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
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
|
/*
* Copyright 2015 The WebRTC 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 in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#include "rtc_base/criticalsection.h"
#include "rtc_base/checks.h"
#include "rtc_base/platform_thread.h"
// TODO(tommi): Split this file up to per-platform implementation files.
namespace rtc {
CriticalSection::CriticalSection() {
#if defined(WEBRTC_WIN)
InitializeCriticalSection(&crit_);
#elif defined(WEBRTC_POSIX)
# if defined(WEBRTC_MAC) && !USE_NATIVE_MUTEX_ON_MAC
lock_queue_ = 0;
owning_thread_ = 0;
recursion_ = 0;
semaphore_ = dispatch_semaphore_create(0);
# else
pthread_mutexattr_t mutex_attribute;
pthread_mutexattr_init(&mutex_attribute);
pthread_mutexattr_settype(&mutex_attribute, PTHREAD_MUTEX_RECURSIVE);
pthread_mutex_init(&mutex_, &mutex_attribute);
pthread_mutexattr_destroy(&mutex_attribute);
# endif
CS_DEBUG_CODE(thread_ = 0);
CS_DEBUG_CODE(recursion_count_ = 0);
RTC_UNUSED(thread_);
RTC_UNUSED(recursion_count_);
#else
# error Unsupported platform.
#endif
}
CriticalSection::~CriticalSection() {
#if defined(WEBRTC_WIN)
DeleteCriticalSection(&crit_);
#elif defined(WEBRTC_POSIX)
# if defined(WEBRTC_MAC) && !USE_NATIVE_MUTEX_ON_MAC
dispatch_release(semaphore_);
# else
pthread_mutex_destroy(&mutex_);
# endif
#else
# error Unsupported platform.
#endif
}
void CriticalSection::Enter() const RTC_EXCLUSIVE_LOCK_FUNCTION() {
#if defined(WEBRTC_WIN)
EnterCriticalSection(&crit_);
#elif defined(WEBRTC_POSIX)
# if defined(WEBRTC_MAC) && !USE_NATIVE_MUTEX_ON_MAC
int spin = 3000;
PlatformThreadRef self = CurrentThreadRef();
bool have_lock = false;
do {
// Instead of calling TryEnter() in this loop, we do two interlocked
// operations, first a read-only one in order to avoid affecting the lock
// cache-line while spinning, in case another thread is using the lock.
if (!IsThreadRefEqual(owning_thread_, self)) {
if (AtomicOps::AcquireLoad(&lock_queue_) == 0) {
if (AtomicOps::CompareAndSwap(&lock_queue_, 0, 1) == 0) {
have_lock = true;
break;
}
}
} else {
AtomicOps::Increment(&lock_queue_);
have_lock = true;
break;
}
sched_yield();
} while (--spin);
if (!have_lock && AtomicOps::Increment(&lock_queue_) > 1) {
// Owning thread cannot be the current thread since TryEnter() would
// have succeeded.
RTC_DCHECK(!IsThreadRefEqual(owning_thread_, self));
// Wait for the lock to become available.
dispatch_semaphore_wait(semaphore_, DISPATCH_TIME_FOREVER);
RTC_DCHECK(owning_thread_ == 0);
RTC_DCHECK(!recursion_);
}
owning_thread_ = self;
++recursion_;
# else
pthread_mutex_lock(&mutex_);
# endif
# if CS_DEBUG_CHECKS
if (!recursion_count_) {
RTC_DCHECK(!thread_);
thread_ = CurrentThreadRef();
} else {
RTC_DCHECK(CurrentThreadIsOwner());
}
++recursion_count_;
# endif
#else
# error Unsupported platform.
#endif
}
bool CriticalSection::TryEnter() const RTC_EXCLUSIVE_TRYLOCK_FUNCTION(true) {
#if defined(WEBRTC_WIN)
return TryEnterCriticalSection(&crit_) != FALSE;
#elif defined(WEBRTC_POSIX)
# if defined(WEBRTC_MAC) && !USE_NATIVE_MUTEX_ON_MAC
if (!IsThreadRefEqual(owning_thread_, CurrentThreadRef())) {
if (AtomicOps::CompareAndSwap(&lock_queue_, 0, 1) != 0)
return false;
owning_thread_ = CurrentThreadRef();
RTC_DCHECK(!recursion_);
} else {
AtomicOps::Increment(&lock_queue_);
}
++recursion_;
# else
if (pthread_mutex_trylock(&mutex_) != 0)
return false;
# endif
# if CS_DEBUG_CHECKS
if (!recursion_count_) {
RTC_DCHECK(!thread_);
thread_ = CurrentThreadRef();
} else {
RTC_DCHECK(CurrentThreadIsOwner());
}
++recursion_count_;
# endif
return true;
