Merge pull request #3 from Clever/made-checkpointer-cacheable

Consumers of this library can now cache the checkpointer object

.gitignore

@@ -1,3 +1,5 @@
+vendor
+
 # osx / sshfs
 ._*
 .DS_Store

cmd/consumer/main.go

@@ -10,7 +10,7 @@ import (
 )
 
 type SampleRecordProcessor struct {
-	sleepDuration     time.Duration
+	checkpointer      *kcl.Checkpointer
 	checkpointRetries int
 	checkpointFreq    time.Duration
 	largestSeq        *big.Int
@@ -20,53 +20,23 @@ type SampleRecordProcessor struct {
 
 func New() *SampleRecordProcessor {
 	return &SampleRecordProcessor{
-		sleepDuration:     5 * time.Second,
 		checkpointRetries: 5,
 		checkpointFreq:    60 * time.Second,
 	}
 }
 
-func (srp *SampleRecordProcessor) Initialize(shardID string) error {
+func (srp *SampleRecordProcessor) Initialize(shardID string, checkpointer *kcl.Checkpointer) error {
 	srp.lastCheckpoint = time.Now()
+	srp.checkpointer = checkpointer
 	return nil
 }
 
-func (srp *SampleRecordProcessor) checkpoint(checkpointer kcl.Checkpointer, sequenceNumber *string, subSequenceNumber *int) {
-	for n := -1; n < srp.checkpointRetries; n++ {
-		err := checkpointer.Checkpoint(sequenceNumber, subSequenceNumber)
-		if err == nil {
-			return
-		}
-
-		if cperr, ok := err.(kcl.CheckpointError); ok {
-			switch cperr.Error() {
-			case "ShutdownException":
-				fmt.Fprintf(os.Stderr, "Encountered shutdown exception, skipping checkpoint\n")
-				return
-			case "ThrottlingException":
-				fmt.Fprintf(os.Stderr, "Was throttled while checkpointing, will attempt again in %s", srp.sleepDuration)
-			case "InvalidStateException":
-				fmt.Fprintf(os.Stderr, "MultiLangDaemon reported an invalid state while checkpointing\n")
-			default:
-				fmt.Fprintf(os.Stderr, "Encountered an error while checkpointing: %s", err)
-			}
-		}
-
-		if n == srp.checkpointRetries {
-			fmt.Fprintf(os.Stderr, "Failed to checkpoint after %d attempts, giving up.\n", srp.checkpointRetries)
-			return
-		}
-
-		time.Sleep(srp.sleepDuration)
-	}
-}
-
 func (srp *SampleRecordProcessor) shouldUpdateSequence(sequenceNumber *big.Int, subSequenceNumber int) bool {
 	return srp.largestSeq == nil || sequenceNumber.Cmp(srp.largestSeq) == 1 ||
 		(sequenceNumber.Cmp(srp.largestSeq) == 0 && subSequenceNumber > srp.largestSubSeq)
 }
 
-func (srp *SampleRecordProcessor) ProcessRecords(records []kcl.Record, checkpointer kcl.Checkpointer) error {
+func (srp *SampleRecordProcessor) ProcessRecords(records []kcl.Record) error {
 	for _, record := range records {
 		seqNumber := new(big.Int)
 		if _, ok := seqNumber.SetString(record.SequenceNumber, 10); !ok {
@@ -80,16 +50,16 @@ func (srp *SampleRecordProcessor) ProcessRecords(records []kcl.Record, checkpoin
 	}
 	if time.Now().Sub(srp.lastCheckpoint) > srp.checkpointFreq {
 		largestSeq := srp.largestSeq.String()
-		srp.checkpoint(checkpointer, &largestSeq, &srp.largestSubSeq)
+		srp.checkpointer.CheckpointWithRetry(&largestSeq, &srp.largestSubSeq, srp.checkpointRetries)
 		srp.lastCheckpoint = time.Now()
 	}
 	return nil
 }
 
-func (srp *SampleRecordProcessor) Shutdown(checkpointer kcl.Checkpointer, reason string) error {
+func (srp *SampleRecordProcessor) Shutdown(reason string) error {
 	if reason == "TERMINATE" {
 		fmt.Fprintf(os.Stderr, "Was told to terminate, will attempt to checkpoint.\n")
-		srp.checkpoint(checkpointer, nil, nil)
+		srp.checkpointer.Shutdown()
 	} else {
 		fmt.Fprintf(os.Stderr, "Shutting down due to failover. Will not checkpoint.\n")
 	}

kcl/kcl.go

@@ -6,19 +6,32 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"os"
+	"sync"
+	"time"
 )
 
