02bb892d7a
This commit splits out synchronization primitives from LibThreading into LibSync. This is because LibThreading depends on LibCore, while LibCore needs the synchronization primitives from LibThreading. This worked while they were header only, but when I tried to add an implementation file it ran into the circular dependency. To abstract away the pthread implementation using cpp files is necessary so the synchronization primitives were moved to a separate library.
36 lines
879 B
C++
36 lines
879 B
C++
/*
|
|
* Copyright (c) 2025, Ryszard Goc <ryszardgoc@gmail.com>
|
|
*
|
|
* SPDX-License-Identifier: BSD-2-Clause
|
|
*/
|
|
|
|
#pragma once
|
|
|
|
#include <AK/Atomic.h>
|
|
#include <AK/Concepts.h>
|
|
#include <LibSync/Mutex.h>
|
|
|
|
namespace Sync {
|
|
|
|
struct OnceFlag {
|
|
Sync::Mutex mutex;
|
|
Atomic<bool> has_been_called { false };
|
|
};
|
|
|
|
template<VoidFunction Callable>
|
|
void call_once(OnceFlag& flag, Callable&& callable)
|
|
{
|
|
if (!flag.has_been_called.load(MemoryOrder::memory_order_acquire)) {
|
|
Sync::MutexLocker lock(flag.mutex);
|
|
|
|
// Another thread may have called the function while we were waiting on the mutex
|
|
// The mutex guarantees exclusivity so we can use relaxed ordering
|
|
if (flag.has_been_called.load(MemoryOrder::memory_order_relaxed))
|
|
return;
|
|
|
|
callable();
|
|
flag.has_been_called.store(true, MemoryOrder::memory_order_release);
|
|
}
|
|
}
|
|
|
|
}
|