(in-package "SB!THREAD")
+;;; CAS Lock
+;;;
+;;; Locks don't come any simpler -- or more lightweight than this. While
+;;; this is probably a premature optimization for most users, we still
+;;; need it internally for implementing condition variables outside Futex
+;;; builds.
+
+(defmacro with-cas-lock ((place) &body body)
+ #!+sb-doc
+ "Runs BODY with interrupts disabled and *CURRENT-THREAD* compare-and-swapped
+into PLACE instead of NIL. PLACE must be a place acceptable to
+COMPARE-AND-SWAP, and must initially hold NIL.
+
+WITH-CAS-LOCK is suitable mostly when the critical section needing protection
+is very small, and cost of allocating a separate lock object would be
+prohibitive. While it is the most lightweight locking constructed offered by
+SBCL, it is also the least scalable if the section is heavily contested or
+long.
+
+WITH-CAS-LOCK can be entered recursively."
+ `(without-interrupts
+ (%with-cas-lock (,place) ,@body)))
+
+(defmacro %with-cas-lock ((place) &body body &environment env)
+ (with-unique-names (self owner)
+ ;; Take care not to multiply-evaluate anything.
+ ;;
+ ;; FIXME: Once we get DEFCAS this can use GET-CAS-EXPANSION.
+ (let* ((placex (sb!xc:macroexpand place env))
+ (place-op (if (consp placex)
+ (car placex)
+ (error "~S: ~S is not a valid place for ~S"
+ 'with-cas-lock
+ place 'sb!ext:compare-and-swap)))
+ (place-args (cdr placex))
+ (temps (make-gensym-list (length place-args) t))
+ (place `(,place-op ,@temps)))
+ `(let* (,@(mapcar #'list temps place-args)
+ (,self *current-thread*)
+ (,owner ,place))
+ (unwind-protect
+ (progn
+ (unless (eq ,owner ,self)
+ (loop while (setf ,owner
+ (or ,place
+ (sb!ext:compare-and-swap ,place nil ,self)))
+ do (thread-yield)))
+ ,@body)
+ (unless (eq ,owner ,self)
+ (sb!ext:compare-and-swap ,place ,self nil)))))))
+
;;; Conditions
(define-condition thread-error (error)
exited. The offending symbol can be accessed using CELL-ERROR-NAME, and the
offending thread using THREAD-ERROR-THREAD."))
-(define-condition join-thread-error (thread-error) ()
+(define-condition join-thread-error (thread-error)
+ ((problem :initarg :problem :reader join-thread-problem))
(:report (lambda (c s)
- (format s "Joining thread failed: thread ~A ~
- did not return normally."
- (thread-error-thread c))))
+ (ecase (join-thread-problem c)
+ (:abort
+ (format s "Joining thread failed: thread ~A ~
+ did not return normally."
+ (thread-error-thread c)))
+ (:timeout
+ (format s "Joining thread timed out: thread ~A ~
+ did not exit in time."
+ (thread-error-thread c))))))
#!+sb-doc
(:documentation
"Signalled when joining a thread fails due to abnormal exit of the thread
(multiple-value-list
(join-thread thread :default cookie))))
(state (if (eq :running info)
- (let* ((lock (thread-waiting-for thread)))
- (typecase lock
+ (let* ((thing (thread-waiting-for thread)))
+ (typecase thing
(cons
- (list "waiting for:" (cdr lock)
- "timeout: " (car lock)))
+ (list "waiting on:" (cdr thing)
+ "timeout: " (car thing)))
(null
(list info))
(t
- (list "waiting for:" lock))))
+ (list "waiting on:" thing))))
(if (eq cookie (car info))
(list :aborted)
:finished)))
(def!method print-object ((mutex mutex) stream)
(print-lock mutex (mutex-name mutex) (mutex-owner mutex) stream))
-(def!method print-object ((spinlock spinlock) stream)
- (print-lock spinlock (spinlock-name spinlock) (spinlock-value spinlock) stream))
-
(defun thread-alive-p (thread)
#!+sb-doc
"Return T if THREAD is still alive. Note that the return value is
(defun block-deferrable-signals ()
(%block-deferrable-signals 0 0))
- #!+sb-lutex
- (progn
- (declaim (inline %lutex-init %lutex-wait %lutex-wake
- %lutex-lock %lutex-unlock))
-
- (define-alien-routine ("lutex_init" %lutex-init)
- int (lutex unsigned-long))
-
- (define-alien-routine ("lutex_wait" %lutex-wait)
- int (queue-lutex unsigned-long) (mutex-lutex unsigned-long))
-
- (define-alien-routine ("lutex_wake" %lutex-wake)
- int (lutex unsigned-long) (n int))
-
- (define-alien-routine ("lutex_lock" %lutex-lock)
- int (lutex unsigned-long))
-
- (define-alien-routine ("lutex_trylock" %lutex-trylock)
- int (lutex unsigned-long))
-
- (define-alien-routine ("lutex_unlock" %lutex-unlock)
- int (lutex unsigned-long))
-
- (define-alien-routine ("lutex_destroy" %lutex-destroy)
- int (lutex unsigned-long))
-
- ;; FIXME: Defining a whole bunch of alien-type machinery just for
- ;; passing primitive lutex objects directly to foreign functions
- ;; doesn't seem like fun right now. So instead we just manually
- ;; pin the lutex, get its address, and let the callee untag it.
