[Sbcl-commits] CVS: sbcl/src/code target-thread.lisp,1.120,1.121

[Tobias R. <tri...@us...>]

Update of /cvsroot/sbcl/sbcl/src/code
In directory sfp-cvsdas-3.v30.ch3.sourceforge.com:/tmp/cvs-serv1164/src/code

Modified Files:
	target-thread.lisp 
Log Message:
1.0.37.6: Add SB-THREAD:TRY-SEMAPHORE.


Index: target-thread.lisp
===================================================================
RCS file: /cvsroot/sbcl/sbcl/src/code/target-thread.lisp,v
retrieving revision 1.120
retrieving revision 1.121
diff -u -d -r1.120 -r1.121
--- target-thread.lisp	11 Mar 2010 10:11:49 -0000	1.120
+++ target-thread.lisp	28 Mar 2010 13:37:22 -0000	1.121
@@ -680,8 +680,26 @@
                        do (condition-wait (semaphore-queue semaphore)
                                           (semaphore-mutex semaphore)))
                  (setf (semaphore-%count semaphore) (1- count)))
+            ;; Even safe when CONDITION-WAIT is unwinded without
+            ;; having reacquired the lock: a) we know at this point
+            ;; that an INCF must have happened before, b) the DECF
+            ;; will become visible to other CPUs as the implicit
+            ;; RELEASE-MUTEX involves a CAS and hence a memory
+            ;; barrier.
             (decf (semaphore-waitcount semaphore)))))))
 
+(defun try-semaphore (semaphore)
+  #!+sb-doc
+  "Try to decrement the count of SEMAPHORE if the count would not be
+negative. Else return NIL."
+  ;; No need for disabling interrupts; the mutex prevents interleaved
+  ;; modifications, and we don't leave temporarily inconsistent state
+  ;; around.
+  (with-mutex ((semaphore-mutex semaphore))
+    (let ((count (semaphore-%count semaphore)))
+      (when (plusp count)
+        (setf (semaphore-%count semaphore) (1- count))))))
+
 (defun signal-semaphore (semaphore &optional (n 1))
   #!+sb-doc
   "Increment the count of SEMAPHORE by N. If there are threads waiting