1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
|
// 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/tc39/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:
// Check that array_buffer[addr] == value, and return "not-equal" 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 "ok", otherwise return "timed-out". 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);
// 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_
|