- (defmacro with-lutex-address ((name lutex) &body body)
- `(let ((,name ,lutex))
- (with-pinned-objects (,name)
- (let ((,name (get-lisp-obj-address ,name)))
- ,@body))))
-
- (defun make-lutex ()
- (/show0 "Entering MAKE-LUTEX")
- ;; Suppress GC until the lutex has been properly registered with
- ;; the GC.
- (without-gcing
- (let ((lutex (sb!vm::%make-lutex)))
- (/show0 "LUTEX=..")
- (/hexstr lutex)
- (with-lutex-address (lutex lutex)
- (%lutex-init lutex))
- lutex))))
-
- #!-sb-lutex
+ #!+sb-futex
(progn
(declaim (inline futex-wait %futex-wait futex-wake))
(sb!vm::current-thread-offset-sap n))
\f
-;;;; Spinlocks
-
-(defmacro with-deadlocks ((thread lock &optional timeout) &body forms)
- (declare (ignorable timeout))
- (with-unique-names (n-thread n-lock n-timeout new)
+(defmacro with-deadlocks ((thread lock &optional (timeout nil timeoutp)) &body forms)
+ (with-unique-names (n-thread n-lock new n-timeout)
`(let* ((,n-thread ,thread)
(,n-lock ,lock)
- (,n-timeout #!-sb-lutex
- ,(when timeout
+ (,n-timeout ,(when timeoutp
`(or ,timeout
(when sb!impl::*deadline*
sb!impl::*deadline-seconds*))))
(,new (if ,n-timeout
+ ;; Using CONS tells the rest of the system there's a
+ ;; timeout in place, so it isn't considered a deadlock.
(cons ,n-timeout ,n-lock)
,n-lock)))
(declare (dynamic-extent ,new))
;; Interrupt handlers and GC save and restore any
;; previous wait marks using WITHOUT-DEADLOCKS below.
(setf (thread-waiting-for ,n-thread) nil)))))
-
-(declaim (inline get-spinlock release-spinlock))
-
-;;; Should always be called with interrupts disabled.
-(defun get-spinlock (spinlock)
- (declare (optimize (speed 3) (safety 0)))
- (let* ((new *current-thread*)
- (old (sb!ext:compare-and-swap (spinlock-value spinlock) nil new)))
- (when old
- (when (eq old new)
- (error "Recursive lock attempt on ~S." spinlock))
- #!+sb-thread
- (with-deadlocks (new spinlock)
- (flet ((cas ()
- (if (sb!ext:compare-and-swap (spinlock-value spinlock) nil new)
- (thread-yield)
- (return-from get-spinlock t))))
- ;; Try once.
- (cas)
- ;; Check deadlocks
- (with-interrupts (check-deadlock))
- (if (and (not *interrupts-enabled*) *allow-with-interrupts*)
- ;; If interrupts are disabled, but we are allowed to
- ;; enabled them, check for pending interrupts every once
- ;; in a while. %CHECK-INTERRUPTS is taking shortcuts, make
- ;; sure that deferrables are unblocked by doing an empty
- ;; WITH-INTERRUPTS once.
- (progn
- (with-interrupts)
- (loop
- (loop repeat 128 do (cas)) ; 128 is arbitrary here
- (sb!unix::%check-interrupts)))
- (loop (cas)))))))
- t)
-
-(defun release-spinlock (spinlock)
- (declare (optimize (speed 3) (safety 0)))
- ;; On x86 and x86-64 we can get away with no memory barriers, (see
- ;; Linux kernel mailing list "spin_unlock optimization(i386)"
- ;; thread, summary at
- ;; http://kt.iserv.nl/kernel-traffic/kt19991220_47.html#1.
- ;;
- ;; If the compiler may reorder this with other instructions, insert
- ;; compiler barrier here.
- ;;
- ;; FIXME: this does not work on SMP Pentium Pro and OOSTORE systems,
- ;; neither on most non-x86 architectures (but we don't have threads
- ;; on those).
- (setf (spinlock-value spinlock) nil)
-
- ;; FIXME: Is a :memory barrier too strong here? Can we use a :write
- ;; barrier instead?
- #!+(not (or x86 x86-64))
- (barrier (:memory)))
\f
-
;;;; Mutexes
#!+sb-doc
(fdocumentation 'mutex-name 'function)
"The name of the mutex. Setfable.")
-#!+(and sb-thread (not sb-lutex))
+#!+(and sb-thread sb-futex)
(progn
(define-structure-slot-addressor mutex-state-address
:structure mutex
(defun check-deadlock ()
(let* ((self *current-thread*)
(origin (thread-waiting-for self)))
- (labels ((lock-owner (lock)
- (etypecase lock
- (mutex (mutex-%owner lock))
- (spinlock (spinlock-value lock))))
- (detect-deadlock (lock)
- (let ((other-thread (lock-owner lock)))
+ (labels ((detect-deadlock (lock)
+ (let ((other-thread (mutex-%owner lock)))
(cond ((not other-thread))
((eq self other-thread)
(let* ((chain (deadlock-chain self origin))
;; If the thread is waiting with a timeout OTHER-LOCK
;; is a cons, and we don't consider it a deadlock -- since
;; it will time out on its own sooner or later.
