6465f94a2d
Without `case <-t.C`, the workers would stop incorrectly, the test won't pass. For the worse case, there might be only one running worker processing the queue items for long time because other workers are stopped. The root cause is related to the logic of doDispatchBatchToWorker. It isn't a serious problem at the moment, so keep it as-is.
350 lines
10 KiB
Go
350 lines
10 KiB
Go
// Copyright 2023 The Gitea Authors. All rights reserved.
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// SPDX-License-Identifier: MIT
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package queue
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import (
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"context"
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"runtime/pprof"
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"sync"
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"sync/atomic"
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"time"
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"code.gitea.io/gitea/modules/log"
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)
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var (
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infiniteTimerC = make(chan time.Time)
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batchDebounceDuration = 100 * time.Millisecond
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workerIdleDuration = 1 * time.Second
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shutdownDefaultTimeout = 2 * time.Second
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unhandledItemRequeueDuration atomic.Int64 // to avoid data race during test
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)
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func init() {
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unhandledItemRequeueDuration.Store(int64(5 * time.Second))
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}
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// workerGroup is a group of workers to work with a WorkerPoolQueue
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type workerGroup[T any] struct {
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q *WorkerPoolQueue[T]
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wg sync.WaitGroup
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ctxWorker context.Context
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ctxWorkerCancel context.CancelFunc
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batchBuffer []T
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popItemChan chan []byte
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popItemErr chan error
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}
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func (wg *workerGroup[T]) doPrepareWorkerContext() {
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wg.ctxWorker, wg.ctxWorkerCancel = context.WithCancel(wg.q.ctxRun)
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}
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// doDispatchBatchToWorker dispatches a batch of items to worker's channel.
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// If the channel is full, it tries to start a new worker if possible.
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func (q *WorkerPoolQueue[T]) doDispatchBatchToWorker(wg *workerGroup[T], flushChan chan flushType) {
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batch := wg.batchBuffer
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wg.batchBuffer = nil
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if len(batch) == 0 {
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return
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}
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full := false
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select {
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case q.batchChan <- batch:
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default:
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full = true
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}
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// TODO: the logic could be improved in the future, to avoid a data-race between "doStartNewWorker" and "workerNum"
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// The root problem is that if we skip "doStartNewWorker" here, the "workerNum" might be decreased by other workers later
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// So ideally, it should check whether there are enough workers by some approaches, and start new workers if necessary.
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q.workerNumMu.Lock()
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noWorker := q.workerNum == 0
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if full || noWorker {
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if q.workerNum < q.workerMaxNum || noWorker && q.workerMaxNum <= 0 {
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q.workerNum++
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q.doStartNewWorker(wg)
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}
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}
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q.workerNumMu.Unlock()
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if full {
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select {
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case q.batchChan <- batch:
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case flush := <-flushChan:
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q.doWorkerHandle(batch)
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q.doFlush(wg, flush)
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case <-q.ctxRun.Done():
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wg.batchBuffer = batch // return the batch to buffer, the "doRun" function will handle it
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}
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}
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}
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// doWorkerHandle calls the safeHandler to handle a batch of items, and it increases/decreases the active worker number.
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// If the context has been canceled, it should not be caller because the "Push" still needs the context, in such case, call q.safeHandler directly
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func (q *WorkerPoolQueue[T]) doWorkerHandle(batch []T) {
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q.workerNumMu.Lock()
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q.workerActiveNum++
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q.workerNumMu.Unlock()
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defer func() {
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q.workerNumMu.Lock()
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q.workerActiveNum--
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q.workerNumMu.Unlock()
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}()
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unhandled := q.safeHandler(batch...)
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// if none of the items were handled, it should back-off for a few seconds
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// in this case the handler (eg: document indexer) may have encountered some errors/failures
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if len(unhandled) == len(batch) && unhandledItemRequeueDuration.Load() != 0 {
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log.Error("Queue %q failed to handle batch of %d items, backoff for a few seconds", q.GetName(), len(batch))
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select {
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case <-q.ctxRun.Done():
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case <-time.After(time.Duration(unhandledItemRequeueDuration.Load())):
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}
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}
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for _, item := range unhandled {
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if err := q.Push(item); err != nil {
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if !q.basePushForShutdown(item) {
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log.Error("Failed to requeue item for queue %q when calling handler: %v", q.GetName(), err)
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}
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}
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}
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}
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// basePushForShutdown tries to requeue items into the base queue when the WorkerPoolQueue is shutting down.
