path: root/util/mutex.h

// Copyright 2007 The RE2 Authors.  All Rights Reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

/*
 * A simple mutex wrapper, supporting locks and read-write locks.
 * You should assume the locks are *not* re-entrant.
 */

#ifndef RE2_UTIL_MUTEX_H_
#define RE2_UTIL_MUTEX_H_

#include <stdlib.h>

#if !defined(_WIN32)
#include <unistd.h>  // For POSIX options
#endif

namespace re2 {

#if !defined(_WIN32)
  // Possible values of POSIX options:
  //   -1 means not supported,
  //    0 means maybe supported (query at runtime),
  //   >0 means supported.
# if defined(_POSIX_THREADS) && _POSIX_THREADS > 0
#   define HAVE_PTHREAD 1
# else
#   define HAVE_PTHREAD 0
# endif
# if defined(_POSIX_READER_WRITER_LOCKS) && _POSIX_READER_WRITER_LOCKS > 0
#   define HAVE_RWLOCK 1
# else
#   define HAVE_RWLOCK 0
# endif
#else
# define HAVE_PTHREAD 0
# define HAVE_RWLOCK 0
#endif

#if defined(NO_THREADS)
  typedef int MutexType;      // to keep a lock-count
#elif HAVE_PTHREAD && HAVE_RWLOCK
  // Needed for pthread_rwlock_*.  If it causes problems, you could take it
  // out, but then you'd have to set HAVE_RWLOCK to 0 (at least on linux --
  // it *does* cause problems for FreeBSD, or MacOSX, but isn't needed
  // for locking there.)
# ifdef __linux__
#   undef _XOPEN_SOURCE
#   define _XOPEN_SOURCE 500  // may be needed to get the rwlock calls
# endif
# include <pthread.h>
  typedef pthread_rwlock_t MutexType;
#elif HAVE_PTHREAD
# include <pthread.h>
  typedef pthread_mutex_t MutexType;
#elif defined(_WIN32)
# ifndef WIN32_LEAN_AND_MEAN
#   define WIN32_LEAN_AND_MEAN  // We only need minimal includes
# endif
# ifdef GMUTEX_TRYLOCK
  // We need Windows NT or later for TryEnterCriticalSection().  If you
  // don't need that functionality, you can remove these _WIN32_WINNT
  // lines, and change TryLock() to assert(0) or something.
#   ifndef _WIN32_WINNT
#     define _WIN32_WINNT 0x0400
#   endif
# endif
# include <windows.h>
  typedef CRITICAL_SECTION MutexType;
#else
# error Need to implement mutex.h for your architecture, or #define NO_THREADS
#endif

class Mutex {
 public:
  // Create a Mutex that is not held by anybody.
  inline Mutex();

  // Destructor
  inline ~Mutex();

  inline void Lock();    // Block if needed until free then acquire exclusively
  inline void Unlock();  // Release a lock acquired via Lock()
  inline bool TryLock(); // If free, Lock() and return true, else return false
  // Note that on systems that don't support read-write locks, these may
  // be implemented as synonyms to Lock() and Unlock().  So you can use
  // these for efficiency, but don't use them anyplace where being able
  // to do shared reads is necessary to avoid deadlock.
  inline void ReaderLock();   // Block until free or shared then acquire a share
  inline void ReaderUnlock(); // Release a read share of this Mutex
  inline void WriterLock() { Lock(); }     // Acquire an exclusive lock
  inline void WriterUnlock() { Unlock(); } // Release a lock from WriterLock()
  inline void AssertHeld() { }

 private:
  MutexType mutex_;

  // Catch the error of writing Mutex when intending MutexLock.
  Mutex(Mutex *ignored);
  // Disallow "evil" constructors
  Mutex(const Mutex&);
  void operator=(const Mutex&);
};

// Now the implementation of Mutex for various systems
#if defined(NO_THREADS)

// When we don't have threads, we can be either reading or writing,
// but not both.  We can have lots of readers at once (in no-threads
// mode, that's most likely to happen in recursive function calls),
// but only one writer.  We represent this by having mutex_ be -1 when
// writing and a number > 0 when reading (and 0 when no lock is held).
//
// In debug mode, we assert these invariants, while in non-debug mode
// we do nothing, for efficiency.  That's why everything is in an
// assert.
#include <assert.h>

Mutex::Mutex() : mutex_(0) { }
Mutex::~Mutex()            { assert(mutex_ == 0); }
void Mutex::Lock()         { assert(--mutex_ == -1); }
void Mutex::Unlock()       { assert(mutex_++ == -1); }
bool Mutex::TryLock()      { if (mutex_) return false; Lock(); return true; }
void Mutex::ReaderLock()   { assert(++mutex_ > 0); }
void Mutex::ReaderUnlock() { assert(mutex_-- > 0); }

