Refactor pmuxlib to allow for restarting a single process within a set

main.go

@@ -1,7 +1,6 @@
 package main
 
 import (
-	"context"
 	"flag"
 	"fmt"
 	"io/ioutil"
@@ -29,19 +28,18 @@ func main() {
 		panic(fmt.Sprintf("couldn't parse cfg file: %v", err))
 	}
 
-	ctx, cancel := context.WithCancel(context.Background())
+	p := pmuxlib.NewPmux(cfg, os.Stdout, os.Stderr)
+	defer p.Stop()
+
+	sigCh := make(chan os.Signal, 2)
+	signal.Notify(sigCh, os.Interrupt, syscall.SIGTERM)
+
+	<-sigCh
+
 	go func() {
-		sigCh := make(chan os.Signal, 2)
-		signal.Notify(sigCh, os.Interrupt, syscall.SIGTERM)
-
-		<-sigCh
-		cancel()
-
 		<-sigCh
 		fmt.Fprintln(os.Stderr, "forcefully exiting pmux process, there may be zombie child processes being left behind, good luck!")
 		os.Stderr.Sync()
 		os.Exit(1)
 	}()
-
-	pmuxlib.Run(ctx, os.Stdout, os.Stderr, cfg)
 }

pmux-example.yml

@@ -12,7 +12,7 @@
 processes:
 
   # each process must have a name and cmd.
-  - name: pinger
+  pinger:
     cmd: /bin/bash
     args:
       - "-c"
@@ -37,7 +37,7 @@ processes:
 
   # This process will not immediately exit when pmux tells it to do so, but pmux
   # will SIGKILL it after sigKillWait has elapsed.
-  - name: stubborn-pinger
+  stubborn-pinger:
     cmd: /bin/bash
     args:
       - "-c"

pmuxlib/pmuxlib.go

@@ -3,25 +3,30 @@
 package pmuxlib
 
 import (
-	"context"
+	"fmt"
 	"io"
 	"sync"
 )
 
 type Config struct {
-	TimeFormat string          `yaml:"timeFormat"`
-	Processes  []ProcessConfig `yaml:"processes"`
+	TimeFormat string `yaml:"timeFormat"`
+
+	// Set of processes to run, keyed by their name.
+	Processes map[string]ProcessConfig `yaml:"processes"`
 }
 
-// Run runs the given configuration as if this was a real pmux process. It will
-// block until the context is canceled and all child processes have been cleaned
-// up.
-func Run(
-	ctx context.Context,
-	stdout, stderr io.Writer,
-	cfg Config,
-) {
+// Pmux manages multiple child Processes. Methods on a Pmux instance are _not_
+// thread-safe.
+//
+// Stop must be called on a Pmux before the program has exited, or there may be
+// a leftover zombie child process.
+type Pmux struct {
+	processes map[string]*Process
+	sysLogger Logger
+}
 
+// NewPmux starts a Pmux with the given configuration.
+func NewPmux(cfg Config, stdout, stderr io.Writer) *Pmux {
 	stdoutLogger := newLogger(stdout, logSepStdout, cfg.TimeFormat)
 	defer stdoutLogger.Close()
 
@@ -29,27 +34,51 @@ func Run(
 	defer stderrLogger.Close()
 
 	sysLogger := stderrLogger.withSep(logSepSys)
-	defer sysLogger.Println("exited gracefully, ciao!")
 
-	var wg sync.WaitGroup
-	defer wg.Wait()
-
-	for _, cfgProc := range cfg.Processes {
-		wg.Add(1)
-		go func(procCfg ProcessConfig) {
-			defer wg.Done()
-
-			stdoutLogger := stdoutLogger.withPName(procCfg.Name)
-			stderrLogger := stderrLogger.withPName(procCfg.Name)
-			sysLogger := sysLogger.withPName(procCfg.Name)
-
-			sysLogger.Println("starting process")
-			defer sysLogger.Println("stopped process handler")
-
-			RunProcess(
-				ctx, stdoutLogger, stderrLogger, sysLogger, procCfg,
-			)
-
-		}(cfgProc)
+	p := &Pmux{
+		processes: map[string]*Process{},
+		sysLogger: sysLogger,
 	}
+
+	for name, cfgProc := range cfg.Processes {
+		stdoutLogger := stdoutLogger.withPName(name)
+		stderrLogger := stderrLogger.withPName(name)
+		sysLogger := sysLogger.withPName(name)
+		p.processes[name] = NewProcess(
+			cfgProc, stdoutLogger, stderrLogger, sysLogger,
+		)
+	}
+
+	return p
+}
+
+// Restart will block until the child process of the given name has been killed
+// and a new one has been spawned. If there is no child of the given name then
+// Restart panics.
+func (p *Pmux) Restart(name string) {
+	proc, ok := p.processes[name]
+	if !ok {
+		panic(fmt.Sprintf("no process named %q", name))
+	}
+	proc.Restart()
+}
+
+// Stop will block until all child processes have been killed. The Pmux should
+// not be used again after this.
+func (p *Pmux) Stop() {
+	var wg sync.WaitGroup
+
+	p.sysLogger.Println("killing child processes")
+	for _, proc := range p.processes {
+		proc := proc
+
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			proc.Stop()
+		}()
+	}
+
+	wg.Wait()
+	p.sysLogger.Println("exited gracefully, ciao!")
 }

pmuxlib/process.go

@@ -14,12 +14,8 @@ import (
 	"time"
 )
 
