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sem_init(3c) [opensolaris man page]

sem_init(3C)						   Standard C Library Functions 					      sem_init(3C)

NAME
sem_init - initialize an unnamed semaphore SYNOPSIS
#include <semaphore.h> int sem_init(sem_t *sem, int pshared, unsigned int value); DESCRIPTION
The sem_init() function is used to initialize the unnamed semaphore referred to by sem. The value of the initialized semaphore is value. Following a successful call to sem_init(), the semaphore may be used in subsequent calls to sem_wait(3C), sem_trywait(3C), sem_post(3C), and sem_destroy(3C). This semaphore remains 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(3C), sem_trywait(3C), sem_post(3C), and sem_destroy(3C) operations. Only sem itself may be used for performing synchronization. The result of referring to copies of sem in calls to sem_wait(3C), sem_try- wait(3C), sem_post(3C), and sem_destroy(3C), 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(3C), sem_trywait(3C), sem_post(3C), and sem_destroy(3C) operations. The use of the semaphore by threads other than those created in the same process is undefined. Attempting to initialize an already initialized semaphore results in undefined behavior. RETURN VALUES
Upon successful completion, the function initializes the semaphore in sem. Otherwise, it returns -1 and sets errno to indicate the error. ERRORS
The sem_init() function will fail if: EINVAL The value argument exceeds SEM_VALUE_MAX. ENOSPC A resource required to initialize the semaphore has been exhausted, or the resources have reached the limit on semaphores (SEM_NSEMS_MAX). ENOSYS The sem_init() function is not supported by the system. EPERM The process lacks the appropriate privileges to initialize the semaphore. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ |ATTRIBUTE TYPE |ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Committed | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe | +-----------------------------+-----------------------------+ |Standard |See standards(5). | +-----------------------------+-----------------------------+ SEE ALSO
sem_destroy(3C), sem_post(3C), sem_wait(3C), attributes(5), standards(5) SunOS 5.11 5 Feb 2008 sem_init(3C)

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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 -pthread. DESCRIPTION
sem_init() initializes the unnamed semaphore at the address pointed to by sem. The value argument specifies the initial value for the sem- aphore. 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 allocated 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 3.44 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 2012-05-13 SEM_INIT(3)
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