replace atomic ops for depth with a channel

ioLoop() now feeds depth into the depthChan synchronously,
only when Depth() is trying to read depthChan

Author: ploxiln

diskqueue.go

@@ -11,7 +11,6 @@ import (
 	"os"
 	"path"
 	"sync"
-	"sync/atomic"
 	"time"
 )
 
@@ -92,6 +91,7 @@ type diskQueue struct {
 	readChan chan []byte
 
 	// internal channels
+	depthChan         chan int64
 	writeChan         chan []byte
 	writeResponseChan chan error
 	emptyChan         chan int
@@ -114,6 +114,7 @@ func New(name string, dataPath string, maxBytesPerFile int64,
 		minMsgSize:        minMsgSize,
 		maxMsgSize:        maxMsgSize,
 		readChan:          make(chan []byte),
+		depthChan:         make(chan int64),
 		writeChan:         make(chan []byte),
 		writeResponseChan: make(chan error),
 		emptyChan:         make(chan int),
@@ -137,7 +138,7 @@ func New(name string, dataPath string, maxBytesPerFile int64,
 
 // Depth returns the depth of the queue
 func (d *diskQueue) Depth() int64 {
-	return atomic.LoadInt64(&d.depth)
+	return <-d.depthChan
 }
 
 // ReadChan returns the receive-only []byte channel for reading data
@@ -256,7 +257,7 @@ func (d *diskQueue) skipToNextRWFile() error {
 	d.readPos = 0
 	d.nextReadFileNum = d.writeFileNum
 	d.nextReadPos = 0
-	atomic.StoreInt64(&d.depth, 0)
+	d.depth = 0
 
 	return err
 }
@@ -385,7 +386,7 @@ func (d *diskQueue) writeOne(data []byte) error {
 
 	totalBytes := int64(4 + dataLen)
 	d.writePos += totalBytes
-	atomic.AddInt64(&d.depth, 1)
+	d.depth += 1
 
 	if d.writePos >= d.maxBytesPerFile {
 		d.writeFileNum++
@@ -446,7 +447,7 @@ func (d *diskQueue) retrieveMetaData() error {
 	if err != nil {
 		return err
 	}
-	atomic.StoreInt64(&d.depth, depth)
+	d.depth = depth
 	d.nextReadFileNum = d.readFileNum
 	d.nextReadPos = d.readPos
 
@@ -468,7 +469,7 @@ func (d *diskQueue) persistMetaData() error {
 	}
 
 	_, err = fmt.Fprintf(f, "%d\n%d,%d\n%d,%d\n",
-		atomic.LoadInt64(&d.depth),
+		d.depth,
 		d.readFileNum, d.readPos,
 		d.writeFileNum, d.writePos)
 	if err != nil {
@@ -508,7 +509,7 @@ func (d *diskQueue) checkTailCorruption(depth int64) {
 				d.name, depth)
 		}
 		// force set depth 0
-		atomic.StoreInt64(&d.depth, 0)
+		d.depth = 0
 		d.needSync = true
 	}
 
@@ -534,7 +535,7 @@ func (d *diskQueue) moveForward() {
 	oldReadFileNum := d.readFileNum
 	d.readFileNum = d.nextReadFileNum
 	d.readPos = d.nextReadPos
-	depth := atomic.AddInt64(&d.depth, -1)
+	d.depth -= 1
 
 	// see if we need to clean up the old file
 	if oldReadFileNum != d.nextReadFileNum {
@@ -548,7 +549,7 @@ func (d *diskQueue) moveForward() {
 		}
 	}
 
-	d.checkTailCorruption(depth)
+	d.checkTailCorruption(d.depth)
 }
 
 func (d *diskQueue) handleReadError() {
@@ -639,6 +640,7 @@ func (d *diskQueue) ioLoop() {
 			count++
 			// moveForward sets needSync flag if a file is removed
 			d.moveForward()
+		case d.depthChan <- d.depth:
 		case <-d.emptyChan:
 			d.emptyResponseChan <- d.deleteAllFiles()
 			count = 0