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74 lines
2.4 KiB
74 lines
2.4 KiB
package common
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import (
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"sync/atomic"
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)
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// val: the value returned after task execution.
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// err: the error returned during task completion.
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// abort: tells Parallel to return, whether or not all tasks have completed.
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type Task func(i int) (val interface{}, err error, abort bool)
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type TaskResult struct {
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Value interface{}
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Error error
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Panic interface{}
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}
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type TaskResultCh <-chan TaskResult
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// Run tasks in parallel, with ability to abort early.
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// Returns ok=false iff any of the tasks returned abort=true.
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// NOTE: Do not implement quit features here. Instead, provide convenient
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// concurrent quit-like primitives, passed implicitly via Task closures. (e.g.
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// it's not Parallel's concern how you quit/abort your tasks).
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func Parallel(tasks ...Task) (chz []TaskResultCh, ok bool) {
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var taskResultChz = make([]TaskResultCh, len(tasks)) // To return.
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var taskDoneCh = make(chan bool, len(tasks)) // A "wait group" channel, early abort if any true received.
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var numPanics = new(int32) // Keep track of panics to set ok=false later.
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ok = true // We will set it to false iff any tasks panic'd or returned abort.
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// Start all tasks in parallel in separate goroutines.
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// When the task is complete, it will appear in the
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// respective taskResultCh (associated by task index).
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for i, task := range tasks {
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var taskResultCh = make(chan TaskResult, 1) // Capacity for 1 result.
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taskResultChz[i] = taskResultCh
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go func(i int, task Task, taskResultCh chan TaskResult) {
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// Recovery
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defer func() {
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if pnk := recover(); pnk != nil {
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atomic.AddInt32(numPanics, 1)
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taskResultCh <- TaskResult{nil, nil, pnk}
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taskDoneCh <- false
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}
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}()
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// Run the task.
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var val, err, abort = task(i)
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// Send val/err to taskResultCh.
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// NOTE: Below this line, nothing must panic/
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taskResultCh <- TaskResult{val, err, nil}
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// Decrement waitgroup.
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taskDoneCh <- abort
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}(i, task, taskResultCh)
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}
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// Wait until all tasks are done, or until abort.
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// DONE_LOOP:
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for i := 0; i < len(tasks); i++ {
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abort := <-taskDoneCh
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if abort {
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ok = false
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break
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}
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}
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// Ok is also false if there were any panics.
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// We must do this check here (after DONE_LOOP).
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ok = ok && (atomic.LoadInt32(numPanics) == 0)
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// Caller can use this however they want.
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// TODO: implement convenience functions to
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// make sense of this structure safely.
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return taskResultChz, ok
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}
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