OperationParker
OperationParker is an interface offered by SPI for the objects, such as
Lock and Semaphore, to be used when a thread needs to wait for a lock to be released.
OperationParker keeps a list of waiters. For each notify operation:
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it looks for a waiter
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it asks the waiter whether it wants to keep waiting
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if the waiter responds no, the service executes its registered operation (operation itself knows where to send a response)
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it rinses and repeats until a waiter wants to keep waiting.
Each waiter can sit on a wait-notify queue for, at most, its operation’s call timeout.
For example, by default, each waiter can wait here for at most 1 minute.
A continuous task scans expired/timed-out waiters and invalidates them with CallTimeoutException.
Each waiter on the remote side should retry and keep waiting if it still wants to wait.
This is a liveness check for remote waiters.
This way, it is possible to distinguish an unresponsive member and a long (~infinite) wait.
On the caller side, if the waiting thread does not get a response for either
a call timeout or for more than 2 times the call-timeout, it will exit with
OperationTimeoutException.
Note that this behavior breaks the fairness. Hazelcast does not support fairness for any of the data structures with blocking operations, such as Lock and Semaphore.
