container: spin instead of block on wait4 ECHILD

Blocking prevents further wait4 processing causing ops to never receive their signals.

Signed-off-by: Ophestra <cat@gensokyo.uk>

container/init.go

@@ -11,6 +11,7 @@ import (
 	"slices"
 	"strconv"
 	"sync"
+	"sync/atomic"
 	. "syscall"
 	"time"
 
@@ -368,8 +369,8 @@ func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 	// when there are no longer any processes left to reap
 	info := make(chan winfo, 1)
 
-	// closed when the initial process has started
-	initialProcessStarted := make(chan struct{})
+	// whether initial process has started
+	var initialProcessStarted atomic.Bool
 
 	k.new(func(k syscallDispatcher) {
 		k.lockOSThread()
@@ -413,11 +414,10 @@ func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 
 		if !errors.Is(err, ECHILD) {
 			k.printf(msg, "unexpected wait4 response: %v", err)
-		} else if initialProcessStarted != nil {
+		} else if !initialProcessStarted.Load() {
 			// initial process has not yet been reached and all daemons
 			// terminated or none were started in the first place
-			<-initialProcessStarted
-			initialProcessStarted = nil
+			time.Sleep(500 * time.Microsecond)
 			goto wait4
 		}
 
@@ -458,7 +458,7 @@ func initEntrypoint(k syscallDispatcher, msg message.Msg) {
 	if err := k.start(cmd); err != nil {
 		k.fatalf(msg, "%v", err)
 	}
-	close(initialProcessStarted)
+	initialProcessStarted.Store(true)
 
 	// handle signals to dump withheld messages
 	sig := make(chan os.Signal, 2)