Hazelcast IMDG Standard Support has expired. Extended support for version 4.1 ends in April 2024. Extended support for version 4.2 ends in September 2024.

We recommend that you try Hazelcast Platform.

In Hazelcast Platform, we’ve combined the in-memory storage of IMDG with the stream processing power of Jet. Find out more in our Platform documentation.

The following topics are a good place to start:

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:

  • it looks for a waiter

  • it asks the waiter whether it wants to keep waiting

  • if the waiter responds no, the service executes its registered operation (operation itself knows where to send a response)

  • 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.