 type RecordProcessor interface {
-	Initialize(shardID string) error
-	ProcessRecords(records []Record, checkpointer Checkpointer) error
-	Shutdown(checkpointer Checkpointer, reason string) error
+	Initialize(shardID string, checkpointer *Checkpointer) error
+	ProcessRecords(records []Record) error
+	Shutdown(reason string) error
+}
+
+type CheckpointError struct {
+	e string
+}
+
+func (ce CheckpointError) Error() string {
+	return ce.e
 }
 
 type Checkpointer struct {
+	mux sync.Mutex
+
 	ioHandler ioHandler
 }
 
-func (c Checkpointer) getAction() (interface{}, error) {
+func (c *Checkpointer) getAction() (interface{}, error) {
 	line, err := c.ioHandler.readLine()
 	if err != nil {
 		return nil, err
@@ -30,15 +43,10 @@ func (c Checkpointer) getAction() (interface{}, error) {
 	return action, nil
 }
 
-type CheckpointError struct {
-	e string
-}
+func (c *Checkpointer) Checkpoint(sequenceNumber *string, subSequenceNumber *int) error {
+	c.mux.Lock()
+	defer c.mux.Unlock()
 
-func (ce CheckpointError) Error() string {
-	return ce.e
-}
-
-func (c Checkpointer) Checkpoint(sequenceNumber *string, subSequenceNumber *int) error {
 	c.ioHandler.writeAction(ActionCheckpoint{
 		Action:            "checkpoint",
 		SequenceNumber:    sequenceNumber,
@@ -62,7 +70,46 @@ func (c Checkpointer) Checkpoint(sequenceNumber *string, subSequenceNumber *int)
 		}
 	}
 	return nil
+}
 
+// CheckpointWithRetry tries to save a checkPoint up to `retryCount` + 1 times.
+// `retryCount` should be >= 0
+func (c *Checkpointer) CheckpointWithRetry(
+	sequenceNumber *string, subSequenceNumber *int, retryCount int,
+) error {
+	sleepDuration := 5 * time.Second
+
+	for n := 0; n <= retryCount; n++ {
+		err := c.Checkpoint(sequenceNumber, subSequenceNumber)
+		if err == nil {
+			return nil
+		}
+
+		if cperr, ok := err.(CheckpointError); ok {
+			switch cperr.Error() {
+			case "ShutdownException":
+				return fmt.Errorf("Encountered shutdown exception, skipping checkpoint")
+			case "ThrottlingException":
+				fmt.Fprintf(os.Stderr, "Was throttled while checkpointing, will attempt again in %s\n", sleepDuration)
+			case "InvalidStateException":
+				fmt.Fprintf(os.Stderr, "MultiLangDaemon reported an invalid state while checkpointing\n")
+			default:
+				fmt.Fprintf(os.Stderr, "Encountered an error while checkpointing: %s", err)
+			}
+		}
+
+		if n == retryCount {
+			return fmt.Errorf("Failed to checkpoint after %d attempts, giving up.", retryCount)
+		}
+
+		time.Sleep(sleepDuration)
+	}
+
+	return nil
+}
+
+func (c *Checkpointer) Shutdown() {
+	c.CheckpointWithRetry(nil, nil, 5)
 }
 
 type ioHandler struct {
@@ -178,7 +225,7 @@ func New(inputFile io.Reader, outputFile, errorFile io.Writer, recordProcessor R
 	}
 	return &KCLProcess{
 		ioHandler: i,
-		checkpointer: Checkpointer{
+		checkpointer: &Checkpointer{
 			ioHandler: i,
 		},
 		recordProcessor: recordProcessor,
@@ -187,7 +234,7 @@ func New(inputFile io.Reader, outputFile, errorFile io.Writer, recordProcessor R
 
 type KCLProcess struct {
 	ioHandler       ioHandler
-	checkpointer    Checkpointer
+	checkpointer    *Checkpointer
 	recordProcessor RecordProcessor
 }
 
@@ -204,11 +251,11 @@ func (kclp *KCLProcess) reportDone(responseFor string) error {
 func (kclp *KCLProcess) performAction(a interface{}) (string, error) {
 	switch action := a.(type) {
 	case ActionInitialize:
-		return action.Action, kclp.recordProcessor.Initialize(action.ShardID)
+		return action.Action, kclp.recordProcessor.Initialize(action.ShardID, kclp.checkpointer)
 	case ActionProcessRecords:
-		return action.Action, kclp.recordProcessor.ProcessRecords(action.Records, kclp.checkpointer)
+		return action.Action, kclp.recordProcessor.ProcessRecords(action.Records)
 	case ActionShutdown:
-		return action.Action, kclp.recordProcessor.Shutdown(kclp.checkpointer, action.Reason)
+		return action.Action, kclp.recordProcessor.Shutdown(action.Reason)
 	default:
 		return "", fmt.Errorf("unknown action to dispatch: %s", action)
 	}