Man Sem_init en anglais
SEM_INIT(3)                Linux Programmer's Manual               SEM_INIT(3)



 

NAME


       sem_init - initialize an unnamed semaphore

 

SYNOPSIS


       #include 

       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
       semaphore.

       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 non-zero, 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 non-zero, 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().  However, virtually  every
       implementation returns zero in this case.

 

SEE ALSO


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

 

COLOPHON


       This  page  is  part of release 3.05 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.



Linux                             2006-03-25                       SEM_INIT(3)