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114 lines
3.2 KiB
114 lines
3.2 KiB
// Copyright 2015 the V8 project authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef V8_FUTEX_EMULATION_H_
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#define V8_FUTEX_EMULATION_H_
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#include <stdint.h>
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#include "src/allocation.h"
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#include "src/base/atomicops.h"
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#include "src/base/lazy-instance.h"
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#include "src/base/macros.h"
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#include "src/base/platform/condition-variable.h"
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#include "src/base/platform/mutex.h"
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#include "src/handles.h"
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// Support for emulating futexes, a low-level synchronization primitive. They
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// are natively supported by Linux, but must be emulated for other platforms.
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// This library emulates them on all platforms using mutexes and condition
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// variables for consistency.
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//
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// This is used by the Futex API defined in the SharedArrayBuffer draft spec,
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// found here: https://github.com/tc39/ecmascript_sharedmem
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namespace v8 {
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namespace base {
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class TimeDelta;
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} // base
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namespace internal {
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class Isolate;
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class JSArrayBuffer;
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class FutexWaitListNode {
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public:
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FutexWaitListNode()
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: prev_(nullptr),
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next_(nullptr),
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backing_store_(nullptr),
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wait_addr_(0),
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waiting_(false),
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interrupted_(false) {}
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void NotifyWake();
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private:
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friend class FutexEmulation;
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friend class FutexWaitList;
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base::ConditionVariable cond_;
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FutexWaitListNode* prev_;
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FutexWaitListNode* next_;
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void* backing_store_;
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size_t wait_addr_;
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bool waiting_;
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bool interrupted_;
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DISALLOW_COPY_AND_ASSIGN(FutexWaitListNode);
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};
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class FutexWaitList {
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public:
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FutexWaitList();
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void AddNode(FutexWaitListNode* node);
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void RemoveNode(FutexWaitListNode* node);
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private:
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friend class FutexEmulation;
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FutexWaitListNode* head_;
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FutexWaitListNode* tail_;
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DISALLOW_COPY_AND_ASSIGN(FutexWaitList);
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};
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class FutexEmulation : public AllStatic {
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public:
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// Check that array_buffer[addr] == value, and return "not-equal" if not. If
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// they are equal, block execution on |isolate|'s thread until woken via
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// |Wake|, or when the time given in |rel_timeout_ms| elapses. Note that
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// |rel_timeout_ms| can be Infinity.
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// If woken, return "ok", otherwise return "timed-out". The initial check and
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// the decision to wait happen atomically.
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static Object* Wait(Isolate* isolate, Handle<JSArrayBuffer> array_buffer,
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size_t addr, int32_t value, double rel_timeout_ms);
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// Wake |num_waiters_to_wake| threads that are waiting on the given |addr|.
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// The rest of the waiters will continue to wait. The return value is the
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// number of woken waiters.
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static Object* Wake(Isolate* isolate, Handle<JSArrayBuffer> array_buffer,
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size_t addr, int num_waiters_to_wake);
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// Return the number of threads waiting on |addr|. Should only be used for
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// testing.
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static Object* NumWaitersForTesting(Isolate* isolate,
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Handle<JSArrayBuffer> array_buffer,
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size_t addr);
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private:
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friend class FutexWaitListNode;
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static base::LazyMutex mutex_;
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static base::LazyInstance<FutexWaitList>::type wait_list_;
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};
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} // namespace internal
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} // namespace v8
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#endif // V8_FUTEX_EMULATION_H_
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