Add procesStates for shim processes

Use the state pattern to handle process transitions from one state to
another and what actions can be performed on a process in a specific
state.

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

linux/shim/exec_state.go

@@ -0,0 +1,166 @@
+// +build !windows
+
+package shim
+
+import (
+	"context"
+
+	"github.com/containerd/console"
+	"github.com/pkg/errors"
+)
+
+type execCreatedState struct {
+	p *execProcess
+}
+
+func (s *execCreatedState) transition(name string) error {
+	switch name {
+	case "running":
+		s.p.processState = &execRunningState{p: s.p}
+	case "stopped":
+		s.p.processState = &execStoppedState{p: s.p}
+	case "deleted":
+		s.p.processState = &deletedState{}
+	default:
+		return errors.Errorf("invalid state transition %q to %q", stateName(s), name)
+	}
+	return nil
+}
+
+func (s *execCreatedState) Resize(ws console.WinSize) error {
+	s.p.mu.Lock()
+	defer s.p.mu.Unlock()
+
+	return s.p.resize(ws)
+}
+
+func (s *execCreatedState) Start(ctx context.Context) error {
+	s.p.mu.Lock()
+	defer s.p.mu.Unlock()
+	if err := s.p.start(ctx); err != nil {
+		return err
+	}
+	return s.transition("running")
+}
+
+func (s *execCreatedState) Delete(ctx context.Context) error {
+	s.p.mu.Lock()
+	defer s.p.mu.Unlock()
+	return s.transition("deleted")
+}
+
+func (s *execCreatedState) Kill(ctx context.Context, sig uint32, all bool) error {
+	s.p.mu.Lock()
+	defer s.p.mu.Unlock()
+
+	return s.p.kill(ctx, sig, all)
+}
+
+func (s *execCreatedState) SetExited(status int) {
+	s.p.mu.Lock()
+	defer s.p.mu.Unlock()
+
+	s.p.setExited(status)
+
+	if err := s.transition("stopped"); err != nil {
+		panic(err)
+	}
+}
+
+type execRunningState struct {
+	p *execProcess
+}
+
+func (s *execRunningState) transition(name string) error {
+	switch name {
+	case "stopped":
+		s.p.processState = &execStoppedState{p: s.p}
+	default:
+		return errors.Errorf("invalid state transition %q to %q", stateName(s), name)
+	}
+	return nil
+}
+
+func (s *execRunningState) Resize(ws console.WinSize) error {
+	s.p.mu.Lock()
+	defer s.p.mu.Unlock()
+
+	return s.p.resize(ws)
+}
+
+func (s *execRunningState) Start(ctx context.Context) error {
+	s.p.mu.Lock()
+	defer s.p.mu.Unlock()
+
+	return errors.Errorf("cannot start a running process")
+}
+
+func (s *execRunningState) Delete(ctx context.Context) error {
+	s.p.mu.Lock()
+	defer s.p.mu.Unlock()
+
+	return errors.Errorf("cannot delete a running process")
+}
+
+func (s *execRunningState) Kill(ctx context.Context, sig uint32, all bool) error {
+	s.p.mu.Lock()
+	defer s.p.mu.Unlock()
+
+	return s.p.kill(ctx, sig, all)
+}
+
+func (s *execRunningState) SetExited(status int) {
+	s.p.mu.Lock()
+	defer s.p.mu.Unlock()
+
+	s.p.setExited(status)
+
+	if err := s.transition("stopped"); err != nil {
+		panic(err)
+	}
+}
+
+type execStoppedState struct {
+	p *execProcess
+}
+
+func (s *execStoppedState) transition(name string) error {
+	switch name {
+	case "deleted":
+		s.p.processState = &deletedState{}
+	default:
+		return errors.Errorf("invalid state transition %q to %q", stateName(s), name)
+	}
+	return nil
+}
+
+func (s *execStoppedState) Resize(ws console.WinSize) error {
+	s.p.mu.Lock()
+	defer s.p.mu.Unlock()
+
+	return errors.Errorf("cannot resize a stopped container")
+}
+
+func (s *execStoppedState) Start(ctx context.Context) error {
+	s.p.mu.Lock()
+	defer s.p.mu.Unlock()
+
+	return errors.Errorf("cannot start a stopped process")
+}
+
+func (s *execStoppedState) Delete(ctx context.Context) error {
+	s.p.mu.Lock()
+	defer s.p.mu.Unlock()
+	return s.transition("deleted")
+}
+
+func (s *execStoppedState) Kill(ctx context.Context, sig uint32, all bool) error {
+	s.p.mu.Lock()
+	defer s.p.mu.Unlock()
+
+	return s.p.kill(ctx, sig, all)
+}
+
+func (s *execStoppedState) SetExited(status int) {
+	// no op
+}