- (when (and other-lock (not (consp other-lock)))
+ (when (mutex-p other-lock)
(detect-deadlock other-lock)))))))
(deadlock-chain (thread lock)
- (let* ((other-thread (lock-owner lock))
+ (let* ((other-thread (mutex-owner lock))
(other-lock (when other-thread
(thread-waiting-for other-thread))))
(cond ((not other-thread)
((consp other-lock)
;; There's a timeout -- no deadlock.
(return-from check-deadlock nil))
+ ((waitqueue-p other-lock)
+ ;; Not a lock.
+ (return-from check-deadlock nil))
((eq self other-thread)
;; Done
(list (list thread lock)))
;; Again, the deadlock is gone?
(return-from check-deadlock nil)))))))
;; Timeout means there is no deadlock
- (unless (consp origin)
+ (when (mutex-p origin)
(detect-deadlock origin)
t))))
-(defun get-mutex (mutex &optional new-owner
- (waitp t) (timeout nil))
- #!+sb-doc
- "Deprecated in favor of GRAB-MUTEX."
- (declare (type mutex mutex) (optimize (speed 3))
- #!-sb-thread (ignore waitp timeout))
- (unless new-owner
- (setq new-owner *current-thread*))
+(defun %try-mutex (mutex new-owner)
+ (declare (type mutex mutex) (optimize (speed 3)))
(barrier (:read))
(let ((old (mutex-%owner mutex)))
(when (eq new-owner old)
(error "Recursive lock attempt ~S." mutex))
#!-sb-thread
(when old
- (error "Strange deadlock on ~S in an unithreaded build?" mutex)))
- #!-sb-thread
- (setf (mutex-%owner mutex) new-owner)
- #!+sb-thread
- (with-deadlocks (new-owner mutex timeout)
- ;; FIXME: Lutexes do not currently support deadlines, as at least
- ;; on Darwin pthread_foo_timedbar functions are not supported:
- ;; this means that we probably need to use the Carbon multiprocessing
- ;; functions on Darwin.
- ;;
- ;; FIXME: This is definitely not interrupt safe: what happens if
- ;; we get hit (1) during the lutex calls (ok, they may be safe,
- ;; but has that been checked?) (2) after the lutex call, but
- ;; before setting the mutex owner.
- #!+sb-lutex
- (progn
- (when timeout
- (error "Mutex timeouts not supported on this platform."))
- (when (zerop (with-lutex-address (lutex (mutex-lutex mutex))
- (if waitp
- (let ((once (%lutex-trylock lutex)))
- (cond ((zerop once)
- ;; No need to wait.
- once)
- (t
- (with-interrupts
- ;; Check for deadlocks before waiting
- (check-deadlock)
- (%lutex-lock lutex)))))
- (%lutex-trylock lutex))))
- ;; FIXME: If %LUTEX-LOCK unwinds due to a signal, we may actually
- ;; be holding the lock already -- and but neglect to mark ourselves
- ;; as the owner here. This is bad.
- (setf (mutex-%owner mutex) new-owner)
- (barrier (:write))
- t))
- #!-sb-lutex
- ;; This is a direct translation of the Mutex 2 algorithm from
- ;; "Futexes are Tricky" by Ulrich Drepper.
- (let ((old (sb!ext:compare-and-swap (mutex-state mutex)
- +lock-free+
- +lock-taken+)))
- (unless (or (eql +lock-free+ old) (not waitp))
- (tagbody
- :retry
- (when (or (eql +lock-contested+ old)
- (not (eql +lock-free+
- (sb!ext:compare-and-swap (mutex-state mutex)
- +lock-taken+
- +lock-contested+))))
- ;; Wait on the contested lock.
- (with-interrupts
- (check-deadlock)
- (loop
- (multiple-value-bind (to-sec to-usec stop-sec stop-usec deadlinep)
- (decode-timeout timeout)
- (declare (ignore stop-sec stop-usec))
- (case (with-pinned-objects (mutex)
- (futex-wait (mutex-state-address mutex)
- (get-lisp-obj-address +lock-contested+)
- (or to-sec -1)
- (or to-usec 0)))
- ((1) (if deadlinep
- (signal-deadline)
- (return-from get-mutex nil)))
- ((2))
- (otherwise (return)))))))
- (setf old (sb!ext:compare-and-swap (mutex-state mutex)
- +lock-free+
- +lock-contested+))
- ;; Did we get it?
- (unless (eql +lock-free+ old)
- (go :retry))))
- (cond ((eql +lock-free+ old)
+ (error "Strange deadlock on ~S in an unithreaded build?" mutex))
+ #!-sb-futex
+ (and (not (mutex-%owner mutex))
+ (not (sb!ext:compare-and-swap (mutex-%owner mutex) nil new-owner)))
+ #!+sb-futex
+ ;; From the Mutex 2 algorithm from "Futexes are Tricky" by Ulrich Drepper.
+ (when (eql +lock-free+ (sb!ext:compare-and-swap (mutex-state mutex)
+ +lock-free+
+ +lock-taken+))
+ (let ((prev (sb!ext:compare-and-swap (mutex-%owner mutex) nil new-owner)))
+ (when prev
+ (bug "Old owner in free mutex: ~S" prev))
+ t))))
+
+#!+sb-thread
+(defun %%wait-for-mutex (mutex new-owner to-sec to-usec stop-sec stop-usec)
+ (declare (type mutex mutex) (optimize (speed 3)))
+ #!-sb-futex
+ (declare (ignore to-sec to-usec))
+ #!-sb-futex
+ (flet ((cas ()
+ (loop repeat 24
+ when (and (not (mutex-%owner mutex))
+ (not (sb!ext:compare-and-swap (mutex-%owner mutex) nil
+ new-owner)))
+ do (return-from cas t))
+ ;; Check for pending interrupts.
