executor_lib 1.1.2

Provides an abstraction for executing jobs.

executor_lib

Provides an abstraction for executing jobs. Features include LIFO order execution, job deduplication, job cancellation, isolates, pooling and queueing.

Overview

Executor abstraction enables creation of asynchronous jobs:

  Future payload(http.Response response) async => executor.submit(
      Job('jsonDecode', jsonDecode, response.body, deduplicationKey: null));

Four different executors are provided:

• DirectExecutor - Submits jobs directly to scheduleMicrotask.
• QueueExecutor - Runs jobs on the UI thread one at a time using scheduleMicrotask. A queue of outstanding jobs is maintained in LIFO order so that newest jobs get run first.
• IsolateExecutor - Runs jobs on an isolate one at a time. A queue of outstanding jobs is maintained in LIFO order so that newest jobs get run first.
• PoolExecutor - Runs jobs on one or more IsolateExecutors in round-robin fashion. Jobs have afinity with other jobs having the same deduplicationKey.

LIFO

Jobs are started in LIFO order, meaning that the more recently submitted jobs are performed before older jobs. This helps with responsiveness of an app since usually jobs relate to user navigation within the app. By completing most recent jobs first, users see the result of what they asked for more quickly.

Deduplication

Jobs may be scheduled to perform the same work more than once. By providing a deduplication key, the result of computing a value can be used to fulfill the result of multiple jobs, avoiding unnecessary work.

Cancellation

Jobs can be cancelled after they are submitted. This is useful in cases where jobs are scheduled based on the need to display information that is no longer needed because the user navigates elsewhere in the UI. By cancelling jobs that have not yet started, unnecessary work is avoided.

Reentrancy

Jobs running on an isolate can safely create another isolate executor and submit jobs on it. Reentrant jobs run directly on the isolate of the outer executor.

Leastconn

PoolExecutor selects an executor for each job using a combination of round-robin and leastconn to improve utilization and minimize queueing.

Development

Continuous Integration

CI with GitHub Actions:

Background

Originally developed as part of vector_map_tiles

License

Copyright 2021 David Green

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

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