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SEM_INIT(3)		   Linux Programmers Manual		  SEM_INIT(3)

       sem_init - initialize an unnamed semaphore


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

       Link with -lrt or -pthread.

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

       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 parents 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.

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

       EINVAL value exceeds SEM_VALUE_MAX.

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


       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.

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

       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)

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