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parallel.go
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parallel.go
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// Copyright 2020 gorse Project Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package parallel
import (
"sync"
"github.com/juju/errors"
"github.com/zhenghaoz/gorse/base/task"
"go.uber.org/atomic"
"modernc.org/mathutil"
)
const (
chanSize = 1024
allocPeriod = 128
)
/* Parallel Schedulers */
// Parallel schedules and runs tasks in parallel. nTask is the number of tasks. nJob is
// the number of executors. worker is the executed function which passed a range of task
// Names (begin, end).
func Parallel(nJobs, nWorkers int, worker func(workerId, jobId int) error) error {
if nWorkers == 1 {
for i := 0; i < nJobs; i++ {
if err := worker(0, i); err != nil {
return errors.Trace(err)
}
}
} else {
c := make(chan int, chanSize)
// producer
go func() {
for i := 0; i < nJobs; i++ {
c <- i
}
close(c)
}()
// consumer
var wg sync.WaitGroup
wg.Add(nWorkers)
errs := make([]error, nJobs)
for j := 0; j < nWorkers; j++ {
// start workers
go func(workerId int) {
defer wg.Done()
for {
// read job
jobId, ok := <-c
if !ok {
return
}
// run job
if err := worker(workerId, jobId); err != nil {
errs[jobId] = err
return
}
}
}(j)
}
wg.Wait()
// check errors
for _, err := range errs {
if err != nil {
return errors.Trace(err)
}
}
}
return nil
}
func DynamicParallel(nJobs int, jobsAlloc *task.JobsAllocator, worker func(workerId, jobId int) error) error {
c := make(chan int, chanSize)
// producer
go func() {
for i := 0; i < nJobs; i++ {
c <- i
}
close(c)
}()
// consumer
for {
exit := atomic.NewBool(true)
numJobs := jobsAlloc.AvailableJobs(nil)
var wg sync.WaitGroup
wg.Add(numJobs)
errs := make([]error, nJobs)
for j := 0; j < numJobs; j++ {
// start workers
go func(workerId int) {
defer wg.Done()
for i := 0; i < allocPeriod; i++ {
// read job
jobId, ok := <-c
if !ok {
return
}
exit.Store(false)
// run job
if err := worker(workerId, jobId); err != nil {
errs[jobId] = err
return
}
}
}(j)
}
wg.Wait()
// check errors
for _, err := range errs {
if err != nil {
return errors.Trace(err)
}
}
// exit if finished
if exit.Load() {
return nil
}
}
}
type batchJob struct {
beginId int
endId int
}
// BatchParallel run parallel jobs in batches to reduce the cost of context switch.
func BatchParallel(nJobs, nWorkers, batchSize int, worker func(workerId, beginJobId, endJobId int) error) error {
if nWorkers == 1 {
return worker(0, 0, nJobs)
}
c := make(chan batchJob, chanSize)
// producer
go func() {
for i := 0; i < nJobs; i += batchSize {
c <- batchJob{beginId: i, endId: mathutil.Min(i+batchSize, nJobs)}
}
close(c)
}()
// consumer
var wg sync.WaitGroup
wg.Add(nWorkers)
errs := make([]error, nJobs)
for j := 0; j < nWorkers; j++ {
// start workers
go func(workerId int) {
defer wg.Done()
for {
// read job
job, ok := <-c
if !ok {
return
}
// run job
if err := worker(workerId, job.beginId, job.endId); err != nil {
errs[job.beginId] = err
return
}
}
}(j)
}
wg.Wait()
// check errors
for _, err := range errs {
if err != nil {
return errors.Trace(err)
}
}
return nil
}