Bug 1052052 - Hoist AutoCxPusher into ScriptSettings.h. r=gabor

dom/base/ScriptSettings.cpp

@@ -9,6 +9,7 @@
 #include "mozilla/Assertions.h"
 
 #include "jsapi.h"
+#include "xpcprivate.h" // For AutoCxPusher guts
 #include "xpcpublic.h"
 #include "nsIGlobalObject.h"
 #include "nsIScriptGlobalObject.h"
@@ -18,6 +19,7 @@
 #include "nsPIDOMWindow.h"
 #include "nsTArray.h"
 #include "nsJSUtils.h"
+#include "nsDOMJSUtils.h"
 
 namespace mozilla {
 namespace dom {
@@ -373,5 +375,66 @@ AutoNoJSAPI::AutoNoJSAPI(bool aIsMainThread)
   }
 }
 
+danger::AutoCxPusher::AutoCxPusher(JSContext* cx, bool allowNull)
+{
+  MOZ_ASSERT_IF(!allowNull, cx);
+
+  // Hold a strong ref to the nsIScriptContext, if any. This ensures that we
+  // only destroy the mContext of an nsJSContext when it is not on the cx stack
+  // (and therefore not in use). See nsJSContext::DestroyJSContext().
+  if (cx)
+    mScx = GetScriptContextFromJSContext(cx);
+
+  XPCJSContextStack *stack = XPCJSRuntime::Get()->GetJSContextStack();
+  if (!stack->Push(cx)) {
+    MOZ_CRASH();
+  }
+  mStackDepthAfterPush = stack->Count();
+
+#ifdef DEBUG
+  mPushedContext = cx;
+  mCompartmentDepthOnEntry = cx ? js::GetEnterCompartmentDepth(cx) : 0;
+#endif
+
+  // Enter a request and a compartment for the duration that the cx is on the
+  // stack if non-null.
+  if (cx) {
+    mAutoRequest.emplace(cx);
+
+    // DOM JSContexts don't store their default compartment object on the cx.
+    JSObject *compartmentObject = mScx ? mScx->GetWindowProxy()
+                                       : js::DefaultObjectForContextOrNull(cx);
+    if (compartmentObject)
+      mAutoCompartment.emplace(cx, compartmentObject);
+  }
+}
+
+danger::AutoCxPusher::~AutoCxPusher()
+{
+  // Leave the compartment and request before popping.
+  mAutoCompartment.reset();
+  mAutoRequest.reset();
+
+  // When we push a context, we may save the frame chain and pretend like we
+  // haven't entered any compartment. This gets restored on Pop(), but we can
+  // run into trouble if a Push/Pop are interleaved with a
+  // JSAutoEnterCompartment. Make sure the compartment depth right before we
+  // pop is the same as it was right after we pushed.
+  MOZ_ASSERT_IF(mPushedContext, mCompartmentDepthOnEntry ==
+                                js::GetEnterCompartmentDepth(mPushedContext));
+  DebugOnly<JSContext*> stackTop;
+  MOZ_ASSERT(mPushedContext == nsXPConnect::XPConnect()->GetCurrentJSContext());
+  XPCJSRuntime::Get()->GetJSContextStack()->Pop();
+  mScx = nullptr;
+}
+
+bool
+danger::AutoCxPusher::IsStackTop() const
+{
+  uint32_t currentDepth = XPCJSRuntime::Get()->GetJSContextStack()->Count();
+  MOZ_ASSERT(currentDepth >= mStackDepthAfterPush);
+  return currentDepth == mStackDepthAfterPush;
+}
+
 } // namespace dom
 } // namespace mozilla