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// If the queue is shutting down, it returns true and try to push the items
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// Otherwise it does nothing and returns false
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func (q *WorkerPoolQueue[T]) basePushForShutdown(items ...T) bool {
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shutdownTimeout := time.Duration(q.shutdownTimeout.Load())
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if shutdownTimeout == 0 {
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return false
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}
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ctxShutdown, ctxShutdownCancel := context.WithTimeout(context.Background(), shutdownTimeout)
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defer ctxShutdownCancel()
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for _, item := range items {
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// if there is still any error, the queue can do nothing instead of losing the items
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if err := q.baseQueue.PushItem(ctxShutdown, q.marshal(item)); err != nil {
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log.Error("Failed to requeue item for queue %q when shutting down: %v", q.GetName(), err)
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}
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}
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return true
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}
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// doStartNewWorker starts a new worker for the queue, the worker reads from worker's channel and handles the items.
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func (q *WorkerPoolQueue[T]) doStartNewWorker(wp *workerGroup[T]) {
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wp.wg.Add(1)
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go func() {
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defer wp.wg.Done()
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log.Debug("Queue %q starts new worker", q.GetName())
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defer log.Debug("Queue %q stops idle worker", q.GetName())
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atomic.AddInt32(&q.workerStartedCounter, 1) // Only increase counter, used for debugging
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t := time.NewTicker(workerIdleDuration)
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defer t.Stop()
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keepWorking := true
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stopWorking := func() {
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q.workerNumMu.Lock()
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keepWorking = false
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q.workerNum--
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q.workerNumMu.Unlock()
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}
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for keepWorking {
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select {
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case <-wp.ctxWorker.Done():
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stopWorking()
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case batch, ok := <-q.batchChan:
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if !ok {
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stopWorking()
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continue
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}
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q.doWorkerHandle(batch)
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// reset the idle ticker, and drain the tick after reset in case a tick is already triggered
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t.Reset(workerIdleDuration)
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select {
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case <-t.C:
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default:
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}
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case <-t.C:
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q.workerNumMu.Lock()
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keepWorking = q.workerNum <= 1 // keep the last worker running
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if !keepWorking {
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q.workerNum--
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}
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q.workerNumMu.Unlock()
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}
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}
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}()
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}
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// doFlush flushes the queue: it tries to read all items from the queue and handles them.
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// It is for testing purpose only. It's not designed to work for a cluster.
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func (q *WorkerPoolQueue[T]) doFlush(wg *workerGroup[T], flush flushType) {
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log.Debug("Queue %q starts flushing", q.GetName())
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defer log.Debug("Queue %q finishes flushing", q.GetName())
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// stop all workers, and prepare a new worker context to start new workers
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wg.ctxWorkerCancel()
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wg.wg.Wait()
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defer func() {
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close(flush)
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wg.doPrepareWorkerContext()
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}()
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// drain the batch channel first
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loop:
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for {
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select {
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case batch := <-q.batchChan:
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q.doWorkerHandle(batch)
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default:
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break loop
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}
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}
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// drain the popItem channel
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emptyCounter := 0
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for {
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select {
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case data, dataOk := <-wg.popItemChan:
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if !dataOk {
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return
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}
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emptyCounter = 0
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if v, jsonOk := q.unmarshal(data); !jsonOk {
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continue
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} else {
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q.doWorkerHandle([]T{v})
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}
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case err := <-wg.popItemErr:
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if !q.isCtxRunCanceled() {
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log.Error("Failed to pop item from queue %q (doFlush): %v", q.GetName(), err)
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}
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return
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case <-q.ctxRun.Done():
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log.Debug("Queue %q is shutting down", q.GetName())
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return
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case <-time.After(20 * time.Millisecond):
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// There is no reliable way to make sure all queue items are consumed by the Flush, there always might be some items stored in some buffers/temp variables.
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// If we run Gitea in a cluster, we can even not guarantee all items are consumed in a deterministic instance.
