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   sem_init    ( 3 )

инициализировать безымянный семафор (initialize an unnamed semaphore)

Имя (Name)

sem_init - initialize an unnamed semaphore

Синопсис (Synopsis)

#include <semaphore.h>

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

Link with -pthread.


Описание (Description)

sem_init() initializes the unnamed semaphore at the address
       pointed to by sem.  The value argument specifies the initial
       value for the semaphore.

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), and so on.

Initializing a semaphore that has already been initialized results in undefined behavior.


Возвращаемое значение (Return value)

sem_init() returns 0 on success; on error, -1 is returned, and
       errno is set to indicate the error.

Ошибки (Error)

EINVAL value exceeds SEM_VALUE_MAX.

ENOSYS pshared is nonzero, but the system does not support process-shared semaphores (see sem_overview(7)).


Атрибуты (Attributes)

For an explanation of the terms used in this section, see
       attributes(7).

┌──────────────────────────────────────┬───────────────┬─────────┐ │Interface Attribute Value │ ├──────────────────────────────────────┼───────────────┼─────────┤ │sem_init() │ Thread safety │ MT-Safe │ └──────────────────────────────────────┴───────────────┴─────────┘


Стандарты (Conforming to)

POSIX.1-2001.

Примечание (Note)

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.

Примеры (Examples)

See shm_open(3) and sem_wait(3).

Смотри также (See also)

sem_destroy(3), sem_post(3), sem_wait(3), sem_overview(7)