+ (with-interrupts nil)))
+ (declare (dynamic-extent #'cas))
+ (sb!impl::%%wait-for #'cas stop-sec stop-usec))
+ #!+sb-futex
+ ;; This is a fairly direct translation of the Mutex 2 algorithm from
+ ;; "Futexes are Tricky" by Ulrich Drepper.
+ (flet ((maybe (old)
+ (when (eql +lock-free+ old)
(let ((prev (sb!ext:compare-and-swap (mutex-%owner mutex)
nil new-owner)))
(when prev
(bug "Old owner in free mutex: ~S" prev))
- t))
- (waitp
- (bug "Failed to acquire lock with WAITP."))))))
+ (return-from %%wait-for-mutex t)))))
+ (prog ((old (sb!ext:compare-and-swap (mutex-state mutex)
+ +lock-free+ +lock-taken+)))
+ ;; Got it right off the bat?
+ (maybe old)
+ :retry
+ ;; Mark it as contested, and sleep. (Exception: it was just released.)
+ (when (or (eql +lock-contested+ old)
+ (not (eql +lock-free+
+ (sb!ext:compare-and-swap
+ (mutex-state mutex) +lock-taken+ +lock-contested+))))
+ (when (eql 1 (with-pinned-objects (mutex)
+ (futex-wait (mutex-state-address mutex)
+ (get-lisp-obj-address +lock-contested+)
+ (or to-sec -1)
+ (or to-usec 0))))
+ ;; -1 = EWOULDBLOCK, possibly spurious wakeup
+ ;; 0 = normal wakeup
+ ;; 1 = ETIMEDOUT ***DONE***
+ ;; 2 = EINTR, a spurious wakeup
+ (return-from %%wait-for-mutex nil)))
+ ;; Try to get it, still marking it as contested.
+ (maybe
+ (sb!ext:compare-and-swap (mutex-state mutex) +lock-free+ +lock-contested+))
+ ;; Update timeout if necessary.
+ (when stop-sec
+ (setf (values to-sec to-usec)
+ (sb!impl::relative-decoded-times stop-sec stop-usec)))
+ ;; Spin.
+ (go :retry))))
+
+(defun %wait-for-mutex (mutex self timeout to-sec to-usec stop-sec stop-usec deadlinep)
+ (with-deadlocks (self mutex timeout)
+ (with-interrupts (check-deadlock))
+ (tagbody
+ :again
+ (return-from %wait-for-mutex
+ (or (%%wait-for-mutex mutex self to-sec to-usec stop-sec stop-usec)
+ (when deadlinep
+ (signal-deadline)
+ ;; FIXME: substract elapsed time from timeout...
+ (setf (values to-sec to-usec stop-sec stop-usec deadlinep)
+ (decode-timeout timeout))
+ (go :again)))))))
+
+(defun get-mutex (mutex &optional new-owner (waitp t) (timeout nil))
+ #!+sb-doc
+ "Deprecated in favor of GRAB-MUTEX."
+ (declare (ignorable waitp timeout))
+ (let ((new-owner (or new-owner *current-thread*)))
+ (or (%try-mutex mutex new-owner)
+ #!+sb-thread
+ (when waitp
+ (multiple-value-call #'%wait-for-mutex
+ mutex new-owner timeout (decode-timeout timeout))))))
(defun grab-mutex (mutex &key (waitp t) (timeout nil))
#!+sb-doc
"Acquire MUTEX for the current thread. If WAITP is true (the default) and
the mutex is not immediately available, sleep until it is available.
-If TIMEOUT is given, it specifies a relative timeout, in seconds, on
-how long GRAB-MUTEX should try to acquire the lock in the contested
-case. Unsupported on :SB-LUTEX platforms (eg. Darwin), where a non-NIL
-TIMEOUT signals an error.
+If TIMEOUT is given, it specifies a relative timeout, in seconds, on how long
+GRAB-MUTEX should try to acquire the lock in the contested case.
-If GRAB-MUTEX returns T, the lock acquisition was successful. In case
-of WAITP being NIL, or an expired TIMEOUT, GRAB-MUTEX may also return
-NIL which denotes that GRAB-MUTEX did -not- acquire the lock.
+If GRAB-MUTEX returns T, the lock acquisition was successful. In case of WAITP
+being NIL, or an expired TIMEOUT, GRAB-MUTEX may also return NIL which denotes
+that GRAB-MUTEX did -not- acquire the lock.
Notes:
(ALLOW-WITH-INTERRUPTS (GRAB-MUTEX ...))
...)
- WITHOUT-INTERRUPTS is necessary to avoid an interrupt unwinding
- the call while the mutex is in an inconsistent state while
- ALLOW-WITH-INTERRUPTS allows the call to be interrupted from
- sleep.
+ WITHOUT-INTERRUPTS is necessary to avoid an interrupt unwinding the call
+ while the mutex is in an inconsistent state while ALLOW-WITH-INTERRUPTS
+ allows the call to be interrupted from sleep.
