1 //===---------------------- shared_mutex.cpp ------------------------------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is dual licensed under the MIT and the University of Illinois Open 6 // Source Licenses. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 10 #define _LIBCPP_BUILDING_SHARED_MUTEX 11 #include "shared_mutex" 12 13 _LIBCPP_BEGIN_NAMESPACE_STD 14 15 shared_timed_mutex::shared_timed_mutex() 16 : __state_(0) 17 { 18 } 19 20 // Exclusive ownership 21 22 void 23 shared_timed_mutex::lock() 24 { 25 unique_lock<mutex> lk(__mut_); 26 while (__state_ & __write_entered_) 27 __gate1_.wait(lk); 28 __state_ |= __write_entered_; 29 while (__state_ & __n_readers_) 30 __gate2_.wait(lk); 31 } 32 33 bool 34 shared_timed_mutex::try_lock() 35 { 36 unique_lock<mutex> lk(__mut_); 37 if (__state_ == 0) 38 { 39 __state_ = __write_entered_; 40 return true; 41 } 42 return false; 43 } 44 45 void 46 shared_timed_mutex::unlock() 47 { 48 lock_guard<mutex> _(__mut_); 49 __state_ = 0; 50 __gate1_.notify_all(); 51 } 52 53 // Shared ownership 54 55 void 56 shared_timed_mutex::lock_shared() 57 { 58 unique_lock<mutex> lk(__mut_); 59 while ((__state_ & __write_entered_) || (__state_ & __n_readers_) == __n_readers_) 60 __gate1_.wait(lk); 61 unsigned num_readers = (__state_ & __n_readers_) + 1; 62 __state_ &= ~__n_readers_; 63 __state_ |= num_readers; 64 } 65 66 bool 67 shared_timed_mutex::try_lock_shared() 68 { 69 unique_lock<mutex> lk(__mut_); 70 unsigned num_readers = __state_ & __n_readers_; 71 if (!(__state_ & __write_entered_) && num_readers != __n_readers_) 72 { 73 ++num_readers; 74 __state_ &= ~__n_readers_; 75 __state_ |= num_readers; 76 return true; 77 } 78 return false; 79 } 80 81 void 82 shared_timed_mutex::unlock_shared() 83 { 84 lock_guard<mutex> _(__mut_); 85 unsigned num_readers = (__state_ & __n_readers_) - 1; 86 __state_ &= ~__n_readers_; 87 __state_ |= num_readers; 88 if (__state_ & __write_entered_) 89 { 90 if (num_readers == 0) 91 __gate2_.notify_one(); 92 } 93 else 94 { 95 if (num_readers == __n_readers_ - 1) 96 __gate1_.notify_one(); 97 } 98 } 99 100 101 _LIBCPP_END_NAMESPACE_STD 102
