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// Copyright 2015 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 V8_FUTEX_EMULATION_H_
#define V8_FUTEX_EMULATION_H_
#include <stdint.h>
#include "src/allocation.h"
#include "src/base/atomicops.h"
#include "src/base/lazy-instance.h"
#include "src/base/macros.h"
#include "src/base/platform/condition-variable.h"
#include "src/base/platform/mutex.h"
#include "src/handles.h"
// Support for emulating futexes, a low-level synchronization primitive. They
// are natively supported by Linux, but must be emulated for other platforms.
// This library emulates them on all platforms using mutexes and condition
// variables for consistency.
//
// This is used by the Futex API defined in the SharedArrayBuffer draft spec,
// found here: https://github.com/lars-t-hansen/ecmascript_sharedmem
namespace v8 {
namespace base {
class TimeDelta;
} // base
namespace internal {
class Isolate;
class JSArrayBuffer;
class FutexWaitListNode {
public:
FutexWaitListNode()
: prev_(nullptr),
next_(nullptr),
backing_store_(nullptr),
wait_addr_(0),
waiting_(false),
interrupted_(false) {}
void NotifyWake();
private:
friend class FutexEmulation;
friend class FutexWaitList;
base::ConditionVariable cond_;
FutexWaitListNode* prev_;
FutexWaitListNode* next_;
void* backing_store_;
size_t wait_addr_;
bool waiting_;
bool interrupted_;
DISALLOW_COPY_AND_ASSIGN(FutexWaitListNode);
};
class FutexWaitList {
public:
FutexWaitList();
void AddNode(FutexWaitListNode* node);
void RemoveNode(FutexWaitListNode* node);
private:
friend class FutexEmulation;
FutexWaitListNode* head_;
FutexWaitListNode* tail_;
DISALLOW_COPY_AND_ASSIGN(FutexWaitList);
};
class FutexEmulation : public AllStatic {
public:
// These must match the values in src/harmony-atomics.js
enum Result {
kOk = 0,
kNotEqual = -1,
kTimedOut = -2,
};
// Check that array_buffer[addr] == value, and return kNotEqual if not. If
// they are equal, block execution on |isolate|'s thread until woken via
// |Wake|, or when the time given in |rel_timeout_ms| elapses. Note that
// |rel_timeout_ms| can be Infinity.
// If woken, return kOk, otherwise return kTimedOut. The initial check and
// the decision to wait happen atomically.
static Object* Wait(Isolate* isolate, Handle<JSArrayBuffer> array_buffer,
size_t addr, int32_t value, double rel_timeout_ms);
// Wake |num_waiters_to_wake| threads that are waiting on the given |addr|.
// The rest of the waiters will continue to wait. The return value is the
// number of woken waiters.
static Object* Wake(Isolate* isolate, Handle<JSArrayBuffer> array_buffer,
size_t addr, int num_waiters_to_wake);
// Check that array_buffer[addr] == value, and return kNotEqual if not. If
// they are equal, wake |num_waiters_to_wake| threads that are waiting on the
// given |addr|. The rest of the waiters will continue to wait, but will now
// be waiting on |addr2| instead of |addr|. The return value is the number of
// woken waiters or kNotEqual as described above.
static Object* WakeOrRequeue(Isolate* isolate,
Handle<JSArrayBuffer> array_buffer, size_t addr,
int num_waiters_to_wake, int32_t value,
size_t addr2);
// Return the number of threads waiting on |addr|. Should only be used for
// testing.
static Object* NumWaitersForTesting(Isolate* isolate,
Handle<JSArrayBuffer> array_buffer,
size_t addr);
private:
friend class FutexWaitListNode;
static base::LazyMutex mutex_;
static base::LazyInstance<FutexWaitList>::type wait_list_;
};
} // namespace internal
} // namespace v8
#endif // V8_FUTEX_EMULATION_H_
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