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package parallel
import (
"context"
"errors"
"fmt"
"sync"
"github.com/sirupsen/logrus"
"golang.org/x/sync/semaphore"
)
var (
// Maximum number of jobs that will be used.
// Set a low, but non-zero, default. We'll be overriding it by default
// anyways.
numThreads uint = 8
// Semaphore to control thread creation and ensure numThreads is
// respected.
jobControl *semaphore.Weighted
// Lock to control changing the semaphore - we don't want to do it
// while anyone is using it.
jobControlLock sync.RWMutex
)
// SetMaxThreads sets the number of threads that will be used for parallel jobs.
func SetMaxThreads(threads uint) error {
if threads == 0 {
return errors.New("must give a non-zero number of threads to execute with")
}
jobControlLock.Lock()
defer jobControlLock.Unlock()
numThreads = threads
jobControl = semaphore.NewWeighted(int64(threads))
logrus.Infof("Setting parallel job count to %d", threads)
return nil
}
// GetMaxThreads returns the current number of threads that will be used for
// parallel jobs.
func GetMaxThreads() uint {
return numThreads
}
// Enqueue adds a single function to the parallel jobs queue. This function will
// be run when an unused thread is available.
// Returns a receive-only error channel that will return the error (if any) from
// the provided function fn when fn has finished executing. The channel will be
// closed after this.
func Enqueue(ctx context.Context, fn func() error) <-chan error {
retChan := make(chan error)
go func() {
jobControlLock.RLock()
defer jobControlLock.RUnlock()
defer close(retChan)
if err := jobControl.Acquire(ctx, 1); err != nil {
retChan <- fmt.Errorf("acquiring job control semaphore: %w", err)
return
}
err := fn()
jobControl.Release(1)
retChan <- err
}()
return retChan
}
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