-threshold)))
+           (length (power-of-two-ceiling (max scaled-size
+                                              (1+ +min-hash-table-size+))))
+           (index-vector (make-array length
+                                     :element-type
+                                     '(unsigned-byte #.sb!vm:n-word-bits)
+                                     :initial-element 0))
+           ;; Needs to be the half the length of the KV vector to link
+           ;; KV entries - mapped to indeces at 2i and 2i+1 -
+           ;; together.
+           (next-vector (make-array size+1
+                                    :element-type
+                                    '(unsigned-byte #.sb!vm:n-word-bits)))
+           (kv-vector (make-array (* 2 size+1)
+                                  :initial-element +empty-ht-slot+))
+           (table (%make-hash-table
+                   :test test
+                   :test-fun test-fun
+                   :hash-fun hash-fun
+                   :rehash-size rehash-size
+                   :rehash-threshold rehash-threshold
+                   :rehash-trigger size
+                   :table kv-vector
+                   :weakness weakness
+                   :index-vector index-vector
+                   :next-vector next-vector
+                   :hash-vector
+                   (unless (eq test 'eq)
+                     (make-array size+1
+                                 :element-type '(unsigned-byte
+                                                 #.sb!vm:n-word-bits)
+                                 :initial-element +magic-hash-vector-value+))
+                   :synchronized-p synchronized)))
       (declare (type index size+1 scaled-size length))
       ;; Set up the free list, all free. These lists are 0 terminated.
       (do ((i 1 (1+ i)))
-	  ((>= i size))
-	(setf (aref next-vector i) (1+ i)))
+          ((>= i size))
+        (setf (aref next-vector i) (1+ i)))
       (setf (aref next-vector size) 0)
       (setf (hash-table-next-free-kv table) 1)
-      (setf (hash-table-needing-rehash table) 0)
       (setf (aref kv-vector 0) table)
       table)))
 
@@ -199,7 +407,7 @@
   #!+sb-doc
   "Return the number of entries in the given HASH-TABLE."
   (declare (type hash-table hash-table)
-	   (values index))
+           (values index))
   (hash-table-number-entries hash-table))
 
 #!+sb-doc
@@ -210,6 +418,10 @@
 (setf (fdocumentation 'hash-table-rehash-threshold 'function)
       "Return the rehash-threshold HASH-TABLE was created with.")
 
+#!+sb-doc
+(setf (fdocumentation 'hash-table-synchronized-p 'function)
+      "Returns T if HASH-TABLE is synchronized.")
+
 (defun hash-table-size (hash-table)
   #!+sb-doc
   "Return a size that can be used with MAKE-HASH-TABLE to create a hash
@@ -222,9 +434,16 @@
       "Return the test HASH-TABLE was created with.")
 
 #!+sb-doc
-(setf (fdocumentation 'hash-table-weak-p 'function)
-      "Return T if HASH-TABLE will not keep entries for keys that would
-   otherwise be garbage, and NIL if it will.")
+(setf (fdocumentation 'hash-table-weakness 'function)
+      "Return the WEAKNESS of HASH-TABLE which is one of NIL, :KEY,
+:VALUE, :KEY-AND-VALUE, :KEY-OR-VALUE.")
+
+;;; Called when we detect circular chains in a hash-table.
+(defun signal-corrupt-hash-table (hash-table)
+  (error "Corrupt NEXT-chain in ~A. This is probably caused by ~
+multiple threads accessing the same hash-table without locking."
+         hash-table))
+
 
 ;;;; accessing functions
 
@@ -232,38 +451,44 @@
 ;;; rehash-size.
 (defun rehash (table)
   (declare (type hash-table table))
+  (aver *gc-inhibit*)
   (let* ((old-kv-vector (hash-table-table table))
-	 (old-next-vector (hash-table-next-vector table))
-	 (old-hash-vector (hash-table-hash-vector table))
-	 (old-size (length old-next-vector))
-	 (new-size
-	  (let ((rehash-size (hash-table-rehash-size table)))
-	    (etypecase rehash-size
-	      (fixnum
-	       (+ rehash-size old-size))
-	      (float
-	       (the index (truncate (* rehash-size old-size)))))))
-	 (new-kv-vector (make-array (* 2 new-size)
-				    :initial-element +empty-ht-slot+))
-	 (new-next-vector (make-array new-size
-				      :element-type '(unsigned-byte 32)
-				      :initial-element 0))
-	 (new-hash-vector (when old-hash-vector
-			    (make-array new-size
-					:element-type '(unsigned-byte 32)
-					:initial-element +magic-hash-vector-value+)))
-	 (old-index-vector (hash-table-index-vector table))
-	 (new-length (almost-primify
-		      (truncate (/ (float new-size)
-				(hash-table-rehash-threshold table)))))
-	 (new-index-vector (make-array new-length
-				       :element-type '(unsigned-byte 32)
-				       :initial-element 0)))
+         (old-next-vector (hash-table-next-vector table))
+         (old-hash-vector (hash-table-hash-vector table))
+         (old-size (length old-next-vector))
+         (new-size
+          (power-of-two-ceiling
+           (let ((rehash-size (hash-table-rehash-size table)))
+             (etypecase rehash-size
+               (fixnum
+                (+ rehash-size old-size))
+               (float
+                (the index (truncate (* rehash-size old-size))))))))
+         (new-kv-vector (make-array (* 2 new-size)
+                                    :initial-element +empty-ht-slot+))
+         (new-next-vector
+          (make-array new-size
+                      :element-type '(unsigned-byte #.sb!vm:n-word-bits)
+                      :initial-element 0))
+         (new-hash-vector
+          (when old-hash-vector
+            (make-array new-size
+                        :element-type '(unsigned-byte #.sb!vm:n-word-bits)
+                        :initial-element +magic-hash-vector-value+)))
+         (new-length new-size)
+         (new-index-vector
+          (make-array new-length
+                      :element-type '(unsigned-byte #.sb!vm:n-word-bits)
+                      :initial-element 0)))
     (declare (type index new-size new-length old-size))
 
