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86 lines
2.5 KiB
Go
86 lines
2.5 KiB
Go
package iter
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import (
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"runtime"
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"sync/atomic"
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"github.com/sourcegraph/conc"
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)
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// defaultMaxGoroutines returns the default maximum number of
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// goroutines to use within this package.
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func defaultMaxGoroutines() int { return runtime.GOMAXPROCS(0) }
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// Iterator can be used to configure the behaviour of ForEach
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// and ForEachIdx. The zero value is safe to use with reasonable
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// defaults.
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//
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// Iterator is also safe for reuse and concurrent use.
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type Iterator[T any] struct {
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// MaxGoroutines controls the maximum number of goroutines
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// to use on this Iterator's methods.
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//
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// If unset, MaxGoroutines defaults to runtime.GOMAXPROCS(0).
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MaxGoroutines int
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}
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// ForEach executes f in parallel over each element in input.
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//
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// It is safe to mutate the input parameter, which makes it
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// possible to map in place.
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//
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// ForEach always uses at most runtime.GOMAXPROCS goroutines.
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// It takes roughly 2µs to start up the goroutines and adds
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// an overhead of roughly 50ns per element of input. For
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// a configurable goroutine limit, use a custom Iterator.
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func ForEach[T any](input []T, f func(*T)) { Iterator[T]{}.ForEach(input, f) }
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// ForEach executes f in parallel over each element in input,
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// using up to the Iterator's configured maximum number of
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// goroutines.
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//
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// It is safe to mutate the input parameter, which makes it
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// possible to map in place.
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//
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// It takes roughly 2µs to start up the goroutines and adds
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// an overhead of roughly 50ns per element of input.
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func (iter Iterator[T]) ForEach(input []T, f func(*T)) {
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iter.ForEachIdx(input, func(_ int, t *T) {
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f(t)
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})
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}
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// ForEachIdx is the same as ForEach except it also provides the
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// index of the element to the callback.
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func ForEachIdx[T any](input []T, f func(int, *T)) { Iterator[T]{}.ForEachIdx(input, f) }
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// ForEachIdx is the same as ForEach except it also provides the
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// index of the element to the callback.
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func (iter Iterator[T]) ForEachIdx(input []T, f func(int, *T)) {
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if iter.MaxGoroutines == 0 {
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// iter is a value receiver and is hence safe to mutate
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iter.MaxGoroutines = defaultMaxGoroutines()
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}
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numInput := len(input)
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if iter.MaxGoroutines > numInput {
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// No more concurrent tasks than the number of input items.
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iter.MaxGoroutines = numInput
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}
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var idx atomic.Int64
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// Create the task outside the loop to avoid extra closure allocations.
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task := func() {
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i := int(idx.Add(1) - 1)
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for ; i < numInput; i = int(idx.Add(1) - 1) {
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f(i, &input[i])
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}
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}
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var wg conc.WaitGroup
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for i := 0; i < iter.MaxGoroutines; i++ {
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wg.Go(task)
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}
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wg.Wait()
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}
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