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upgrade_mutex.cpp
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upgrade_mutex.cpp
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//--------------------------- upgrade_mutex.cpp --------------------------------
//
// This software is in the public domain. The only restriction on its use is
// that no one can remove it from the public domain by claiming ownership of it,
// including the original authors.
//
// There is no warranty of correctness on the software contained herein. Use
// at your own risk.
//
//------------------------------------------------------------------------------
#include "upgrade_mutex.h"
namespace acme
{
upgrade_mutex::upgrade_mutex()
: state_(0)
{
}
upgrade_mutex::~upgrade_mutex() = default;
// Exclusive ownership
void
upgrade_mutex::lock()
{
std::unique_lock<std::mutex> lk(mut_);
while (state_ & (write_entered_ | upgradable_entered_))
gate1_.wait(lk);
state_ |= write_entered_;
while (state_ & n_readers_)
gate2_.wait(lk);
}
bool
upgrade_mutex::try_lock()
{
std::unique_lock<std::mutex> lk(mut_);
if (state_ == 0)
{
state_ = write_entered_;
return true;
}
return false;
}
void
upgrade_mutex::unlock()
{
std::lock_guard<std::mutex> _(mut_);
state_ = 0;
gate1_.notify_all();
}
// Shared ownership
void
upgrade_mutex::lock_shared()
{
std::unique_lock<std::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
upgrade_mutex::try_lock_shared()
{
std::unique_lock<std::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
upgrade_mutex::unlock_shared()
{
std::lock_guard<std::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();
}
}
// Upgrade ownership
void
upgrade_mutex::lock_upgrade()
{
std::unique_lock<std::mutex> lk(mut_);
while ((state_ & (write_entered_ | upgradable_entered_)) ||
(state_ & n_readers_) == n_readers_)
gate1_.wait(lk);
unsigned num_readers = (state_ & n_readers_) + 1;
state_ &= ~n_readers_;
state_ |= upgradable_entered_ | num_readers;
}
bool
upgrade_mutex::try_lock_upgrade()
{
std::unique_lock<std::mutex> lk(mut_);
unsigned num_readers = state_ & n_readers_;
if (!(state_ & (write_entered_ | upgradable_entered_))
&& num_readers != n_readers_)
{
++num_readers;
state_ &= ~n_readers_;
state_ |= upgradable_entered_ | num_readers;
return true;
}
return false;
}
void
upgrade_mutex::unlock_upgrade()
{
{
std::lock_guard<std::mutex> _(mut_);
unsigned num_readers = (state_ & n_readers_) - 1;
state_ &= ~(upgradable_entered_ | n_readers_);
state_ |= num_readers;
}
gate1_.notify_all();
}
// Shared <-> Exclusive
bool
upgrade_mutex::try_unlock_shared_and_lock()
{
std::unique_lock<std::mutex> lk(mut_);
if (state_ == 1)
{
state_ = write_entered_;
return true;
}
return false;
}
void
upgrade_mutex::unlock_and_lock_shared()
{
{
std::lock_guard<std::mutex> _(mut_);
state_ = 1;
}
gate1_.notify_all();
}
// Shared <-> Upgrade
bool
upgrade_mutex::try_unlock_shared_and_lock_upgrade()
{
std::unique_lock<std::mutex> lk(mut_);
if (!(state_ & (write_entered_ | upgradable_entered_)))
{
state_ |= upgradable_entered_;
return true;
}
return false;
}
void
upgrade_mutex::unlock_upgrade_and_lock_shared()
{
{
std::lock_guard<std::mutex> _(mut_);
state_ &= ~upgradable_entered_;
}
gate1_.notify_all();
}
// Upgrade <-> Exclusive
void
upgrade_mutex::unlock_upgrade_and_lock()
{
std::unique_lock<std::mutex> lk(mut_);
unsigned num_readers = (state_ & n_readers_) - 1;
state_ &= ~(upgradable_entered_ | n_readers_);
state_ |= write_entered_ | num_readers;
while (state_ & n_readers_)
gate2_.wait(lk);
}
bool
upgrade_mutex::try_unlock_upgrade_and_lock()
{
std::unique_lock<std::mutex> lk(mut_);
if (state_ == (upgradable_entered_ | 1))
{
state_ = write_entered_;
return true;
}
return false;
}
void
upgrade_mutex::unlock_and_lock_upgrade()
{
{
std::lock_guard<std::mutex> _(mut_);
state_ = upgradable_entered_ | 1;
}
gate1_.notify_all();
}
} // acme