NAME
seminit - initialize an unnamed semaphore SYNOPSIS
#include
int seminit(semt *sem, int pshared, unsigned int value); Link with -pthread. DESCRIPTION seminit() initializes the unnamed semaphore at the address pointed to by sem. The value argument specifies the initial value for the sema‐ phore. 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 nonzero, then the semaphore is shared between processes, and should be located in a region of shared memory (see shmopen(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 sempost(3), semwait(3), etc. Initializing a semaphore that has already been initialized results in undefined behavior. RETURN VALUE
seminit() returns 0 on success; on error, -1 is returned, and errno is set to indicate the error. ERRORS EINVAL value exceeds SEMVALUEMAX.
ENOSYS pshared is nonzero, but the system does not support process- shared semaphores (see semoverview(7)). ATTRIBUTES For an explanation of the terms used in this section, see attributes(7). ┌───────────┬───────────────┬─────────┐ │Interface │ Attribute │ Value │ ├───────────┼───────────────┼─────────┤
│seminit() │ Thread safety │ MT-Safe │ └───────────┴───────────────┴─────────┘ CONFORMING TO
POSIX.1-2001. NOTES
Bizarrely, POSIX.1-2001 does not specify the value that should be
returned by a successful call to seminit(). POSIX.1-2008 rectifies this, specifying the zero return on success. SEE ALSO semdestroy(3), sempost(3), semwait(3), semoverview(7) COLOPHON
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Linux 2012-05-13 SEMINIT(3)