Idempotency for Methods

In general, the RGM does not call a method more than once in succession on the same resource with the same arguments. However, if a START method fails, the RGM could call a STOP method on a resource even though the resource was never started. Likewise, a resource daemon could die of its own accord and the RGM might still invoke its STOP method on it. The same scenarios apply to the MONITOR_START and MONITOR_STOP methods.

For these reasons, you must build idempotency into your STOP and MONITOR_STOP methods, which means that repeated calls of STOP or MONITOR_STOP on the same resource with the same parameters achieve the same results as a single call.

One implication of idempotency is that STOP and MONITOR_STOP should return 0 (success) even if the resource or monitor is already stopped and no work is to done.

The INIT, FINI, BOOT, and UPDATE methods must also be idempotent. A START method need not be idempotent.