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

SYNOPSIS
  #include <semaphore.h>

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

LIBRARY
  Realtime Library (librt)

PARAMETERS
  sem Specifies a location to receive the descriptor of the initialized
      semaphore.

  pshared
      Specifies a value indicating whether the semaphore should be sharable
      between the creating process and its descendants (non-zero value) or
      not (zero).

  value
      Specifies the initial value to be given to the 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 obtain 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 function returns the value 0 (zero);
  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.

SEE ALSO
  Functions: sem_destroy(3), sem_post(3), sem_trywait(3), sem_wait(3)

  Guide to Realtime Programming

Index for Section 3

Alphabetical listing for S

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