Dispose subprocess descendants after leader exit

internal/adapters/subprocess/process_tree_unix.go

@@ -4,11 +4,15 @@ package subprocess
 
 import (
 	"errors"
+	"fmt"
 	"os"
 	"os/exec"
 	"syscall"
+	"time"
 )
 
+const processGroupPollInterval = 10 * time.Millisecond
+
 type unixProcessTree struct {
 	processGroupID int
 }
@@ -34,8 +38,26 @@ func (tree *unixProcessTree) TerminateForcefully() error {
 	return tree.signal(syscall.SIGKILL)
 }
 
-func (tree *unixProcessTree) Close() error {
-	return nil
+func (tree *unixProcessTree) Dispose() error {
+	hasMembers, err := tree.hasMembers()
+	if err != nil || !hasMembers {
+		return err
+	}
+
+	cleanupErr := tree.TerminateGracefully()
+	empty, waitErr := tree.waitUntilEmpty(gracefulTerminationWait)
+	cleanupErr = joinErrors(cleanupErr, waitErr)
+	if empty {
+		return cleanupErr
+	}
+
+	cleanupErr = joinErrors(cleanupErr, tree.TerminateForcefully())
+	empty, waitErr = tree.waitUntilEmpty(forcefulTerminationWait)
+	cleanupErr = joinErrors(cleanupErr, waitErr)
+	if !empty {
+		cleanupErr = joinErrors(cleanupErr, fmt.Errorf("owned subprocess group did not exit within %s after forceful termination", forcefulTerminationWait))
+	}
+	return cleanupErr
 }
 
 func (tree *unixProcessTree) signal(signal syscall.Signal) error {
@@ -48,3 +70,35 @@ func (tree *unixProcessTree) signal(signal syscall.Signal) error {
 	}
 	return err
 }
+
+func (tree *unixProcessTree) hasMembers() (bool, error) {
+	if tree.processGroupID <= 0 {
+		return false, nil
+	}
+	err := syscall.Kill(-tree.processGroupID, 0)
+	if err == nil || errors.Is(err, syscall.EPERM) {
+		return true, nil
+	}
+	if errors.Is(err, syscall.ESRCH) || errors.Is(err, os.ErrProcessDone) {
+		return false, nil
+	}
+	return false, fmt.Errorf("inspect owned subprocess group: %w", err)
+}
+
+func (tree *unixProcessTree) waitUntilEmpty(timeout time.Duration) (bool, error) {
+	deadline := time.Now().Add(timeout)
+	for {
+		hasMembers, err := tree.hasMembers()
+		if err != nil || !hasMembers {
+			return !hasMembers, err
+		}
+		remaining := time.Until(deadline)
+		if remaining <= 0 {
+			return false, nil
+		}
+		if remaining > processGroupPollInterval {
+			remaining = processGroupPollInterval
+		}
+		time.Sleep(remaining)
+	}
+}