master/worker pattern

  1. A master process/thread sets up a pool of workers (processes/threads) and a bag of tasks.
  2. Workers take tasks from the bag, and process them in a concurrent fashion.

Each worker continues processing, until all tasks have been processed or some other condition has been reached. In some implementations no explicit master is present.

– It is suitable for non-deterministic execution time of tasks.

– It is used when tasks should be distributed among workers.

– Since creating and terminating processes/threads is expensive workers should be reused.

– Not applicable when tasks are interdependent.

– Usually the number of tasks exceeds the number of UEs.

– Usually number of workers <= PE.

How tasks are assigned to workers?

Using a single shared queue  as bag of tasks, tuple space, monotonic counter.

Each worker enters a loop, at the top of the loop in a synchronized way the worker takes a task from the bag.

UE: Unit of execution (process/thread)

PE: Processing element (core/processor)

A note from Patterns for Parallel Programming by Mattson, Sanders ,Massingill

See also: fork/join and loop parallelism patterns.

 

Some implementations:

Ruby: parallel processing made simple and fast

Java: ThreadPooolExecutor

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