     ;; Disable GC tricks on the OLD-KV-VECTOR.
     (set-header-data old-kv-vector sb!vm:vector-normal-subtype)
 
+    ;; Non-empty weak hash tables always need GC support.
+    (when (and (hash-table-weakness table) (plusp (hash-table-count table)))
+      (set-header-data new-kv-vector sb!vm:vector-valid-hashing-subtype))
+
     ;; FIXME: here and in several other places in the hash table code,
     ;; loops like this one are used when FILL or REPLACE would be
     ;; appropriate.  why are standard CL functions not used?
@@ -278,356 +503,491 @@
     ;; Copy over the hash-vector.
     (when old-hash-vector
       (dotimes (i old-size)
-	(setf (aref new-hash-vector i) (aref old-hash-vector i))))
+        (setf (aref new-hash-vector i) (aref old-hash-vector i))))
 
     (setf (hash-table-next-free-kv table) 0)
-    (setf (hash-table-needing-rehash table) 0)
     ;; Rehash all the entries; last to first so that after the pushes
     ;; the chains are first to last.
     (do ((i (1- new-size) (1- i)))
-	((zerop i))
+        ((zerop i))
+      (declare (type index/2 i))
       (let ((key (aref new-kv-vector (* 2 i)))
-	    (value (aref new-kv-vector (1+ (* 2 i)))))
-	(cond ((and (eq key +empty-ht-slot+)
-		    (eq value +empty-ht-slot+))
-	       ;; Slot is empty, push it onto the free list.
-	       (setf (aref new-next-vector i)
-		     (hash-table-next-free-kv table))
-	       (setf (hash-table-next-free-kv table) i))
-	      ((and new-hash-vector
-		    (not (= (aref new-hash-vector i) +magic-hash-vector-value+)))
-	       ;; Can use the existing hash value (not EQ based)
-	       (let* ((hashing (aref new-hash-vector i))
-		      (index (rem hashing new-length))
-		      (next (aref new-index-vector index)))
-		 (declare (type index index)
-			  (type hash hashing))
-		 ;; Push this slot into the next chain.
-		 (setf (aref new-next-vector i) next)
-		 (setf (aref new-index-vector index) i)))
-	      (t
-	       ;; EQ base hash.
-	       ;; Enable GC tricks.
-	       (set-header-data new-kv-vector
-				sb!vm:vector-valid-hashing-subtype)
-	       (let* ((hashing (pointer-hash key))
-		      (index (rem hashing new-length))
-		      (next (aref new-index-vector index)))
-		 (declare (type index index)
-			  (type hash hashing))
-		 ;; Push this slot onto the next chain.
-		 (setf (aref new-next-vector i) next)
-		 (setf (aref new-index-vector index) i))))))
+            (value (aref new-kv-vector (1+ (* 2 i)))))
+        (cond ((and (eq key +empty-ht-slot+)
+                    (eq value +empty-ht-slot+))
+               ;; Slot is empty, push it onto the free list.
+               (setf (aref new-next-vector i)
+                     (hash-table-next-free-kv table))
+               (setf (hash-table-next-free-kv table) i))
+              ((and new-hash-vector
+                    (not (= (aref new-hash-vector i)
+                            +magic-hash-vector-value+)))
+               ;; Can use the existing hash value (not EQ based)
+               (let* ((hashing (aref new-hash-vector i))
+                      (index (index-for-hashing hashing new-length))
+                      (next (aref new-index-vector index)))
+                 (declare (type index index)
+                          (type hash hashing))
+                 ;; Push this slot into the next chain.
+                 (setf (aref new-next-vector i) next)
+                 (setf (aref new-index-vector index) i)))
+              (t
+               ;; EQ base hash.
+               ;; Enable GC tricks.
+               (set-header-data new-kv-vector
+                                sb!vm:vector-valid-hashing-subtype)
+               (let* ((hashing (pointer-hash key))
+                      (index (index-for-hashing hashing new-length))
+                      (next (aref new-index-vector index)))
+                 (declare (type index index)
+                          (type hash hashing))
+                 ;; Push this slot onto the next chain.
+                 (setf (aref new-next-vector i) next)
+                 (setf (aref new-index-vector index) i))))))
     (setf (hash-table-table table) new-kv-vector)
     (setf (hash-table-index-vector table) new-index-vector)
     (setf (hash-table-next-vector table) new-next-vector)
     (setf (hash-table-hash-vector table) new-hash-vector)
-    ;; Shrink the old vectors to 0 size to help the conservative GC.
-    (shrink-vector old-kv-vector 0)
-    (shrink-vector old-index-vector 0)
-    (shrink-vector old-next-vector 0)
-    (when old-hash-vector
-      (shrink-vector old-hash-vector 0))
-    (setf (hash-table-rehash-trigger table) new-size))
+    ;; Fill the old kv-vector with 0 to help the conservative GC. Even
+    ;; if nothing else were zeroed, it's important to clear the
+    ;; special first cells in old-kv-vector.
+    (fill old-kv-vector 0)
+    (setf (hash-table-rehash-trigger table) new-size)
+    (setf (hash-table-needs-rehash-p table) nil))
   (values))
 
 ;;; Use the same size as before, re-using the vectors.
 (defun rehash-without-growing (table)
   (declare (type hash-table table))
+  (aver *gc-inhibit*)
   (let* ((kv-vector (hash-table-table table))
-	 (next-vector (hash-table-next-vector table))
-	 (hash-vector (hash-table-hash-vector table))
-	 (size (length next-vector))
-	 (index-vector (hash-table-index-vector table))
-	 (length (length index-vector)))
+         (next-vector (hash-table-next-vector table))
+         (hash-vector (hash-table-hash-vector table))
+         (size (length next-vector))
+         (index-vector (hash-table-index-vector table))
+         (length (length index-vector)))
     (declare (type index size length))
 
