minio/cmd/merge-walk-pool.go

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/*
* MinIO Cloud Storage, (C) 2019 MinIO, Inc.
*
* 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 cmd
import (
"reflect"
"sync"
"time"
)
const (
globalMergeLookupTimeout = time.Minute * 1 // 1 minutes.
)
// mergeWalk - represents the go routine that does the merge walk.
type mergeWalk struct {
entryChs []FileInfoCh
endWalkCh chan struct{} // To signal when mergeWalk go-routine should end.
endTimerCh chan<- struct{} // To signal when timer go-routine should end.
}
// MergeWalkPool - pool of mergeWalk go routines.
// A mergeWalk is added to the pool by Set() and removed either by
// doing a Release() or if the concerned timer goes off.
// mergeWalkPool's purpose is to maintain active mergeWalk go-routines in a map so that
// it can be looked up across related list calls.
type MergeWalkPool struct {
sync.Mutex
pool map[listParams][]mergeWalk
timeOut time.Duration
}
// NewMergeWalkPool - initialize new tree walk pool.
func NewMergeWalkPool(timeout time.Duration) *MergeWalkPool {
tPool := &MergeWalkPool{
pool: make(map[listParams][]mergeWalk),
timeOut: timeout,
}
return tPool
}
// Release - selects a mergeWalk from the pool based on the input
// listParams, removes it from the pool, and returns the MergeWalkResult
// channel.
// Returns nil if listParams does not have an asccociated mergeWalk.
func (t *MergeWalkPool) Release(params listParams) ([]FileInfoCh, chan struct{}) {
t.Lock()
defer t.Unlock()
walks, ok := t.pool[params] // Pick the valid walks.
if ok {
if len(walks) > 0 {
// Pop out the first valid walk entry.
walk := walks[0]
walks = walks[1:]
if len(walks) > 0 {
t.pool[params] = walks
} else {
delete(t.pool, params)
}
walk.endTimerCh <- struct{}{}
return walk.entryChs, walk.endWalkCh
}
}
// Release return nil if params not found.
return nil, nil
}
// Set - adds a mergeWalk to the mergeWalkPool.
// Also starts a timer go-routine that ends when:
// 1) time.After() expires after t.timeOut seconds.
// The expiration is needed so that the mergeWalk go-routine resources are freed after a timeout
// if the S3 client does only partial listing of objects.
// 2) Relase() signals the timer go-routine to end on endTimerCh.
// During listing the timer should not timeout and end the mergeWalk go-routine, hence the
// timer go-routine should be ended.
func (t *MergeWalkPool) Set(params listParams, resultChs []FileInfoCh, endWalkCh chan struct{}) {
t.Lock()
defer t.Unlock()
// Should be a buffered channel so that Release() never blocks.
endTimerCh := make(chan struct{}, 1)
walkInfo := mergeWalk{
entryChs: resultChs,
endWalkCh: endWalkCh,
endTimerCh: endTimerCh,
}
// Append new walk info.
t.pool[params] = append(t.pool[params], walkInfo)
// Timer go-routine which times out after t.timeOut seconds.
go func(endTimerCh <-chan struct{}, walkInfo mergeWalk) {
select {
// Wait until timeOut
case <-time.After(t.timeOut):
// Timeout has expired. Remove the mergeWalk from mergeWalkPool and
// end the mergeWalk go-routine.
t.Lock()
walks, ok := t.pool[params]
if ok {
// Trick of filtering without allocating
// https://github.com/golang/go/wiki/SliceTricks#filtering-without-allocating
nwalks := walks[:0]
// Look for walkInfo, remove it from the walks list.
for _, walk := range walks {
if !reflect.DeepEqual(walk, walkInfo) {
nwalks = append(nwalks, walk)
}
}
if len(nwalks) == 0 {
// No more mergeWalk go-routines associated with listParams
// hence remove map entry.
delete(t.pool, params)
} else {
// There are more mergeWalk go-routines associated with listParams
// hence save the list in the map.
t.pool[params] = nwalks
}
}
// Signal the mergeWalk go-routine to die.
close(endWalkCh)
t.Unlock()
case <-endTimerCh:
return
}
}(endTimerCh, walkInfo)
}