Unbuffer callbacks so they are executed in order

Before this used to block

main.go

@@ -45,9 +45,10 @@ func NewShellRunnerWithShell(shell string) *ShellRunner {
 		cmdQueue:   make(chan func() *CommandResult),
 		results:    make(chan *CommandResult, MAX_RESULTS),
 		stopChan:   make(chan struct{}),
-		callbacks:  make(chan func(), MAX_RESULTS),
+		callbacks:  make(chan func()),
 		shell:      shell,
 		activeCmds: make(map[*exec.Cmd]struct{}),
+		isStopped:  true,
 	}
 }
 
@@ -75,16 +76,20 @@ func (sr *ShellRunner) Start() {
 			}
 		}
 	}()
+
+	sr.isStopped = false
 }
 
 // AddCommand adds a shell command to be executed with an optional callback.
-// No commands can be added if the runner has been stopped.
+// No commands can be added if the runner has been stopped or not yet started.
+// The callback is executed asynchronously after the command has completed.
+// The order of command execution and callback invocation can be expected to be preserved.
 func (sr *ShellRunner) AddCommand(command string, callback func(*CommandResult)) error {
 	sr.mu.Lock()
 	defer sr.mu.Unlock()
 
 	if sr.isStopped {
-		return errors.New("runner has been stopped, cannot add new commands")
+		return errors.New("runner is stopped, cannot add new commands")
 	}
 
 	sr.cmdQueue <- func() *CommandResult {

main_test.go

@@ -1,6 +1,7 @@
 package tortoise_test
 
 import (
+	"sync"
 	"testing"
 	"time"
 
@@ -49,36 +50,55 @@ func TestShellRunnerCallback(t *testing.T) {
 	runner.Start()
 
 	// Test command with callback
-	done := make(chan struct{})
+	outputString := ""
+	callbackWait := sync.WaitGroup{}
 
-	callbackReached := false
+	callbackWait.Add(1)
 
-	if err := runner.AddCommand("echo callback test", func(result *tortoise.CommandResult) {
-		callbackReached = true
-		if result.Output != "callback test\n" {
-			t.Fatalf("expected 'callback test', got '%s'", result.Output)
+	if err := runner.AddCommand("echo callback a", func(result *tortoise.CommandResult) {
+		if result.Output != "callback a\n" {
+			t.Fatalf("expected 'callback a', got '%s'", result.Output)
 		}
-		close(done)
+		outputString = outputString + "a"
+		callbackWait.Done()
 	}); err != nil {
 		t.Fatalf("unexpected error adding command: %v", err)
 	}
 
-	// Timeout waiting for callback
+	callbackWait.Add(1)
+
+	if err := runner.AddCommand("echo callback b", func(result *tortoise.CommandResult) {
+		if result.Output != "callback b\n" {
+			t.Fatalf("expected 'callback b', got '%s'", result.Output)
+		}
+		outputString = outputString + "b"
+		callbackWait.Done()
+	}); err != nil {
+		t.Fatalf("unexpected error adding command: %v", err)
+	}
+
+	// Timeout waiting for callbacks
+	done := make(chan struct{})
+	go func() {
+		callbackWait.Wait()
+		close(done)
+	}()
+
 	select {
 	case <-done:
 	case <-time.After(2 * time.Second):
-		t.Fatal("callback timed out")
+		t.Fatal("callbacks timed out")
 	}
 
-	if !callbackReached {
-		t.Fatal("callback was not reached")
+	if outputString != "ab" {
+		t.Fatal("callbacks was not reached in order:", outputString)
 	}
 
 	runner.Stop()
 
 	// Make sure stop and kill both exit gracefully after the runner is stopped
 	runner.Stop()
-	runner.Stop()
+	runner.Kill()
 }
 
 func TestShellRunnerKillWithTimeout(t *testing.T) {
@@ -122,3 +142,12 @@ func TestStopPreventsNewCommands(t *testing.T) {
 		t.Fatal("expected error when adding command after stop, but got none")
 	}
 }
+
+func TestAddingPriorToStart(t *testing.T) {
+	runner := tortoise.NewShellRunner()
+
+	err := runner.AddCommand("echo should not run", nil)
+	if err == nil {
+		t.Fatal("Should have failed to add prior to starting runner")
+	}
+}