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//===---------------------- shared_mutex.cpp ------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "__config"
#ifndef _LIBCPP_HAS_NO_THREADS
#include "shared_mutex"
#if defined(__unix__) && !defined(__ANDROID__) && defined(__ELF__) && defined(_LIBCPP_HAS_COMMENT_LIB_PRAGMA)
#pragma comment(lib, "pthread")
#endif
_LIBCPP_BEGIN_NAMESPACE_STD
// Shared Mutex Base
__shared_mutex_base::__shared_mutex_base()
: __state_(0)
{
}
// Exclusive ownership
void
__shared_mutex_base::lock()
{
unique_lock<mutex> lk(__mut_);
while (__state_ & __write_entered_)
__gate1_.wait(lk);
__state_ |= __write_entered_;
while (__state_ & __n_readers_)
__gate2_.wait(lk);
}
bool
__shared_mutex_base::try_lock()
{
unique_lock<mutex> lk(__mut_);
if (__state_ == 0)
{
__state_ = __write_entered_;
return true;
}
return false;
}
void
__shared_mutex_base::unlock()
{
lock_guard<mutex> _(__mut_);
__state_ = 0;
__gate1_.notify_all();
}
// Shared ownership
void
__shared_mutex_base::lock_shared()
{
unique_lock<mutex> lk(__mut_);
while ((__state_ & __write_entered_) || (__state_ & __n_readers_) == __n_readers_)
__gate1_.wait(lk);
unsigned num_readers = (__state_ & __n_readers_) + 1;
__state_ &= ~__n_readers_;
__state_ |= num_readers;
}
bool
__shared_mutex_base::try_lock_shared()
{
unique_lock<mutex> lk(__mut_);
unsigned num_readers = __state_ & __n_readers_;
if (!(__state_ & __write_entered_) && num_readers != __n_readers_)
{
++num_readers;
__state_ &= ~__n_readers_;
__state_ |= num_readers;
return true;
}
return false;
}
void
__shared_mutex_base::unlock_shared()
{
lock_guard<mutex> _(__mut_);
unsigned num_readers = (__state_ & __n_readers_) - 1;
__state_ &= ~__n_readers_;
__state_ |= num_readers;
if (__state_ & __write_entered_)
{
if (num_readers == 0)
__gate2_.notify_one();
}
else
{
if (num_readers == __n_readers_ - 1)
__gate1_.notify_one();
}
}
// Shared Timed Mutex
// These routines are here for ABI stability
shared_timed_mutex::shared_timed_mutex() : __base() {}
void shared_timed_mutex::lock() { return __base.lock(); }
bool shared_timed_mutex::try_lock() { return __base.try_lock(); }
void shared_timed_mutex::unlock() { return __base.unlock(); }
void shared_timed_mutex::lock_shared() { return __base.lock_shared(); }
bool shared_timed_mutex::try_lock_shared() { return __base.try_lock_shared(); }
void shared_timed_mutex::unlock_shared() { return __base.unlock_shared(); }
_LIBCPP_END_NAMESPACE_STD
#endif // !_LIBCPP_HAS_NO_THREADS
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