Rewrite queue (#24505)

# ⚠️ Breaking

Many deprecated queue config options are removed (actually, they should
have been removed in 1.18/1.19).

If you see the fatal message when starting Gitea: "Please update your
app.ini to remove deprecated config options", please follow the error
messages to remove these options from your app.ini.

Example:

```
2023/05/06 19:39:22 [E] Removed queue option: `[indexer].ISSUE_INDEXER_QUEUE_TYPE`. Use new options in `[queue.issue_indexer]`
2023/05/06 19:39:22 [E] Removed queue option: `[indexer].UPDATE_BUFFER_LEN`. Use new options in `[queue.issue_indexer]`
2023/05/06 19:39:22 [F] Please update your app.ini to remove deprecated config options
```

Many options in `[queue]` are are dropped, including:
`WRAP_IF_NECESSARY`, `MAX_ATTEMPTS`, `TIMEOUT`, `WORKERS`,
`BLOCK_TIMEOUT`, `BOOST_TIMEOUT`, `BOOST_WORKERS`, they can be removed
from app.ini.

# The problem

The old queue package has some legacy problems:

* complexity: I doubt few people could tell how it works.
* maintainability: Too many channels and mutex/cond are mixed together,
too many different structs/interfaces depends each other.
* stability: due to the complexity & maintainability, sometimes there
are strange bugs and difficult to debug, and some code doesn't have test
(indeed some code is difficult to test because a lot of things are mixed
together).
* general applicability: although it is called "queue", its behavior is
not a well-known queue.
* scalability: it doesn't seem easy to make it work with a cluster
without breaking its behaviors.

It came from some very old code to "avoid breaking", however, its
technical debt is too heavy now. It's a good time to introduce a better
"queue" package.

# The new queue package

It keeps using old config and concept as much as possible.

* It only contains two major kinds of concepts:
    * The "base queue": channel, levelqueue, redis
* They have the same abstraction, the same interface, and they are
tested by the same testing code.
* The "WokerPoolQueue", it uses the "base queue" to provide "worker
pool" function, calls the "handler" to process the data in the base
queue.
* The new code doesn't do "PushBack"
* Think about a queue with many workers, the "PushBack" can't guarantee
the order for re-queued unhandled items, so in new code it just does
"normal push"
* The new code doesn't do "pause/resume"
* The "pause/resume" was designed to handle some handler's failure: eg:
document indexer (elasticsearch) is down
* If a queue is paused for long time, either the producers blocks or the
new items are dropped.
* The new code doesn't do such "pause/resume" trick, it's not a common
queue's behavior and it doesn't help much.
* If there are unhandled items, the "push" function just blocks for a
few seconds and then re-queue them and retry.
* The new code doesn't do "worker booster"
* Gitea's queue's handlers are light functions, the cost is only the
go-routine, so it doesn't make sense to "boost" them.
* The new code only use "max worker number" to limit the concurrent
workers.
* The new "Push" never blocks forever
* Instead of creating more and more blocking goroutines, return an error
is more friendly to the server and to the end user.

There are more details in code comments: eg: the "Flush" problem, the
strange "code.index" hanging problem, the "immediate" queue problem.

Almost ready for review.

TODO:

* [x] add some necessary comments during review
* [x] add some more tests if necessary
* [x] update documents and config options
* [x] test max worker / active worker
* [x] re-run the CI tasks to see whether any test is flaky
* [x] improve the `handleOldLengthConfiguration` to provide more
friendly messages
* [x] fine tune default config values (eg: length?)

## Code coverage:

![image](https://user-images.githubusercontent.com/2114189/236620635-55576955-f95d-4810-b12f-879026a3afdf.png)

