Keep the purple bit in sync with the purple buffer when suspect and forget calls are dropped on the floor. b=385548 r=graydon

xpcom/base/nsCycleCollector.cpp

@@ -834,8 +834,8 @@ struct nsCycleCollector
     nsCycleCollector();
     ~nsCycleCollector();
 
-    void Suspect(nsISupports *n, PRBool current = PR_FALSE);
-    void Forget(nsISupports *n);
+    PRBool Suspect(nsISupports *n, PRBool current = PR_FALSE);
+    PRBool Forget(nsISupports *n);
     void Allocated(void *n, size_t sz);
     void Freed(void *n);
     void Collect(PRUint32 aTryCollections = 1);
@@ -1365,7 +1365,8 @@ nsCycleCollector::CollectWhite(GCGraph &graph)
 
             if (pinfo->mWasPurple) {
                 nsISupports* s = NS_STATIC_CAST(nsISupports*, p);
-                Forget(s);
+                PRBool forgetResult = Forget(s);
+                NS_ASSERTION(forgetResult, "Forget failed");
             }
         }
         else if (pinfo->mWasPurple) {
@@ -1380,7 +1381,8 @@ nsCycleCollector::CollectWhite(GCGraph &graph)
                          "QI should return the same participant!");
 #endif
             cp->UnmarkPurple(s);
-            Forget(s);
+            PRBool forgetResult = Forget(s);
+            NS_ASSERTION(forgetResult, "Forget failed");
         }
     }
 
@@ -1831,7 +1833,7 @@ nsCycleCollector_isScanSafe(nsISupports *s)
 }
 #endif
 
-void 
+PRBool
 nsCycleCollector::Suspect(nsISupports *n, PRBool current)
 {
     // Re-entering ::Suspect during collection used to be a fault, but
@@ -1839,20 +1841,20 @@ nsCycleCollector::Suspect(nsISupports *n, PRBool current)
     // see some spurious refcount traffic here. 
 
     if (mScanInProgress)
-        return;
+        return PR_FALSE;
 
     NS_ASSERTION(nsCycleCollector_isScanSafe(n),
                  "suspected a non-scansafe pointer");
     NS_ASSERTION(NS_IsMainThread(), "trying to suspect from non-main thread");
 
     if (mParams.mDoNothing)
-        return;
+        return PR_FALSE;
 
 #ifdef DEBUG_CC
     mStats.mSuspectNode++;
 
     if (nsCycleCollector_shouldSuppress(n))
-        return;
+        return PR_FALSE;
 
 #ifndef __MINGW32__
     if (mParams.mHookMalloc)
@@ -1870,10 +1872,12 @@ nsCycleCollector::Suspect(nsISupports *n, PRBool current)
         mBuf.Push(n);
     else
         mPurpleBuf.Put(n);
+
+    return PR_TRUE;
 }
 
 
-void 
+PRBool
 nsCycleCollector::Forget(nsISupports *n)
 {
     // Re-entering ::Forget during collection used to be a fault, but
@@ -1881,12 +1885,12 @@ nsCycleCollector::Forget(nsISupports *n)
     // see some spurious refcount traffic here. 
 
     if (mScanInProgress)
-        return;
+        return PR_FALSE;
 
     NS_ASSERTION(NS_IsMainThread(), "trying to forget from non-main thread");
     
     if (mParams.mDoNothing)
-        return;
+        return PR_TRUE; // it's as good as forgotten
 
 #ifdef DEBUG_CC
     mStats.mForgetNode++;
@@ -1904,6 +1908,7 @@ nsCycleCollector::Forget(nsISupports *n)
 #endif
 
     mPurpleBuf.Remove(n);
+    return PR_TRUE;
 }
 
 #ifdef DEBUG_CC
@@ -2371,27 +2376,31 @@ nsCycleCollector_forgetRuntime(PRUint32 langID)
 }
 
 
-void 
+PRBool
 nsCycleCollector_suspect(nsISupports *n)
 {
     if (sCollector)
-        sCollector->Suspect(n);
+        return sCollector->Suspect(n);
+    return PR_FALSE;
 }
 
 
 void 
 nsCycleCollector_suspectCurrent(nsISupports *n)
 {
-    if (sCollector)
-        sCollector->Suspect(n, PR_TRUE);
+    if (sCollector) {
+        PRBool res = sCollector->Suspect(n, PR_TRUE);
+        NS_ASSERTION(res, "suspectCurrent should not fail");
+    }
 }
 
 
-void 
+PRBool
 nsCycleCollector_forget(nsISupports *n)
 {
     if (sCollector)
-        sCollector->Forget(n);
+        return sCollector->Forget(n);
+    return PR_FALSE;
 }
 
 

xpcom/base/nsCycleCollector.h

@@ -51,9 +51,9 @@ struct nsCycleCollectionLanguageRuntime
     virtual nsCycleCollectionParticipant *ToParticipant(void *p) = 0;
 };
 
-NS_COM void nsCycleCollector_suspect(nsISupports *n);
+NS_COM PRBool nsCycleCollector_suspect(nsISupports *n);
 NS_COM void nsCycleCollector_suspectCurrent(nsISupports *n);
-NS_COM void nsCycleCollector_forget(nsISupports *n);
+NS_COM PRBool nsCycleCollector_forget(nsISupports *n);
 nsresult nsCycleCollector_startup();
 NS_COM void nsCycleCollector_collect();
 void nsCycleCollector_shutdown();

xpcom/glue/nsISupportsImpl.h

@@ -130,7 +130,8 @@ public:
 
     if (NS_UNLIKELY(purple)) {
       NS_ASSERTION(tmp != 0, "purple ISupports pointer with zero refcnt");
-      nsCycleCollector_forget(owner);
+      if (!nsCycleCollector_forget(owner))
+        tmp |= NS_PURPLE_BIT;
     }
 
     mValue = tmp + 1;
@@ -154,9 +155,12 @@ public:
     PRBool shouldBePurple = tmp > 1;
 
     if (NS_UNLIKELY(shouldBePurple && !purple)) {
-      nsCycleCollector_suspect(owner);
+      if (!nsCycleCollector_suspect(owner))
+        shouldBePurple = PR_FALSE;
     } else if (NS_UNLIKELY(tmp == 1 && purple)) {
-      nsCycleCollector_forget(owner);
+      if (!nsCycleCollector_forget(owner)) {
+        NS_NOTREACHED("forget should not fail when reference count hits 0");
+      }
     }
 
     --tmp;