frostfs-s3-gw/cmd/tree-walk-pool.go

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/*
* MinIO Cloud Storage, (C) 2016 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 (
"errors"
"reflect"
"sync"
"time"
)
// Global lookup timeout.
const (
globalLookupTimeout = time.Minute * 30 // 30minutes.
treeWalkEntryLimit = 50
treeWalkSameEntryLimit = 4
)
// listParams - list object params used for list object map
type listParams struct {
bucket string
recursive bool
marker string
prefix string
}
// errWalkAbort - returned by doTreeWalk() if it returns prematurely.
// doTreeWalk() can return prematurely if
// 1) treeWalk is timed out by the timer go-routine.
// 2) there is an error during tree walk.
var errWalkAbort = errors.New("treeWalk abort")
// treeWalk - represents the go routine that does the file tree walk.
type treeWalk struct {
added time.Time
resultCh chan TreeWalkResult
endWalkCh chan struct{} // To signal when treeWalk go-routine should end.
endTimerCh chan<- struct{} // To signal when timer go-routine should end.
}
// TreeWalkPool - pool of treeWalk go routines.
// A treeWalk is added to the pool by Set() and removed either by
// doing a Release() or if the concerned timer goes off.
// treeWalkPool's purpose is to maintain active treeWalk go-routines in a map so that
// it can be looked up across related list calls.
type TreeWalkPool struct {
sync.Mutex
pool map[listParams][]treeWalk
timeOut time.Duration
}
// NewTreeWalkPool - initialize new tree walk pool.
func NewTreeWalkPool(timeout time.Duration) *TreeWalkPool {
tPool := &TreeWalkPool{
pool: make(map[listParams][]treeWalk),
timeOut: timeout,
}
return tPool
}
// Release - selects a treeWalk from the pool based on the input
// listParams, removes it from the pool, and returns the TreeWalkResult
// channel.
// Returns nil if listParams does not have an associated treeWalk.
func (t *TreeWalkPool) Release(params listParams) (resultCh chan TreeWalkResult, endWalkCh 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[0] = treeWalk{} // clear references.
walks = walks[1:]
if len(walks) > 0 {
t.pool[params] = walks
} else {
delete(t.pool, params)
}
walk.endTimerCh <- struct{}{}
return walk.resultCh, walk.endWalkCh
}
}
// Release return nil if params not found.
return nil, nil
}
// Set - adds a treeWalk to the treeWalkPool.
// Also starts a timer go-routine that ends when:
// 1) time.After() expires after t.timeOut seconds.
// The expiration is needed so that the treeWalk go-routine resources are freed after a timeout
// if the S3 client does only partial listing of objects.
// 2) Release() signals the timer go-routine to end on endTimerCh.
// During listing the timer should not timeout and end the treeWalk go-routine, hence the
// timer go-routine should be ended.
func (t *TreeWalkPool) Set(params listParams, resultCh chan TreeWalkResult, endWalkCh chan struct{}) {
t.Lock()
defer t.Unlock()
// If we are above the limit delete at least one entry from the pool.
if len(t.pool) > treeWalkEntryLimit {
age := time.Now()
var oldest listParams
for k, v := range t.pool {
if len(v) == 0 {
delete(t.pool, k)
continue
}
// The first element is the oldest, so we only check that.
if v[0].added.Before(age) {
oldest = k
}
}
// Invalidate and delete oldest.
if walks, ok := t.pool[oldest]; ok {
walk := walks[0]
walks[0] = treeWalk{} // clear references.
walks = walks[1:]
if len(walks) > 0 {
t.pool[params] = walks
} else {
delete(t.pool, params)
}
walk.endTimerCh <- struct{}{}
}
}
// Should be a buffered channel so that Release() never blocks.
endTimerCh := make(chan struct{}, 1)
walkInfo := treeWalk{
added: UTCNow(),
resultCh: resultCh,
endWalkCh: endWalkCh,
endTimerCh: endTimerCh,
}
// Append new walk info.
walks := t.pool[params]
if len(walks) < treeWalkSameEntryLimit {
t.pool[params] = append(walks, walkInfo)
} else {
// We are at limit, invalidate oldest, move list down and add new as last.
walks[0].endTimerCh <- struct{}{}
copy(walks, walks[1:])
walks[len(walks)-1] = walkInfo
}
// Timer go-routine which times out after t.timeOut seconds.
go func(endTimerCh <-chan struct{}) {
select {
// Wait until timeOut
case <-time.After(t.timeOut):
// Timeout has expired. Remove the treeWalk from treeWalkPool and
// end the treeWalk 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 treeWalk go-routines associated with listParams
// hence remove map entry.
delete(t.pool, params)
} else {
// There are more treeWalk go-routines associated with listParams
// hence save the list in the map.
t.pool[params] = nwalks
}
}
// Signal the treeWalk go-routine to die.
close(endWalkCh)
t.Unlock()
case <-endTimerCh:
return
}
}(endTimerCh)
}