X-Git-Url: http://repo.macrolet.net/gitweb/?a=blobdiff_plain;ds=sidebyside;f=src%2Fcode%2Fsysmacs.lisp;h=aca1cc59e23687ce4b5f616f956c3ce6dd82f9d6;hb=355e6c09a8f7f528a838f7a50b99ad77811b51a2;hp=bcb82555a2fccde30c1a3ea614784a1f82bde9b5;hpb=7beac8a1fb3cfdeda0e168eb597a701951032270;p=sbcl.git

diff --git a/src/code/sysmacs.lisp b/src/code/sysmacs.lisp
index bcb8255..aca1cc5 100644
--- a/src/code/sysmacs.lisp
+++ b/src/code/sysmacs.lisp
@@ -32,19 +32,30 @@
 
 (defmacro without-gcing (&body body)
   #!+sb-doc
-  "Executes the forms in the body without doing a garbage
-collection. It inhibits both automatically and explicitly triggered
-gcs. Finally, upon leaving the BODY if gc is not inhibited it runs the
-pending gc. Similarly, if gc is triggered in another thread then it
-waits until gc is enabled in this thread."
+  "Executes the forms in the body without doing a garbage collection. It
+inhibits both automatically and explicitly triggered collections. Finally,
+upon leaving the BODY if gc is not inhibited it runs the pending gc.
+Similarly, if gc is triggered in another thread then it waits until gc is
+enabled in this thread.
+
+Implies SB-SYS:WITHOUT-INTERRUPTS for BODY, and causes any nested
+SB-SYS:WITH-INTERRUPTS to signal a warning during execution of the BODY.
+
+Should be used with great care, and not at all in multithreaded application
+code: Any locks that are ever acquired while GC is inhibited need to be always
+held with GC inhibited to prevent deadlocks: if T1 holds the lock and is
+stopped for GC while T2 is waiting for the lock inside WITHOUT-GCING the
+system will be deadlocked. Since SBCL does not currently document its internal
+locks, application code can never be certain that this invariant is
+maintained."
   `(unwind-protect
-    (let ((*gc-inhibit* t))
-      ,@body)
-    ;; the test is racy, but it can err only on the overeager side
-    (when (and (not *gc-inhibit*)
-               (or #!+sb-thread *stop-for-gc-pending*
-                   *gc-pending*))
-      (sb!unix::receive-pending-interrupt))))
+        (let* ((*interrupts-enabled* nil)
+               (*gc-inhibit* t))
+          ,@body)
+     (when (or (and *interrupts-enabled* *interrupt-pending*)
+               (and (not *gc-inhibit*)
+                    (or *gc-pending* #!+sb-thread *stop-for-gc-pending*)))
+       (sb!unix::receive-pending-interrupt))))
 
 
 ;;; EOF-OR-LOSE is a useful macro that handles EOF.
@@ -119,6 +130,9 @@ waits until gc is enabled in this thread."
 ;;; This macro sets up some local vars for use by the
 ;;; FAST-READ-CHAR macro within the enclosed lexical scope. The stream
 ;;; is assumed to be a ANSI-STREAM.
+;;;
+;;; KLUDGE: Some functions (e.g. ANSI-STREAM-READ-LINE) use these variables
+;;; directly, instead of indirecting through FAST-READ-CHAR.
 (defmacro prepare-for-fast-read-char (stream &body forms)
   `(let* ((%frc-stream% ,stream)
           (%frc-method% (ansi-stream-in %frc-stream%))
@@ -134,7 +148,7 @@ waits until gc is enabled in this thread."
   `(setf (ansi-stream-in-index %frc-stream%) %frc-index%))
 
 ;;; a macro with the same calling convention as READ-CHAR, to be used
-;;; within the scope of a PREPARE-FOR-FAST-READ-CHAR
+;;; within the scope of a PREPARE-FOR-FAST-READ-CHAR.
 (defmacro fast-read-char (&optional (eof-error-p t) (eof-value ()))
   `(cond
     ((not %frc-buffer%)