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f067730f6b
The kernel's Lock class now uses a proper wait queue internally instead of just having everyone wake up regularly to try to acquire the lock. We also keep the donation mechanism, so that whenever someone tries to take the lock and fails, that thread donates the remainder of its timeslice to the current lock holder. After unlocking a Lock, the unlocking thread calls WaitQueue::wake_one, which unblocks the next thread in queue.
76 lines
2.3 KiB
C++
76 lines
2.3 KiB
C++
#include <Kernel/Lock.h>
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#include <Kernel/Thread.h>
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void Lock::lock()
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{
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ASSERT(!Scheduler::is_active());
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if (!are_interrupts_enabled()) {
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kprintf("Interrupts disabled when trying to take Lock{%s}\n", m_name);
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dump_backtrace();
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hang();
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}
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for (;;) {
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bool expected = false;
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if (m_lock.compare_exchange_strong(expected, true, AK::memory_order_acq_rel)) {
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if (!m_holder || m_holder == current) {
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m_holder = current;
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++m_level;
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m_lock.store(false, AK::memory_order_release);
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return;
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}
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m_lock.store(false, AK::memory_order_release);
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(void)current->donate_remaining_timeslice_and_block<Thread::WaitQueueBlocker>(m_holder, m_name, m_queue);
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}
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}
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}
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void Lock::unlock()
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{
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for (;;) {
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bool expected = false;
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if (m_lock.compare_exchange_strong(expected, true, AK::memory_order_acq_rel)) {
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ASSERT(m_holder == current);
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ASSERT(m_level);
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--m_level;
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if (m_level) {
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m_lock.store(false, AK::memory_order_release);
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return;
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}
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m_holder = nullptr;
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m_queue.wake_one();
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m_lock.store(false, AK::memory_order_release);
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return;
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}
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// I don't know *who* is using "m_lock", so just yield.
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Scheduler::yield();
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}
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}
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bool Lock::unlock_if_locked()
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{
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for (;;) {
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bool expected = false;
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if (m_lock.compare_exchange_strong(expected, true, AK::memory_order_acq_rel)) {
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if (m_level == 0) {
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m_lock.store(false, AK::memory_order_release);
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return false;
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}
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if (m_holder != current) {
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m_lock.store(false, AK::memory_order_release);
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return false;
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}
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ASSERT(m_level);
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--m_level;
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if (m_level) {
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m_lock.store(false, AK::memory_order_release);
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return false;
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}
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m_holder = nullptr;
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m_lock.store(false, AK::memory_order_release);
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m_queue.wake_one();
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return true;
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}
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// I don't know *who* is using "m_lock", so just yield.
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Scheduler::yield();
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}
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}
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