Introduce v8::MicrotasksScope.

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index db4c31e9042a855982f19b0323a0ed8496ede895..71bff6ae2ed78c1b33803f55cde1a2586dfe998b 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -5450,6 +5450,21 @@ class V8_EXPORT Isolate {
     kMinorGarbageCollection
   };
 
+
+  /**
+   * Policy for running microtasks:
+   *   - explicit: microtasks are invoked with RunMicrotasks() method;
+   *   - scoped: microtasks invocation is controlled by MicrotasksScope objects;
+   *   - auto: microtasks are invoked when the script call depth decrements
+   *           to zero.
+   */
+  enum MicrotasksPolicy {

[jochen (gone - plz use gerrit), 2016/03/01 14:26:08]

i'd prefer an enum class

[dgozman, 2016/03/03 01:22:06]

Done.

+    kExplicitMicrotasksInvocation,
+    kScopedMicrotasksInvocation,
+    kAutoMicrotasksInvocation
+  };
+
+
   /**
    * Features reported via the SetUseCounterCallback callback. Do not change
    * assigned numbers of existing items; add new features to the end of this
@@ -5884,17 +5899,22 @@ class V8_EXPORT Isolate {
    */
   void EnqueueMicrotask(MicrotaskCallback microtask, void* data = NULL);
 
-   /**
-   * Experimental: Controls whether the Microtask Work Queue is automatically
-   * run when the script call depth decrements to zero.
+  /**
+   * Experimental: Controls how Microtasks are invoked. See MicrotasksPolicy
+   * for details.
    */
-  void SetAutorunMicrotasks(bool autorun);
+  void SetMicrotasksPolicy(MicrotasksPolicy policy);
+  V8_DEPRECATE_SOON(
+      "Use SetMicrotasksPolicy",
+      void SetAutorunMicrotasks(bool autorun));
 
   /**
-   * Experimental: Returns whether the Microtask Work Queue is automatically
-   * run when the script call depth decrements to zero.
+   * Experimental: Returns the policy controlling how Microtasks are invoked.
    */
-  bool WillAutorunMicrotasks() const;
+  MicrotasksPolicy GetMicrotasksPolicy() const;
+  V8_DEPRECATE_SOON(
+      "Use GetMicrotasksPolicy",
+      bool WillAutorunMicrotasks() const);
 
   /**
    * Experimental: adds a callback to notify the host application after
@@ -6144,6 +6164,41 @@ class V8_EXPORT StartupData {
 
 
 /**
+ * This scope is used to control microtasks when kScopeMicrotasksInvocation
+ * is used on Isolate. In this mode every non-primitive call to V8 should be
+ * done inside some MicrotasksScope.
+ * Microtasks are executed when topmost MicrotasksScope marked as kRunMicrotasks
+ * exits.
+ * kDoNotRunMicrotasks should be used to annotate calls not intended to trigger
+ * microtasks.
+ */
+class V8_EXPORT MicrotasksScope {
+ public:
+  enum Type { kRunMicrotasks, kDoNotRunMicrotasks };
+
+  MicrotasksScope(Isolate* isolate, Type type);
+  ~MicrotasksScope();
+
+  /**
+   * Runs microtasks if no kRunMicrotasks scope is currently active.
+   */
+  static void PerformCheckpoint(Isolate*);
+
+  /**
+   * Returns current recursion level of scope objects.
+   */
+  static int GetRecursionLevel(Isolate*);
+
+ private:
+  void* internal_;
+
+  // Prevent copying.
+  MicrotasksScope(const MicrotasksScope&);
+  MicrotasksScope& operator=(const MicrotasksScope&);
+};
+
+
+/**
  * EntropySource is used as a callback function when v8 needs a source
  * of entropy.
  */