external/bsd/libc++/dist/libcxx/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 #define _LIBCPP_BUILDING_SHARED_MUTEX
  11 #include "shared_mutex"
  12
  13 _LIBCPP_BEGIN_NAMESPACE_STD
  14
  15 shared_mutex::shared_mutex()
  16     : __state_(0)
  17 {
  18 }
  19
  20 // Exclusive ownership
  21
  22 void
  23 shared_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_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_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_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_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_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