Mutex::Autolock for c++

• Mutex.cpp

#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
#include "Mutex.h"

int ret = 1234;
Mutex mLock;

void* show_message(void* ptr)
{
    char* message;
    int x = 5;

    Mutex::Autolock _l(mLock);

    message = (char*) ptr;

    for (x = 5 ; x > 0 ; --x) {
        printf("%s \n", message);
        usleep(300);
    }

    pthread_exit((void*)&ret);
}

int main() {
    pthread_t thread1;
    pthread_t thread2;
    int *ret1 = NULL;
    int *ret2 = NULL;

    pthread_create(&thread1, NULL , show_message , (void*) "Thread 1");
    pthread_create(&thread2, NULL , show_message , (void*) "Thread 2");
    pthread_join( thread1, (void**)&ret1);
    pthread_join( thread2, (void**)&ret2);
    printf("return value from thread1 = %d\n", *ret1);
    printf("return value from thread2 = %d\n", *ret2);

    return 0;
}

g++ -o Mutex Mutex.cpp -lpthread

• Mutex.h

/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef _LIBS_UTILS_MUTEX_H
#define _LIBS_UTILS_MUTEX_H

#include <stdint.h>
#include <sys/types.h>
#include <time.h>

#define HAVE_PTHREADS
typedef int status_t;

#if defined(HAVE_PTHREADS)
# include <pthread.h>
#endif

// ---------------------------------------------------------------------------

/*
 * Simple mutex class.  The implementation is system-dependent.
 *
 * The mutex must be unlocked by the thread that locked it.  They are not
 * recursive, i.e. the same thread can't lock it multiple times.
 */
class Mutex {
public:
    enum {
        PRIVATE = 0,
        SHARED = 1
    };

                Mutex();
                Mutex(const char* name);
                Mutex(int type, const char* name = NULL);
                ~Mutex();

    // lock or unlock the mutex
    status_t    lock();
    void        unlock();

    // lock if possible; returns 0 on success, error otherwise
    status_t    tryLock();

    // Manages the mutex automatically. It'll be locked when Autolock is
    // constructed and released when Autolock goes out of scope.
    class Autolock {
    public:
        inline Autolock(Mutex& mutex) : mLock(mutex)  { mLock.lock(); }
        inline Autolock(Mutex* mutex) : mLock(*mutex) { mLock.lock(); }
        inline ~Autolock() { mLock.unlock(); }
    private:
        Mutex& mLock;
    };

private:
    // A mutex cannot be copied
                Mutex(const Mutex&);
    Mutex&      operator = (const Mutex&);

#if defined(HAVE_PTHREADS)
    pthread_mutex_t mMutex;
#else
    void    _init();
    void*   mState;
#endif
};

// ---------------------------------------------------------------------------

#if defined(HAVE_PTHREADS)

inline Mutex::Mutex() {
    pthread_mutex_init(&mMutex, NULL);
}
inline Mutex::Mutex(__attribute__((unused)) const char* name) {
    pthread_mutex_init(&mMutex, NULL);
}
inline Mutex::Mutex(int type, __attribute__((unused)) const char* name) {
    if (type == SHARED) {
        pthread_mutexattr_t attr;
        pthread_mutexattr_init(&attr);
        pthread_mutexattr_setpshared(&attr, PTHREAD_PROCESS_SHARED);
        pthread_mutex_init(&mMutex, &attr);
        pthread_mutexattr_destroy(&attr);
    } else {
        pthread_mutex_init(&mMutex, NULL);
    }
}
inline Mutex::~Mutex() {
    pthread_mutex_destroy(&mMutex);
}
inline status_t Mutex::lock() {
    return -pthread_mutex_lock(&mMutex);
}
inline void Mutex::unlock() {
    pthread_mutex_unlock(&mMutex);
}
inline status_t Mutex::tryLock() {
    return -pthread_mutex_trylock(&mMutex);
}

#endif // HAVE_PTHREADS

// ---------------------------------------------------------------------------

/*
 * Automatic mutex.  Declare one of these at the top of a function.
 * When the function returns, it will go out of scope, and release the
 * mutex.
 */

typedef Mutex::Autolock AutoMutex;

// ---------------------------------------------------------------------------

#endif // _LIBS_UTILS_MUTEX_H