1 files changed, 0 insertions, 160 deletions

diff --git a/modules/queue/queue_channel.go b/modules/queue/queue_channel.go
deleted file mode 100644
index baac097393..0000000000
--- a/modules/queue/queue_channel.go
+++ /dev/null
@@ -1,160 +0,0 @@
-// Copyright 2019 The Gitea Authors. All rights reserved.
-// SPDX-License-Identifier: MIT
-
-package queue
-
-import (
-	"context"
-	"fmt"
-	"runtime/pprof"
-	"sync/atomic"
-	"time"
-
-	"code.gitea.io/gitea/modules/log"
-)
-
-// ChannelQueueType is the type for channel queue
-const ChannelQueueType Type = "channel"
-
-// ChannelQueueConfiguration is the configuration for a ChannelQueue
-type ChannelQueueConfiguration struct {
-	WorkerPoolConfiguration
-	Workers int
-}
-
-// ChannelQueue implements Queue
-//
-// A channel queue is not persistable and does not shutdown or terminate cleanly
-// It is basically a very thin wrapper around a WorkerPool
-type ChannelQueue struct {
-	*WorkerPool
-	shutdownCtx        context.Context
-	shutdownCtxCancel  context.CancelFunc
-	terminateCtx       context.Context
-	terminateCtxCancel context.CancelFunc
-	exemplar           interface{}
-	workers            int
-	name               string
-}
-
-// NewChannelQueue creates a memory channel queue
-func NewChannelQueue(handle HandlerFunc, cfg, exemplar interface{}) (Queue, error) {
-	configInterface, err := toConfig(ChannelQueueConfiguration{}, cfg)
-	if err != nil {
-		return nil, err
-	}
-	config := configInterface.(ChannelQueueConfiguration)
-	if config.BatchLength == 0 {
-		config.BatchLength = 1
-	}
-
-	terminateCtx, terminateCtxCancel := context.WithCancel(context.Background())
-	shutdownCtx, shutdownCtxCancel := context.WithCancel(terminateCtx)
-
-	queue := &ChannelQueue{
-		shutdownCtx:        shutdownCtx,
-		shutdownCtxCancel:  shutdownCtxCancel,
-		terminateCtx:       terminateCtx,
-		terminateCtxCancel: terminateCtxCancel,
-		exemplar:           exemplar,
-		workers:            config.Workers,
-		name:               config.Name,
-	}
-	queue.WorkerPool = NewWorkerPool(func(data ...Data) []Data {
-		unhandled := handle(data...)
-		if len(unhandled) > 0 {
-			// We can only pushback to the channel if we're paused.
-			if queue.IsPaused() {
-				atomic.AddInt64(&queue.numInQueue, int64(len(unhandled)))
-				go func() {
-					for _, datum := range data {
-						queue.dataChan <- datum
-					}
-				}()
-				return nil
-			}
-		}
-		return unhandled
-	}, config.WorkerPoolConfiguration)
-
-	queue.qid = GetManager().Add(queue, ChannelQueueType, config, exemplar)
-	return queue, nil
-}
-
-// Run starts to run the queue
-func (q *ChannelQueue) Run(atShutdown, atTerminate func(func())) {
-	pprof.SetGoroutineLabels(q.baseCtx)
-	atShutdown(q.Shutdown)
-	atTerminate(q.Terminate)
-	log.Debug("ChannelQueue: %s Starting", q.name)
-	_ = q.AddWorkers(q.workers, 0)
-}
-
-// Push will push data into the queue
-func (q *ChannelQueue) Push(data Data) 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)
-	}
-	q.WorkerPool.Push(data)
-	return nil
-}
-
-// Flush flushes the channel with a timeout - the Flush worker will be registered as a flush worker with the manager
-func (q *ChannelQueue) 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 *ChannelQueue) Shutdown() {
-	q.lock.Lock()
-	defer q.lock.Unlock()
-	select {
-	case <-q.shutdownCtx.Done():
-		log.Trace("ChannelQueue: %s Already Shutting down", q.name)
-		return
-	default:
-	}
-	log.Trace("ChannelQueue: %s Shutting down", q.name)
-	go func() {
-		log.Trace("ChannelQueue: %s Flushing", q.name)
-		// We can't use Cleanup here because that will close the channel
-		if err := q.FlushWithContext(q.terminateCtx); err != nil {
-			count := atomic.LoadInt64(&q.numInQueue)
-			if count > 0 {
-				log.Warn("ChannelQueue: %s Terminated before completed flushing", q.name)
-			}
-			return
-		}
-		log.Debug("ChannelQueue: %s Flushed", q.name)
-	}()
-	q.shutdownCtxCancel()
-	log.Debug("ChannelQueue: %s Shutdown", q.name)
-}
-
-// Terminate this queue and close the queue
-func (q *ChannelQueue) Terminate() {
-	log.Trace("ChannelQueue: %s Terminating", q.name)
-	q.Shutdown()
-	select {
-	case <-q.terminateCtx.Done():
-		return
-	default:
-	}
-	q.terminateCtxCancel()
-	q.baseCtxFinished()
-	log.Debug("ChannelQueue: %s Terminated", q.name)
-}
-
-// Name returns the name of this queue
-func (q *ChannelQueue) Name() string {
-	return q.name
-}
-
-func init() {
-	queuesMap[ChannelQueueType] = NewChannelQueue
-}