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// 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_
namespace re2 {
#define HAVE_PTHREAD 1
#define HAVE_RWLOCK 1
#if defined(NO_THREADS)
typedef int MutexType; // to keep a lock-count
#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 -- 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 defined(HAVE_PTHREAD)
# include <pthread.h>
typedef pthread_mutex_t MutexType;
#elif defined(WIN32)
# define WIN32_LEAN_AND_MEAN // We only need minimal includes
# 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 defined(HAVE_PTHREAD) && defined(HAVE_RWLOCK)
#include <stdlib.h> // for abort()
#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 defined(HAVE_PTHREAD)
#include <stdlib.h> // for abort()
#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_ */
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