Bug 1045945 - Initialize the destroy principals callback for workers r=bent

dom/workers/Principal.cpp

@@ -6,23 +6,37 @@
 #include "Principal.h"
 
 #include "jsapi.h"
+#include "mozilla/Assertions.h"
 
 BEGIN_WORKERS_NAMESPACE
 
 JSPrincipals*
 GetWorkerPrincipal()
 {
-  static Atomic<bool> sInitialized(false);
   static JSPrincipals sPrincipal;
 
-  bool isInitialized = sInitialized.exchange(true);
-  if (!isInitialized) {
-    sPrincipal.refcount = 1;
+  /*
+   * To make sure the the principals refcount is initialized to one, atomically
+   * increment it on every pass though this function. If we discover this wasn't
+   * the first time, decrement it again. This avoids the need for
+   * synchronization.
+   */
+  int32_t prevRefcount = sPrincipal.refcount++;
+  if (prevRefcount > 0) {
+    --sPrincipal.refcount;
+  } else {
 #ifdef DEBUG
     sPrincipal.debugToken = kJSPrincipalsDebugToken;
 #endif
   }
+
   return &sPrincipal;
 }
 
+void
+DestroyWorkerPrincipals(JSPrincipals* aPrincipals)
+{
+  MOZ_ASSERT_UNREACHABLE("Worker principals refcount should never fall below one");
+}
+
 END_WORKERS_NAMESPACE

dom/workers/Principal.h

@@ -13,6 +13,9 @@ BEGIN_WORKERS_NAMESPACE
 JSPrincipals*
 GetWorkerPrincipal();
 
+void
+DestroyWorkerPrincipals(JSPrincipals* aPrincipals);
+
 END_WORKERS_NAMESPACE
 
 #endif /* mozilla_dom_workers_principal_h__ */

dom/workers/RuntimeService.cpp

@@ -61,6 +61,7 @@
 #include "nsThreadManager.h"
 #endif
 
+#include "Principal.h"
 #include "ServiceWorker.h"
 #include "SharedWorker.h"
 #include "WorkerPrivate.h"
@@ -852,6 +853,7 @@ public:
                               WORKER_DEFAULT_NURSERY_SIZE),
     mWorkerPrivate(aWorkerPrivate)
   {
+    JS_InitDestroyPrincipalsCallback(Runtime(), DestroyWorkerPrincipals);
   }
 
   ~WorkerJSRuntime()

js/public/Principals.h

@@ -24,6 +24,8 @@ struct JSPrincipals {
     uint32_t    debugToken;
 #endif
 
+    JSPrincipals() : refcount(0) {}
+
     void setDebugToken(uint32_t token) {
 # ifdef JS_DEBUG
         debugToken = token;