Added routines package

routines/routines.go

@@ -0,0 +1,87 @@
+package routines
+
+import "io"
+import "fmt"
+import "log"
+import "time"
+import "sync"
+
+// Routine represents an object that can be run.
+type Routine interface {
+	// Run starts the routine and does not return until it is finished. An
+	// error is returned if the routine exited due to an error.
+	Run () error
+}
+
+// Manager is a system capable of managing multiple routines, and restarting
+// them if they fail.
+type Manager struct {
+	// Routines specifies a list of routines to manage. These are started
+	// when Run() is called.
+	Routines []Routine
+
+	// RestartDeadline specifies the amount of time a routine has to be
+	// running before failing to be restarted. This is to prevent routines
+	// that immediately fail from just being restarted over and over again.
+	RestartDeadline time.Duration
+
+	// Logger, if non-nil, is where log messages will be written to. If it
+	// is nil, messages will be written to the standard logger. To disable
+	// logging altogether, this can be set to io.Discard.
+	Logger io.Writer
+}
+
+// Run spawns all routines in the Routines slice. If a routine exits with an
+// error and it was running for longer than RestartDeadline, it is restarted.
+// Run returns  only when all routines have exited.
+func (manager *Manager) Run () error {
+	var waitGroup sync.WaitGroup
+	var errExit   error
+	
+	for _, routine := range manager.Routines {
+		if routine != nil {
+			waitGroup.Add(1)
+			go manager.runRoutine(routine, &waitGroup, &errExit)
+		}
+	}
+	
+	waitGroup.Wait()
+	return errExit
+}
+
+func (manager *Manager) log (message ...any) {
+	if manager.Logger == nil {
+		log.Println(message...)
+	} else {
+		fmt.Fprintln(manager.Logger, message...)
+	}
+}
+
+func (manager *Manager) runRoutine (routine Routine, group *sync.WaitGroup, errExit *error) {
+	defer group.Done()
+
+	var err error
+	for {
+		// TODO: recover from panics
+		lastStart := time.Now()
+		err = routine.Run()
+
+		if err == nil {
+			manager.log("(i) routine exited")
+			break
+		} else {
+			manager.log("XXX routine failed:", err)
+		}
+		
+		if time.Since(lastStart) < manager.RestartDeadline {
+			manager.log("!!! not restarting routine, failed too soon")
+			break
+		} else {
+			manager.log("(i) routine is being restarted")
+		}
+	}
+	
+	if err != nil {
+		*errExit = err
+	}
+}