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, 25 insertions, 30 deletions

diff --git a/modules/indexer/code/indexer.go b/modules/indexer/code/indexer.go
index 2c493ccf94..a5e40b52c1 100644
--- a/modules/indexer/code/indexer.go
+++ b/modules/indexer/code/indexer.go
@@ -44,7 +44,6 @@ type SearchResultLanguages struct {
 // Indexer defines an interface to index and search code contents
 type Indexer interface {
 	Ping() bool
-	SetAvailabilityChangeCallback(callback func(bool))
 	Index(ctx context.Context, repo *repo_model.Repository, sha string, changes *repoChanges) error
 	Delete(repoID int64) error
 	Search(ctx context.Context, repoIDs []int64, language, keyword string, page, pageSize int, isMatch bool) (int64, []*SearchResult, []*SearchResultLanguages, error)
@@ -81,7 +80,7 @@ type IndexerData struct {
 	RepoID int64
 }
 
-var indexerQueue queue.UniqueQueue
+var indexerQueue *queue.WorkerPoolQueue[*IndexerData]
 
 func index(ctx context.Context, indexer Indexer, repoID int64) error {
 	repo, err := repo_model.GetRepositoryByID(ctx, repoID)
@@ -137,37 +136,45 @@ func Init() {
 	// Create the Queue
 	switch setting.Indexer.RepoType {
 	case "bleve", "elasticsearch":
-		handler := func(data ...queue.Data) []queue.Data {
+		handler := func(items ...*IndexerData) (unhandled []*IndexerData) {
 			idx, err := indexer.get()
 			if idx == nil || err != nil {
 				log.Error("Codes indexer handler: unable to get indexer!")
-				return data
+				return items
 			}
 
-			unhandled := make([]queue.Data, 0, len(data))
-			for _, datum := range data {
-				indexerData, ok := datum.(*IndexerData)
-				if !ok {
-					log.Error("Unable to process provided datum: %v - not possible to cast to IndexerData", datum)
-					continue
-				}
+			for _, indexerData := range items {
 				log.Trace("IndexerData Process Repo: %d", indexerData.RepoID)
 
+				// FIXME: it seems there is a bug in `CatFileBatch` or `nio.Pipe`, which will cause the process to hang forever in rare cases
+				/*
+					sync.(*Cond).Wait(cond.go:70)
+					github.com/djherbis/nio/v3.(*PipeReader).Read(sync.go:106)
+					bufio.(*Reader).fill(bufio.go:106)
+					bufio.(*Reader).ReadSlice(bufio.go:372)
+					bufio.(*Reader).collectFragments(bufio.go:447)
+					bufio.(*Reader).ReadString(bufio.go:494)
+					code.gitea.io/gitea/modules/git.ReadBatchLine(batch_reader.go:149)
+					code.gitea.io/gitea/modules/indexer/code.(*BleveIndexer).addUpdate(bleve.go:214)
+					code.gitea.io/gitea/modules/indexer/code.(*BleveIndexer).Index(bleve.go:296)
+					code.gitea.io/gitea/modules/indexer/code.(*wrappedIndexer).Index(wrapped.go:74)
+					code.gitea.io/gitea/modules/indexer/code.index(indexer.go:105)
+				*/
 				if err := index(ctx, indexer, indexerData.RepoID); err != nil {
-					if !setting.IsInTesting {
-						log.Error("indexer index error for repo %v: %v", indexerData.RepoID, err)
-					}
-					if indexer.Ping() {
+					if !idx.Ping() {
+						log.Error("Code indexer handler: indexer is unavailable.")
+						unhandled = append(unhandled, indexerData)
 						continue
 					}
-					// Add back to queue
-					unhandled = append(unhandled, datum)
+					if !setting.IsInTesting {
+						log.Error("Codes indexer handler: index error for repo %v: %v", indexerData.RepoID, err)
+					}
 				}
 			}
 			return unhandled
 		}
 
-		indexerQueue = queue.CreateUniqueQueue("code_indexer", handler, &IndexerData{})
+		indexerQueue = queue.CreateUniqueQueue("code_indexer", handler)
 		if indexerQueue == nil {
 			log.Fatal("Unable to create codes indexer queue")
 		}
@@ -224,18 +231,6 @@ func Init() {
 
 		indexer.set(rIndexer)
 
-		if queue, ok := indexerQueue.(queue.Pausable); ok {
-			rIndexer.SetAvailabilityChangeCallback(func(available bool) {
-				if !available {
-					log.Info("Code index queue paused")
-					queue.Pause()
-				} else {
-					log.Info("Code index queue resumed")
-					queue.Resume()
-				}
-			})
-		}
-
 		// Start processing the queue
 		go graceful.GetManager().RunWithShutdownFns(indexerQueue.Run)