Changeset 14412 in vbox for trunk

Timestamp:

Nov 20, 2008 1:27:06 PM (16 years ago)

Author:

vboxsync

Message:

semevent-linux.cpp: Use ASMAtomicCmpXchgExU32 to avoid doing unlocked accesses.

File:

• trunk/src/VBox/Runtime/r3/linux/semevent-linux.cpp (modified) (3 diffs)

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

@@ -120 +120 @@
      * Invalidate the semaphore and wake up anyone waiting on it.
      */
-    ASMAtomicXchgSize(&pThis->iMagic, RTSEMEVENT_MAGIC + 1);
+    ASMAtomicXchgSize(&pThis->iMagic, RTSEMEVENT_MAGIC | UINT32_C(0x80000000));
     if (ASMAtomicXchgS32(&pThis->cWaiters, INT32_MIN / 2) > 0)
     {
@@ -148 +148 @@
     for (unsigned i = 0;; i++)
     {
-        int32_t iCur = pThis->cWaiters;
-        if (iCur == 0)
-        {
-            if (ASMAtomicCmpXchgS32(&pThis->cWaiters, -1, 0))
-                break; /* nobody is waiting */
-        }
+        int32_t iCur;
+        if (ASMAtomicCmpXchgExS32(&pThis->cWaiters, -1, 0, &iCur))
+            break; /* nobody is waiting */
         else if (iCur < 0)
             break; /* already signaled */
@@ -189 +186 @@
             }
         }
+
+        /* Check the magic to fend off races with RTSemEventDestroy. */
+        if (RT_UNLIKELY(pThis->iMagic != RTSEMEVENT_MAGIC))
+            return VERR_SEM_DESTROYED;
     }
     return VINF_SUCCESS;