Idempotence of 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 can 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 run its Stop method on it. The same scenarios apply to the Monitor_start and Monitor_stop methods.

For these reasons, you must build idempotence into your Stop and Monitor_stop methods. In other words, repeated calls to Stop or Monitor_stop on the same resource with the same arguments must achieve the same results as a single call.

One implication of idempotence is that Stop and Monitor_stop must return 0 (success) even if the resource or monitor is already stopped and no work is to be done.

The Init, Fini, Boot, and Update methods must also be idempotent. A Start method need not be idempotent.