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/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include <Kernel/KSyms.h>
#include <Kernel/Lock.h>
#include <Kernel/Thread.h>
namespace Kernel {
void Lock::lock()
{
ASSERT(!Scheduler::is_active());
if (!are_interrupts_enabled()) {
klog() << "Interrupts disabled when trying to take Lock{" << m_name << "}";
dump_backtrace();
hang();
}
for (;;) {
bool expected = false;
if (m_lock.compare_exchange_strong(expected, true, AK::memory_order_acq_rel)) {
if (!m_holder || m_holder == Thread::current) {
m_holder = Thread::current;
++m_level;
m_lock.store(false, AK::memory_order_release);
return;
}
Thread::current->wait_on(m_queue, &m_lock, m_holder, m_name);
}
}
}
void Lock::unlock()
{
for (;;) {
bool expected = false;
if (m_lock.compare_exchange_strong(expected, true, AK::memory_order_acq_rel)) {
ASSERT(m_holder == Thread::current);
ASSERT(m_level);
--m_level;
if (m_level) {
m_lock.store(false, AK::memory_order_release);
return;
}
m_holder = nullptr;
m_queue.wake_one(&m_lock);
return;
}
// I don't know *who* is using "m_lock", so just yield.
Scheduler::yield();
}
}
bool Lock::force_unlock_if_locked()
{
InterruptDisabler disabler;
if (m_holder != Thread::current)
return false;
ASSERT(m_level == 1);
ASSERT(m_holder == Thread::current);
m_holder = nullptr;
--m_level;
m_queue.wake_one();
return true;
}
void Lock::clear_waiters()
{
InterruptDisabler disabler;
m_queue.clear();
}
}
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