Changeset 6731 in vbox

Timestamp:

Feb 1, 2008 7:34:27 PM (17 years ago)

Author:

vboxsync

Message:

Fix bug in mutex semaphore reimplementation without pthreads. The releasing of the semaphore was incorrectly using non-atomic operations. Also removed the unneeded setting of the mutex state on timeout, and told the compiler about how to optimize the control flow. Still disabled, as there is no testcase.

File:

• trunk/src/VBox/Runtime/r3/linux/sems-linux.cpp (modified) (4 diffs)

trunk/src/VBox/Runtime/r3/linux/sems-linux.cpp

@@ -866 +866 @@
     int32_t iOld;
     ASMAtomicCmpXchgExS32(&pIntMutexSem->iState, 1, 0, &iOld);
-    if (iOld != 0)
-    {
-        iOld = ASMAtomicXchgS32(&pIntMutexSem->iState, 2);
-        while (iOld != 0)
-        {
+    if (RT_UNLIKELY(iOld != 0))
+    {
+        iOld = ASMAtomicXchgS32(&pIntMutexSem->iState, 2);
+        while (iOld != 0)
+        {
             /*
              * Go to sleep.
@@ -884 +884 @@
             {
                 Assert(pTimeout);
-                iOld = ASMAtomicXchgS32(&pIntMutexSem->iState, 2);
                 return VERR_TIMEOUT;
             }
-            if (rc == 0)
-                /* we'll leave the loop now unless another thread is faster */;
+            if (rc == 0)
+                /* we'll leave the loop now unless another thread is faster */;
             else if (rc == -EWOULDBLOCK)
                 /* retry with new value. */;
@@ -903 +902 @@
             }
 
-            iOld = ASMAtomicXchgS32(&pIntMutexSem->iState, 2);
-        }
+            iOld = ASMAtomicXchgS32(&pIntMutexSem->iState, 2);
+        }
     }
 
@@ -976 +975 @@
     {
         /* somebody is waiting, try wake up one of them. */
-        pIntMutexSem->iState = 0;
+        ASMAtomicXchgS32(&pIntMutexSem->iState, 0);
         (void)sys_futex(&pIntMutexSem->iState, FUTEX_WAKE, 1, NULL, NULL, 0);
     }