ReadWriteLock.h

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/*
 * Copyright (C) 1996-2025 The Squid Software Foundation and contributors
 *
 * Squid software is distributed under GPLv2+ license and includes
 * contributions from numerous individuals and organizations.
 * Please see the COPYING and CONTRIBUTORS files for details.
 */
 
#ifndef SQUID_SRC_IPC_READWRITELOCK_H
#define SQUID_SRC_IPC_READWRITELOCK_H
 
#include <atomic>
#include <iosfwd>
 
class StoreEntry;
 
namespace Ipc
{
 
class ReadWriteLockStats;
 
class ReadWriteLock
{
public:
    ReadWriteLock() : readers(0), writing(false), appending(false), readLevel(0), writeLevel(0)
    {}
 
    bool lockShared(); 
    bool lockExclusive(); 
    bool lockHeaders(); 
    void unlockShared(); 
    void unlockExclusive(); 
    void unlockHeaders(); 
    void switchExclusiveToShared(); 
    bool unlockSharedAndSwitchToExclusive();
 
    void startAppending(); 
 
    bool stopAppendingAndRestoreExclusive();
 
    void updateStats(ReadWriteLockStats &stats) const;
 
public:
    mutable std::atomic<uint32_t> readers; 
    std::atomic<bool> writing; 
    std::atomic<bool> appending; 
    std::atomic_flag updating; 
 
private:
    bool finalizeExclusive();
 
    mutable std::atomic<uint32_t> readLevel; 
    std::atomic<uint32_t> writeLevel; 
};
 
std::ostream &operator <<(std::ostream &, const ReadWriteLock &);
 
class ReadWriteLockStats
{
public:
    ReadWriteLockStats();
 
    void dump(StoreEntry &e) const;
 
    int count; 
    int readable; 
    int writeable; 
    int idle; 
    int readers; 
    int writers; 
    int appenders; 
};
 
void AssertFlagIsSet(std::atomic_flag &flag);
 
} // namespace Ipc
 
#endif /* SQUID_SRC_IPC_READWRITELOCK_H */