terraform: early exit and cancellation

terraform/context.go

@@ -32,9 +32,13 @@ type Context2 struct {
 	module       *module.Tree
 	providers    map[string]ResourceProviderFactory
 	provisioners map[string]ResourceProvisionerFactory
+	sh           *stopHook
 	state        *State
 	stateLock    sync.RWMutex
 	variables    map[string]string
+
+	l     sync.Mutex // Lock acquired during any task
+	runCh <-chan struct{}
 }
 
 // NewContext creates a new Context structure.
@@ -43,6 +47,13 @@ type Context2 struct {
 // should not be mutated in any way, since the pointers are copied, not
 // the values themselves.
 func NewContext2(opts *ContextOpts) *Context2 {
+	// Copy all the hooks and add our stop hook. We don't append directly
+	// to the Config so that we're not modifying that in-place.
+	sh := new(stopHook)
+	hooks := make([]Hook, len(opts.Hooks)+1)
+	copy(hooks, opts.Hooks)
+	hooks[len(opts.Hooks)] = sh
+
 	state := opts.State
 	if state == nil {
 		state = new(State)
@@ -51,10 +62,11 @@ func NewContext2(opts *ContextOpts) *Context2 {
 
 	return &Context2{
 		diff:         opts.Diff,
-		hooks:        opts.Hooks,
+		hooks:        hooks,
 		module:       opts.Module,
 		providers:    opts.Providers,
 		provisioners: opts.Provisioners,
+		sh:           sh,
 		state:        state,
 		variables:    opts.Variables,
 	}
@@ -88,6 +100,9 @@ func (c *Context2) GraphBuilder() GraphBuilder {
 // In addition to returning the resulting state, this context is updated
 // with the latest state.
 func (c *Context2) Apply() (*State, error) {
+	v := c.acquireRun()
+	defer c.releaseRun(v)
+
 	// Copy our own state
 	c.state = c.state.deepcopy()
 
@@ -108,6 +123,9 @@ func (c *Context2) Apply() (*State, error) {
 // Plan also updates the diff of this context to be the diff generated
 // by the plan, so Apply can be called after.
 func (c *Context2) Plan(opts *PlanOpts) (*Plan, error) {
+	v := c.acquireRun()
+	defer c.releaseRun(v)
+
 	p := &Plan{
 		Module: c.module,
 		Vars:   c.variables,
@@ -157,6 +175,9 @@ func (c *Context2) Plan(opts *PlanOpts) (*Plan, error) {
 // Even in the case an error is returned, the state will be returned and
 // will potentially be partially updated.
 func (c *Context2) Refresh() (*State, []error) {
+	v := c.acquireRun()
+	defer c.releaseRun(v)
+
 	// Copy our own state
 	c.state = c.state.deepcopy()
 
@@ -172,8 +193,32 @@ func (c *Context2) Refresh() (*State, []error) {
 	return c.state, nil
 }
 
+// Stop stops the running task.
+//
+// Stop will block until the task completes.
+func (c *Context2) Stop() {
+	c.l.Lock()
+	ch := c.runCh
+
+	// If we aren't running, then just return
+	if ch == nil {
+		c.l.Unlock()
+		return
+	}
+
+	// Tell the hook we want to stop
+	c.sh.Stop()
+
+	// Wait for us to stop
+	c.l.Unlock()
+	<-ch
+}
+
 // Validate validates the configuration and returns any warnings or errors.
 func (c *Context2) Validate() ([]string, []error) {
+	v := c.acquireRun()
+	defer c.releaseRun(v)
+
 	var errs error
 
 	// Validate the configuration itself
@@ -201,6 +246,32 @@ func (c *Context2) Validate() ([]string, []error) {
 	return walker.ValidationWarnings, rerrs.Errors
 }
 
