wai_sem

Outline

Acquire semaphore resource (waiting forever).

C format

 ER      wai_sem (ID semid);

Parameter(s)

I/O	Parameter	Description
I	ID semid;	ID number of the semaphore.

Explanation

This service call acquires a resource from the semaphore specified by parameter semid (subtracts 1 from the semaphore counter).

If no resources are acquired from the target semaphore when this service call is issued (no available resources exist), this service call does not acquire resources but queues the invoking task to the target semaphore wait queue and moves it from the RUNNING state to the WAITING state (resource acquisition wait state).

The WAITING state for a semaphore resource is cancelled in the following cases.

WAITING State for a Semaphore Resource Cancel Operation	Return Value
The resource was released to the target semaphore as a result of issuing sig_sem.	E_OK
The resource was released to the target semaphore as a result of issuing isig_sem.	E_OK
Forced release from waiting (accept rel_wai while waiting).	E_RLWAI
Forced release from waiting (accept irel_wai while waiting).	E_RLWAI

Note Invoking tasks are queued to the target semaphore wait queue in the order defined during configuration (FIFO order or current priority order).

Return value

Macro	Value	Description
E_OK	0	Normal completion.
E_ID	-18	Invalid ID number. - semid < 0 - semid > VTMAX_SEM
E_CTX	-25	Context error. - This service call was issued from a non-task. - This service call was issued in the CPU locked state. - This service call was issued in the dispatching disabled state. - This service call was issued in the status "PSW.IPL > kernel interrupt mask level".
E_RLWAI	-49	Forced release from the WAITING state. - Accept rel_wai/irel_wai while waiting.