使用信号量的一些问题

Question

现在我正在处理我的项目,我有一个关于信号量初始化的问题.实际上我是在Mac OS X上编程,但我试图在Linux上编译我的项目并且它不能编译.在OS X上,它会编译,但每次只是在初始化时崩溃.

sem_t *mutex_1, *mutex_2, *mutex_3, *reader, *writer;

int initialization_semaphores (void) 
{
    int ERROR = EOK;
    if ((mutex_1 = mmap(NULL, sizeof(sem_t), PROT_READ | PROT_WRITE, MAP_ANON | MAP_SHARED, 0, 0)) == MAP_FAILED)
        ERROR = ESEM;
    if ((mutex_2 = mmap(NULL, sizeof(sem_t), PROT_READ | PROT_WRITE, MAP_ANON | MAP_SHARED, 0, 0)) == MAP_FAILED)
        ERROR = ESEM;
    if ((mutex_3 = mmap(NULL, sizeof(sem_t), PROT_READ | PROT_WRITE, MAP_ANON | MAP_SHARED, 0, 0)) == MAP_FAILED)
        ERROR = ESEM;
    if ((reader = mmap(NULL, sizeof(sem_t), PROT_READ | PROT_WRITE, MAP_ANON | MAP_SHARED, 0, 0)) == MAP_FAILED)
        ERROR = ESEM;
    if ((writer = mmap(NULL, sizeof(sem_t), PROT_READ | PROT_WRITE, MAP_ANON | MAP_SHARED, 0, 0)) == MAP_FAILED)
        ERROR = ESEM;

    if (ERROR == EOK) {
        if (sem_init(mutex_1, 1, 1) == -1)
            ERROR = ESEM;
        if (sem_init(mutex_2, 1, 1) == -1)
            ERROR = ESEM;
        if (sem_init(mutex_3, 1, 1) == -1)
            ERROR = ESEM;
        if (sem_init(reader, 1, 1) == -1)
            ERROR = ESEM;
        if (sem_init(writer, 1, 1) == -1)
            ERROR = ESEM;
    }
}

当我尝试在linux上编译它时,我看到了这个:

/tmp/ccmkN9G7.o: In function `initialization_semaphores':
readerWriter.c:(.text+0x1a2): undefined reference to `sem_init'
readerWriter.c:(.text+0x1cb): undefined reference to `sem_init'
readerWriter.c:(.text+0x1f4): undefined reference to `sem_init'
readerWriter.c:(.text+0x21d): undefined reference to `sem_init'
readerWriter.c:(.text+0x246): undefined reference to `sem_init'
readerWriter.c:(.text+0x275): undefined reference to `shm_open'

这样对吗？:

int ERROR = EOK;
mutex_1 = sem_open("mutex1", O_CREAT, S_IRUSR | S_IWUSR, 1);   
mutex_2 = sem_open("mutex2", O_CREAT, S_IRUSR | S_IWUSR, 1);  
mutex_3 = sem_open("mutex3", O_CREAT, S_IRUSR | S_IWUSR, 1); 
reader = sem_open("reader", O_CREAT, S_IRUSR | S_IWUSR, 1); 
writer = sem_open("writer", O_CREAT, S_IRUSR | S_IWUSR, 1);   

Answer 1

Mac OSX不符合要求且不支持sem_init.该函数存在,但它无声地失败或更糟,留下一个不工作的信号量.

我鼓励你向Apple提交一个错误,因为这是一个真正的,长期存在的问题,严重影响了应用程序的可移植性.抱怨的人越多,就越有希望得到修复.

至于解决它,您可以尝试查找/编写所有POSIX信号量函数的替换实现并将您的程序链接到该函数,或者您可以切换到使用sem_open而不是mmap和sem_init.

(只要你已经经历了为每个信号量映射整个页面的开销,sem_open实际上不会花费你更多的东西.这个bug实际上是一个显示阻塞的地方就是当你想要在现有信号中包含你的信号量时struct.)