From c4ee57e5e63c209f79c441c5b5de6647f1f547a8 Mon Sep 17 00:00:00 2001
From: Karl Tomlinson <karlt+@karlt.net>
Date: Mon, 16 Apr 2018 19:43:56 +1200
Subject: [PATCH] bug 1455210 call CycleCollectedJSContext::Get() only once in
 EnterDebuggerEventLoop() r=baku

The WorkerJSContext is created and destroyed after entry and before exit from
WorkerThreadPrimaryRunnable::Run().  WorkerPrivate::EnterDebuggerEventLoop()
is called only while WorkerThreadPrimaryRunnable::Run is on the stack, and so
the CycleCollectedJSContext will not change.

MozReview-Commit-ID: HMJ8fpKC6E3

--HG--
extra : rebase_source : d481f4513f9e5ed29224ce01534fa3de95bc7ae4
---
 dom/workers/WorkerPrivate.cpp | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/dom/workers/WorkerPrivate.cpp b/dom/workers/WorkerPrivate.cpp
index 5fd87da83b9b..207c45ba1528 100644
--- a/dom/workers/WorkerPrivate.cpp
+++ b/dom/workers/WorkerPrivate.cpp
@@ -4402,6 +4402,7 @@ WorkerPrivate::EnterDebuggerEventLoop()
 
   JSContext* cx = GetJSContext();
   MOZ_ASSERT(cx);
+  CycleCollectedJSContext* ccjscx = CycleCollectedJSContext::Get();
 
   uint32_t currentEventLoopLevel = ++mDebuggerEventLoopLevel;
 
@@ -4424,9 +4425,8 @@ WorkerPrivate::EnterDebuggerEventLoop()
     {
       MutexAutoLock lock(mMutex);
 
-      CycleCollectedJSContext* context = CycleCollectedJSContext::Get();
       std::queue<RefPtr<MicroTaskRunnable>>& debuggerMtQueue =
-        context->GetDebuggerMicroTaskQueue();
+        ccjscx->GetDebuggerMicroTaskQueue();
       while (mControlQueue.IsEmpty() &&
              !(debuggerRunnablesPending = !mDebuggerQueue.IsEmpty()) &&
              debuggerMtQueue.empty()) {
@@ -4437,8 +4437,7 @@ WorkerPrivate::EnterDebuggerEventLoop()
 
       // XXXkhuey should we abort JS on the stack here if we got Abort above?
     }
-    CycleCollectedJSContext* context = CycleCollectedJSContext::Get();
-    context->PerformDebuggerMicroTaskCheckpoint();
+    ccjscx->PerformDebuggerMicroTaskCheckpoint();
     if (debuggerRunnablesPending) {
       // Start the periodic GC timer if it is not already running.
       SetGCTimerMode(PeriodicTimer);
@@ -4455,8 +4454,7 @@ WorkerPrivate::EnterDebuggerEventLoop()
       static_cast<nsIRunnable*>(runnable)->Run();
       runnable->Release();
 
-      CycleCollectedJSContext* ccjs = CycleCollectedJSContext::Get();
-      ccjs->PerformDebuggerMicroTaskCheckpoint();
+      ccjscx->PerformDebuggerMicroTaskCheckpoint();
 
       // Now *might* be a good time to GC. Let the JS engine make the decision.
       if (JS::CurrentGlobalOrNull(cx)) {