-// ProcessConfig is used to configure a process via RunProcess.
+// ProcessConfig is used to configure a process.
 type ProcessConfig struct {
-
-	// Name of the process to be run. This only gets used by RunPmux.
-	Name string
-
 	// Cmd and Args describe the actual process to run.
 	Cmd  string   `yaml:"cmd"`
 	Args []string `yaml:"args"`
@@ -32,7 +28,7 @@ type ProcessConfig struct {
 	Dir string `yaml:"dir"`
 
 	// MinWait and MaxWait are the minimum and maximum amount of time between
-	// restarts that RunProcess will wait.
+	// restarts that Process will wait.
 	//
 	// MinWait defaults to 1 second.
 	// MaxWait defaults to 64 seconds.
@@ -40,7 +36,7 @@ type ProcessConfig struct {
 	MaxWait time.Duration `yaml:"maxWait"`
 
 	// SigKillWait is the amount of time after the process is sent a SIGINT
-	// before RunProcess sends it a SIGKILL.
+	// before a SIGKILL is sent.
 	//
 	// Defalts to 10 seconds.
 	SigKillWait time.Duration `yaml:"sigKillWait"`
@@ -207,8 +203,11 @@ func RunProcessOnce(
 	return cmd.ProcessState.ExitCode(), nil
 }
 
-// RunProcess runs a process (configured by ProcessConfig) until the context is
-// canceled, at which point the process is killed and RunProcess returns.
+// Process is used to manage a running process. Methods on a Process are _not_
+// thread-safe.
+//
+// Stop must be called on a Process before the program has exited, or there may
+// be a leftover zombie child process.
 //
 // The process will be restarted if it exits of its own accord. There will be a
 // brief wait time between each restart, with an exponential backoff mechanism
@@ -216,50 +215,77 @@ func RunProcessOnce(
 //
 // The stdout and stderr of the process will be written to the corresponding
 // Loggers. Various runtime events will be written to the sysLogger.
-func RunProcess(
-	ctx context.Context,
-	stdoutLogger, stderrLogger, sysLogger Logger,
-	cfg ProcessConfig,
-) {
+type Process struct {
+	cfg                                   ProcessConfig
+	stdoutLogger, stderrLogger, sysLogger Logger
 
-	cfg = cfg.withDefaults()
+	stopFn context.CancelFunc
+	doneCh chan struct{}
+}
 
+// NewProcess returns a new Process instance based on the given config.
+func NewProcess(
+	cfg ProcessConfig, stdoutLogger, stderrLogger, sysLogger Logger,
+) *Process {
+	p := &Process{
+		cfg:          cfg.withDefaults(),
+		stdoutLogger: stdoutLogger,
+		stderrLogger: stderrLogger,
+		sysLogger:    sysLogger,
+	}
+	p.run()
+	return p
+}
+
+func (p *Process) run() {
+	var ctx context.Context
+	ctx, p.stopFn = context.WithCancel(context.Background())
+	p.doneCh = make(chan struct{})
+
+	go func() {
+		defer close(p.doneCh)
+		p.restartLoop(ctx)
+	}()
+}
+
+func (p *Process) restartLoop(ctx context.Context) {
 	var wait time.Duration
 
 	for {
 		start := time.Now()
 		exitCode, err := RunProcessOnce(
 			ctx,
-			stdoutLogger, stderrLogger, sysLogger,
-			cfg,
+			p.stdoutLogger, p.stderrLogger, p.sysLogger,
+			p.cfg,
 		)
 		took := time.Since(start)
 
+		// TODO check if error was due to StartAfterFunc, change the log if so.
 		if err != nil {
-			sysLogger.Printf("exited: %v", err)
+			p.sysLogger.Printf("exited: %v", err)
 		} else {
-			sysLogger.Printf("exit code: %d", exitCode)
+			p.sysLogger.Printf("exit code: %d", exitCode)
 		}
 
 		if err := ctx.Err(); err != nil {
 			return
 		}
 
-		for i := range cfg.NoRestartOn {
-			if cfg.NoRestartOn[i] == exitCode {
+		for i := range p.cfg.NoRestartOn {
+			if p.cfg.NoRestartOn[i] == exitCode {
 				return
 			}
 		}
 
 		wait = ((wait * 2) - took).Truncate(time.Millisecond)
 
-		if wait < cfg.MinWait {
-			wait = cfg.MinWait
-		} else if wait > cfg.MaxWait {
-			wait = cfg.MaxWait
+		if wait < p.cfg.MinWait {
+			wait = p.cfg.MinWait
+		} else if wait > p.cfg.MaxWait {
+			wait = p.cfg.MaxWait
 		}
 
-		sysLogger.Printf("will restart process in %v", wait)
+		p.sysLogger.Printf("will restart process in %v", wait)
 
 		select {
 		case <-time.After(wait):
@@ -268,3 +294,17 @@ func RunProcess(
 		}
 	}
 }
+
+// Restart will block until the currently running child process has been killed
+// and a new one has been spawned.
+func (p *Process) Restart() {
+	p.Stop()
+	p.run()
+}
+
+// Stop will block until the child process has been killed. The Process should
+// not be used again after this.
+func (p *Process) Stop() {
+	p.stopFn()
+	<-p.doneCh
+}