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67 lines
3.0 KiB
Go
67 lines
3.0 KiB
Go
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/*
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Package workerpool queues work to a limited number of goroutines.
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The purpose of the worker pool is to limit the concurrency of tasks
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executed by the workers. This is useful when performing tasks that require
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sufficient resources (CPU, memory, etc.), and running too many tasks at the
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same time would exhaust resources.
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Non-blocking task submission
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A task is a function submitted to the worker pool for execution. Submitting
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tasks to this worker pool will not block, regardless of the number of tasks.
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Tasks read from the input task queue are immediately dispatched to an available
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worker. If no worker is immediately available, or there are already tasks
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waiting for an available worker, then the task is put on a waiting queue to
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wait for an available worker. This clears the incoming task from the input
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task queue immediately, whether or not a worker is currently available, and
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will not block the submission of tasks.
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The intent of the worker pool is to limit the concurrency of task execution,
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not limit the number of tasks queued to be executed. Therefore, this unbounded
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input of tasks is acceptable as the tasks cannot be discarded. If the number
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of inbound tasks is too many to even queue for pending processing, then the
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solution is outside the scope of workerpool, and should be solved by
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distributing load over multiple systems, and/or storing input for pending
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processing in intermediate storage such as a database, file system, distributed
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message queue, etc.
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Dispatcher
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This worker pool uses a single dispatcher goroutine to read tasks from the
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input task queue and dispatch them to a worker goroutine. This allows for a
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small input channel, and lets the dispatcher queue as many tasks as are
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submitted when there are no available workers. Additionally, the dispatcher
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can adjust the number of workers as appropriate for the work load, without
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having to utilize locked counters and checks incurred on task submission.
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When no tasks have been submitted for a period of time, a worker is removed by
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the dispatcher. This is done until there are no more workers to remove. The
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minimum number of workers is always zero, because the time to start new workers
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is insignificant.
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Usage note
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It is advisable to use different worker pools for tasks that are bound by
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different resources, or that have different resource use patterns. For
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example, tasks that use X Mb of memory may need different concurrency limits
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than tasks that use Y Mb of memory.
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Waiting queue vs goroutines
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When there are no available workers to handle incoming tasks, the tasks are put
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on a waiting queue. In previous versions of workerpool, these tasks were
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passed to goroutines. Using a queue is faster and has less memory overhead
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than creating a separate goroutine for each waiting task, allowing a much
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higher number of waiting tasks.
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Credits
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This implementation builds on ideas from the following:
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http://marcio.io/2015/07/handling-1-million-requests-per-minute-with-golang
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http://nesv.github.io/golang/2014/02/25/worker-queues-in-go.html
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*/
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package workerpool
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