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// Luckily, the "Flush" trick is only used in tests, so far so good.
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if cnt, _ := q.baseQueue.Len(q.ctxRun); cnt == 0 && len(wg.popItemChan) == 0 {
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emptyCounter++
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}
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if emptyCounter >= 2 {
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return
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}
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}
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}
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}
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func (q *WorkerPoolQueue[T]) isCtxRunCanceled() bool {
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select {
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case <-q.ctxRun.Done():
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return true
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default:
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return false
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}
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}
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var skipFlushChan = make(chan flushType) // an empty flush chan, used to skip reading other flush requests
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// doRun is the main loop of the queue. All related "doXxx" functions are executed in its context.
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func (q *WorkerPoolQueue[T]) doRun() {
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pprof.SetGoroutineLabels(q.ctxRun)
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log.Debug("Queue %q starts running", q.GetName())
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defer log.Debug("Queue %q stops running", q.GetName())
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wg := &workerGroup[T]{q: q}
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wg.doPrepareWorkerContext()
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wg.popItemChan, wg.popItemErr = popItemByChan(q.ctxRun, q.baseQueue.PopItem)
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defer func() {
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q.ctxRunCancel()
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// drain all data on the fly
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// since the queue is shutting down, the items can't be dispatched to workers because the context is canceled
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// it can't call doWorkerHandle either, because there is no chance to push unhandled items back to the queue
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var unhandled []T
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close(q.batchChan)
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for batch := range q.batchChan {
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unhandled = append(unhandled, batch...)
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}
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unhandled = append(unhandled, wg.batchBuffer...)
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for data := range wg.popItemChan {
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if v, ok := q.unmarshal(data); ok {
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unhandled = append(unhandled, v)
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}
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}
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shutdownTimeout := time.Duration(q.shutdownTimeout.Load())
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if shutdownTimeout != 0 {
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// if there is a shutdown context, try to push the items back to the base queue
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q.basePushForShutdown(unhandled...)
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workerDone := make(chan struct{})
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// the only way to wait for the workers, because the handlers do not have context to wait for
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go func() { wg.wg.Wait(); close(workerDone) }()
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select {
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case <-workerDone:
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case <-time.After(shutdownTimeout):
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log.Error("Queue %q is shutting down, but workers are still running after timeout", q.GetName())
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}
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} else {
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// if there is no shutdown context, just call the handler to try to handle the items. if the handler fails again, the items are lost
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q.safeHandler(unhandled...)
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}
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close(q.shutdownDone)
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}()
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var batchDispatchC <-chan time.Time = infiniteTimerC
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for {
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select {
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case data, dataOk := <-wg.popItemChan:
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if !dataOk {
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return
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}
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if v, jsonOk := q.unmarshal(data); !jsonOk {
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testRecorder.Record("pop:corrupted:%s", data) // in rare cases the levelqueue(leveldb) might be corrupted
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continue
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} else {
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wg.batchBuffer = append(wg.batchBuffer, v)
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}
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if len(wg.batchBuffer) >= q.batchLength {
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q.doDispatchBatchToWorker(wg, q.flushChan)
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} else if batchDispatchC == infiniteTimerC {
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batchDispatchC = time.After(batchDebounceDuration)
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} // else: batchDispatchC is already a debounce timer, it will be triggered soon
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case <-batchDispatchC:
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batchDispatchC = infiniteTimerC
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q.doDispatchBatchToWorker(wg, q.flushChan)
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case flush := <-q.flushChan:
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// before flushing, it needs to try to dispatch the batch to worker first, in case there is no worker running
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// after the flushing, there is at least one worker running, so "doFlush" could wait for workers to finish
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// since we are already in a "flush" operation, so the dispatching function shouldn't read the flush chan.
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q.doDispatchBatchToWorker(wg, skipFlushChan)
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q.doFlush(wg, flush)
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case err := <-wg.popItemErr:
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if !q.isCtxRunCanceled() {
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log.Error("Failed to pop item from queue %q (doRun): %v", q.GetName(), err)
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}
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return
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case <-q.ctxRun.Done():
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log.Debug("Queue %q is shutting down", q.GetName())
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return
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}
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}
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}
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