-    ;; Disable GC tricks, they will be re-enabled during the re-hash
-    ;; if necesary.
-    (set-header-data kv-vector sb!vm:vector-normal-subtype)
+    ;; Non-empty weak hash tables always need GC support.
+    (unless (and (hash-table-weakness table) (plusp (hash-table-count table)))
+      ;; Disable GC tricks, they will be re-enabled during the re-hash
+      ;; if necessary.
+      (set-header-data kv-vector sb!vm:vector-normal-subtype))
 
     ;; Rehash all the entries.
     (setf (hash-table-next-free-kv table) 0)
-    (setf (hash-table-needing-rehash table) 0)
     (dotimes (i size)
       (setf (aref next-vector i) 0))
     (dotimes (i length)
       (setf (aref index-vector i) 0))
     (do ((i (1- size) (1- i)))
-	((zerop i))
+        ((zerop i))
+      (declare (type index/2 i))
       (let ((key (aref kv-vector (* 2 i)))
-	    (value (aref kv-vector (1+ (* 2 i)))))
-	(cond ((and (eq key +empty-ht-slot+)
-		    (eq value +empty-ht-slot+))
-	       ;; Slot is empty, push it onto free list.
-	       (setf (aref next-vector i) (hash-table-next-free-kv table))
-	       (setf (hash-table-next-free-kv table) i))
-	      ((and hash-vector (not (= (aref hash-vector i) +magic-hash-vector-value+)))
-	       ;; Can use the existing hash value (not EQ based)
-	       (let* ((hashing (aref hash-vector i))
-		      (index (rem hashing length))
-		      (next (aref index-vector index)))
-		 (declare (type index index))
-		 ;; Push this slot into the next chain.
-		 (setf (aref next-vector i) next)
-		 (setf (aref index-vector index) i)))
-	      (t
-	       ;; EQ base hash.
-	       ;; Enable GC tricks.
-	       (set-header-data kv-vector sb!vm:vector-valid-hashing-subtype)
-	       (let* ((hashing (pointer-hash key))
-		      (index (rem hashing length))
-		      (next (aref index-vector index)))
-		 (declare (type index index)
-			  (type hash hashing))
-		 ;; Push this slot into the next chain.
-		 (setf (aref next-vector i) next)
-		 (setf (aref index-vector index) i)))))))
+            (value (aref kv-vector (1+ (* 2 i)))))
+        (cond ((and (eq key +empty-ht-slot+)
+                    (eq value +empty-ht-slot+))
+               ;; Slot is empty, push it onto free list.
+               (setf (aref next-vector i) (hash-table-next-free-kv table))
+               (setf (hash-table-next-free-kv table) i))
+              ((and hash-vector (not (= (aref hash-vector i)
+                                        +magic-hash-vector-value+)))
+               ;; Can use the existing hash value (not EQ based)
+               (let* ((hashing (aref hash-vector i))
+                      (index (index-for-hashing hashing length))
+                      (next (aref index-vector index)))
+                 (declare (type index index))
+                 ;; Push this slot into the next chain.
+                 (setf (aref next-vector i) next)
+                 (setf (aref index-vector index) i)))
+              (t
+               ;; EQ base hash.
+               ;; Enable GC tricks.
+               (set-header-data kv-vector sb!vm:vector-valid-hashing-subtype)
+               (let* ((hashing (pointer-hash key))
+                      (index (index-for-hashing hashing length))
+                      (next (aref index-vector index)))
+                 (declare (type index index)
+                          (type hash hashing))
+                 ;; Push this slot into the next chain.
+                 (setf (aref next-vector i) next)
+                 (setf (aref index-vector index) i)))))))
+  ;; Clear the rehash bit only at the very end, otherwise another thread
+  ;; might see a partially rehashed table as a normal one.
+  (setf (hash-table-needs-rehash-p table) nil)
   (values))
 
-(defun flush-needing-rehash (table)
-  (let* ((kv-vector (hash-table-table table))
-	 (index-vector (hash-table-index-vector table))
-	 (next-vector (hash-table-next-vector table))
-	 (length (length index-vector)))
-    (do ((next (hash-table-needing-rehash table)))
-	((zerop next))
-      (declare (type index next))
-      (let* ((key (aref kv-vector (* 2 next)))
-	     (hashing (pointer-hash key))
-	     (index (rem hashing length))
-	     (temp (aref next-vector next)))
-	(setf (aref next-vector next) (aref index-vector index))
-	(setf (aref index-vector index) next)
-	(setf next temp))))
-  (setf (hash-table-needing-rehash table) 0)
-  (values))
+(declaim (inline maybe-rehash))
+(defun maybe-rehash (hash-table ensure-free-slot-p)
+  (when (hash-table-weakness hash-table)
+    (aver *gc-inhibit*))
+  (flet ((rehash-p ()
+           (and ensure-free-slot-p
+                (zerop (hash-table-next-free-kv hash-table))))
+         (rehash-without-growing-p ()
+           (hash-table-needs-rehash-p hash-table)))
+    (declare (inline rehash-p rehash-without-growing-p))
+    (cond ((rehash-p)
+           ;; Use recursive locks since for weak tables the lock has
+           ;; already been acquired. GC must be inhibited to prevent
+           ;; the GC from seeing a rehash in progress.
+           (sb!thread::with-recursive-system-lock
+               ((hash-table-lock hash-table) :without-gcing t)
+             ;; Repeat the condition inside the lock to ensure that if
+             ;; two reader threads enter MAYBE-REHASH at the same time
+             ;; only one rehash is performed.
+             (when (rehash-p)
+               (rehash hash-table))))
+          ((rehash-without-growing-p)
+           (sb!thread::with-recursive-system-lock
+               ((hash-table-lock hash-table) :without-gcing t)
+             (when (rehash-without-growing-p)
+               (rehash-without-growing hash-table)))))))
+
+(declaim (inline update-hash-table-cache))
+(defun update-hash-table-cache (hash-table index)
+  (unless (hash-table-weakness hash-table)
+    (setf (hash-table-cache hash-table) index)))
+
+(defmacro with-hash-table-locks ((hash-table
+                                  &key (operation :write) inline pin
+                                  (synchronized `(hash-table-synchronized-p ,hash-table)))
+                                 &body body)
+  (declare (type (member :read :write) operation))
+  (with-unique-names (body-fun)
+    `(flet ((,body-fun ()
+              (with-concurrent-access-check ,hash-table ,operation
+                (locally (declare (inline ,@inline))
+                  ,@body))))
+       (if (hash-table-weakness ,hash-table)
+           (sb!thread::with-recursive-system-lock
+               ((hash-table-lock ,hash-table) :without-gcing t)
+             (,body-fun))
+           (with-pinned-objects ,pin
+             (if ,synchronized
+                 ;; We use a "system" lock here because it is very
+                 ;; slightly faster, as it doesn't re-enable
+                 ;; interrupts.
+                 (sb!thread::with-recursive-system-lock
+                     ((hash-table-lock ,hash-table))
+                   (,body-fun))
+                 (,body-fun)))))))
 
