Ability to exit work loop gracefully

This change adds the ability to call Shutdown on a gearman-go worker which causes the
worker to wait for all currently active jobs to finish and then close the connection.

It does this by keeping tracking of the number of currently active transactions, disallowing
new job creation, and using a WaitGroup to wait for all active jobs to finish.

worker/worker.go

@@ -23,6 +23,10 @@ type Worker struct {
 	in           chan *inPack
 	running      bool
 	ready        bool
+	shuttingDown bool
+	activeJobs   int
+	// Used during shutdown to wait for all active jobs to finish
+	finishedDraining sync.WaitGroup
 
 	Id           string
 	ErrorHandler ErrorHandler
@@ -43,6 +47,7 @@ func New(limit int) (worker *Worker) {
 		funcs:  make(jobFuncs),
 		in:     make(chan *inPack, queueSize),
 	}
+	worker.finishedDraining.Add(1)
 	if limit != Unlimited {
 		worker.limit = make(chan bool, limit-1)
 	}
@@ -137,7 +142,9 @@ func (worker *Worker) handleInPack(inpack *inPack) {
 	case dtNoJob:
 		inpack.a.PreSleep()
 	case dtNoop:
+		if !worker.shuttingDown {
 			inpack.a.Grab()
+		}
 	case dtJobAssign, dtJobAssignUniq:
 		go func() {
 			if err := worker.exec(inpack); err != nil {
@@ -147,7 +154,9 @@ func (worker *Worker) handleInPack(inpack *inPack) {
 		if worker.limit != nil {
 			worker.limit <- true
 		}
+		if !worker.shuttingDown {
 			inpack.a.Grab()
+		}
 	case dtError:
 		worker.err(inpack.Err())
 		fallthrough
@@ -224,6 +233,19 @@ func (worker *Worker) Close() {
 	}
 }
 
+// Shutdown server gracefully. This function will block until all active work has finished.
+func (worker *Worker) Shutdown() {
+	worker.Lock()
+	worker.shuttingDown = true
+	if worker.activeJobs == 0 {
+		worker.finishedDraining.Done()
+	}
+	worker.Unlock()
+	// Wait for the mutex
+	worker.finishedDraining.Wait()
+	worker.Close()
+}
+
 // Echo
 func (worker *Worker) Echo(data []byte) {
 	outpack := getOutPack()
@@ -250,6 +272,29 @@ func (worker *Worker) SetId(id string) {
 	worker.broadcast(outpack)
 }
 
+// IncrementActive increments the count of active jobs. This will return false if no more
+// jobs can't be started because the worker is shutting down.
+func (worker *Worker) incrementActive() bool {
+	worker.Lock()
+	defer worker.Unlock()
+	if worker.shuttingDown {
+		return false
+	}
+	worker.activeJobs = worker.activeJobs + 1
+	return true
+}
+
+// DecrementActive decrements the count of active jobs. If the process is shutting down
+// it will set the finishedDraining flag if there are no more active jobs.
+func (worker *Worker) decrementActive() {
+	worker.Lock()
+	defer worker.Unlock()
+	worker.activeJobs = worker.activeJobs - 1
+	if worker.shuttingDown && worker.activeJobs == 0 {
+		worker.finishedDraining.Done()
+	}
+}
+
 // inner job executing
 func (worker *Worker) exec(inpack *inPack) (err error) {
 	defer func() {
@@ -263,7 +308,11 @@ func (worker *Worker) exec(inpack *inPack) (err error) {
 				err = ErrUnknown
 			}
 		}
+		worker.decrementActive()
 	}()
+	if !worker.incrementActive() {
+		return
+	}
 	f, ok := worker.funcs[inpack.fn]
 	if !ok {
 		return fmt.Errorf("The function does not exist: %s", inpack.fn)

worker/worker_test.go

@@ -1,6 +1,7 @@
 package worker
 
 import (
+	"strconv"
 	"sync"
 	"testing"
 	"time"
@@ -62,6 +63,7 @@ func TestWorkerRemoveFunc(t *testing.T) {
 }
 
 func TestWork(t *testing.T) {
+	// TODO: Worth looking at this for shutdown (WaitGroup)
 	var wg sync.WaitGroup
 	worker.JobHandler = func(job Job) error {
 		t.Logf("%s", job.Data())
@@ -78,7 +80,6 @@ func TestWork(t *testing.T) {
 	wg.Wait()
 }
 
-
 func TestWorkerClose(t *testing.T) {
 	worker.Close()
 }
@@ -97,8 +98,8 @@ func TestWorkWithoutReady(t * testing.T){
 	done := make(chan bool, 1)
 
 	other_worker.JobHandler = func(j Job) error {
-		if( ! other_worker.ready ){
+		if !other_worker.ready {
-			t.Error("Worker not ready as expected");
+			t.Error("Worker not ready as expected")
 		}
 		done <- true
 		return nil
@@ -109,14 +110,14 @@ func TestWorkWithoutReady(t * testing.T){
 	}()
 
 	go func() {
-		other_worker.Work();
+		other_worker.Work()
 	}()
 
