sem_init(3p) [centos man page]

SEM_INIT(3P)						     POSIX Programmer's Manual						      SEM_INIT(3P)

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

       sem_init - initialize an unnamed semaphore (REALTIME)

SYNOPSIS

       #include <semaphore.h>

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

DESCRIPTION

       The sem_init() function shall initialize the unnamed semaphore referred to by sem. The value of the initialized semaphore shall	be  value.
       Following  a  successful  call  to  sem_init(), the semaphore may be used in subsequent calls to sem_wait(), sem_trywait(), sem_post(), and
       sem_destroy().  This semaphore shall remain usable until the semaphore is destroyed.

       If the pshared argument has a non-zero value, then the semaphore is shared between processes; in this case, any process that can access the
       semaphore sem can use sem for performing sem_wait(), sem_trywait(), sem_post(), and sem_destroy() operations.

       Only  sem  itself  may  be  used for performing synchronization.  The result of referring to copies of sem in calls to sem_wait(), sem_try-
       wait(), sem_post(), and sem_destroy() is undefined.

       If the pshared argument is zero, then the semaphore is shared between threads of the process; any thread in this process can  use  sem  for
       performing  sem_wait(),	sem_trywait(), sem_post(), and sem_destroy() operations. The use of the semaphore by threads other than those cre-
       ated in the same process is undefined.

       Attempting to initialize an already initialized semaphore results in undefined behavior.

RETURN VALUE

       Upon successful completion, the sem_init() function shall initialize the semaphore in sem. Otherwise, it shall return -1 and set  errno	to
       indicate the error.

ERRORS

       The sem_init() function shall fail if:

       EINVAL The value argument exceeds {SEM_VALUE_MAX}.

       ENOSPC A resource required to initialize the semaphore has been exhausted, or the limit on semaphores ( {SEM_NSEMS_MAX}) has been reached.

       EPERM  The process lacks the appropriate privileges to initialize the semaphore.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       The sem_init() function is part of the Semaphores option and need not be available on all implementations.

RATIONALE

       Although  this volume of IEEE Std 1003.1-2001 fails to specify a successful return value, it is likely that a later version may require the
       implementation to return a value of zero if the call to sem_init() is successful.

FUTURE DIRECTIONS

       None.

SEE ALSO

       sem_destroy(), sem_post(), sem_timedwait(), sem_trywait(), sem_wait(), the Base Definitions volume of IEEE Std 1003.1-2001, <semaphore.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and  the  original  IEEE
       and  The  Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained
       online at http://www.opengroup.org/unix/online.html .

IEEE
/The Open Group						       2003							      SEM_INIT(3P)

Check Out this Related Man Page

sem_init(3)						     Library Functions Manual						       sem_init(3)

NAME

       sem_init - Initializes an unnamed semaphore (P1003.1b)

LIBRARY

       Realtime Library (librt.so, librt.a)

SYNOPSIS

       #include <semaphore.h>

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

PARAMETERS

       sem	   Specifies a location to receive the descriptor of the initialized semaphore.

       pshared Specifies a value indicating whether the semaphore should be sharable between processes (non-zero value) or not (zero).

       value   Specifies the initial value to be given to the semaphore.

DESCRIPTION

       The  sem_init function creates a new counting semaphore with a specific value.  A semaphore is used to limit access to a critical resource.
       When a process requires access to the resource without interference from other processes, it attempts to establish a  connection  with  the
       associated semaphore.  If the semaphore value is greater than zero, the connection is established and the semaphore value is decremented by
       one.  If the semaphore value is less than or equal to zero, the process attempting to access the resource is  blocked  and  must  wait  for
       another process to release the semaphore and increment the semaphore value.

       The  sem_init function establishes a connection between an unnamed semaphore and a process; the sem_wait and sem_trywait functions lock the
       semaphore; and the sem_post function unlocks the semaphore.  Use the sem_destroy function to deallocate system resources allocated  to  the
       process for use with the semaphore.  You can use the sem_getvalue function to obtain the value of a semaphore.

       A semaphore created by a call to the sem_init function remains valid until the semaphore is removed by a call to the sem_destroy function.

RETURN VALUES

       On  successful completion, the function returns the value 0 (zero); otherwise, the function returns the value -1 and sets errno to indicate
       the error.

ERRORS

       The sem_init function fails under the following conditions:

       [EINVAL] 	   The value argument exceeds {SEM_VALUE_MAX}.

       [ENOSPC] 	   A resource required to initialize the semaphore has been exhausted.	The limit on semaphores ({SEM_NSEMS_MAX}) has been
			   reached.

       [EPERM]		   The process lacks the appropriate privilege to initialize the semaphore.

RELATED INFORMATION

       Functions: sem_destroy(3), sem_post(3), sem_trywait(3),sem_wait(3)

       Guide to Realtime Programming delim off

																       sem_init(3)

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