+func (c *Context2) acquireRun() chan<- struct{} {
+	c.l.Lock()
+	defer c.l.Unlock()
+
+	// Wait for no channel to exist
+	for c.runCh != nil {
+		c.l.Unlock()
+		ch := c.runCh
+		<-ch
+		c.l.Lock()
+	}
+
+	ch := make(chan struct{})
+	c.runCh = ch
+	return ch
+}
+
+func (c *Context2) releaseRun(ch chan<- struct{}) {
+	c.l.Lock()
+	defer c.l.Unlock()
+
+	close(ch)
+	c.runCh = nil
+	c.sh.Reset()
+}
+
 func (c *Context2) walk(operation walkOperation) (*ContextGraphWalker, error) {
 	// Build the graph
 	graph, err := c.GraphBuilder().Build(RootModulePath)

terraform/context_test.go

@@ -2846,13 +2846,12 @@ func TestContext2Apply_badDiff(t *testing.T) {
 	}
 }
 
-/*
-func TestContextApply_cancel(t *testing.T) {
+func TestContext2Apply_cancel(t *testing.T) {
 	stopped := false
 
 	m := testModule(t, "apply-cancel")
 	p := testProvider("aws")
-	ctx := testContext(t, &ContextOpts{
+	ctx := testContext2(t, &ContextOpts{
 		Module: m,
 		Providers: map[string]ResourceProviderFactory{
 			"aws": testProviderFuncFixed(p),
@@ -2907,7 +2906,7 @@ func TestContextApply_cancel(t *testing.T) {
 
 	mod := state.RootModule()
 	if len(mod.Resources) != 1 {
-		t.Fatalf("bad: %#v", mod.Resources)
+		t.Fatalf("bad: %s", state.String())
 	}
 
 	actual := strings.TrimSpace(state.String())
@@ -2916,7 +2915,6 @@ func TestContextApply_cancel(t *testing.T) {
 		t.Fatalf("bad: \n%s", actual)
 	}
 }
-*/
 
 func TestContext2Apply_compute(t *testing.T) {
 	m := testModule(t, "apply-compute")

terraform/eval.go

@@ -36,10 +36,23 @@ func (EvalEarlyExitError) Error() string { return "early exit" }
 // Eval evaluates the given EvalNode with the given context, properly
 // evaluating all args in the correct order.
 func Eval(n EvalNode, ctx EvalContext) (interface{}, error) {
+	// Call the lower level eval which doesn't understand early exit,
+	// and if we early exit, it isn't an error.
+	result, err := eval(n, ctx)
+	if err != nil {
+		if _, ok := err.(EvalEarlyExitError); ok {
+			return nil, nil
+		}
+	}
+
+	return result, err
+}
+
+func eval(n EvalNode, ctx EvalContext) (interface{}, error) {
 	argNodes, _ := n.Args()
 	args := make([]interface{}, len(argNodes))
 	for i, n := range argNodes {
-		v, err := Eval(n, ctx)
+		v, err := eval(n, ctx)
 		if err != nil {
 			return nil, err
 		}

terraform/eval_apply.go

@@ -43,7 +43,7 @@ func (n *EvalApply) Eval(
 		}
 	}
 
-	/*
+	{
 		// Call pre-apply hook
 		err := ctx.Hook(func(h Hook) (HookAction, error) {
 			return h.PreApply(n.Info, state, diff)
@@ -51,7 +51,7 @@ func (n *EvalApply) Eval(
 		if err != nil {
 			return nil, err
 		}
-	*/
+	}
 
 	// With the completed diff, apply!
 	log.Printf("[DEBUG] apply: %s: executing Apply", n.Info.Id)

terraform/eval_context_builtin.go

@@ -2,6 +2,7 @@ package terraform
 
 import (
 	"fmt"
+	"log"
 	"sync"
 
 	"github.com/hashicorp/terraform/config"
@@ -40,6 +41,7 @@ func (ctx *BuiltinEvalContext) Hook(fn func(Hook) (HookAction, error)) error {
 			continue
 		case HookActionHalt:
 			// Return an early exit error to trigger an early exit
+			log.Printf("[WARN] Early exit triggered by hook: %T", h)
 			return EvalEarlyExitError{}
 		}
 	}