#elif HAVE_PTHREAD && HAVE_RWLOCK

#define SAFE_PTHREAD(fncall)  do { if ((fncall) != 0) abort(); } while (0)

Mutex::Mutex()             { SAFE_PTHREAD(pthread_rwlock_init(&mutex_, NULL)); }
Mutex::~Mutex()            { SAFE_PTHREAD(pthread_rwlock_destroy(&mutex_)); }
void Mutex::Lock()         { SAFE_PTHREAD(pthread_rwlock_wrlock(&mutex_)); }
void Mutex::Unlock()       { SAFE_PTHREAD(pthread_rwlock_unlock(&mutex_)); }
bool Mutex::TryLock()      { return pthread_rwlock_trywrlock(&mutex_) == 0; }
void Mutex::ReaderLock()   { SAFE_PTHREAD(pthread_rwlock_rdlock(&mutex_)); }
void Mutex::ReaderUnlock() { SAFE_PTHREAD(pthread_rwlock_unlock(&mutex_)); }

#undef SAFE_PTHREAD

#elif HAVE_PTHREAD

#define SAFE_PTHREAD(fncall)  do { if ((fncall) != 0) abort(); } while (0)

Mutex::Mutex()             { SAFE_PTHREAD(pthread_mutex_init(&mutex_, NULL)); }
Mutex::~Mutex()            { SAFE_PTHREAD(pthread_mutex_destroy(&mutex_)); }
void Mutex::Lock()         { SAFE_PTHREAD(pthread_mutex_lock(&mutex_)); }
void Mutex::Unlock()       { SAFE_PTHREAD(pthread_mutex_unlock(&mutex_)); }
bool Mutex::TryLock()      { return pthread_mutex_trylock(&mutex_) == 0; }
void Mutex::ReaderLock()   { Lock(); }      // we don't have read-write locks
void Mutex::ReaderUnlock() { Unlock(); }
#undef SAFE_PTHREAD

#elif defined(_WIN32)

Mutex::Mutex()             { InitializeCriticalSection(&mutex_); }
Mutex::~Mutex()            { DeleteCriticalSection(&mutex_); }
void Mutex::Lock()         { EnterCriticalSection(&mutex_); }
void Mutex::Unlock()       { LeaveCriticalSection(&mutex_); }
bool Mutex::TryLock()      { return TryEnterCriticalSection(&mutex_) != 0; }
void Mutex::ReaderLock()   { Lock(); }      // we don't have read-write locks
void Mutex::ReaderUnlock() { Unlock(); }

#endif


// --------------------------------------------------------------------------
// Some helper classes

// MutexLock(mu) acquires mu when constructed and releases it when destroyed.
class MutexLock {
 public:
  explicit MutexLock(Mutex *mu) : mu_(mu) { mu_->Lock(); }
  ~MutexLock() { mu_->Unlock(); }
 private:
  Mutex * const mu_;
  // Disallow "evil" constructors
  MutexLock(const MutexLock&);
  void operator=(const MutexLock&);
};

// ReaderMutexLock and WriterMutexLock do the same, for rwlocks
class ReaderMutexLock {
 public:
  explicit ReaderMutexLock(Mutex *mu) : mu_(mu) { mu_->ReaderLock(); }
  ~ReaderMutexLock() { mu_->ReaderUnlock(); }
 private:
  Mutex * const mu_;
  // Disallow "evil" constructors
  ReaderMutexLock(const ReaderMutexLock&);
  void operator=(const ReaderMutexLock&);
};

class WriterMutexLock {
 public:
  explicit WriterMutexLock(Mutex *mu) : mu_(mu) { mu_->WriterLock(); }
  ~WriterMutexLock() { mu_->WriterUnlock(); }
 private:
  Mutex * const mu_;
  // Disallow "evil" constructors
  WriterMutexLock(const WriterMutexLock&);
  void operator=(const WriterMutexLock&);
};

// Catch bug where variable name is omitted, e.g. MutexLock (&mu);
#define MutexLock(x) COMPILE_ASSERT(0, mutex_lock_decl_missing_var_name)
#define ReaderMutexLock(x) COMPILE_ASSERT(0, rmutex_lock_decl_missing_var_name)
#define WriterMutexLock(x) COMPILE_ASSERT(0, wmutex_lock_decl_missing_var_name)

}  // namespace re2

#endif  /* #define RE2_UTIL_MUTEX_H_ */