#else
# error Unsupported platform.
#endif
}
void CriticalSection::Leave() const RTC_UNLOCK_FUNCTION() {
RTC_DCHECK(CurrentThreadIsOwner());
#if defined(WEBRTC_WIN)
LeaveCriticalSection(&crit_);
#elif defined(WEBRTC_POSIX)
# if CS_DEBUG_CHECKS
--recursion_count_;
RTC_DCHECK(recursion_count_ >= 0);
if (!recursion_count_)
thread_ = 0;
# endif
# if defined(WEBRTC_MAC) && !USE_NATIVE_MUTEX_ON_MAC
RTC_DCHECK(IsThreadRefEqual(owning_thread_, CurrentThreadRef()));
RTC_DCHECK_GE(recursion_, 0);
--recursion_;
if (!recursion_)
owning_thread_ = 0;
if (AtomicOps::Decrement(&lock_queue_) > 0 && !recursion_)
dispatch_semaphore_signal(semaphore_);
# else
pthread_mutex_unlock(&mutex_);
# endif
#else
# error Unsupported platform.
#endif
}
bool CriticalSection::CurrentThreadIsOwner() const {
#if defined(WEBRTC_WIN)
// OwningThread has type HANDLE but actually contains the Thread ID:
// http://stackoverflow.com/questions/12675301/why-is-the-owningthread-member-of-critical-section-of-type-handle-when-it-is-de
// Converting through size_t avoids the VS 2015 warning C4312: conversion from
// 'type1' to 'type2' of greater size
return crit_.OwningThread ==
reinterpret_cast<HANDLE>(static_cast<size_t>(GetCurrentThreadId()));
#elif defined(WEBRTC_POSIX)
# if CS_DEBUG_CHECKS
return IsThreadRefEqual(thread_, CurrentThreadRef());
# else
return true;
# endif // CS_DEBUG_CHECKS
#else
# error Unsupported platform.
#endif
}
CritScope::CritScope(const CriticalSection* cs) : cs_(cs) { cs_->Enter(); }
CritScope::~CritScope() { cs_->Leave(); }
TryCritScope::TryCritScope(const CriticalSection* cs)
: cs_(cs), locked_(cs->TryEnter()) {
CS_DEBUG_CODE(lock_was_called_ = false);
RTC_UNUSED(lock_was_called_);
}
TryCritScope::~TryCritScope() {
CS_DEBUG_CODE(RTC_DCHECK(lock_was_called_));
if (locked_)
cs_->Leave();
}
bool TryCritScope::locked() const {
CS_DEBUG_CODE(lock_was_called_ = true);
return locked_;
}
void GlobalLockPod::Lock() {
#if !defined(WEBRTC_WIN) && (!defined(WEBRTC_MAC) || USE_NATIVE_MUTEX_ON_MAC)
const struct timespec ts_null = {0};
#endif
while (AtomicOps::CompareAndSwap(&lock_acquired, 0, 1)) {
#if defined(WEBRTC_WIN)
::Sleep(0);
#elif defined(WEBRTC_MAC) && !USE_NATIVE_MUTEX_ON_MAC
sched_yield();
#else
nanosleep(&ts_null, nullptr);
#endif
}
}
void GlobalLockPod::Unlock() {
int old_value = AtomicOps::CompareAndSwap(&lock_acquired, 1, 0);
RTC_DCHECK_EQ(1, old_value) << "Unlock called without calling Lock first";
}
GlobalLock::GlobalLock() {
lock_acquired = 0;
}
GlobalLockScope::GlobalLockScope(GlobalLockPod* lock)
: lock_(lock) {
lock_->Lock();
}
GlobalLockScope::~GlobalLockScope() {
lock_->Unlock();
}
} // namespace rtc
|
