Programming: Concurrency Patterns

Resources

Wikipedia: Concurrency Patterns

https://en.wikipedia.org/wiki/Concurrency_pattern

Monitor Object

Safely share an object between multiple threads,
automatically wait in caller until a perform is done.
The caller does not need to know about the perform-lock, it will simply block until the monitor is able to process a new task.

Say we only ever want to perform IO from one thread.
We create a WriterMonitor, which might have methods read/write

• in thread-1, we call read(), which blocks while in the background creates and performs a thread
• in thread-2, we call write(), it will block until it is notified that thread-1's read() is finished

https://www.youtube.com/watch?v=_p-TM1x48zk

Active Object

Decouple thread an object is created in from the thread the object's code will be executed in.
without exposing lock/queue/etc details to the caller.

Thread/Subprocess objects are frequently exposed this way (ex: QtCore.QThread)

• Caller instantiates a proxy object
• On a method call, the proxy returns a Future/Promise object is created (in background, a request is enqueued)
• In background, a worker performs item from queue
• You may wait/join on the Future/Promise to wait for it to return it's results

Producer/Consumer

Safely parallelized task enqueueing/execution.

• A producer adds data to a synchronized queue
• A variable number of consumers process data from a synchronized queue in a loop
• When producer is finished, send a poison pill for each worker, informing it to break/exit the loop gracefully
• Join on worker threads (wait to close)