- (GRAB-MUTEX <mutex> :timeout 0.0) differs from
(GRAB-MUTEX <mutex> :waitp nil) in that the former may signal a
- DEADLINE-TIMEOUT if the global deadline was due already on
- entering GRAB-MUTEX.
+ DEADLINE-TIMEOUT if the global deadline was due already on entering
+ GRAB-MUTEX.
- The exact interplay of GRAB-MUTEX and deadlines are reserved to
- change in future versions.
+ The exact interplay of GRAB-MUTEX and deadlines are reserved to change in
+ future versions.
- - It is recommended that you use WITH-MUTEX instead of calling
- GRAB-MUTEX directly.
+ - It is recommended that you use WITH-MUTEX instead of calling GRAB-MUTEX
+ directly.
"
- (get-mutex mutex nil waitp timeout))
+ (declare (ignorable waitp timeout))
+ (let ((self *current-thread*))
+ (or (%try-mutex mutex self)
+ #!+sb-thread
+ (when waitp
+ (multiple-value-call #'%wait-for-mutex
+ mutex self timeout (decode-timeout timeout))))))
(defun release-mutex (mutex &key (if-not-owner :punt))
#!+sb-doc
;; Order matters: set owner to NIL before releasing state.
(let* ((self *current-thread*)
(old-owner (sb!ext:compare-and-swap (mutex-%owner mutex) self nil)))
- (unless (eql self old-owner)
+ (unless (eq self old-owner)
(ecase if-not-owner
((:punt) (return-from release-mutex nil))
((:warn)
(warn "Releasing ~S, owned by another thread: ~S" mutex old-owner))
- ((:force))))
- #!+sb-thread
- (when old-owner
+ ((:force)))
(setf (mutex-%owner mutex) nil)
- #!+sb-lutex
- (with-lutex-address (lutex (mutex-lutex mutex))
- (%lutex-unlock lutex))
- #!-sb-lutex
+ ;; FIXME: Is a :memory barrier too strong here? Can we use a :write
+ ;; barrier instead?
+ (barrier (:memory)))
+ #!+sb-futex
+ (when old-owner
;; FIXME: once ATOMIC-INCF supports struct slots with word sized
;; unsigned-byte type this can be used:
;;
;;;; Waitqueues/condition variables
+#!+(or (not sb-thread) sb-futex)
(defstruct (waitqueue (:constructor %make-waitqueue))
#!+sb-doc
"Waitqueue type."
(name nil :type (or null thread-name))
- #!+(and sb-lutex sb-thread)
- (lutex (make-lutex))
- #!-sb-lutex
+ #!+sb-futex
(token nil))
+#!+(and sb-thread (not sb-futex))
+(progn
+ (defstruct (waitqueue (:constructor %make-waitqueue))
+ #!+sb-doc
+ "Waitqueue type."
+ (name nil :type (or null thread-name))
+ ;; For WITH-CAS-LOCK: because CONDITION-WAIT must be able to call
+ ;; %WAITQUEUE-WAKEUP without re-aquiring the mutex, we need a separate
+ ;; lock. In most cases this should be uncontested thanks to the mutex --
+ ;; the only case where that might not be true is when CONDITION-WAIT
+ ;; unwinds and %WAITQUEUE-DROP is called.
+ %owner
+ %head
+ %tail)
+
+ (defun %waitqueue-enqueue (thread queue)
+ (setf (thread-waiting-for thread) queue)
+ (let ((head (waitqueue-%head queue))
+ (tail (waitqueue-%tail queue))
+ (new (list thread)))
+ (unless head
+ (setf (waitqueue-%head queue) new))
+ (when tail
+ (setf (cdr tail) new))
+ (setf (waitqueue-%tail queue) new)
+ nil))
+ (defun %waitqueue-drop (thread queue)
+ (setf (thread-waiting-for thread) nil)
+ (let ((head (waitqueue-%head queue)))
+ (do ((list head (cdr list))
+ (prev nil))
+ ((eq (car list) thread)
+ (let ((rest (cdr list)))
+ (cond (prev
+ (setf (cdr prev) rest))
+ (t
+ (setf (waitqueue-%head queue) rest
+ prev rest)))
+ (unless rest
+ (setf (waitqueue-%tail queue) prev))))
+ (setf prev list)))
+ nil)
+ (defun %waitqueue-wakeup (queue n)
+ (declare (fixnum n))
+ (loop while (plusp n)
+ for next = (let ((head (waitqueue-%head queue))
+ (tail (waitqueue-%tail queue)))
+ (when head
+ (if (eq head tail)
+ (setf (waitqueue-%head queue) nil
+ (waitqueue-%tail queue) nil)
+ (setf (waitqueue-%head queue) (cdr head)))
+ (car head)))
+ while next
+ do (when (eq queue (sb!ext:compare-and-swap (thread-waiting-for next) queue nil))
+ (decf n)))
+ nil))
+
(def!method print-object ((waitqueue waitqueue) stream)
(print-unreadable-object (waitqueue stream :type t :identity t)
(format stream "~@[~A~]" (waitqueue-name waitqueue))))
(setf (fdocumentation 'waitqueue-name 'function)
"The name of the waitqueue. Setfable.")
