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e3eb550a7d
* Implement parallel scanning and generation, and combined scanning/preview/sprite generation. * Added UI component for preview/sprite generation during scan, and configurable number of parallel tasks. * Add v050 changelog entry
84 lines
2.3 KiB
Go
84 lines
2.3 KiB
Go
// Based upon sync.WaitGroup, SizedWaitGroup allows to start multiple
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// routines and to wait for their end using the simple API.
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// SizedWaitGroup adds the feature of limiting the maximum number of
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// concurrently started routines. It could for example be used to start
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// multiples routines querying a database but without sending too much
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// queries in order to not overload the given database.
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//
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// Rémy Mathieu © 2016
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package sizedwaitgroup
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import (
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"context"
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"math"
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"sync"
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)
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// SizedWaitGroup has the same role and close to the
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// same API as the Golang sync.WaitGroup but adds a limit of
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// the amount of goroutines started concurrently.
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type SizedWaitGroup struct {
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Size int
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current chan struct{}
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wg sync.WaitGroup
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}
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// New creates a SizedWaitGroup.
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// The limit parameter is the maximum amount of
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// goroutines which can be started concurrently.
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func New(limit int) SizedWaitGroup {
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size := math.MaxInt32 // 2^32 - 1
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if limit > 0 {
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size = limit
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}
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return SizedWaitGroup{
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Size: size,
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current: make(chan struct{}, size),
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wg: sync.WaitGroup{},
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}
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}
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// Add increments the internal WaitGroup counter.
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// It can be blocking if the limit of spawned goroutines
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// has been reached. It will stop blocking when Done is
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// been called.
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//
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// See sync.WaitGroup documentation for more information.
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func (s *SizedWaitGroup) Add() {
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s.AddWithContext(context.Background())
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}
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// AddWithContext increments the internal WaitGroup counter.
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// It can be blocking if the limit of spawned goroutines
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// has been reached. It will stop blocking when Done is
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// been called, or when the context is canceled. Returns nil on
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// success or an error if the context is canceled before the lock
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// is acquired.
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//
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// See sync.WaitGroup documentation for more information.
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func (s *SizedWaitGroup) AddWithContext(ctx context.Context) error {
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select {
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case <-ctx.Done():
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return ctx.Err()
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case s.current <- struct{}{}:
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break
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}
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s.wg.Add(1)
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return nil
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}
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// Done decrements the SizedWaitGroup counter.
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// See sync.WaitGroup documentation for more information.
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func (s *SizedWaitGroup) Done() {
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<-s.current
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s.wg.Done()
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}
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// Wait blocks until the SizedWaitGroup counter is zero.
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// See sync.WaitGroup documentation for more information.
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func (s *SizedWaitGroup) Wait() {
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s.wg.Wait()
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}
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