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)

2 files changed, 26 insertions, 38 deletions

diff --git a/services/pull/check.go b/services/pull/check.go
index 02d9015414..8bc2bdff1d 100644
--- a/services/pull/check.go
+++ b/services/pull/check.go
@@ -30,7 +30,7 @@ import (
 )
 
 // prPatchCheckerQueue represents a queue to handle update pull request tests
-var prPatchCheckerQueue queue.UniqueQueue
+var prPatchCheckerQueue *queue.WorkerPoolQueue[string]
 
 var (
 	ErrIsClosed              = errors.New("pull is closed")
@@ -44,16 +44,14 @@ var (
 
 // AddToTaskQueue adds itself to pull request test task queue.
 func AddToTaskQueue(pr *issues_model.PullRequest) {
-	err := prPatchCheckerQueue.PushFunc(strconv.FormatInt(pr.ID, 10), func() error {
-		pr.Status = issues_model.PullRequestStatusChecking
-		err := pr.UpdateColsIfNotMerged(db.DefaultContext, "status")
-		if err != nil {
-			log.Error("AddToTaskQueue(%-v).UpdateCols.(add to queue): %v", pr, err)
-		} else {
-			log.Trace("Adding %-v to the test pull requests queue", pr)
-		}
-		return err
-	})
+	pr.Status = issues_model.PullRequestStatusChecking
+	err := pr.UpdateColsIfNotMerged(db.DefaultContext, "status")
+	if err != nil {
+		log.Error("AddToTaskQueue(%-v).UpdateCols.(add to queue): %v", pr, err)
+		return
+	}
+	log.Trace("Adding %-v to the test pull requests queue", pr)
+	err = prPatchCheckerQueue.Push(strconv.FormatInt(pr.ID, 10))
 	if err != nil && err != queue.ErrAlreadyInQueue {
 		log.Error("Error adding %-v to the test pull requests queue: %v", pr, err)
 	}
@@ -315,10 +313,8 @@ func InitializePullRequests(ctx context.Context) {
 		case <-ctx.Done():
 			return
 		default:
-			if err := prPatchCheckerQueue.PushFunc(strconv.FormatInt(prID, 10), func() error {
-				log.Trace("Adding PR[%d] to the pull requests patch checking queue", prID)
-				return nil
-			}); err != nil {
+			log.Trace("Adding PR[%d] to the pull requests patch checking queue", prID)
+			if err := prPatchCheckerQueue.Push(strconv.FormatInt(prID, 10)); err != nil {
 				log.Error("Error adding PR[%d] to the pull requests patch checking queue %v", prID, err)
 			}
 		}
@@ -326,10 +322,9 @@ func InitializePullRequests(ctx context.Context) {
 }
 
 // handle passed PR IDs and test the PRs
-func handle(data ...queue.Data) []queue.Data {
-	for _, datum := range data {
-		id, _ := strconv.ParseInt(datum.(string), 10, 64)
-
+func handler(items ...string) []string {
+	for _, s := range items {
+		id, _ := strconv.ParseInt(s, 10, 64)
 		testPR(id)
 	}
 	return nil
@@ -389,7 +384,7 @@ func CheckPRsForBaseBranch(baseRepo *repo_model.Repository, baseBranchName strin
 
 // Init runs the task queue to test all the checking status pull requests
 func Init() error {
-	prPatchCheckerQueue = queue.CreateUniqueQueue("pr_patch_checker", handle, "")
+	prPatchCheckerQueue = queue.CreateUniqueQueue("pr_patch_checker", handler)
 
 	if prPatchCheckerQueue == nil {
 		return fmt.Errorf("Unable to create pr_patch_checker Queue")
diff --git a/services/pull/check_test.go b/services/pull/check_test.go
index 590065250f..52209b4d35 100644
--- a/services/pull/check_test.go
+++ b/services/pull/check_test.go
@@ -12,6 +12,7 @@ import (
 	issues_model "code.gitea.io/gitea/models/issues"
 	"code.gitea.io/gitea/models/unittest"
 	"code.gitea.io/gitea/modules/queue"
+	"code.gitea.io/gitea/modules/setting"
 
 	"github.com/stretchr/testify/assert"
 )
@@ -20,27 +21,18 @@ func TestPullRequest_AddToTaskQueue(t *testing.T) {
 	assert.NoError(t, unittest.PrepareTestDatabase())
 
 	idChan := make(chan int64, 10)
-
-	q, err := queue.NewChannelUniqueQueue(func(data ...queue.Data) []queue.Data {
-		for _, datum := range data {
-			id, _ := strconv.ParseInt(datum.(string), 10, 64)
+	testHandler := func(items ...string) []string {
+		for _, s := range items {
+			id, _ := strconv.ParseInt(s, 10, 64)
 			idChan <- id
 		}
 		return nil
-	}, queue.ChannelUniqueQueueConfiguration{
-		WorkerPoolConfiguration: queue.WorkerPoolConfiguration{
-			QueueLength: 10,
-			BatchLength: 1,
-			Name:        "temporary-queue",
-		},
-		Workers: 1,
-	}, "")
-	assert.NoError(t, err)
-
-	queueShutdown := []func(){}
-	queueTerminate := []func(){}
+	}
 
-	prPatchCheckerQueue = q.(queue.UniqueQueue)
+	cfg, err := setting.GetQueueSettings(setting.CfgProvider, "pr_patch_checker")
+	assert.NoError(t, err)
+	prPatchCheckerQueue, err = queue.NewWorkerPoolQueueBySetting("pr_patch_checker", cfg, testHandler, true)
+	assert.NoError(t, err)
 
 	pr := unittest.AssertExistsAndLoadBean(t, &issues_model.PullRequest{ID: 2})
 	AddToTaskQueue(pr)
@@ -54,7 +46,8 @@ func TestPullRequest_AddToTaskQueue(t *testing.T) {
 	assert.True(t, has)
 	assert.NoError(t, err)
 
-	prPatchCheckerQueue.Run(func(shutdown func()) {
+	var queueShutdown, queueTerminate []func()
+	go prPatchCheckerQueue.Run(func(shutdown func()) {
 		queueShutdown = append(queueShutdown, shutdown)
 	}, func(terminate func()) {
 		queueTerminate = append(queueTerminate, terminate)