(setf (fdocumentation 'make-mutex 'function)
"Create a mutex."
(fdocumentation 'mutex-name 'function)
- "The name of the mutex. Setfable."
- (fdocumentation 'mutex-value 'function)
- "The value of the mutex. NIL if the mutex is free. Setfable.")
+ "The name of the mutex. Setfable.")
#!+(and sb-thread (not sb-lutex))
-(define-structure-slot-addressor mutex-value-address
+(progn
+ (define-structure-slot-addressor mutex-state-address
:structure mutex
- :slot value)
-
-(defun get-mutex (mutex &optional (new-value *current-thread*) (waitp t))
+ :slot state)
+ ;; Important: current code assumes these are fixnums or other
+ ;; lisp objects that don't need pinning.
+ (defconstant +lock-free+ 0)
+ (defconstant +lock-taken+ 1)
+ (defconstant +lock-contested+ 2))
+
+(defun get-mutex (mutex &optional (new-owner *current-thread*) (waitp t))
#!+sb-doc
- "Acquire MUTEX, setting it to NEW-VALUE or some suitable default value if
-NIL. If WAITP is non-NIL and the mutex is in use, sleep until it is available."
+ "Acquire MUTEX for NEW-OWNER, which must be a thread or NIL. If
+NEW-OWNER is NIL, it defaults to the current thread. If WAITP is
+non-NIL and the mutex is in use, sleep until it is available.
+
+Note: using GET-MUTEX to assign a MUTEX to another thread then the
+current one is not recommended, and liable to be deprecated.
+
+GET-MUTEX is not interrupt safe. The correct way to call it is:
+
+ (WITHOUT-INTERRUPTS
+ ...
+ (ALLOW-WITH-INTERRUPTS (GET-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.
+
+It is recommended that you use WITH-MUTEX instead of calling GET-MUTEX
+directly."
(declare (type mutex mutex) (optimize (speed 3)))
- (/show0 "Entering GET-MUTEX")
- (unless new-value
- (setq new-value *current-thread*))
- #!-sb-thread
- (let ((old (mutex-value mutex)))
- (when (and old waitp)
- (error "In unithread mode, mutex ~S was requested with WAITP ~S and ~
- new-value ~S, but has already been acquired (with value ~S)."
- mutex waitp new-value old))
- (setf (mutex-value mutex) new-value)
- t)
+ (unless new-owner
+ (setq new-owner *current-thread*))
+ (when (eql new-owner (mutex-%owner mutex))
+ (error "Recursive lock attempt ~S." mutex))
#!+sb-thread
(progn
- (when (eql new-value (mutex-value mutex))
- (warn "recursive lock attempt ~S~%" mutex)
- (format *debug-io* "Thread: ~A~%" *current-thread*)
- (sb!debug:backtrace most-positive-fixnum *debug-io*)
- (force-output *debug-io*))
;; 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
;; 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 value.
+ ;; before setting the mutex owner.
#!+sb-lutex
(when (zerop (with-lutex-address (lutex (mutex-lutex mutex))
(if waitp
(with-interrupts (%lutex-lock lutex))
(%lutex-trylock lutex))))
- (setf (mutex-value mutex) new-value))
+ (setf (mutex-%owner mutex) new-owner)
+ t)
#!-sb-lutex
- (let (old)
- (when (and (setf old (sb!ext:compare-and-swap (mutex-value mutex) nil new-value))
- waitp)
- (loop while old
- do (multiple-value-bind (to-sec to-usec) (decode-timeout nil)
- (when (= 1 (with-pinned-objects (mutex old)
- (futex-wait (mutex-value-address mutex)
- (get-lisp-obj-address old)
- (or to-sec -1)
- (or to-usec 0))))
- (signal-deadline)))
- (setf old (sb!ext:compare-and-swap (mutex-value mutex) nil new-value))))
- (not old))))
+ (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.
+ (multiple-value-bind (to-sec to-usec) (decode-timeout nil)
+ (when (= 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))))
+ (signal-deadline))))
+ (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)
+ (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."))))))
(defun release-mutex (mutex)
#!+sb-doc
"Release MUTEX by setting it to NIL. Wake up threads waiting for
-this mutex."
+this mutex.
+
+RELEASE-MUTEX is not interrupt safe: interrupts should be disabled
+around calls to it.
+
+Signals a WARNING is current thread is not the current owner of the
+mutex."
(declare (type mutex mutex))
- (/show0 "Entering RELEASE-MUTEX")
- (setf (mutex-value mutex) nil)
+ ;; 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)
+ (warn "Releasing ~S, owned by another thread: ~S" mutex old-owner)
+ (setf (mutex-%owner mutex) nil)))
#!+sb-thread
(progn
#!+sb-lutex
(with-lutex-address (lutex (mutex-lutex mutex))
(%lutex-unlock lutex))
#!-sb-lutex
- (futex-wake (mutex-value-address mutex) 1)))
+ (let ((old (sb!ext:compare-and-swap (mutex-state mutex)
+ +lock-taken+ +lock-free+)))
+ (when (eql old +lock-contested+)
+ (sb!ext:compare-and-swap (mutex-state mutex)
+ +lock-contested+ +lock-free+)
+ (with-pinned-objects (mutex)
+ (futex-wake (mutex-state-address mutex) 1))))
+ nil))
;;;; waitqueues/condition variables
(assert mutex)
#!-sb-thread (error "Not supported in unithread builds.")
#!+sb-thread
- (let ((value (mutex-value mutex)))
+ (let ((owner (mutex-%owner mutex)))
(/show0 "CONDITION-WAITing")
#!+sb-lutex
(progn
;; FIXME: This doesn't look interrupt safe!
- (setf (mutex-value mutex) nil)
+ (setf (mutex-%owner mutex) nil)
(with-lutex-address (queue-lutex-address (waitqueue-lutex queue))
(with-lutex-address (mutex-lutex-address (mutex-lutex mutex))
(%lutex-wait queue-lutex-address mutex-lutex-address)))
- (setf (mutex-value mutex) value))
+ (setf (mutex-%owner mutex) owner))
#!-sb-lutex
(unwind-protect
(let ((me *current-thread*))
;; before returning. Ideally, in the case of an unhandled signal,
;; we should do them before entering the debugger, but this is
;; better than nothing.
- (get-mutex mutex value))))
+ (get-mutex mutex owner))))
(defun condition-notify (queue &optional (n 1))
#!+sb-doc
projects / sbcl.git / commitdiff