 (defun gethash (key hash-table &optional default)
   #!+sb-doc
-  "Finds the entry in HASH-TABLE whose key is KEY and returns the associated
-   value and T as multiple values, or returns DEFAULT and NIL if there is no
-   such entry. Entries can be added using SETF."
+  "Finds the entry in HASH-TABLE whose key is KEY and returns the
+associated value and T as multiple values, or returns DEFAULT and NIL
+if there is no such entry. Entries can be added using SETF."
   (declare (type hash-table hash-table)
-	   (values t (member t nil)))
-  (without-gcing
-   (cond ((= (get-header-data (hash-table-table hash-table))
-	     sb!vm:vector-must-rehash-subtype)
-	  (rehash-without-growing hash-table))
-	 ((not (zerop (hash-table-needing-rehash hash-table)))
-	  (flush-needing-rehash hash-table)))
-   ;; Search for key in the hash table.
-   (multiple-value-bind (hashing eq-based)
-       (funcall (hash-table-hash-fun hash-table) key)
-     (declare (type hash hashing))
-     (let* ((index-vector (hash-table-index-vector hash-table))
-	    (length (length index-vector))
-	    (index (rem hashing length))
-	    (next (aref index-vector index))
-	    (table (hash-table-table hash-table))
-	    (next-vector (hash-table-next-vector hash-table))
-	    (hash-vector (hash-table-hash-vector hash-table))
-	    (test-fun (hash-table-test-fun hash-table)))
-       (declare (type index index))
-       ;; Search next-vector chain for a matching key.
-       (if (or eq-based (not hash-vector))
-	   (do ((next next (aref next-vector next)))
-	       ((zerop next) (values default nil))
-	     (declare (type index next))
-	     (when (eq key (aref table (* 2 next)))
-	       (return (values (aref table (1+ (* 2 next))) t))))
-	   (do ((next next (aref next-vector next)))
-	       ((zerop next) (values default nil))
-	     (declare (type index next))
-	     (when (and (= hashing (aref hash-vector next))
-			(funcall test-fun key (aref table (* 2 next))))
-	       ;; Found.
-	       (return (values (aref table (1+ (* 2 next))) t)))))))))
+           (values t (member t nil)))
+  (gethash3 key hash-table default))
+
+(declaim (maybe-inline %gethash3))
+(defun %gethash3 (key hash-table default)
+  (declare (type hash-table hash-table)
+           (optimize speed)
+           (values t (member t nil)))
+  (tagbody
+   start
+     (let ((start-epoch sb!kernel::*gc-epoch*))
+       (macrolet ((result (value foundp)
+                    ;; When the table has multiple concurrent readers,
+                    ;; it's possible that there was a GC after this
+                    ;; thread called MAYBE-REHASH from %GETHASH3, and
+                    ;; some other thread then rehashed the table. If
+                    ;; this happens, we might not find the key even if
+                    ;; it's in the table. To protect against this,
+                    ;; redo the lookup if the GC epoch counter has changed.
+                    ;; -- JES,  2007-09-30
+                    `(if (and (not ,foundp)
+                              (not (eq start-epoch sb!kernel::*gc-epoch*)))
+                         (go start)
+                         (return-from %gethash3 (values ,value ,foundp))))
+                  (overflow ()
+                    ;; The next-vector chain is circular. This is caused
+                    ;; caused by thread-unsafe mutations of the table.
+                    `(signal-corrupt-hash-table hash-table)))
+         (maybe-rehash hash-table nil)
+         ;; Note that it's OK for a GC + a REHASH-WITHOUT-GROWING to
+         ;; be triggered by another thread after this point, since the
+         ;; GC epoch check will catch it.
+         (let ((cache (hash-table-cache hash-table))
+               (table (hash-table-table hash-table)))
+           ;; First check the cache.  Use EQ here for speed.
+           (if (and cache
+                    (< cache (length table))
+                    (eq (aref table cache) key))
+               (let ((value (aref table (1+ cache))))
+                 (result value t))
+               ;; Search for key in the hash table.
+               (multiple-value-bind (hashing eq-based)
+                   (funcall (hash-table-hash-fun hash-table) key)
+                 (declare (type hash hashing))
+                 (let* ((index-vector (hash-table-index-vector hash-table))
+                        (length (length index-vector))
+                        (index (index-for-hashing hashing length))
+                        (next (aref index-vector index))
+                        (next-vector (hash-table-next-vector hash-table))
+                        (hash-vector (hash-table-hash-vector hash-table))
+                        (test-fun (hash-table-test-fun hash-table)))
+                   (declare (type index index))
+                   ;; Search next-vector chain for a matching key.
+                   (if (or eq-based (not hash-vector))
+                       (do ((next next (aref next-vector next))
+                            (i 0 (1+ i)))
+                           ((zerop next) (result default nil))
+                         (declare (type index/2 next i))
+                         (when (> i length)
+                           (overflow))
+                         (when (eq key (aref table (* 2 next)))
+                           (update-hash-table-cache hash-table (* 2 next))
+                           (let ((value (aref table (1+ (* 2 next)))))
+                             (result value t))))
+                       (do ((next next (aref next-vector next))
+                            (i 0 (1+ i)))
+                           ((zerop next) (result default nil))
+                         (declare (type index/2 next i))
+                         (when (> i length)
+                           (overflow))
+                         (when (and (= hashing (aref hash-vector next))
+                                    (funcall test-fun key
+                                             (aref table (* 2 next))))
+                           ;; Found.
+                           (update-hash-table-cache hash-table (* 2 next))
+                           (let ((value (aref table (1+ (* 2 next)))))
+                             (result value t)))))))))))))
+
+(defun gethash3 (key hash-table default)
+  "Three argument version of GETHASH"
+  (declare (type hash-table hash-table))
+  (with-hash-table-locks (hash-table :operation :read :inline (%gethash3)
+                                     :pin (key))
+    (%gethash3 key hash-table default)))
 
