(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."
- `(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))))
-
+ "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."
+ (with-unique-names (without-gcing-body)
+ `(flet ((,without-gcing-body ()
+ ,@body))
+ (if *gc-inhibit*
+ (,without-gcing-body)
+ (without-interrupts
+ ;; We need to disable interrupts before disabling GC, so that
+ ;; signal handlers using locks don't accidentally try to grab
+ ;; them with GC inhibited.
+ ;;
+ ;; It would be nice to implement this with just a single UWP, but
+ ;; unfortunately it seems that it cannot be done: the naive
+ ;; solution of binding both *INTERRUPTS-ENABLED* and
+ ;; *GC-INHIBIT*, and checking for both pending GC and interrupts
+ ;; in the cleanup breaks if we have a GC pending, but no
+ ;; interrupts, and we receive an asynch unwind while checking for
+ ;; the pending GC: we unwind before handling the pending GC, and
+ ;; will be left running with further GCs blocked due to the GC
+ ;; pending flag.
+ (unwind-protect
+ (let ((*gc-inhibit* t))
+ (,without-gcing-body))
+ (when (or *gc-pending* #!+sb-thread *stop-for-gc-pending*)
+ (sb!unix::receive-pending-interrupt))))))))
\f
;;; EOF-OR-LOSE is a useful macro that handles EOF.
(defmacro eof-or-lose (stream eof-error-p eof-value)
`(funcall (,slot stream) stream ,@args))))
(defmacro with-out-stream (stream (slot &rest args) &optional stream-dispatch)
- `(with-out-stream/no-synonym ,stream (,slot ,@args) ,stream-dispatch))
+ `(with-out-stream/no-synonym (out-synonym-of ,stream)
+ (,slot ,@args) ,stream-dispatch))
\f
;;;; These are hacks to make the reader win.
;;; 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%))
`(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%)
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