contrib/libc++/src/shared_mutex.cpp

   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 #include "__config"
  11 #ifndef _LIBCPP_HAS_NO_THREADS
  12
  13 #define _LIBCPP_BUILDING_SHARED_MUTEX
  14 #include "shared_mutex"
  15
  16 _LIBCPP_BEGIN_NAMESPACE_STD
  17
  18 // Shared Mutex Base
  19 __shared_mutex_base::__shared_mutex_base()
  20     : __state_(0)
  21 {
  22 }
  23
  24 // Exclusive ownership
  25
  26 void
  27 __shared_mutex_base::lock()
  28 {
  29     unique_lock<mutex> lk(__mut_);
  30     while (__state_ & __write_entered_)
  31         __gate1_.wait(lk);
  32     __state_ |= __write_entered_;
  33     while (__state_ & __n_readers_)
  34         __gate2_.wait(lk);
  35 }
  36
  37 bool
  38 __shared_mutex_base::try_lock()
  39 {
  40     unique_lock<mutex> lk(__mut_);
  41     if (__state_ == 0)
  42     {
  43         __state_ = __write_entered_;
  44         return true;
  45     }
  46     return false;
  47 }
  48
  49 void
  50 __shared_mutex_base::unlock()
  51 {
  52     lock_guard<mutex> _(__mut_);
  53     __state_ = 0;
  54     __gate1_.notify_all();
  55 }
  56
  57 // Shared ownership
  58
  59 void
  60 __shared_mutex_base::lock_shared()
  61 {
  62     unique_lock<mutex> lk(__mut_);
  63     while ((__state_ & __write_entered_) || (__state_ & __n_readers_) == __n_readers_)
  64         __gate1_.wait(lk);
  65     unsigned num_readers = (__state_ & __n_readers_) + 1;
  66     __state_ &= ~__n_readers_;
  67     __state_ |= num_readers;
  68 }
  69
  70 bool
  71 __shared_mutex_base::try_lock_shared()
  72 {
  73     unique_lock<mutex> lk(__mut_);
  74     unsigned num_readers = __state_ & __n_readers_;
  75     if (!(__state_ & __write_entered_) && num_readers != __n_readers_)
  76     {
  77         ++num_readers;
  78         __state_ &= ~__n_readers_;
  79         __state_ |= num_readers;
  80         return true;
  81     }
  82     return false;
  83 }
  84
  85 void
  86 __shared_mutex_base::unlock_shared()
  87 {
  88     lock_guard<mutex> _(__mut_);
  89     unsigned num_readers = (__state_ & __n_readers_) - 1;
  90     __state_ &= ~__n_readers_;
  91     __state_ |= num_readers;
  92     if (__state_ & __write_entered_)
  93     {
  94         if (num_readers == 0)
  95             __gate2_.notify_one();
  96     }
  97     else
  98     {
  99         if (num_readers == __n_readers_ - 1)
 100             __gate1_.notify_one();
 101     }
 102 }
 103
 104
 105 // Shared Timed Mutex
 106 // These routines are here for ABI stability
 107 shared_timed_mutex::shared_timed_mutex() : __base() {}
 108 void shared_timed_mutex::lock()     { return __base.lock(); }
 109 bool shared_timed_mutex::try_lock() { return __base.try_lock(); }
 110 void shared_timed_mutex::unlock()   { return __base.unlock(); }
 111 void shared_timed_mutex::lock_shared() { return __base.lock_shared(); }
 112 bool shared_timed_mutex::try_lock_shared() { return __base.try_lock_shared(); }
 113 void shared_timed_mutex::unlock_shared() { return __base.unlock_shared(); }
 114
 115 _LIBCPP_END_NAMESPACE_STD
 116
 117 #endif // !_LIBCPP_HAS_NO_THREADS