 ;;; so people can call #'(SETF GETHASH)
 (defun (setf gethash) (new-value key table &optional default)
   (declare (ignore default))
   (%puthash key table new-value))
 
+(declaim (maybe-inline %%puthash))
+(defun %%puthash (key hash-table value)
+  (declare (optimize speed))
+  ;; We need to rehash here so that a current key can be found if it
+  ;; exists. Check that there is room for one more entry. May not be
+  ;; needed if the key is already present.
+  (maybe-rehash hash-table t)
+  ;; Search for key in the hash table.
+  (multiple-value-bind (hashing eq-based)
+      (funcall (hash-table-hash-fun hash-table) key)
+    (declare (type hash hashing))
+    (let* ((index-vector (hash-table-index-vector hash-table))
+           (length (length index-vector))
+           (index (index-for-hashing hashing length))
+           (next (aref index-vector index))
+           (kv-vector (hash-table-table hash-table))
+           (next-vector (hash-table-next-vector hash-table))
+           (hash-vector (hash-table-hash-vector hash-table))
+           (test-fun (hash-table-test-fun hash-table)))
+      (declare (type index index next))
+      (when (hash-table-weakness hash-table)
+        (set-header-data kv-vector sb!vm:vector-valid-hashing-subtype))
+      (cond ((or eq-based (not hash-vector))
+             (when eq-based
+               (set-header-data kv-vector
+                                sb!vm:vector-valid-hashing-subtype))
+             ;; Search next-vector chain for a matching key.
+             (do ((next next (aref next-vector next))
+                  (i 0 (1+ i)))
+                 ((zerop next))
+               (declare (type index/2 next i))
+               (when (> i length)
+                 (signal-corrupt-hash-table hash-table))
+               (when (eq key (aref kv-vector (* 2 next)))
+                 ;; Found, just replace the value.
+                 (update-hash-table-cache hash-table (* 2 next))
+                 (setf (aref kv-vector (1+ (* 2 next))) value)
+                 (return-from %%puthash value))))
+            (t
+             ;; Search next-vector chain for a matching key.
+             (do ((next next (aref next-vector next))
+                  (i 0 (1+ i)))
+                 ((zerop next))
+               (declare (type index/2 next i))
+               (when (> i length)
+                 (signal-corrupt-hash-table hash-table))
+               (when (and (= hashing (aref hash-vector next))
+                          (funcall test-fun key
+                                   (aref kv-vector (* 2 next))))
+                 ;; Found, just replace the value.
+                 (update-hash-table-cache hash-table (* 2 next))
+                 (setf (aref kv-vector (1+ (* 2 next))) value)
+                 (return-from %%puthash value)))))
+      ;; Pop a KV slot off the free list
+      (let ((free-kv-slot (hash-table-next-free-kv hash-table)))
+        (declare (type index/2 free-kv-slot))
+        ;; Double-check for overflow.
+        (aver (not (zerop free-kv-slot)))
+        (setf (hash-table-next-free-kv hash-table)
+              (aref next-vector free-kv-slot))
+        (incf (hash-table-number-entries hash-table))
+        (update-hash-table-cache hash-table (* 2 free-kv-slot))
+        (setf (aref kv-vector (* 2 free-kv-slot)) key)
+        (setf (aref kv-vector (1+ (* 2 free-kv-slot))) value)
+        ;; Setup the hash-vector if necessary.
+        (when hash-vector
+          (if (not eq-based)
+              (setf (aref hash-vector free-kv-slot) hashing)
+              (aver (= (aref hash-vector free-kv-slot)
+                       +magic-hash-vector-value+))))
+        ;; Push this slot into the next chain.
+        (setf (aref next-vector free-kv-slot) next)
+        (setf (aref index-vector index) free-kv-slot)))
+    value))
+
 (defun %puthash (key hash-table value)
   (declare (type hash-table hash-table))
   (aver (hash-table-index-vector hash-table))
-  (without-gcing
-   ;; We need to rehash here so that a current key can be found if it
-   ;; exists. Check that there is room for one more entry. May not be
-   ;; needed if the key is already present.
-   (cond ((zerop (hash-table-next-free-kv hash-table))
-	  (rehash hash-table))
-	 ((= (get-header-data (hash-table-table hash-table))
-	     sb!vm:vector-must-rehash-subtype)
-	  (rehash-without-growing hash-table))
-	 ((not (zerop (hash-table-needing-rehash hash-table)))
-	  (flush-needing-rehash hash-table)))
-
-   ;; Search for key in the hash table.
-   (multiple-value-bind (hashing eq-based)
-       (funcall (hash-table-hash-fun hash-table) key)
-     (declare (type hash hashing))
-     (let* ((index-vector (hash-table-index-vector hash-table))
-	    (length (length index-vector))
-	    (index (rem hashing length))
-	    (next (aref index-vector index))
-	    (kv-vector (hash-table-table hash-table))
-	    (next-vector (hash-table-next-vector hash-table))
-	    (hash-vector (hash-table-hash-vector hash-table))
-	    (test-fun (hash-table-test-fun hash-table)))
-       (declare (type index index))
-
-       (cond ((or eq-based (not hash-vector))
-	      (when eq-based
-		(set-header-data kv-vector sb!vm:vector-valid-hashing-subtype))
-
-	      ;; Search next-vector chain for a matching key.
-	      (do ((next next (aref next-vector next)))
-		  ((zerop next))
-		(declare (type index next))
-		(when (eq key (aref kv-vector (* 2 next)))
-		  ;; Found, just replace the value.
-		  (setf (aref kv-vector (1+ (* 2 next))) value)
-		  (return-from %puthash value))))
-	     (t
-	      ;; Search next-vector chain for a matching key.
-	      (do ((next next (aref next-vector next)))
-		  ((zerop next))
-		(declare (type index next))
-		(when (and (= hashing (aref hash-vector next))
-			   (funcall test-fun key
-				    (aref kv-vector (* 2 next))))