 	// With the all-in-one Work() we don't know if the
 	// worker is ready at this stage so we may have to wait a sec:
 	go func() {
 		tries := 3
-		for( tries > 0 ){
+		for tries > 0 {
 			if other_worker.ready {
 				other_worker.Echo([]byte("Hello"))
 				break
@@ -153,7 +154,7 @@ func TestWorkWithoutReadyWithPanic(t * testing.T){
 			t.Error("Work should raise a panic.")
 			done <- true
 		}()
-		other_worker.Work();
+		other_worker.Work()
 	}()
 	go func() {
 		time.Sleep(2 * time.Second)
@@ -167,3 +168,108 @@ func TestWorkWithoutReadyWithPanic(t * testing.T){
 	}
 
 }
+
+// initWorker creates a worker and adds the localhost server to it
+func initWorker(t *testing.T) *Worker {
+	otherWorker := New(Unlimited)
+	if err := otherWorker.AddServer(Network, "127.0.0.1:4730"); err != nil {
+		t.Error(err)
+	}
+	return otherWorker
+}
+
+// submitEmptyInPack sends an empty inpack with the specified fn name to the worker. It uses
+// the first agent of the worker.
+func submitEmptyInPack(t *testing.T, worker *Worker, function string) {
+	if l := len(worker.agents); l != 1 {
+		t.Error("The worker has no agents")
+	}
+	inpack := getInPack()
+	inpack.dataType = dtJobAssign
+	inpack.fn = function
+	inpack.a = worker.agents[0]
+	worker.in <- inpack
+}
+
+// TestShutdownSuccessJob tests that shutdown waits for the currently running job to
+// complete.
+func TestShutdownSuccessJob(t *testing.T) {
+	otherWorker := initWorker(t)
+	output := 0
+	var wg sync.WaitGroup
+	successJob := func(job Job) ([]byte, error) {
+		wg.Done()
+		// Sleep for 100ms to ensure that the shutdown waits for this to finish
+		time.Sleep(time.Duration(100 * time.Millisecond))
+		output = 1
+		return nil, nil
+	}
+	if err := otherWorker.AddFunc("test", successJob, 0); err != nil {
+		t.Error(err)
+	}
+	if err := otherWorker.Ready(); err != nil {
+		t.Error(err)
+		return
+	}
+	submitEmptyInPack(t, otherWorker, "test")
+	go otherWorker.Work()
+	// Wait for the success_job to start so that we know we didn't shutdown before even
+	// beginning to process the job.
+	wg.Add(1)
+	wg.Wait()
+	otherWorker.Shutdown()
+	if output != 1 {
+		t.Error("Expected 1, output was: " + strconv.Itoa(output))
+	}
+}
+
+func TestShutdownFailureJob(t *testing.T) {
+	otherWorker := initWorker(t)
+	output := 0
+	var wg sync.WaitGroup
+	failureJob := func(job Job) ([]byte, error) {
+		wg.Done()
+		// Sleep for 100ms to ensure that shutdown waits for this to finish
+		time.Sleep(time.Duration(100 * time.Millisecond))
+		output = 1
+		return nil, nil //new Error()
+	}
+
+	if err := otherWorker.AddFunc("test", failureJob, 0); err != nil {
+		t.Error(err)
+	}
+	if err := otherWorker.Ready(); err != nil {
+		t.Error(err)
+		return
+	}
+	submitEmptyInPack(t, otherWorker, "test")
+	go otherWorker.Work()
+	// Wait for the success_job to start so that we know we didn't shutdown before even
+	// beginning to process the job.
+	wg.Add(1)
+	wg.Wait()
+	otherWorker.Shutdown()
+	if output != 1 {
+		t.Error("Expected 1, output was: " + strconv.Itoa(output))
+	}
+}
+
+func TestSubmitJobAfterShutdown(t *testing.T) {
+	otherWorker := initWorker(t)
+	noRunJob := func(job Job) ([]byte, error) {
+		t.Error("This job shouldn't have been run")
+		return nil, nil
+	}
+	if err := otherWorker.AddFunc("test", noRunJob, 0); err != nil {
+		t.Error(err)
+	}
+	if err := otherWorker.Ready(); err != nil {
+		t.Error(err)
+		return
+	}
+	go otherWorker.Work()
+	otherWorker.Shutdown()
+	submitEmptyInPack(t, otherWorker, "test")
+	// Sleep for 100ms to make sure that the job doesn't actually run
+	time.Sleep(time.Duration(100 * time.Millisecond))
+}