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/*
* Copyright (c) 2021, the SerenityOS developers.
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/Atomic.h>
#include <Kernel/Arch/x86/Processor.h>
namespace Kernel {
template<typename AtomicRefCountType>
class AtomicEdgeAction {
public:
template<typename FirstRefAction>
bool ref(FirstRefAction first_ref_action)
{
AtomicRefCountType expected = 0;
AtomicRefCountType desired = (1 << 1) | 1;
// Least significant bit indicates we're busy protecting/unprotecting
for (;;) {
if (m_atomic_ref_count.compare_exchange_strong(expected, desired, AK::memory_order_relaxed))
break;
Processor::wait_check();
expected &= ~1;
desired = expected + (1 << 1);
VERIFY(desired > expected);
if (expected == 0)
desired |= 1;
}
atomic_thread_fence(AK::memory_order_acquire);
if (expected == 0) {
first_ref_action();
// drop the busy flag
m_atomic_ref_count.store(desired & ~1, AK::memory_order_release);
return true;
}
return false;
}
template<typename LastRefAction>
bool unref(LastRefAction last_ref_action)
{
AtomicRefCountType expected = 1 << 1;
AtomicRefCountType desired = (1 << 1) | 1;
// Least significant bit indicates we're busy protecting/unprotecting
for (;;) {
if (m_atomic_ref_count.compare_exchange_strong(expected, desired, AK::memory_order_relaxed))
break;
Processor::wait_check();
expected &= ~1;
VERIFY(expected != 0); // Someone should always have at least one reference
if (expected == 1 << 1) {
desired = (1 << 1) | 1;
} else {
desired = expected - (1 << 1);
VERIFY(desired < expected);
}
}
AK::atomic_thread_fence(AK::memory_order_release);
if (expected == 1 << 1) {
last_ref_action();
// drop the busy flag and release reference
m_atomic_ref_count.store(0, AK::memory_order_release);
return true;
}
return false;
}
private:
Atomic<AtomicRefCountType> m_atomic_ref_count { 0 };
};
}
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