completed runner pattern

concurrency/runner/main.go

@@ -1,22 +1,43 @@
 package main
 
+// Example provided with help from Gabriel Aszalos.
+// Package runner manages the running and lifetime of a process.
 import (
 	"errors"
+	"log"
 	"os"
 	"os/signal"
 	"time"
 )
 
+// Runner runs a set of tasks within a given timeout and can be
+// shut down on an operating system interrupt.
+// a concurrency pattern for task-oriented programs that
+// run unattended on a schedule. It’s designed with three possible termination points:
+// The program can finish its work within the allotted amount of time and terminate normally.
+// The program doesn’t finish in time and kills itself.
+// An operating system interrupt event is received and the program attempts to
+// immediately shut down cleanly.
 type Runner struct {
+	// interrupt channel reports a signal from the
+	// operating system.
 	interrupt chan os.Signal
-	complete  chan error
-	timeout   <-chan time.Time
-	tasks     []func(int)
+	// complete channel reports that processing is done.
+	complete chan error
+	// timeout reports that time has run out.
+	timeout <-chan time.Time
+	// tasks holds a set of functions that are executed
+	// synchronously in index order.
+	tasks []func(int)
 }
 
-var ErrTimeout = errors.New("Received Timeout")
-var ErrInterrupt = errors.New("Received Interrupt")
+// ErrTimeout is returned when a value is received on the timeout.
+var ErrTimeout = errors.New("received timeout")
 
+// ErrInterrupt is returned when an event from the OS is received.
+var ErrInterrupt = errors.New("received interrupt")
+
+// New returns a new ready-to-use Runner.
 func New(d time.Duration) *Runner {
 	return &Runner{
 		interrupt: make(chan os.Signal, 1),
@@ -25,10 +46,86 @@ func New(d time.Duration) *Runner {
 	}
 }
 
+// Add attaches tasks to the Runner. A task is a function that
+// takes an int ID.
 func (r *Runner) Add(tasks ...func(int)) {
 	r.tasks = append(r.tasks, tasks...)
 }
 
+// Start runs all tasks and monitors channel events.
 func (r *Runner) Start() error {
+	// We want to receive all interrupt based signals.
 	signal.Notify(r.interrupt, os.Interrupt)
+	// Run the different tasks on a different goroutine.
+	go func() {
+		r.complete <- r.run()
+	}()
+	select {
+	// Signaled when processing is done.
+	case err := <-r.complete:
+		return err
+	// Signaled when we run out of time.
+	case <-r.timeout:
+		return ErrTimeout
+	}
+}
+
+// run executes each registered task.
+func (r *Runner) run() error {
+	for id, task := range r.tasks {
+		// Check for an interrupt signal from the OS.
+		if r.gotInterrupt() {
+			return ErrInterrupt
+		}
+		// Execute the registered task.
+		task(id)
+	}
+	return nil
+}
+
+// gotInterrupt verifies if the interrupt signal has been issued.
+func (r *Runner) gotInterrupt() bool {
+	select {
+	// Signaled when an interrupt event is sent.
+	case <-r.interrupt:
+		// Stop receiving any further signals.
+		signal.Stop(r.interrupt)
+		return true
+	// Continue running as normal.
+	default:
+		return false
+	}
+}
+
+// timeout is the number of second the program has to finish.
+const timeout = 3 * time.Second
+
+// main is the entry point for the program.
+func main() {
+	log.Println("Starting work.")
+	// Create a new timer value for this run.
+	r := New(timeout)
+	// Add the tasks to be run.
+	r.Add(createTask(), createTask(), createTask())
+	// Run the tasks and handle the result.
+	if err := r.Start(); err != nil {
+		switch err {
+		case ErrTimeout:
+			log.Println("Terminating due to timeout.")
+			os.Exit(1)
+		case ErrInterrupt:
+			log.Println("Terminating due to interrupt.")
+			os.Exit(2)
+		}
+	}
+	log.Println("Process ended.")
+}
+
+// createTask returns an example task that sleeps for the specified
+// number of seconds based on the id.
+func createTask() func(int) {
+	return func(id int) {
+		log.Printf("Processor - Task #%d.", id)
+		time.Sleep(time.Duration(id) * time.Second)
+	}
 }