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#pragma once
#include <shared_mutex>
#ifdef OS_LINUX /// Because of futex
#include <base/types.h>
#include <base/defines.h>
#include <atomic>
namespace DB
{
// Faster implementation of `std::shared_mutex` based on a pair of futexes
class TSA_CAPABILITY("SharedMutex") SharedMutex
{
public:
SharedMutex();
~SharedMutex() = default;
SharedMutex(const SharedMutex &) = delete;
SharedMutex & operator=(const SharedMutex &) = delete;
// Exclusive ownership
void lock() TSA_ACQUIRE();
bool try_lock() TSA_TRY_ACQUIRE(true);
void unlock() TSA_RELEASE();
// Shared ownership
void lock_shared() TSA_ACQUIRE_SHARED();
bool try_lock_shared() TSA_TRY_ACQUIRE_SHARED(true);
void unlock_shared() TSA_RELEASE_SHARED();
private:
static constexpr UInt64 readers = (1ull << 32ull) - 1ull; // Lower 32 bits of state
static constexpr UInt64 writers = ~readers; // Upper 32 bits of state
alignas(64) std::atomic<UInt64> state;
std::atomic<UInt32> waiters;
};
}
#else
namespace DB
{
using SharedMutex = std::shared_mutex;
}
#endif
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