1//===----------------------------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#include <mutex>
10#include <shared_mutex>
11#if defined(__ELF__) && defined(_LIBCPP_LINK_PTHREAD_LIB)
12# pragma comment(lib, "pthread")
13#endif
14
15_LIBCPP_BEGIN_NAMESPACE_STD
16
17// Shared Mutex Base
18__shared_mutex_base::__shared_mutex_base() : __state_(0) {}
19
20// Exclusive ownership
21
22void __shared_mutex_base::lock() {
23 unique_lock<mutex> lk(__mut_);
24 while (__state_ & __write_entered_)
25 __gate1_.wait(lk);
26 __state_ |= __write_entered_;
27 while (__state_ & __n_readers_)
28 __gate2_.wait(lk);
29}
30
31bool __shared_mutex_base::try_lock() {
32 unique_lock<mutex> lk(__mut_);
33 if (__state_ == 0) {
34 __state_ = __write_entered_;
35 return true;
36 }
37 return false;
38}
39
40void __shared_mutex_base::unlock() {
41 lock_guard<mutex> _(__mut_);
42 __state_ = 0;
43 __gate1_.notify_all();
44}
45
46// Shared ownership
47
48void __shared_mutex_base::lock_shared() {
49 unique_lock<mutex> lk(__mut_);
50 while ((__state_ & __write_entered_) || (__state_ & __n_readers_) == __n_readers_)
51 __gate1_.wait(lk);
52 unsigned num_readers = (__state_ & __n_readers_) + 1;
53 __state_ &= ~__n_readers_;
54 __state_ |= num_readers;
55}
56
57bool __shared_mutex_base::try_lock_shared() {
58 unique_lock<mutex> lk(__mut_);
59 unsigned num_readers = __state_ & __n_readers_;
60 if (!(__state_ & __write_entered_) && num_readers != __n_readers_) {
61 ++num_readers;
62 __state_ &= ~__n_readers_;
63 __state_ |= num_readers;
64 return true;
65 }
66 return false;
67}
68
69void __shared_mutex_base::unlock_shared() {
70 lock_guard<mutex> _(__mut_);
71 unsigned num_readers = (__state_ & __n_readers_) - 1;
72 __state_ &= ~__n_readers_;
73 __state_ |= num_readers;
74 if (__state_ & __write_entered_) {
75 if (num_readers == 0)
76 __gate2_.notify_one();
77 } else {
78 if (num_readers == __n_readers_ - 1)
79 __gate1_.notify_one();
80 }
81}
82
83// Shared Timed Mutex
84// These routines are here for ABI stability
85shared_timed_mutex::shared_timed_mutex() : __base_() {}
86void shared_timed_mutex::lock() { return __base_.lock(); }
87bool shared_timed_mutex::try_lock() { return __base_.try_lock(); }
88void shared_timed_mutex::unlock() { return __base_.unlock(); }
89void shared_timed_mutex::lock_shared() { return __base_.lock_shared(); }
90bool shared_timed_mutex::try_lock_shared() { return __base_.try_lock_shared(); }
91void shared_timed_mutex::unlock_shared() { return __base_.unlock_shared(); }
92
93_LIBCPP_END_NAMESPACE_STD
94

source code of libcxx/src/shared_mutex.cpp