-		  ;; Found, just replace the value.
-		  (setf (aref kv-vector (1+ (* 2 next))) value)
-		  (return-from %puthash value)))))
-
-       ;; Pop a KV slot off the free list
-       (let ((free-kv-slot (hash-table-next-free-kv hash-table)))
-	 ;; Double-check for overflow.
-	 (aver (not (zerop free-kv-slot)))
-	 (setf (hash-table-next-free-kv hash-table)
-	       (aref next-vector free-kv-slot))
-	 (incf (hash-table-number-entries hash-table))
-
-	 (setf (aref kv-vector (* 2 free-kv-slot)) key)
-	 (setf (aref kv-vector (1+ (* 2 free-kv-slot))) value)
-
-	 ;; Setup the hash-vector if necessary.
-	 (when hash-vector
-	   (if (not eq-based)
-	       (setf (aref hash-vector free-kv-slot) hashing)
-	       (aver (= (aref hash-vector free-kv-slot) +magic-hash-vector-value+))))
-
-	 ;; Push this slot into the next chain.
-	 (setf (aref next-vector free-kv-slot) next)
-	 (setf (aref index-vector index) free-kv-slot)))))
-  value)
+  (macrolet ((put-it (lockedp)
+               `(let ((cache (hash-table-cache hash-table))
+                      (kv-vector (hash-table-table hash-table)))
+                  ;; Check the cache
+                  (if (and cache
+                           (< cache (length kv-vector))
+                           (eq (aref kv-vector cache) key))
+                      ;; If cached, just store here
+                      (setf (aref kv-vector (1+ cache)) value)
+                      ;; Otherwise do things the hard way
+                      ,(if lockedp
+                           '(%%puthash key hash-table value)
+                           '(with-hash-table-locks
+                             (hash-table :inline (%%puthash) :pin (key)
+                              :synchronized nil)
+                             (%%puthash key hash-table value)))))))
+    (if (hash-table-synchronized-p hash-table)
+        (with-hash-table-locks (hash-table :pin (key) :synchronized t)
+          (put-it t))
+        (put-it nil))))
+
+(declaim (maybe-inline %remhash))
+(defun %remhash (key hash-table)
+  ;; We need to rehash here so that a current key can be found if it
+  ;; exists.
+  ;;
+  ;; Note that if a GC happens after MAYBE-REHASH returns and another
+  ;; thread the accesses the table (triggering a rehash), we might not
+  ;; find the key even if it is in the table. But that's ok, since the
+  ;; only concurrent case that we safely allow is multiple readers
+  ;; with no writers.
+  (maybe-rehash hash-table nil)
+  ;; Search for key in the hash table.
+  (multiple-value-bind (hashing eq-based)
+      (funcall (hash-table-hash-fun hash-table) key)
+    (declare (type hash hashing))
+    (let* ((index-vector (hash-table-index-vector hash-table))
+           (length (length index-vector))
+           (index (index-for-hashing hashing length))
+           (next (aref index-vector index))
+           (table (hash-table-table hash-table))
+           (next-vector (hash-table-next-vector hash-table))
+           (hash-vector (hash-table-hash-vector hash-table))
+           (test-fun (hash-table-test-fun hash-table)))
+      (declare (type index index)
+               (type index/2 next))
+      (flet ((clear-slot (chain-vector prior-slot-location slot-location)
+               (declare (type index/2 slot-location))
+               ;; Mark slot as empty.
+               (setf (aref table (* 2 slot-location)) +empty-ht-slot+
+                     (aref table (1+ (* 2 slot-location))) +empty-ht-slot+)
+               ;; Update the prior pointer in the chain to skip this.
+               (setf (aref chain-vector prior-slot-location)
+                     (aref next-vector slot-location))
+               ;; Push KV slot onto free chain.
+               (setf (aref next-vector slot-location)
+                     (hash-table-next-free-kv hash-table))
+               (setf (hash-table-next-free-kv hash-table) slot-location)
+               (when hash-vector
+                 (setf (aref hash-vector slot-location)
+                       +magic-hash-vector-value+))
+               ;; On parallel accesses this may turn out to be a
+               ;; type-error, so don't turn down the safety!
+               (decf (hash-table-number-entries hash-table))
+               t))
+        (cond ((zerop next)
+               nil)
+              ((if (or eq-based (not hash-vector))
+                   (eq key (aref table (* 2 next)))
+                   (and (= hashing (aref hash-vector next))
+                        (funcall test-fun key (aref table (* 2 next)))))
+               (clear-slot index-vector index next))
+              ;; Search next-vector chain for a matching key.
+              ((or eq-based (not hash-vector))
+               ;; EQ based
+               (do ((prior next next)
+                    (i 0 (1+ i))
+                    (next (aref next-vector next) (aref next-vector next)))
+                   ((zerop next) nil)
+                 (declare (type index next))
+                 (when (> i length)
+                   (signal-corrupt-hash-table hash-table))
+                 (when (eq key (aref table (* 2 next)))
+                   (return-from %remhash (clear-slot next-vector prior next)))))
+              (t
+               ;; not EQ based
+               (do ((prior next next)
+                    (i 0 (1+ i))
+                    (next (aref next-vector next) (aref next-vector next)))
+                   ((zerop next) nil)
+                 (declare (type index/2 next))
+                 (when (> i length)
+                   (signal-corrupt-hash-table hash-table))
+                 (when (and (= hashing (aref hash-vector next))
+                            (funcall test-fun key (aref table (* 2 next))))
+                   (return-from %remhash
+                     (clear-slot next-vector prior next))))))))))
 
