Manpage of SEM_INIT
SEM_INITSection: Linux Programmer's Manual (3)
NAMEsem_init - initialize an unnamed semaphore
#include <semaphore.h>int sem_init(sem_t *sem, int pshared, unsigned int value);
DESCRIPTIONsem_init() initializes the unnamed semaphore at the address pointed to by sem. The valueargument specifies the initial value for the semaphore.
The psharedargument indicates whether this semaphore is to be shared between the threads of a process, or between processes.
If psharedhas 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 psharedis 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), and so on.
RETURN VALUEsem_init() returns 0 on success; on error, -1 is returned, and errnois set to indicate the error.
- valueexceeds SEM_VALUE_MAX.
- psharedis nonzero, but the system does not support process-shared semaphores (see sem_overview(7)).
ATTRIBUTESFor an explanation of the terms used in this section, see attributes(7).
NOTESBizarrely, 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 ALSOsem_destroy(3), sem_post(3), sem_wait(3), sem_overview(7)
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