-#!+(and sb-thread (not sb-lutex))
+#!+(and sb-thread sb-futex)
(define-structure-slot-addressor waitqueue-token-address
:structure waitqueue
:slot token)
-(defun condition-wait (queue mutex)
+(defun condition-wait (queue mutex &key timeout)
#!+sb-doc
- "Atomically release MUTEX and enqueue ourselves on QUEUE. Another thread may
-subsequently notify us using CONDITION-NOTIFY, at which time we reacquire
-MUTEX and return to the caller.
+ "Atomically release MUTEX and start waiting on QUEUE for till another thread
+wakes us up using either CONDITION-NOTIFY or CONDITION-BROADCAST on that
+queue, at which point we re-acquire MUTEX and return T.
+
+Spurious wakeups are possible.
+
+If TIMEOUT is given, it is the maximum number of seconds to wait, including
+both waiting for the wakeup and the time to re-acquire MUTEX. Unless both
+wakeup and re-acquisition do not occur within the given time, returns NIL
+without re-acquiring the mutex.
-Important: CONDITION-WAIT may return without CONDITION-NOTIFY having occurred.
-The correct way to write code that uses CONDITION-WAIT is to loop around the
-call, checking the the associated data:
+If CONDITION-WAIT unwinds, it may do so with or without the mutex being held.
+
+Important: Since CONDITION-WAIT may return without CONDITION-NOTIFY having
+occurred the correct way to write code that uses CONDITION-WAIT is to loop
+around the call, checking the the associated data:
(defvar *data* nil)
(defvar *queue* (make-waitqueue))
(defvar *lock* (make-mutex))
;; Consumer
- (defun pop-data ()
+ (defun pop-data (&optional timeout)
(with-mutex (*lock*)
(loop until *data*
- do (condition-wait *queue* *lock*))
+ do (or (condition-wait *queue* *lock* :timeout timeout)
+ ;; Lock not held, must unwind without touching *data*.
+ (return-from pop-data nil)))
(pop *data*)))
;; Producer
(with-mutex (*lock*)
(push data *data*)
(condition-notify *queue*)))
-
-Also note that if CONDITION-WAIT unwinds (due to eg. a timeout) instead of
-returning normally, it may do so without holding the mutex."
- #!-sb-thread (declare (ignore queue))
+"
+ #!-sb-thread (declare (ignore queue timeout))
(assert mutex)
- #!-sb-thread (error "Not supported in unithread builds.")
+ #!-sb-thread
+ (wait-for nil :timeout timeout) ; Yeah...
#!+sb-thread
(let ((me *current-thread*))
(barrier (:read))
(assert (eq me (mutex-%owner mutex)))
- (/show0 "CONDITION-WAITing")
- #!+sb-lutex
- ;; Need to disable interrupts so that we don't miss setting the
- ;; owner on our way out. (pthread_cond_wait handles the actual
- ;; re-acquisition.)
- (without-interrupts
- (unwind-protect
- (progn
- (setf (mutex-%owner mutex) nil)
- (with-lutex-address (queue-lutex-address (waitqueue-lutex queue))
- (with-lutex-address (mutex-lutex-address (mutex-lutex mutex))
- (with-local-interrupts
- (%lutex-wait queue-lutex-address mutex-lutex-address)))))
- (barrier (:write)
- (setf (mutex-%owner mutex) me))))
- #!-sb-lutex
- ;; Need to disable interrupts so that we don't miss grabbing the
- ;; mutex on our way out.
- (without-interrupts
- ;; This setf becomes visible to other CPUS due to the usual
- ;; memory barrier semantics of lock acquire/release. This must
- ;; not be moved into the loop else wakeups may be lost upon
- ;; continuing after a deadline or EINTR.
- (setf (waitqueue-token queue) me)
- (loop
- (multiple-value-bind (to-sec to-usec)
- (allow-with-interrupts (decode-timeout nil))
- (case (unwind-protect
- (with-pinned-objects (queue me)
- ;; RELEASE-MUTEX is purposefully as close to
- ;; FUTEX-WAIT as possible to reduce the size of
- ;; the window where the token may be set by a
- ;; notifier.
- (release-mutex mutex)
- ;; Now we go to sleep using futex-wait. If
- ;; anyone else manages to grab MUTEX and call
- ;; CONDITION-NOTIFY during this comment, it
- ;; will change the token, and so futex-wait
- ;; returns immediately instead of sleeping.
- ;; Ergo, no lost wakeup. We may get spurious
- ;; wakeups, but that's ok.
- (allow-with-interrupts
- (futex-wait (waitqueue-token-address queue)
- (get-lisp-obj-address me)
- ;; our way of saying "no
- ;; timeout":
- (or to-sec -1)
- (or to-usec 0))))
- ;; If we are interrupted while waiting, we should
- ;; do these things before returning. Ideally, in
- ;; the case of an unhandled signal, we should do
- ;; them before entering the debugger, but this is
- ;; better than nothing.
- (allow-with-interrupts (get-mutex mutex)))
- ;; ETIMEDOUT; we know it was a timeout, yet we cannot
- ;; signal a deadline unconditionally here because the
- ;; call to GET-MUTEX may already have signaled it.
- ((1))
- ;; EINTR; we do not need to return to the caller because
- ;; an interleaved wakeup would change the token causing an
- ;; EWOULDBLOCK in the next iteration.
- ((2))
- ;; EWOULDBLOCK, -1 here, is the possible spurious wakeup
- ;; case. 0 is the normal wakeup.
