diachron/master/runexpress.go

package main

import (
	"fmt"
	"io"
	"log"
	"os"
	"os/exec"
	"sync"
	"syscall"
	"time"
)

// worker tracks the state of a single express worker process
type worker struct {
	port     int
	addr     string
	cmd      *exec.Cmd
	stopping bool
	mu       sync.Mutex
}

func runExpress(changes <-chan FileChange, numProcesses int, basePort int, pool *WorkerPool) {
	var currentWorkers []*worker
	var mu sync.Mutex

	// Helper to start a worker and monitor it for crashes
	startWorker := func(port int) *worker {
		w := &worker{
			port: port,
			addr: fmt.Sprintf("127.0.0.1:%d", port),
		}

		// start spawns the worker process. Caller must NOT hold w.mu.
		start := func() bool {
			cmd := exec.Command("../backend/run.sh", "--listen", w.addr)
			cmd.Stdout = os.Stdout
			cmd.Stderr = os.Stderr

			if err := cmd.Start(); err != nil {
				log.Printf("[express:%d] Failed to start: %v", port, err)
				return false
			}

			w.mu.Lock()
			w.cmd = cmd
			w.mu.Unlock()

			log.Printf("[express:%d] Started (pid %d)", port, cmd.Process.Pid)
			return true
		}

		if !start() {
			return nil
		}

		// Monitor and restart on crash
		go func() {
			for {
				w.mu.Lock()
				currentCmd := w.cmd
				stopping := w.stopping
				w.mu.Unlock()

				if stopping {
					return
				}

				if currentCmd == nil {
					time.Sleep(time.Second)
					w.mu.Lock()
					if w.stopping {
						w.mu.Unlock()
						return
					}
					w.mu.Unlock()

					if start() {
						pool.AddWorker(w.addr)
					}
					continue
				}

				err := currentCmd.Wait()

				w.mu.Lock()
				if w.stopping {
					w.mu.Unlock()
					return
				}
				w.cmd = nil
				w.mu.Unlock()

				// Worker crashed - remove from pool and restart
				pool.RemoveWorker(w.addr)

				if err != nil {
					log.Printf("[express:%d] Process crashed: %v, restarting...", w.port, err)
				} else {
					log.Printf("[express:%d] Process exited unexpectedly, restarting...", w.port)
				}

				time.Sleep(time.Second)

				w.mu.Lock()
				if w.stopping {
					w.mu.Unlock()
					return
				}
				w.mu.Unlock()

				if start() {
					pool.AddWorker(w.addr)
				}
				// If start failed, cmd is still nil and next iteration will retry
			}
		}()

		return w
	}

	// Helper to stop a worker (for intentional shutdown)
	stopWorker := func(w *worker) {
		if w == nil {
			return
		}

		w.mu.Lock()
		w.stopping = true
		cmd := w.cmd
		w.mu.Unlock()

		if cmd == nil || cmd.Process == nil {
			return
		}

		pid := cmd.Process.Pid
		log.Printf("[express:%d] Stopping (pid %d)", w.port, pid)
		cmd.Process.Signal(syscall.SIGTERM)

		// Wait briefly for graceful shutdown
		done := make(chan struct{})
		go func() {
			cmd.Wait()
			close(done)
		}()

		select {
		case <-done:
			log.Printf("[express:%d] Stopped gracefully (pid %d)", w.port, pid)
		case <-time.After(5 * time.Second):
			log.Printf("[express:%d] Force killing (pid %d)", w.port, pid)
			cmd.Process.Kill()
		}
	}

	// Helper to stop all workers
	stopAllWorkers := func(workers []*worker) {
		for _, w := range workers {
			stopWorker(w)
		}
	}

	// Helper to start all workers and update the worker pool
	startAllWorkers := func() []*worker {
		workers := make([]*worker, 0, numProcesses)
		addresses := make([]string, 0, numProcesses)
		for i := 0; i < numProcesses; i++ {
			port := basePort + i
			w := startWorker(port)
			if w != nil {
				workers = append(workers, w)
				addresses = append(addresses, w.addr)
			}
		}
		// Update the worker pool with new worker addresses
		pool.SetWorkers(addresses)
		return workers
	}

	// Helper to run the build
	runBuild := func() bool {
		log.Printf("[build] Starting ncc build...")

		cmd := exec.Command("../backend/build.sh")

		stdout, _ := cmd.StdoutPipe()
		stderr, _ := cmd.StderrPipe()

		if err := cmd.Start(); err != nil {
			log.Printf("[build] Failed to start: %v", err)
			return false
		}

		// Copy output
		go io.Copy(os.Stdout, stdout)
		go io.Copy(os.Stderr, stderr)

		err := cmd.Wait()
		if err != nil {
			log.Printf("[build] Failed: %v", err)
			return false
		}

		log.Printf("[build] Success")
		return true
	}

	// Debounce timer
	var debounceTimer *time.Timer
	const debounceDelay = 100 * time.Millisecond

	// Initial build and start
	log.Printf("[master] Initial build...")
	if runBuild() {
		currentWorkers = startAllWorkers()
	} else {
		log.Printf("[master] Initial build failed")
	}

	for change := range changes {
		log.Printf("[watch] %s: %s", change.Operation, change.Path)

		// Reset debounce timer
		if debounceTimer != nil {
			debounceTimer.Stop()
		}

		debounceTimer = time.AfterFunc(debounceDelay, func() {
			if !runBuild() {
				log.Printf("[master] Build failed, keeping current workers")
				return
			}

			mu.Lock()
			defer mu.Unlock()

			// Stop all old workers (this sets stopping=true to prevent auto-restart)
			stopAllWorkers(currentWorkers)

			// Start all new workers
			currentWorkers = startAllWorkers()
		})
	}
}