s3fs-fuse/src/mutex.h

/*
 * s3fs - FUSE-based file system backed by Amazon S3
 *
 * Copyright(C) 2007 Randy Rizun <rrizun@gmail.com>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 */

#ifndef S3FS_MUTEX_H_
#define S3FS_MUTEX_H_

#include <mutex>

// Taken from: https://clang.llvm.org/docs/ThreadSafetyAnalysis.html

#if defined(__clang__)
#define THREAD_ANNOTATION_ATTRIBUTE__(x)   __attribute__((x))
#else
#define THREAD_ANNOTATION_ATTRIBUTE__(x)   // no-op
#endif

// These wrappers are necessary with GNU libstdc++.  clang libc++ should have these already.
#define CAPABILITY(x) \
  THREAD_ANNOTATION_ATTRIBUTE__(capability(x))

#define SCOPED_CAPABILITY \
  THREAD_ANNOTATION_ATTRIBUTE__(scoped_lockable)

#define GUARDED_BY(x) \
  THREAD_ANNOTATION_ATTRIBUTE__(guarded_by(x))

#define PT_GUARDED_BY(x) \
  THREAD_ANNOTATION_ATTRIBUTE__(pt_guarded_by(x))

#define ACQUIRED_BEFORE(...) \
  THREAD_ANNOTATION_ATTRIBUTE__(acquired_before(__VA_ARGS__))

#define ACQUIRED_AFTER(...) \
  THREAD_ANNOTATION_ATTRIBUTE__(acquired_after(__VA_ARGS__))

#define REQUIRES(...) \
  THREAD_ANNOTATION_ATTRIBUTE__(requires_capability(__VA_ARGS__))

#define ACQUIRE(...) \
  THREAD_ANNOTATION_ATTRIBUTE__(acquire_capability(__VA_ARGS__))

#define RELEASE(...) \
  THREAD_ANNOTATION_ATTRIBUTE__(release_capability(__VA_ARGS__))

#define RELEASE_GENERIC(...) \
  THREAD_ANNOTATION_ATTRIBUTE__(release_generic_capability(__VA_ARGS__))

#define TRY_ACQUIRE(...) \
  THREAD_ANNOTATION_ATTRIBUTE__(try_acquire_capability(__VA_ARGS__))


// Defines an annotated interface for mutexes.
// These methods can be implemented to use any internal mutex implementation.
class CAPABILITY("mutex") Mutex {
public:
  // Acquire/lock this mutex exclusively.  Only one thread can have exclusive
  // access at any one time.  Write operations to guarded data require an
  // exclusive lock.
  void Lock() ACQUIRE() {
    lock.lock();
  }

  // Release/unlock an exclusive mutex.
  void Unlock() RELEASE();

  // Generic unlock, can unlock exclusive and shared mutexes.
  void GenericUnlock() RELEASE_GENERIC() {
    lock.unlock();
  }

  // Try to acquire the mutex.  Returns true on success, and false on failure.
  bool TryLock() TRY_ACQUIRE(true) {
    return lock.try_lock();
  }

  Mutex() {}
  Mutex(const Mutex&) = delete;
  Mutex(Mutex&&) = delete;
  Mutex& operator=(const Mutex&) = delete;
  Mutex& operator=(Mutex&&) = delete;

private:
  std::mutex lock;
};

// MutexLocker is an RAII class that acquires a mutex in its constructor, and
// releases it in its destructor.
class SCOPED_CAPABILITY MutexLocker {
private:
  Mutex* mut;
  bool locked;

public:
  // Acquire mu, implicitly acquire *this and associate it with mu.
  explicit MutexLocker(Mutex *mu) ACQUIRE(mu) : mut(mu), locked(true) {
    mu->Lock();
  }

  // Release *this and all associated mutexes, if they are still held.
  // There is no warning if the scope was already unlocked before.
  ~MutexLocker() RELEASE() {
    if (locked)
      mut->GenericUnlock();
  }

  // Acquire all associated mutexes exclusively.
  void Lock() ACQUIRE() {
    mut->Lock();
    locked = true;
  }

  // Try to acquire all associated mutexes exclusively.
  bool TryLock() TRY_ACQUIRE(true) {
    return locked = mut->TryLock();
  }

  // Release all associated mutexes. Warn on double unlock.
  void Unlock() RELEASE() {
    mut->Unlock();
    locked = false;
  }
};

#endif // S3FS_MUTEX_H_

/*
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* c-basic-offset: 4
* End:
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*/