Add memory pressure notification API

include/v8.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /** \mainpage V8 API Reference Guide
  *
  * V8 is Google's open source JavaScript engine.
  *
  * This set of documents provides reference material generated from the
  * V8 header file, include/v8.h.
@@ skipping 5332 matching lines @@
 /**
  * Interface for iterating through all the persistent handles in the heap.
  */
 class V8_EXPORT PersistentHandleVisitor {  // NOLINT
  public:
   virtual ~PersistentHandleVisitor() {}
   virtual void VisitPersistentHandle(Persistent<Value>* value,
                                      uint16_t class_id) {}
 };
 
+/**
+ * Memory pressure level for the MemoryPressureNotification.
+ * kNone hints V8 that there is no memory pressure.
+ * kModerate hints V8 to speed up incremental garbage collection at the cost of
+ * of higher latency due to garbage collection pauses.
+ * kCritical hints V8 to free memory as soon as possible. Garbage collection
+ * pauses at this level will be large.
+ */
+enum class MemoryPressureLevel { kNone, kModerate, kCritical };
 
 /**
  * Isolate represents an isolated instance of the V8 engine.  V8 isolates have
  * completely separate states.  Objects from one isolate must not be used in
  * other isolates.  The embedder can create multiple isolates and use them in
  * parallel in multiple threads.  An isolate can be entered by at most one
  * thread at any given time.  The Locker/Unlocker API must be used to
  * synchronize.
  */
 class V8_EXPORT Isolate {
@@ skipping 221 matching lines @@
    * then V8 will abort if either:
    * - no custom callback is set.
    * - the custom callback set returns true.
    * Otherwise, the custom callback will not be called and V8 will not abort.
    */
   typedef bool (*AbortOnUncaughtExceptionCallback)(Isolate*);
   void SetAbortOnUncaughtExceptionCallback(
       AbortOnUncaughtExceptionCallback callback);
 
   /**
+   * Optional notification that the system is running low on memory.
+   * V8 uses these notifications to guide heuristics.
+   * It is allowed to call this function from another thread while
+   * the isolate is executing long running JavaScript code.
+   */
+  void MemoryPressureNotification(MemoryPressureLevel level);
+
+  /**
    * Methods below this point require holding a lock (using Locker) in
    * a multi-threaded environment.
    */
 
   /**
    * Sets this isolate as the entered one for the current thread.
    * Saves the previously entered one (if any), so that it can be
    * restored when exiting.  Re-entering an isolate is allowed.
    */
   void Enter();
@@ skipping 3066 matching lines @@
  */
 
 
 }  // namespace v8
 
 
 #undef TYPE_CHECK
 
 
 #endif  // INCLUDE_V8_H_