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sem_init(3) [osf1 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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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)
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