Bug 937317 - Implement basic script settings stack machinery. r=bz

dom/base/ScriptSettings.cpp

@@ -5,14 +5,92 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "mozilla/dom/ScriptSettings.h"
+#include "mozilla/ThreadLocal.h"
+#include "mozilla/Assertions.h"
 
+#include "jsapi.h"
+#include "nsIGlobalObject.h"
 #include "nsIScriptGlobalObject.h"
 #include "nsIScriptContext.h"
 #include "nsContentUtils.h"
+#include "nsTArray.h"
 
 namespace mozilla {
 namespace dom {
 
+class ScriptSettingsStack;
+static mozilla::ThreadLocal<ScriptSettingsStack*> sScriptSettingsTLS;
+
+ScriptSettingsStackEntry ScriptSettingsStackEntry::SystemSingleton;
+
+class ScriptSettingsStack {
+public:
+  static ScriptSettingsStack& Ref() {
+    return *sScriptSettingsTLS.get();
+  }
+  ScriptSettingsStack() {};
+
+  void Push(ScriptSettingsStackEntry* aSettings) {
+    // The bottom-most entry must always be a candidate entry point.
+    MOZ_ASSERT_IF(mStack.Length() == 0 || mStack.LastElement()->IsSystemSingleton(),
+                  aSettings->mIsCandidateEntryPoint);
+    mStack.AppendElement(aSettings);
+  }
+
+  void PushSystem() {
+    mStack.AppendElement(&ScriptSettingsStackEntry::SystemSingleton);
+  }
+
+  void Pop() {
+    MOZ_ASSERT(mStack.Length() > 0);
+    mStack.RemoveElementAt(mStack.Length() - 1);
+  }
+
+  nsIGlobalObject* Incumbent() {
+    if (!mStack.Length()) {
+      return nullptr;
+    }
+    return mStack.LastElement()->mGlobalObject;
+  }
+
+  nsIGlobalObject* EntryPoint() {
+    if (!mStack.Length())
+      return nullptr;
+    for (int i = mStack.Length() - 1; i >= 0; --i) {
+      if (mStack[i]->mIsCandidateEntryPoint) {
+        return mStack[i]->mGlobalObject;
+      }
+    }
+    MOZ_ASSUME_UNREACHABLE("Non-empty stack should always have an entry point");
+  }
+
+private:
+  // These pointers are caller-owned.
+  nsTArray<ScriptSettingsStackEntry*> mStack;
+};
+
+void
+InitScriptSettings()
+{
+  if (!sScriptSettingsTLS.initialized()) {
+    bool success = sScriptSettingsTLS.init();
+    if (!success) {
+      MOZ_CRASH();
+    }
+  }
+
+  ScriptSettingsStack* ptr = new ScriptSettingsStack();
+  sScriptSettingsTLS.set(ptr);
+}
+
+void DestroyScriptSettings()
+{
+  ScriptSettingsStack* ptr = sScriptSettingsTLS.get();
+  MOZ_ASSERT(ptr);
+  sScriptSettingsTLS.set(nullptr);
+  delete ptr;
+}
+
 AutoEntryScript::AutoEntryScript(nsIGlobalObject* aGlobalObject,
                                  bool aIsMainThread,
                                  JSContext* aCx)

dom/base/ScriptSettings.h

@@ -11,6 +11,7 @@
 
 #include "nsCxPusher.h"
 #include "MainThreadUtils.h"
+#include "nsIGlobalObject.h"
 
 #include "mozilla/Maybe.h"
 
@@ -19,6 +20,42 @@ class nsIGlobalObject;
 namespace mozilla {
 namespace dom {
 
+/*
+ * System-wide setup/teardown routines. Init and Destroy should be invoked
+ * once each, at startup and shutdown (respectively).
+ */
+void InitScriptSettings();
+void DestroyScriptSettings();
+
+struct ScriptSettingsStackEntry {
+  nsCOMPtr<nsIGlobalObject> mGlobalObject;
+  bool mIsCandidateEntryPoint;
+
+  ScriptSettingsStackEntry(nsIGlobalObject *aGlobal, bool aCandidate)
+    : mGlobalObject(aGlobal)
+    , mIsCandidateEntryPoint(aCandidate)
+  {
+    MOZ_ASSERT(mGlobalObject);
+    MOZ_ASSERT(mGlobalObject->GetGlobalJSObject(),
+               "Must have an actual JS global for the duration on the stack");
+    MOZ_ASSERT(JS_IsGlobalObject(mGlobalObject->GetGlobalJSObject()),
+               "No outer windows allowed");
+  }
+
+  ~ScriptSettingsStackEntry() {
+    // We must have an actual JS global for the entire time this is on the stack.
+    MOZ_ASSERT_IF(mGlobalObject, mGlobalObject->GetGlobalJSObject());
+  }
+
+  bool IsSystemSingleton() { return this == &SystemSingleton; }
+  static ScriptSettingsStackEntry SystemSingleton;
+
+private:
+  ScriptSettingsStackEntry() : mGlobalObject(nullptr)
+                             , mIsCandidateEntryPoint(true)
+  {}
+};
+
 /*
  * A class that represents a new script entry point.
  */

mfbt/ThreadLocal.h

@@ -54,7 +54,10 @@ typedef sig_atomic_t sig_safe_t;
  *
  * API usage:
  *
- * // Create a TLS item
+ * // Create a TLS item.
+ * //
+ * // Note that init() should be invoked exactly once, before any usage of set()
+ * // or get().
  * mozilla::ThreadLocal<int> tlsKey;
  * if (!tlsKey.init()) {
  *   // deal with the error

xpcom/base/CycleCollectedJSRuntime.cpp

@@ -59,6 +59,7 @@
 #include "mozilla/MemoryReporting.h"
 #include "mozilla/dom/BindingUtils.h"
 #include "mozilla/dom/DOMJSClass.h"
+#include "mozilla/dom/ScriptSettings.h"
 #include "jsprf.h"
 #include "nsCycleCollectionNoteRootCallback.h"
 #include "nsCycleCollectionParticipant.h"
@@ -441,6 +442,8 @@ CycleCollectedJSRuntime::CycleCollectedJSRuntime(uint32_t aMaxbytes,
     mJSRuntime(nullptr),
     mJSHolders(512)
 {
+  mozilla::dom::InitScriptSettings();
+
   mJSRuntime = JS_NewRuntime(aMaxbytes, aUseHelperThreads);
   if (!mJSRuntime) {
     MOZ_CRASH();
@@ -470,6 +473,8 @@ CycleCollectedJSRuntime::~CycleCollectedJSRuntime()
   JS_DestroyRuntime(mJSRuntime);
   mJSRuntime = nullptr;
   nsCycleCollector_forgetJSRuntime();
+
+  mozilla::dom::DestroyScriptSettings();
 }
 
 size_t