- (otherwise (return))))))))
+ (multiple-value-bind (to-sec to-usec stop-sec stop-usec deadlinep)
+ (decode-timeout timeout)
+ (let ((status :interrupted))
+ ;; Need to disable interrupts so that we don't miss grabbing the
+ ;; mutex on our way out.
+ (without-interrupts
+ (unwind-protect
+ (progn
+ #!-sb-futex
+ (progn
+ (%waitqueue-enqueue me queue)
+ (release-mutex mutex)
+ (setf status
+ (or (flet ((wakeup ()
+ (when (neq queue (thread-waiting-for me))
+ :ok)))
+ (declare (dynamic-extent #'wakeup))
+ (allow-with-interrupts
+ (sb!impl::%%wait-for #'wakeup stop-sec stop-usec)))
+ :timeout)))
+ #!+sb-futex
+ (with-pinned-objects (queue me)
+ (setf (waitqueue-token queue) me)
+ (release-mutex mutex)
+ ;; Now we go to sleep using futex-wait. If anyone else
+ ;; manages to grab MUTEX and call CONDITION-NOTIFY during
+ ;; this comment, it will change the token, and so futex-wait
+ ;; returns immediately instead of sleeping. Ergo, no lost
+ ;; wakeup. We may get spurious wakeups, but that's ok.
+ (setf status
+ (case (allow-with-interrupts
+ (futex-wait (waitqueue-token-address queue)
+ (get-lisp-obj-address me)
+ ;; our way of saying "no
+ ;; timeout":
+ (or to-sec -1)
+ (or to-usec 0)))
+ ((1)
+ ;; 1 = ETIMEDOUT
+ :timeout)
+ (t
+ ;; -1 = EWOULDBLOCK, possibly spurious wakeup
+ ;; 0 = normal wakeup
+ ;; 2 = EINTR, a spurious wakeup
+ :ok)))))
+ #!-sb-futex
+ (%with-cas-lock ((waitqueue-%owner queue))
+ (if (eq queue (thread-waiting-for me))
+ (%waitqueue-drop me queue)
+ (unless (eq :ok status)
+ ;; CONDITION-NOTIFY thinks we've been woken up, but really
+ ;; we're unwinding. Wake someone else up.
+ (%waitqueue-wakeup queue 1))))
+ ;; Update timeout for mutex re-aquisition.
+ (when (and (eq :ok status) to-sec)
+ (setf (values to-sec to-usec)
+ (sb!impl::relative-decoded-times stop-sec stop-usec)))
+ ;; If we ran into deadline, try to get the mutex before
+ ;; signaling. If we don't unwind it will look like a normal
+ ;; return from user perspective.
+ (when (and (eq :timeout status) deadlinep)
+ (let ((got-it (%try-mutex mutex me)))
+ (allow-with-interrupts
+ (signal-deadline)
+ (cond (got-it
+ (return-from condition-wait t))
+ (t
+ ;; The deadline may have changed.
+ (setf (values to-sec to-usec stop-sec stop-usec deadlinep)
+ (decode-timeout timeout))
+ (setf status :ok))))))
+ ;; Re-acquire the mutex for normal return.
+ (when (eq :ok status)
+ (unless (or (%try-mutex mutex me)
+ (allow-with-interrupts
+ (%wait-for-mutex mutex me timeout
+ to-sec to-usec
+ stop-sec stop-usec deadlinep)))
+ (setf status :timeout)))))
+ (or (eq :ok status)
+ (unless (eq :timeout status)
+ ;; The only case we return normally without re-acquiring the
+ ;; mutex is when there is a :TIMEOUT that runs out.
+ (bug "CONDITION-WAIT: invalid status on normal return: ~S" status)))))))
(defun condition-notify (queue &optional (n 1))
#!+sb-doc
- "Notify N threads waiting on QUEUE. The same mutex that is used in
-the corresponding CONDITION-WAIT must be held by this thread during
-this call."
- #!-sb-thread (declare (ignore queue n))
- #!-sb-thread (error "Not supported in unithread builds.")
+ "Notify N threads waiting on QUEUE.
+
+IMPORTANT: The same mutex that is used in the corresponding CONDITION-WAIT
+must be held by this thread during this call."
+ #!-sb-thread
+ (declare (ignore queue n))
+ #!-sb-thread
+ (error "Not supported in unithread builds.")
#!+sb-thread
(declare (type (and fixnum (integer 1)) n))
(/show0 "Entering CONDITION-NOTIFY")
#!+sb-thread
(progn
- #!+sb-lutex
- (with-lutex-address (lutex (waitqueue-lutex queue))
- (%lutex-wake lutex n))
+ #!-sb-futex
+ (with-cas-lock ((waitqueue-%owner queue))
+ (%waitqueue-wakeup queue n))
+ #!+sb-futex
+ (progn
;; No problem if >1 thread notifies during the comment in condition-wait:
;; as long as the value in queue-data isn't the waiting thread's id, it
;; matters not what it is -- using the queue object itself is handy.
;; is visible to all CPUs.
;;
;; ^-- surely futex_wake() involves a memory barrier?
- #!-sb-lutex
- (progn
(setf (waitqueue-token queue) queue)
(with-pinned-objects (queue)
(futex-wake (waitqueue-token-address queue) n)))))
(defun condition-broadcast (queue)
#!+sb-doc
- "Notify all threads waiting on QUEUE."
+ "Notify all threads waiting on QUEUE.
