Index for Section 3

Alphabetical listing for S

Bottom of page

sem_init(3)
NAME
  sem_init - Initialize an unnamed semaphore (P1003.1b)

SYNOPSIS
  #include <semaphore.h>

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

PARAMETERS
  sem	  Indicates the specific semaphore to be initialized.

  pshared A non-zero value indicates that the semaphore can be shared between
	  processes.

  value	  The value of the initialized 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 get 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 sem_init function creates the semaphore;
  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)

Index for Section 3

Alphabetical listing for S

Top of page