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
|
// Copyright 2017 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
#ifndef ABSL_SYNCHRONIZATION_INTERNAL_WAITER_H_
#define ABSL_SYNCHRONIZATION_INTERNAL_WAITER_H_
#include "absl/base/config.h"
#ifdef _WIN32
#include <windows.h>
#else
#include <pthread.h>
#endif
#ifdef ABSL_HAVE_SEMAPHORE_H
#include <semaphore.h>
#endif
#include <atomic>
#include "absl/base/internal/thread_identity.h"
#include "absl/synchronization/internal/kernel_timeout.h"
// May be chosen at compile time via -DABSL_FORCE_WAITER_MODE=<index>
#define ABSL_WAITER_MODE_FUTEX 0
#define ABSL_WAITER_MODE_SEM 1
#define ABSL_WAITER_MODE_CONDVAR 2
#define ABSL_WAITER_MODE_WIN32 3
#if defined(ABSL_FORCE_WAITER_MODE)
#define ABSL_WAITER_MODE ABSL_FORCE_WAITER_MODE
#elif defined(_WIN32)
#define ABSL_WAITER_MODE ABSL_WAITER_MODE_WIN32
#elif defined(__linux__)
#define ABSL_WAITER_MODE ABSL_WAITER_MODE_FUTEX
#elif defined(ABSL_HAVE_SEMAPHORE_H)
#define ABSL_WAITER_MODE ABSL_WAITER_MODE_SEM
#else
#define ABSL_WAITER_MODE ABSL_WAITER_MODE_CONDVAR
#endif
namespace absl {
namespace synchronization_internal {
// Waiter is an OS-specific semaphore.
class Waiter {
public:
// No constructor, instances use the reserved space in ThreadIdentity.
// All initialization logic belongs in `Init()`.
Waiter() = delete;
Waiter(const Waiter&) = delete;
Waiter& operator=(const Waiter&) = delete;
// Prepare any data to track waits.
void Init();
// Blocks the calling thread until a matching call to `Post()` or
// `t` has passed. Returns `true` if woken (`Post()` called),
// `false` on timeout.
bool Wait(KernelTimeout t);
// Restart the caller of `Wait()` as with a normal semaphore.
void Post();
// If anyone is waiting, wake them up temporarily and cause them to
// call `MaybeBecomeIdle()`. They will then return to waiting for a
// `Post()` or timeout.
void Poke();
// Returns the Waiter associated with the identity.
static Waiter* GetWaiter(base_internal::ThreadIdentity* identity) {
static_assert(
sizeof(Waiter) <= sizeof(base_internal::ThreadIdentity::WaiterState),
"Insufficient space for Waiter");
return reinterpret_cast<Waiter*>(identity->waiter_state.data);
}
// How many periods to remain idle before releasing resources
#ifndef THREAD_SANITIZER
static const int kIdlePeriods = 60;
#else
// Memory consumption under ThreadSanitizer is a serious concern,
// so we release resources sooner. The value of 1 leads to 1 to 2 second
// delay before marking a thread as idle.
static const int kIdlePeriods = 1;
#endif
private:
#if ABSL_WAITER_MODE == ABSL_WAITER_MODE_FUTEX
// Futexes are defined by specification to be ints.
// Thus std::atomic<int> must be just an int with lockfree methods.
std::atomic<int> futex_;
static_assert(sizeof(int) == sizeof(futex_), "Wrong size for futex");
#elif ABSL_WAITER_MODE == ABSL_WAITER_MODE_CONDVAR
pthread_mutex_t mu_;
pthread_cond_t cv_;
std::atomic<int> waiter_count_;
std::atomic<int> wakeup_count_; // Unclaimed wakeups, written under lock.
#elif ABSL_WAITER_MODE == ABSL_WAITER_MODE_SEM
sem_t sem_;
// This seems superfluous, but for Poke() we need to cause spurious
// wakeups on the semaphore. Hence we can't actually use the
// semaphore's count.
std::atomic<int> wakeups_;
#elif ABSL_WAITER_MODE == ABSL_WAITER_MODE_WIN32
// The Windows API has lots of choices for synchronization
// primivitives. We are using SRWLOCK and CONDITION_VARIABLE
// because they don't require a destructor to release system
// resources.
SRWLOCK mu_;
CONDITION_VARIABLE cv_;
std::atomic<int> waiter_count_;
std::atomic<int> wakeup_count_;
#else
#error Unknown ABSL_WAITER_MODE
#endif
};
} // namespace synchronization_internal
} // namespace absl
#endif // ABSL_SYNCHRONIZATION_INTERNAL_WAITER_H_
|
