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/* Copyright (c) 2007, Google Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following disclaimer
* in the documentation and/or other materials provided with the
* distribution.
* * Neither the name of Google Inc. nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* ---
* Author: Craig Silverstein.
*
* A simple mutex wrapper, supporting locks and read-write locks.
*
* To use: you should define the following macros in your configure.ac:
* ACX_PTHREAD
* AC_RWLOCK
* The latter is defined in ../autoconf.
*
* This class is meant to be internal-only, so it's defined in the
* global namespace. If you want to expose it, you'll want to move
* it to the Google namespace.
*/
#include "config.h" // to figure out pthreads support
#if defined(NO_THREADS)
typedef int MutexType; // some dummy type; it won't be used
#elif defined(HAVE_PTHREAD) && defined(HAVE_RWLOCK)
// Needed for pthread_rwlock_*. If it causes problems, you could take
// it out, but then you'd have to unset HAVE_RWLOCK (at least on linux).
# define _XOPEN_SOURCE 500 // needed to get the rwlock calls
# include <pthread.h>
typedef pthread_rwlock_t MutexType;
#elif defined(HAVE_PTHREAD)
# include <pthread.h>
typedef pthread_mutex_t MutexType;
#else
# error Need to implement mutex.h/cc for your architecture, or #define NO_THREADS
#endif
class Mutex {
public:
// Create a Mutex that is not held by anybody.
Mutex();
// Destructor
~Mutex();
void Lock(); // Block if necessary until free, then acquire exclusively
void Unlock(); // Release. Caller must hold it exclusively (via Lock())
// 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.
void ReaderLock(); // Block until free or shared, then acquire a share
void ReaderUnlock(); // Release a read share of this Mutex
void WriterLock() { Lock(); } // Block until free, then acquire exclusively
void WriterUnlock() { Unlock(); } // Release the exclusive lock of this Mutex
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&);
};
// 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)
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