sem_init()--Initialize Unnamed Semaphore

 #include <semaphore.h>

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

The sem_init() function initializes an unnamed semaphore and sets its initial value. The maximum value of the semaphore is set to SEM_VALUE_MAX. The title for the semaphore is set to the character representation of the address of the semaphore. If an unnamed semaphore already exists at sem, then it will be destroyed and a new semaphore will be initialized.

Parameters

sem

(Input) A pointer to the storage of an uninitialized unnamed semaphore. The pointer must be aligned on a 16-byte boundary. This semaphore is initialized.

shared

(Input) An indication to the system of how the semaphore is going to be used. A value of zero indicates that the semaphore will be used only by threads within the current process. A nonzero value indicates that the semaphore may be used by threads from other processes.

value

(Input) The value used to initialize the value of the semaphore.

Authorities

None

Return Value

Error Conditions

If sem_init() is not successful, errno usually indicates one of the following errors. Under some conditions, errno could indicate an error other than those listed here.

[EINVAL]

The value specified for the argument is not correct.

A function was passed incorrect argument values, or an operation was attempted on an object and the operation specified is not supported for that type of object.

An argument value is not valid, out of range, or NULL.

The value parameter is greater than SEM_VALUE_MAX.

[ENOSPC]

No space available.

System semaphore resources have been exhausted.

Error Messages

None.

Related Information

• The <semaphore.h> file (see )
  
  
• sem_destroy()--Destroy Unnamed Semaphore
  
  
• sem_getvalue()--Get Semaphore Value
  
  
• sem_init_np()--Initialize Unnamed Semaphore with Maximum Value
  
  
• sem_post()--Post to Semaphore
  
  
• sem_post_np()--Post Value to Semaphore
  
  
• sem_trywait()--Try to Decrement Semaphore
  
  
• sem_wait()--Wait for Semaphore
  
  
• sem_wait_np()--Wait for Semaphore with Timeout

Example

See Code disclaimer information for information pertaining to code examples.

The following example initializes an unnamed semaphore, my_semaphore, that will be used by threads of the current process. Its value is set to 10.

#include <semaphore.h>
main() {
  sem_t my_semaphore;
  int rc;

  rc = sem_init(&my_semaphore, 0, 10);

}