 (defun remhash (key hash-table)
   #!+sb-doc
-  "Remove the entry in HASH-TABLE associated with KEY. Return T if there
-   was such an entry, or NIL if not."
+  "Remove the entry in HASH-TABLE associated with KEY. Return T if
+there was such an entry, or NIL if not."
   (declare (type hash-table hash-table)
-	   (values (member t nil)))
-  (without-gcing
-   ;; We need to rehash here so that a current key can be found if it
-   ;; exists.
-   (cond ((= (get-header-data (hash-table-table hash-table))
-	     sb!vm:vector-must-rehash-subtype)
-	  (rehash-without-growing hash-table))
-	 ((not (zerop (hash-table-needing-rehash hash-table)))
-	  (flush-needing-rehash hash-table)))
-
-   ;; Search for key in the hash table.
-   (multiple-value-bind (hashing eq-based)
-       (funcall (hash-table-hash-fun hash-table) key)
-     (declare (type hash hashing))
-     (let* ((index-vector (hash-table-index-vector hash-table))
-	    (length (length index-vector))
-	    (index (rem hashing length))
-	    (next (aref index-vector index))
-	    (table (hash-table-table hash-table))
-	    (next-vector (hash-table-next-vector hash-table))
-	    (hash-vector (hash-table-hash-vector hash-table))
-	    (test-fun (hash-table-test-fun hash-table)))
-       (declare (type index index next))
-       (flet ((clear-slot (chain-vector prior-slot-location slot-location)
-                ;; Mark slot as empty.
-                (setf (aref table (* 2 slot-location)) +empty-ht-slot+
-                      (aref table (1+ (* 2 slot-location))) +empty-ht-slot+)
-                ;; Update the prior pointer in the chain to skip this.
-                (setf (aref chain-vector prior-slot-location)
-                      (aref next-vector slot-location))
-                ;; Push KV slot onto free chain.
-                (setf (aref next-vector slot-location)
-                      (hash-table-next-free-kv hash-table))
-                (setf (hash-table-next-free-kv hash-table) slot-location)
-                (when hash-vector
-                  (setf (aref hash-vector slot-location) +magic-hash-vector-value+))
-                (decf (hash-table-number-entries hash-table))
-                t))
-         (cond ((zerop next)
-                nil)
-               ((if (or eq-based (not hash-vector))
-                    (eq key (aref table (* 2 next)))
-                    (and (= hashing (aref hash-vector next))
-                         (funcall test-fun key (aref table (* 2 next)))))
-                (clear-slot index-vector index next))
-               ;; Search next-vector chain for a matching key.
-               ((or eq-based (not hash-vector))
-                ;; EQ based
-                (do ((prior next next)
-                     (next (aref next-vector next) (aref next-vector next)))
-                    ((zerop next) nil)
-                  (declare (type index next))
-                  (when (eq key (aref table (* 2 next)))
-                    (return-from remhash (clear-slot next-vector prior next)))))
-               (t
-                ;; not EQ based
-                (do ((prior next next)
-                     (next (aref next-vector next) (aref next-vector next)))
-                    ((zerop next) nil)
-                  (declare (type index next))
-                  (when (and (= hashing (aref hash-vector next))
-                             (funcall test-fun key (aref table (* 2 next))))
-                    (return-from remhash (clear-slot next-vector prior next)))))))))))
+           (values (member t nil)))
+  (with-hash-table-locks (hash-table :inline (%remhash) :pin (key))
+    ;; For now, just clear the cache
+    (setf (hash-table-cache hash-table) nil)
+    (%remhash key hash-table)))
 
 (defun clrhash (hash-table)
   #!+sb-doc
-  "This removes all the entries from HASH-TABLE and returns the hash table
-   itself."
-  (let* ((kv-vector (hash-table-table hash-table))
-	 (kv-length (length kv-vector))
-	 (next-vector (hash-table-next-vector hash-table))
-	 (hash-vector (hash-table-hash-vector hash-table))
-	 (size (length next-vector))
-	 (index-vector (hash-table-index-vector hash-table))
-	 (length (length index-vector)))
-    ;; Disable GC tricks.
-    (set-header-data kv-vector sb!vm:vector-normal-subtype)
-    ;; Mark all slots as empty by setting all keys and values to magic
-    ;; tag.
-    (do ((i 2 (1+ i)))
-	((>= i kv-length))
-      (setf (aref kv-vector i) +empty-ht-slot+))
-    (aver (eq (aref kv-vector 0) hash-table))
-    ;; Set up the free list, all free.
-    (do ((i 1 (1+ i)))
-	((>= i (1- size)))
-      (setf (aref next-vector i) (1+ i)))
-    (setf (aref next-vector (1- size)) 0)
-    (setf (hash-table-next-free-kv hash-table) 1)
-    (setf (hash-table-needing-rehash hash-table) 0)
-    ;; Clear the index-vector.
-    (dotimes (i length)
-      (setf (aref index-vector i) 0))
-    ;; Clear the hash-vector.
-    (when hash-vector
-      (dotimes (i size)
-	(setf (aref hash-vector i) +magic-hash-vector-value+))))
-  (setf (hash-table-number-entries hash-table) 0)
+  "This removes all the entries from HASH-TABLE and returns the hash
+table itself."
+  (when (plusp (hash-table-number-entries hash-table))
+    (with-hash-table-locks (hash-table)
+      (let* ((kv-vector (hash-table-table hash-table))
+             (next-vector (hash-table-next-vector hash-table))
+             (hash-vector (hash-table-hash-vector hash-table))
+             (size (length next-vector))
+             (index-vector (hash-table-index-vector hash-table)))
+        ;; Disable GC tricks.
+        (set-header-data kv-vector sb!vm:vector-normal-subtype)
+        ;; Mark all slots as empty by setting all keys and values to magic
+        ;; tag.
+        (aver (eq (aref kv-vector 0) hash-table))
+        (fill kv-vector +empty-ht-slot+ :start 2)
+        ;; Set up the free list, all free.
+        (do ((i 1 (1+ i)))
+            ((>= i (1- size)))
+          (setf (aref next-vector i) (1+ i)))
+        (setf (aref next-vector (1- size)) 0)
+        (setf (hash-table-next-free-kv hash-table) 1)
+        ;; Clear the index-vector.
+        (fill index-vector 0)
+        ;; Clear the hash-vector.
+        (when hash-vector
+          (fill hash-vector +magic-hash-vector-value+)))
+      (setf (hash-table-cache hash-table) nil)
+      (setf (hash-table-number-entries hash-table) 0)))
   hash-table)
+
 
