What does Semaphor.drainPermits do if no permits are available?

Question

I'm trying to understand the contract of drainPermits in the Java Semaphore class

The JavaDoc simply reads:

public int drainPermits()

Acquire and return all permits that are immediately available.

Returns:
    the number of permits

If no permits are currently available, does it block and wait until one is available?

Answer 1

No, it will return 0 immediately. It doesn't require any permits to be available.