Bug 963895. Add threadsafe versions of AutoJSContext/AutoSafeJSContext. r=bholley

dom/bindings/Exceptions.cpp

@@ -378,10 +378,7 @@ NS_IMETHODIMP JSStackFrame::GetFilename(nsACString& aFilename)
   if (!mFilenameInitialized) {
     JS::FrameDescription& desc = mStackDescription->FrameAt(mIndex);
     if (desc.script()) {
-      // This cx dance is silly, since JS_GetScriptFilename ignores
-      // its cx argument.
-      JSContext* cx = nsContentUtils::GetDefaultJSContextForThread();
-      JSAutoRequest ar(cx);
+      ThreadsafeAutoSafeJSContext cx;
       JSAutoCompartment ac(cx, desc.script());
       const char* filename = JS_GetScriptFilename(cx, desc.script());
       if (filename) {
@@ -407,8 +404,7 @@ NS_IMETHODIMP JSStackFrame::GetName(nsACString& aFunction)
   if (!mFunnameInitialized) {
     JS::FrameDescription& desc = mStackDescription->FrameAt(mIndex);
     if (desc.fun() && desc.script()) {
-      JSContext* cx = nsContentUtils::GetDefaultJSContextForThread();
-      JSAutoRequest ar(cx);
+      ThreadsafeAutoSafeJSContext cx;
       JSAutoCompartment ac(cx, desc.script());
       JS::Rooted<JSFunction*> fun(cx, desc.fun());
       JS::Rooted<JSString*> funid(cx, JS_GetFunctionDisplayId(fun));

js/xpconnect/src/moz.build

@@ -91,6 +91,7 @@ LOCAL_INCLUDES += [
     '/content/svg/content/src',
     '/dom/base',
     '/dom/events',
+    '/dom/workers',
     '/js/ipc',
     '/layout/base',
     '/layout/style',

js/xpconnect/src/nsCxPusher.cpp

@@ -10,6 +10,7 @@
 #include "mozilla/dom/EventTarget.h"
 #include "nsDOMJSUtils.h"
 #include "xpcprivate.h"
+#include "WorkerPrivate.h"
 
 using mozilla::dom::EventTarget;
 using mozilla::DebugOnly;
@@ -198,11 +199,55 @@ AutoJSContext::operator JSContext*() const
   return mCx;
 }
 
+ThreadsafeAutoJSContext::ThreadsafeAutoJSContext(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM_IN_IMPL)
+{
+  MOZ_GUARD_OBJECT_NOTIFIER_INIT;
+
+  if (NS_IsMainThread()) {
+    mCx = nullptr;
+    mAutoJSContext.construct();
+  } else {
+    mCx = mozilla::dom::workers::GetCurrentThreadJSContext();
+    mRequest.construct(mCx);
+  }
+}
+
+ThreadsafeAutoJSContext::operator JSContext*() const
+{
+  if (mCx) {
+    return mCx;
+  } else {
+    return mAutoJSContext.ref();
+  }
+}
+
 AutoSafeJSContext::AutoSafeJSContext(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM_IN_IMPL)
   : AutoJSContext(true MOZ_GUARD_OBJECT_NOTIFIER_PARAM_TO_PARENT)
 {
 }
 
+ThreadsafeAutoSafeJSContext::ThreadsafeAutoSafeJSContext(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM_IN_IMPL)
+{
+  MOZ_GUARD_OBJECT_NOTIFIER_INIT;
+
+  if (NS_IsMainThread()) {
+    mCx = nullptr;
+    mAutoSafeJSContext.construct();
+  } else {
+    mCx = mozilla::dom::workers::GetCurrentThreadJSContext();
+    mRequest.construct(mCx);
+  }
+}
+
+ThreadsafeAutoSafeJSContext::operator JSContext*() const
+{
+  if (mCx) {
+    return mCx;
+  } else {
+    return mAutoSafeJSContext.ref();
+  }
+}
+
 AutoPushJSContext::AutoPushJSContext(JSContext *aCx) : mCx(aCx)
 {
   if (mCx && mCx != nsXPConnect::XPConnect()->GetCurrentJSContext()) {

js/xpconnect/src/nsCxPusher.h

@@ -114,6 +114,22 @@ private:
   MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
 };
 
+/**
+ * Use ThreadsafeAutoJSContext when you want an AutoJSContext but might be
+ * running on a worker thread.
+ */
+class MOZ_STACK_CLASS ThreadsafeAutoJSContext {
+public:
+  ThreadsafeAutoJSContext(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM);
+  operator JSContext*() const;
+
+private:
+  JSContext* mCx; // Used on workers.  Null means mainthread.
+  Maybe<JSAutoRequest> mRequest; // Used on workers.
+  Maybe<AutoJSContext> mAutoJSContext; // Used on main thread.
+  MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
+};
+
 /**
  * AutoSafeJSContext is similar to AutoJSContext but will only return the safe
  * JS context. That means it will never call ::GetCurrentJSContext().
@@ -123,6 +139,21 @@ public:
   AutoSafeJSContext(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM);
 };
 
+/**
+ * Like AutoSafeJSContext but can be used safely on worker threads.
+ */
+class MOZ_STACK_CLASS ThreadsafeAutoSafeJSContext {
+public:
+  ThreadsafeAutoSafeJSContext(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM);
+  operator JSContext*() const;
+
+private:
+  JSContext* mCx; // Used on workers.  Null means mainthread.
+  Maybe<JSAutoRequest> mRequest; // Used on workers.
+  Maybe<AutoSafeJSContext> mAutoSafeJSContext; // Used on main thread.
+  MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
+};
+
 /**
  * Use AutoPushJSContext when you want to use a specific JSContext that may or
  * may not be already on the stack. This differs from nsCxPusher in that it only