 ;;;; MAPHASH
 
@@ -640,43 +1000,51 @@
 (declaim (inline maphash))
 (defun maphash (function-designator hash-table)
   #!+sb-doc
-  "For each entry in HASH-TABLE, call the designated two-argument function
-   on the key and value of the entry. Return NIL."
+  "For each entry in HASH-TABLE, call the designated two-argument function on
+the key and value of the entry. Return NIL.
+
+Consequences are undefined if HASH-TABLE is mutated during the call to
+MAPHASH, except for changing or removing elements corresponding to the
+current key. The applies to all threads, not just the current one --
+even for synchronized hash-tables. If the table may be mutated by
+another thread during iteration, use eg. SB-EXT:WITH-LOCKED-HASH-TABLE
+to protect the MAPHASH call."
+  ;; This essentially duplicates WITH-HASH-TABLE-ITERATOR, so
+  ;; any changes here should be reflected there as well.
   (let ((fun (%coerce-callable-to-fun function-designator))
-	(size (length (hash-table-next-vector hash-table))))
+        (size (length (hash-table-next-vector hash-table))))
     (declare (type function fun))
     (do ((i 1 (1+ i)))
-	((>= i size))
-      (declare (type index i))
+        ((>= i size))
+      (declare (type index/2 i))
       (let* ((kv-vector (hash-table-table hash-table))
-	     (key (aref kv-vector (* 2 i)))
-	     (value (aref kv-vector (1+ (* 2 i)))))
-	(unless (and (eq key +empty-ht-slot+)
-		     (eq value +empty-ht-slot+))
-	  (funcall fun key value))))))
+             (key (aref kv-vector (* 2 i)))
+             (value (aref kv-vector (1+ (* 2 i)))))
+        ;; We are running without locking or WITHOUT-GCING. For a weak
+        ;; :VALUE hash table it's possible that the GC hit after KEY
+        ;; was read and now the entry is gone. So check if either the
+        ;; key or the value is empty.
+        (unless (or (eq key +empty-ht-slot+)
+                    (eq value +empty-ht-slot+))
+          (funcall fun key value))))))
 
 ;;;; methods on HASH-TABLE
 
 ;;; Return a list of keyword args and values to use for MAKE-HASH-TABLE
 ;;; when reconstructing HASH-TABLE.
 (defun %hash-table-ctor-args (hash-table)
-  (when (hash-table-weak-p hash-table)
-    ;; FIXME: This might actually work with no trouble, but as of
-    ;; sbcl-0.6.12.10 when this code was written, weak hash tables
-    ;; weren't working yet, so I couldn't test it. When weak hash
-    ;; tables are supported again, this should be fixed.
-    (error "can't dump weak hash tables readably")) ; defensive programming..
   `(:test             ',(hash-table-test             hash-table)
     :size             ',(hash-table-size             hash-table)
     :rehash-size      ',(hash-table-rehash-size      hash-table)
-    :rehash-threshold ',(hash-table-rehash-threshold hash-table)))
+    :rehash-threshold ',(hash-table-rehash-threshold hash-table)
+    :weakness         ',(hash-table-weakness         hash-table)))
 
 ;;; Return an association list representing the same data as HASH-TABLE.
 (defun %hash-table-alist (hash-table)
   (let ((result nil))
     (maphash (lambda (key value)
-	       (push (cons key value) result))
-	     hash-table)
+               (push (cons key value) result))
+             hash-table)
     result))
 
 ;;; Stuff an association list into HASH-TABLE. Return the hash table,
@@ -690,23 +1058,23 @@
 
 (def!method print-object ((hash-table hash-table) stream)
   (declare (type stream stream))
-  (cond ((not *print-readably*)
-	 (print-unreadable-object (hash-table stream :type t :identity t)
-	   (format stream
-		   ":TEST ~S :COUNT ~S"
-		   (hash-table-test hash-table)
-		   (hash-table-count hash-table))))
-	((not *read-eval*)
-	 (error "can't print hash tables readably without *READ-EVAL*"))
-	(t
-	 (with-standard-io-syntax
-	  (format stream
-		  "#.~W"
-		  `(%stuff-hash-table (make-hash-table ,@(%hash-table-ctor-args
-							  hash-table))
-				     ',(%hash-table-alist hash-table)))))))
+  (cond ((or (not *print-readably*) (not *read-eval*))
+         (print-unreadable-object (hash-table stream :type t :identity t)
+           (format stream
+                   ":TEST ~S :COUNT ~S~@[ :WEAKNESS ~S~]"
+                   (hash-table-test hash-table)
+                   (hash-table-count hash-table)
+                   (hash-table-weakness hash-table))))
+        (t
+         (write-string "#." stream)
+         (write `(%stuff-hash-table (make-hash-table ,@(%hash-table-ctor-args
+                                                          hash-table))
+                                     ',(%hash-table-alist hash-table))
+                :stream stream))))
 
 (def!method make-load-form ((hash-table hash-table) &optional environment)
   (declare (ignore environment))
   (values `(make-hash-table ,@(%hash-table-ctor-args hash-table))
-	  `(%stuff-hash-table ,hash-table ',(%hash-table-alist hash-table))))
+          `(%stuff-hash-table ,hash-table ',(%hash-table-alist hash-table))))
+
+