lean2/src/util/shared_mutex.cpp

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/**
Copyright (c) 2013 Microsoft Corporation. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Author: Leonardo de Moura
C++11 does not support std::shared_mutex and std::shared_lock yet.
This piece of code is based on the proposal submitted to the C++
standardization committee. The proposal was written by Howard
Hinnant. The proposal is also part of the Boost library which is
licensed under http://www.boost.org/LICENSE_1_0.txt
*/
#include "util/debug.h"
#include "util/shared_mutex.h"
namespace lean {
shared_mutex::shared_mutex():m_rw_counter(0), m_state(0) {}
shared_mutex::~shared_mutex() {
lock_guard<mutex> lock(m_mutex);
}
void shared_mutex::lock() {
unique_lock<mutex> lock(m_mutex);
if (m_rw_owner == this_thread::get_id()) {
m_rw_counter++;
return; // already has the lock
}
while (m_state & write_entered)
m_gate1.wait(lock);
m_state |= write_entered;
while (m_state & readers)
m_gate2.wait(lock);
lean_assert(m_rw_counter == 0);
m_rw_owner = this_thread::get_id();
m_rw_counter = 1;
}
bool shared_mutex::try_lock() {
unique_lock<mutex> lock(m_mutex);
if (m_rw_owner == this_thread::get_id()) {
m_rw_counter++;
return true; // already has the lock
}
if (m_state == 0) {
m_state = write_entered;
lean_assert(m_rw_counter == 0);
m_rw_owner = this_thread::get_id();
m_rw_counter = 1;
return true;
}
return false;
}
void shared_mutex::unlock() {
lock_guard<mutex> lock(m_mutex);
lean_assert(m_rw_owner == this_thread::get_id());
lean_assert(m_rw_counter > 0);
m_rw_counter--;
if (m_rw_counter > 0)
return; // keep the lock
m_rw_owner = thread::id(); // reset owner
lean_assert(m_rw_counter == 0);
lean_assert(m_rw_owner != this_thread::get_id());
m_state = 0;
m_gate1.notify_all();
}
void shared_mutex::lock_shared() {
unique_lock<mutex> lock(m_mutex);
if (m_rw_owner == this_thread::get_id()) {
lean_assert(m_rw_counter > 0);
m_rw_counter++;
return; // already has the lock
}
while ((m_state & write_entered) || (m_state & readers) == readers)
m_gate1.wait(lock);
unsigned num_readers = (m_state & readers) + 1;
m_state &= ~readers;
m_state |= num_readers;
}
bool shared_mutex::try_lock_shared() {
unique_lock<mutex> lock(m_mutex);
if (m_rw_owner == this_thread::get_id()) {
lean_assert(m_rw_counter > 0);
m_rw_counter++;
return true; // already has the lock
}
unsigned num_readers = m_state & readers;
if (!(m_state & write_entered) && num_readers != readers) {
++num_readers;
m_state &= ~readers;
m_state |= num_readers;
return true;
}
return false;
}
void shared_mutex::unlock_shared() {
lock_guard<mutex> lock(m_mutex);
if (m_rw_owner == this_thread::get_id()) {
// if we have a rw (aka unshared) lock, then
// the shared lock must be nested.
lean_assert(m_rw_counter > 1);
m_rw_counter--;
return;
}
lean_assert(m_rw_counter == 0);
unsigned num_readers = (m_state & readers) - 1;
m_state &= ~readers;
m_state |= num_readers;
if (m_state & write_entered) {
if (num_readers == 0)
m_gate2.notify_one();
} else {
if (num_readers == readers - 1)
m_gate1.notify_one();
}
}
}