Semaphore

Decrease the number of grants available from this semaphore, possibly waiting if none is available.

Signal that listener k is dead (i.e. will always fail to acquire locks from now on), and should be removed from onComplete queues.

This permits original, (i.e. non-derived) sources like futures or channels to drop the listener from their waiting sets.

Once data is available, pass it to the listener k. onComplete is always non-blocking.

Note that k's methods will be executed on the same thread as the Source, usually in sequence. It is hence important that the listener itself does not perform expensive operations.

Checks whether data is available at present and pass it to k if so. Calls to poll are always synchronous and non-blocking.

The process is as follows:

• If no data is immediately available, return false immediately.
• If there is data available, attempt to lock k.
  • If k is no longer available, true is returned to signal this source's general availability.
  • If locking k succeeds:
    • If data is still available, complete k and return true.
    • Otherwise, unlock k and return false.

Note that in all cases, a return value of false indicates that k should be put into onComplete to receive data in a later point in time.

Similar to poll, but instead of passing in a listener, directly return the value T if it is available.

Waits for an item to arrive from the source. Suspends until an item returns.

This is an utility method for direct waiting with Async, instead of going through listeners.