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// Copyright 2021 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. #ifndef INCLUDE_V8_LOCKER_H_ #define INCLUDE_V8_LOCKER_H_ #include "v8config.h" // NOLINT(build/include_directory) namespace v8 { namespace internal { class Isolate; } // namespace internal class Isolate; /** * Multiple threads in V8 are allowed, but only one thread at a time is allowed * to use any given V8 isolate, see the comments in the Isolate class. The * definition of 'using a V8 isolate' includes accessing handles or holding onto * object pointers obtained from V8 handles while in the particular V8 isolate. * It is up to the user of V8 to ensure, perhaps with locking, that this * constraint is not violated. In addition to any other synchronization * mechanism that may be used, the v8::Locker and v8::Unlocker classes must be * used to signal thread switches to V8. * * v8::Locker is a scoped lock object. While it's active, i.e. between its * construction and destruction, the current thread is allowed to use the locked * isolate. V8 guarantees that an isolate can be locked by at most one thread at * any time. In other words, the scope of a v8::Locker is a critical section. * * Sample usage: * \code * ... * { * v8::Locker locker(isolate); * v8::Isolate::Scope isolate_scope(isolate); * ... * // Code using V8 and isolate goes here. * ... * } // Destructor called here * \endcode * * If you wish to stop using V8 in a thread A you can do this either by * destroying the v8::Locker object as above or by constructing a v8::Unlocker * object: * * \code * { * isolate->Exit(); * v8::Unlocker unlocker(isolate); * ... * // Code not using V8 goes here while V8 can run in another thread. * ... * } // Destructor called here. * isolate->Enter(); * \endcode * * The Unlocker object is intended for use in a long-running callback from V8, * where you want to release the V8 lock for other threads to use. * * The v8::Locker is a recursive lock, i.e. you can lock more than once in a * given thread. This can be useful if you have code that can be called either * from code that holds the lock or from code that does not. The Unlocker is * not recursive so you can not have several Unlockers on the stack at once, and * you cannot use an Unlocker in a thread that is not inside a Locker's scope. * * An unlocker will unlock several lockers if it has to and reinstate the * correct depth of locking on its destruction, e.g.: * * \code * // V8 not locked. * { * v8::Locker locker(isolate); * Isolate::Scope isolate_scope(isolate); * // V8 locked. * { * v8::Locker another_locker(isolate); * // V8 still locked (2 levels). * { * isolate->Exit(); * v8::Unlocker unlocker(isolate); * // V8 not locked. * } * isolate->Enter(); * // V8 locked again (2 levels). * } * // V8 still locked (1 level). * } * // V8 Now no longer locked. * \endcode */ class V8_EXPORT Unlocker { public: /** * Initialize Unlocker for a given Isolate. */ V8_INLINE explicit Unlocker(Isolate* isolate) { Initialize(isolate); } ~Unlocker(); private: void Initialize(Isolate* isolate); internal::Isolate* isolate_; }; class V8_EXPORT Locker { public: /** * Initialize Locker for a given Isolate. */ V8_INLINE explicit Locker(Isolate* isolate) { Initialize(isolate); } ~Locker(); /** * Returns whether or not the locker for a given isolate, is locked by the * current thread. */ static bool IsLocked(Isolate* isolate); /** * Returns whether any v8::Locker has ever been used in this process. * TODO(cbruni, chromium:1240851): Fix locking checks on a per-thread basis. * The current implementation is quite confusing and leads to unexpected * results if anybody uses v8::Locker in the current process. */ V8_DEPRECATE_SOON("This method will be removed.") static bool WasEverUsed(); V8_DEPRECATED("Use WasEverUsed instead") static bool IsActive(); // Disallow copying and assigning. Locker(const Locker&) = delete; void operator=(const Locker&) = delete; private: void Initialize(Isolate* isolate); bool has_lock_; bool top_level_; internal::Isolate* isolate_; }; } // namespace v8 #endif // INCLUDE_V8_LOCKER_H_