+
+IMPORTANT: The same mutex that is used in the corresponding CONDITION-WAIT
+must be held by this thread during this call."
(condition-notify queue
;; On a 64-bit platform truncating M-P-F to an int
;; results in -1, which wakes up only one thread.
(declaim (inline semaphore-count))
(defun semaphore-count (instance)
"Returns the current count of the semaphore INSTANCE."
+ (barrier (:read))
(semaphore-%count instance))
(defun make-semaphore (&key name (count 0))
"Create a semaphore with the supplied COUNT and NAME."
(%make-semaphore name count))
-(defun wait-on-semaphore (semaphore)
+(defun wait-on-semaphore (semaphore &key timeout)
#!+sb-doc
- "Decrement the count of SEMAPHORE if the count would not be
-negative. Else blocks until the semaphore can be decremented."
+ "Decrement the count of SEMAPHORE if the count would not be negative. Else
+blocks until the semaphore can be decremented. Returns T on success.
+
+If TIMEOUT is given, it is the maximum number of seconds to wait. If the count
+cannot be decremented in that time, returns NIL without decrementing the
+count."
;; A more direct implementation based directly on futexes should be
;; possible.
;;
;; We need to disable interrupts so that we don't forget to
;; decrement the waitcount (which would happen if an asynch
;; interrupt should catch us on our way out from the loop.)
+ ;;
+ ;; FIXME: No timeout on initial mutex acquisition.
(with-system-mutex ((semaphore-mutex semaphore) :allow-with-interrupts t)
;; Quick check: is it positive? If not, enter the wait loop.
(let ((count (semaphore-%count semaphore)))
;; at most one increment per thread waiting on the semaphore.
(sb!ext:atomic-incf (semaphore-waitcount semaphore))
(loop until (plusp (setf count (semaphore-%count semaphore)))
- do (condition-wait (semaphore-queue semaphore)
- (semaphore-mutex semaphore)))
+ do (or (condition-wait (semaphore-queue semaphore)
+ (semaphore-mutex semaphore)
+ :timeout timeout)
+ (return-from wait-on-semaphore nil)))
(setf (semaphore-%count semaphore) (1- count)))
;; Need to use ATOMIC-DECF instead of DECF, as CONDITION-WAIT
;; may unwind without the lock being held due to timeouts.
- (sb!ext:atomic-decf (semaphore-waitcount semaphore)))))))
+ (sb!ext:atomic-decf (semaphore-waitcount semaphore))))))
+ t)
(defun try-semaphore (semaphore &optional (n 1))
#!+sb-doc
"Try to decrement the count of SEMAPHORE by N. If the count were to
become negative, punt and return NIL, otherwise return true."
(declare (type (integer 1) n))
- (with-mutex ((semaphore-mutex semaphore))
+ (with-system-mutex ((semaphore-mutex semaphore) :allow-with-interrupts t)
(let ((new-count (- (semaphore-%count semaphore) n)))
(when (not (minusp new-count))
(setf (semaphore-%count semaphore) new-count)))))
(setf (thread-os-thread thread) nil)
(setq *all-threads* (delete thread *all-threads*))
(when *session*
- (%delete-thread-from-session thread *session*)))
- #!+sb-lutex
- (without-gcing
- (/show0 "FREEING MUTEX LUTEX")
- (with-lutex-address (lutex (mutex-lutex (thread-interruptions-lock thread)))
- (%lutex-destroy lutex))))
+ (%delete-thread-from-session thread *session*))))
(defun terminate-session ()
#!+sb-doc
(wait-on-semaphore setup-sem)
thread)))))
-(defun join-thread (thread &key (default nil defaultp))
+(defun join-thread (thread &key (default nil defaultp) timeout)
#!+sb-doc
- "Suspend current thread until THREAD exits. Returns the result
-values of the thread function. If the thread does not exit normally,
-return DEFAULT if given or else signal JOIN-THREAD-ERROR."
- (with-system-mutex ((thread-result-lock thread) :allow-with-interrupts t)
- (cond ((car (thread-result thread))
- (return-from join-thread
- (values-list (cdr (thread-result thread)))))
- (defaultp
- (return-from join-thread default))))
- (error 'join-thread-error :thread thread))
+ "Suspend current thread until THREAD exits. Return the result values of the
+thread function.
+
+If the thread does not exit normally within TIMEOUT seconds return DEFAULT if
+given, or else signal JOIN-THREAD-ERROR.
+
+NOTE: Return convention in case of a timeout is exprimental and subject to
+change."
+ (let ((lock (thread-result-lock thread))
+ (got-it nil)
+ (problem :timeout))
+ (without-interrupts
+ (unwind-protect
+ (if (setf got-it
+ (allow-with-interrupts
+ ;; Don't use the timeout if the thread is not alive anymore.
+ (grab-mutex lock :timeout (and (thread-alive-p thread) timeout))))
+ (cond ((car (thread-result thread))
+ (return-from join-thread
+ (values-list (cdr (thread-result thread)))))
+ (defaultp
+ (return-from join-thread default))
+ (t
+ (setf problem :abort)))
+ (when defaultp
+ (return-from join-thread default)))
+ (when got-it
+ (release-mutex lock))))
+ (error 'join-thread-error :thread thread :problem problem)))
(defun destroy-thread (thread)
#!+sb-doc
projects / sbcl.git / blobdiff