[supervisor] fixes not recycle zombie processes

Co-authored-by: Christian Weichel <chris@gitpod.io>

Author: iQQBot

components/supervisor/pkg/supervisor/supervisor.go

@@ -500,39 +500,37 @@ func reaper(terminatingReaper <-chan bool) {
 case terminating = <-terminatingReaper:
 continue
 }
-
-// wait on the process, hence remove it from the process table
-pid, err := unix.Wait4(-1, nil, 0, nil)
-// if we've been interrupted, try again until we're done
-for err == syscall.EINTR {
-pid, err = unix.Wait4(-1, nil, 0, nil)
-}
-if err == unix.ECHILD {
-// The calling process does not have any unwaited-for children.
-// Not really an error for us
-err = nil
-}
-if err != nil {
-log.WithField("pid", pid).WithError(err).Debug("cannot call waitpid() for re-parented child")
-}
-
-if !terminating {
-continue
-}
-proc, err := os.FindProcess(pid)
-if err != nil {
-log.WithField("pid", pid).WithError(err).Debug("cannot find re-parented process")
-continue
-}
-err = proc.Signal(syscall.SIGTERM)
-if err != nil {
-if !strings.Contains(err.Error(), "os: process already finished") {
-log.WithField("pid", pid).WithError(err).Debug("cannot send SIGTERM to re-parented process")
+for {
+// wait on the process, hence remove it from the process table
+pid, err := unix.Wait4(-1, nil, 0, nil)
+// if we've been interrupted, try again until we're done
+for err == syscall.EINTR {
+pid, err = unix.Wait4(-1, nil, 0, nil)
 }
-
-continue
+// The calling process does not have any unwaited-for children. Let's wait for a SIGCHLD notification.
+if err == unix.ECHILD {
+break
+}
+if err != nil {
+log.WithField("pid", pid).WithError(err).Debug("cannot call waitpid() for re-parented child")
+}
+if !terminating {
+continue
+}
+proc, err := os.FindProcess(pid)
+if err != nil {
+log.WithField("pid", pid).WithError(err).Debug("cannot find re-parented process")
+continue
+}
+err = proc.Signal(syscall.SIGTERM)
+if err != nil {
+if !strings.Contains(err.Error(), "os: process already finished") {
+log.WithField("pid", pid).WithError(err).Debug("cannot send SIGTERM to re-parented process")
+}
+continue
+}
+log.WithField("pid", pid).Debug("SIGTERM'ed reparented child process")
 }
-log.WithField("pid", pid).Debug("SIGTERM'ed reparented child process")
 }
 }