forgejo/modules/queue/unique_queue_channel.go
zeripath 3ad62127df
Correctly handle select on multiple channels in Queues (#22146) (#22428)
Backport #22146

There are a few places in FlushQueueWithContext which make an incorrect
assumption about how `select` on multiple channels works.

The problem is best expressed by looking at the following example:

```go
package main

import "fmt"

func main() {
    closedChan := make(chan struct{})
    close(closedChan)
    toClose := make(chan struct{})
    count := 0

    for {
        select {
        case <-closedChan:
            count++
            fmt.Println(count)
            if count == 2 {
                close(toClose)
            }
        case <-toClose:
            return
        }
    }
}
```

This PR double-checks that the contexts are closed outside of checking
if there is data in the dataChan. It also rationalises the WorkerPool
FlushWithContext because the previous implementation failed to handle
pausing correctly. This will probably fix the underlying problem in
 #22145

Fix #22145

Signed-off-by: Andrew Thornton <art27@cantab.net>
2023-01-13 20:42:42 +00:00

212 lines
5.8 KiB
Go

// Copyright 2020 The Gitea Authors. All rights reserved.
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file.
package queue
import (
"context"
"fmt"
"runtime/pprof"
"sync"
"time"
"code.gitea.io/gitea/modules/container"
"code.gitea.io/gitea/modules/json"
"code.gitea.io/gitea/modules/log"
)
// ChannelUniqueQueueType is the type for channel queue
const ChannelUniqueQueueType Type = "unique-channel"
// ChannelUniqueQueueConfiguration is the configuration for a ChannelUniqueQueue
type ChannelUniqueQueueConfiguration ChannelQueueConfiguration
// ChannelUniqueQueue implements UniqueQueue
//
// It is basically a thin wrapper around a WorkerPool but keeps a store of
// what has been pushed within a table.
//
// Please note that this Queue does not guarantee that a particular
// task cannot be processed twice or more at the same time. Uniqueness is
// only guaranteed whilst the task is waiting in the queue.
type ChannelUniqueQueue struct {
*WorkerPool
lock sync.Mutex
table container.Set[string]
shutdownCtx context.Context
shutdownCtxCancel context.CancelFunc
terminateCtx context.Context
terminateCtxCancel context.CancelFunc
exemplar interface{}
workers int
name string
}
// NewChannelUniqueQueue create a memory channel queue
func NewChannelUniqueQueue(handle HandlerFunc, cfg, exemplar interface{}) (Queue, error) {
configInterface, err := toConfig(ChannelUniqueQueueConfiguration{}, cfg)
if err != nil {
return nil, err
}
config := configInterface.(ChannelUniqueQueueConfiguration)
if config.BatchLength == 0 {
config.BatchLength = 1
}
terminateCtx, terminateCtxCancel := context.WithCancel(context.Background())
shutdownCtx, shutdownCtxCancel := context.WithCancel(terminateCtx)
queue := &ChannelUniqueQueue{
table: make(container.Set[string]),
shutdownCtx: shutdownCtx,
shutdownCtxCancel: shutdownCtxCancel,
terminateCtx: terminateCtx,
terminateCtxCancel: terminateCtxCancel,
exemplar: exemplar,
workers: config.Workers,
name: config.Name,
}
queue.WorkerPool = NewWorkerPool(func(data ...Data) (unhandled []Data) {
for _, datum := range data {
// No error is possible here because PushFunc ensures that this can be marshalled
bs, _ := json.Marshal(datum)
queue.lock.Lock()
queue.table.Remove(string(bs))
queue.lock.Unlock()
if u := handle(datum); u != nil {
if queue.IsPaused() {
// We can only pushback to the channel if we're paused.
go func() {
if err := queue.Push(u[0]); err != nil {
log.Error("Unable to push back to queue %d. Error: %v", queue.qid, err)
}
}()
} else {
unhandled = append(unhandled, u...)
}
}
}
return unhandled
}, config.WorkerPoolConfiguration)
queue.qid = GetManager().Add(queue, ChannelUniqueQueueType, config, exemplar)
return queue, nil
}
// Run starts to run the queue
func (q *ChannelUniqueQueue) Run(atShutdown, atTerminate func(func())) {
pprof.SetGoroutineLabels(q.baseCtx)
atShutdown(q.Shutdown)
atTerminate(q.Terminate)
log.Debug("ChannelUniqueQueue: %s Starting", q.name)
_ = q.AddWorkers(q.workers, 0)
}
// Push will push data into the queue if the data is not already in the queue
func (q *ChannelUniqueQueue) Push(data Data) error {
return q.PushFunc(data, nil)
}
// PushFunc will push data into the queue
func (q *ChannelUniqueQueue) PushFunc(data Data, fn func() error) error {
if !assignableTo(data, q.exemplar) {
return fmt.Errorf("unable to assign data: %v to same type as exemplar: %v in queue: %s", data, q.exemplar, q.name)
}
bs, err := json.Marshal(data)
if err != nil {
return err
}
q.lock.Lock()
locked := true
defer func() {
if locked {
q.lock.Unlock()
}
}()
if !q.table.Add(string(bs)) {
return ErrAlreadyInQueue
}
// FIXME: We probably need to implement some sort of limit here
// If the downstream queue blocks this table will grow without limit
if fn != nil {
err := fn()
if err != nil {
q.table.Remove(string(bs))
return err
}
}
locked = false
q.lock.Unlock()
q.WorkerPool.Push(data)
return nil
}
// Has checks if the data is in the queue
func (q *ChannelUniqueQueue) Has(data Data) (bool, error) {
bs, err := json.Marshal(data)
if err != nil {
return false, err
}
q.lock.Lock()
defer q.lock.Unlock()
return q.table.Contains(string(bs)), nil
}
// Flush flushes the channel with a timeout - the Flush worker will be registered as a flush worker with the manager
func (q *ChannelUniqueQueue) Flush(timeout time.Duration) error {
if q.IsPaused() {
return nil
}
ctx, cancel := q.commonRegisterWorkers(1, timeout, true)
defer cancel()
return q.FlushWithContext(ctx)
}
// Shutdown processing from this queue
func (q *ChannelUniqueQueue) Shutdown() {
log.Trace("ChannelUniqueQueue: %s Shutting down", q.name)
select {
case <-q.shutdownCtx.Done():
return
default:
}
go func() {
log.Trace("ChannelUniqueQueue: %s Flushing", q.name)
if err := q.FlushWithContext(q.terminateCtx); err != nil {
log.Warn("ChannelUniqueQueue: %s Terminated before completed flushing", q.name)
return
}
log.Debug("ChannelUniqueQueue: %s Flushed", q.name)
}()
q.shutdownCtxCancel()
log.Debug("ChannelUniqueQueue: %s Shutdown", q.name)
}
// Terminate this queue and close the queue
func (q *ChannelUniqueQueue) Terminate() {
log.Trace("ChannelUniqueQueue: %s Terminating", q.name)
q.Shutdown()
select {
case <-q.terminateCtx.Done():
return
default:
}
q.terminateCtxCancel()
q.baseCtxFinished()
log.Debug("ChannelUniqueQueue: %s Terminated", q.name)
}
// Name returns the name of this queue
func (q *ChannelUniqueQueue) Name() string {
return q.name
}
func init() {
queuesMap[ChannelUniqueQueueType] = NewChannelUniqueQueue
}