X-Git-Url: https://git.arvados.org/arvados.git/blobdiff_plain/4de0af809ffbef43d89cd1751e5d611a4b5445e9..b4209cce618b79a1cc022a85f860268a988201f1:/services/keepstore/work_queue.go

diff --git a/services/keepstore/work_queue.go b/services/keepstore/work_queue.go
index 6ec52742a5..56c6376ad3 100644
--- a/services/keepstore/work_queue.go
+++ b/services/keepstore/work_queue.go
@@ -1,3 +1,7 @@
+// Copyright (C) The Arvados Authors. All rights reserved.
+//
+// SPDX-License-Identifier: AGPL-3.0
+
 package main
 
 /* A WorkQueue is an asynchronous thread-safe queue manager.  It
@@ -84,18 +88,23 @@ package main
 
 import "container/list"
 
+// WorkQueue definition
 type WorkQueue struct {
-	countInProgress  chan int
-	countOutstanding chan int
-	countQueued      chan int
-	newlist          chan *list.List
+	getStatus chan WorkQueueStatus
+	newlist   chan *list.List
 	// Workers get work items by reading from this channel.
 	NextItem <-chan interface{}
-	// Each worker must send struct{}{} to ReportDone exactly once
+	// Each worker must send struct{}{} to DoneItem exactly once
 	// for each work item received from NextItem, when it stops
 	// working on that item (regardless of whether the work was
 	// successful).
-	ReportDone chan<- struct{}
+	DoneItem chan<- struct{}
+}
+
+// WorkQueueStatus reflects the queue status.
+type WorkQueueStatus struct {
+	InProgress int
+	Queued     int
 }
 
 // NewWorkQueue returns a new empty WorkQueue.
@@ -105,33 +114,34 @@ func NewWorkQueue() *WorkQueue {
 	reportDone := make(chan struct{})
 	newList := make(chan *list.List)
 	b := WorkQueue{
-		countQueued:      make(chan int),
-		countInProgress:  make(chan int),
-		countOutstanding: make(chan int),
-		newlist:          newList,
-		NextItem:         nextItem,
-		ReportDone:       reportDone,
+		getStatus: make(chan WorkQueueStatus),
+		newlist:   newList,
+		NextItem:  nextItem,
+		DoneItem:  reportDone,
 	}
 	go func() {
 		// Read new work lists from the newlist channel.
-		// Reply to "length" and "get next item" queries by
-		// sending to the countQueued and nextItem channels
+		// Reply to "status" and "get next item" queries by
+		// sending to the getStatus and nextItem channels
 		// respectively. Return when the newlist channel
 		// closes.
 
 		todo := &list.List{}
-		countInProgress := 0
+		status := WorkQueueStatus{}
 
 		// When we're done, close the output channel; workers will
 		// shut down next time they ask for new work.
 		defer close(nextItem)
-		defer close(b.countInProgress)
-		defer close(b.countOutstanding)
-		defer close(b.countQueued)
+		defer close(b.getStatus)
 
+		// nextChan and nextVal are both nil when we have
+		// nothing to send; otherwise they are, respectively,
+		// the nextItem channel and the next work item to send
+		// to it.
 		var nextChan chan interface{}
 		var nextVal interface{}
-		for newList != nil || countInProgress > 0 {
+
+		for newList != nil || status.InProgress > 0 {
 			select {
 			case p, ok := <-newList:
 				if !ok {
@@ -142,7 +152,8 @@ func NewWorkQueue() *WorkQueue {
 				if todo == nil {
 					todo = &list.List{}
 				}
-				if todo.Len() == 0 {
+				status.Queued = todo.Len()
+				if status.Queued == 0 {
 					// Stop sending work
 					nextChan = nil
 					nextVal = nil
@@ -151,9 +162,10 @@ func NewWorkQueue() *WorkQueue {
 					nextVal = todo.Front().Value
 				}
 			case nextChan <- nextVal:
-				countInProgress++
 				todo.Remove(todo.Front())
-				if todo.Len() == 0 {
+				status.InProgress++
+				status.Queued--
+				if status.Queued == 0 {
 					// Stop sending work
 					nextChan = nil
 					nextVal = nil
@@ -161,10 +173,8 @@ func NewWorkQueue() *WorkQueue {
 					nextVal = todo.Front().Value
 				}
 			case <-reportDone:
-				countInProgress--
-			case b.countInProgress <- countInProgress:
-			case b.countOutstanding <- todo.Len() + countInProgress:
-			case b.countQueued <- todo.Len():
+				status.InProgress--
+			case b.getStatus <- status:
 			}
 		}
 	}()
@@ -184,31 +194,19 @@ func (b *WorkQueue) ReplaceQueue(list *list.List) {
 // abandons any pending requests, but allows any pull request already
 // in progress to continue.
 //
-// After Close, CountX methods will return correct values, NextItem
-// will be closed, and ReplaceQueue will panic.
+// After Close, Status will return correct values, NextItem will be
+// closed, and ReplaceQueue will panic.
 //
 func (b *WorkQueue) Close() {
 	close(b.newlist)
 }
 
-// CountOutstanding returns the number of items in the queue or in
-// progress. A return value of 0 guarantees all existing work (work
-// that was sent to ReplaceQueue before CountOutstanding was called)
-// has completed.
-//
-func (b *WorkQueue) CountOutstanding() int {
-	// If the channel is closed, we get zero, which is correct.
-	return <-b.countOutstanding
-}
-
-// CountQueued returns the number of items in the current queue.
-//
-func (b *WorkQueue) CountQueued() int {
-	return <-b.countQueued
-}
-
-// Len returns the number of items in progress.
+// Status returns an up-to-date WorkQueueStatus reflecting the current
+// queue status.
 //
-func (b *WorkQueue) CountInProgress() int {
-	return <-b.countInProgress
+func (b *WorkQueue) Status() WorkQueueStatus {
+	// If the channel is closed, we get the nil value of
+	// WorkQueueStatus, which is an accurate description of a
+	// finished queue.
+	return <-b.getStatus
 }