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  • Linux线程同步---信号量初始化

    SEM_INIT(3)                Linux Programmer's Manual               SEM_INIT(3)

    NAME        sem_init - initialize an unnamed semaphore

    SYNOPSIS        #include <semaphore.h>

           int sem_init(sem_t *sem, int pshared, unsigned int value);

           Link with -lrt or -pthread.

    DESCRIPTION        sem_init()  initializes the unnamed semaphore at the address pointed to        by sem.  The value argument specifies the initial value for  the  sema‐        phore.

           The  pshared  argument indicates whether this semaphore is to be shared        between the threads of a process, or between processes.

           If pshared has the value 0, then the semaphore is  shared  between  the        threads  of  a  process,  and should be located at some address that is        visible to all threads (e.g., a global variable, or  a  variable  allo‐        cated dynamically on the heap).

           If  pshared is nonzero, then the semaphore is shared between processes,        and should be located in a region of shared  memory  (see  shm_open(3),        mmap(2),  and  shmget(2)).   (Since a child created by fork(2) inherits        its parent's memory mappings, it can also access the  semaphore.)   Any        process  that  can  access  the shared memory region can operate on the        semaphore using sem_post(3), sem_wait(3), etc.

           Initializing a semaphore that has already been initialized  results  in        undefined behavior.

    RETURN VALUE        sem_init() returns 0 on success; on error, -1 is returned, and errno is        set to indicate the error.

    ERRORS        EINVAL value exceeds SEM_VALUE_MAX.

           ENOSYS pshared is nonzero, but the system  does  not  support  process-               shared semaphores (see sem_overview(7)).

    CONFORMING TO        POSIX.1-2001.

    NOTES        Bizarrely,  POSIX.1-2001  does  not  specify  the  value that should be        returned by a successful call to  sem_init().   POSIX.1-2008  rectifies        this, specifying the zero return on success.

    SEE ALSO        sem_destroy(3), sem_post(3), sem_wait(3), sem_overview(7)

    COLOPHON        This  page  is  part of release 3.35 of the Linux man-pages project.  A        description of the project, and information about reporting  bugs,  can        be found at http://man7.org/linux/man-pages/.

    Linux                             2008-07-27                       SEM_INIT(3)

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  • 原文地址:https://www.cnblogs.com/farbeyond/p/4477510.html
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