Terminate owned subprocess trees

internal/adapters/subprocess/process_tree.go

@@ -0,0 +1,65 @@
+package subprocess
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"os/exec"
+	"time"
+)
+
+const (
+	gracefulTerminationWait = 2 * time.Second
+	forcefulTerminationWait = 2 * time.Second
+)
+
+// ownedProcessTree owns every process started by a command invocation.
+// Implementations must tolerate a leader that has already exited.
+type ownedProcessTree interface {
+	Start(*exec.Cmd) error
+	TerminateGracefully() error
+	TerminateForcefully() error
+	Close() error
+}
+
+func waitForOwnedCommand(ctx context.Context, tree ownedProcessTree, waitCh <-chan error) (waitErr, ctxErr, cleanupErr error) {
+	select {
+	case waitErr = <-waitCh:
+		return waitErr, nil, nil
+	case <-ctx.Done():
+		ctxErr = ctx.Err()
+	}
+
+	cleanupErr = tree.TerminateGracefully()
+	gracefulTimer := time.NewTimer(gracefulTerminationWait)
+	defer gracefulTimer.Stop()
+
+	select {
+	case waitErr = <-waitCh:
+		// The leader may exit before descendants finish graceful shutdown.
+		cleanupErr = joinErrors(cleanupErr, tree.TerminateForcefully())
+		return waitErr, ctxErr, cleanupErr
+	case <-gracefulTimer.C:
+	}
+
+	cleanupErr = joinErrors(cleanupErr, tree.TerminateForcefully())
+	forcefulTimer := time.NewTimer(forcefulTerminationWait)
+	defer forcefulTimer.Stop()
+
+	select {
+	case waitErr = <-waitCh:
+		return waitErr, ctxErr, cleanupErr
+	case <-forcefulTimer.C:
+		return nil, ctxErr, joinErrors(cleanupErr, fmt.Errorf("owned subprocess did not reap within %s after forceful termination", forcefulTerminationWait))
+	}
+}
+
+func joinErrors(errs ...error) error {
+	filtered := make([]error, 0, len(errs))
+	for _, err := range errs {
+		if err != nil {
+			filtered = append(filtered, err)
+		}
+	}
+	return errors.Join(filtered...)
+}