internal_workflow.go

// Copyright (c) 2017 Uber Technologies, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

package internal

// All code in this file is private to the package.

import (
	"errors"
	"fmt"
	"reflect"
	"runtime"
	"strings"
	"sync"
	"time"
	"unicode"

	"go.uber.org/atomic"
	"go.uber.org/cadence/.gen/go/shared"
	"go.uber.org/cadence/encoded"
	"go.uber.org/cadence/internal/common"
	"go.uber.org/cadence/internal/common/metrics"
	"go.uber.org/zap"
)

const (
	defaultSignalChannelSize = 100000 // really large buffering size(100K)

	panicIllegalAccessCoroutinueState = "getState: illegal access from outside of workflow context"
)

type (
	syncWorkflowDefinition struct {
		workflow   workflow
		dispatcher dispatcher
		cancel     CancelFunc
		rootCtx    Context
	}

	workflowResult struct {
		workflowResult []byte
		error          error
	}

	futureImpl struct {
		value   interface{}
		err     error
		ready   bool
		channel *channelImpl
		chained []asyncFuture // Futures that are chained to this one
	}

	// Dispatcher is a container of a set of coroutines.
	dispatcher interface {
		// ExecuteUntilAllBlocked executes coroutines one by one in deterministic order
		// until all of them are completed or blocked on Channel or Selector
		ExecuteUntilAllBlocked() (err *PanicError)
		// IsDone returns true when all of coroutines are completed
		IsDone() bool
		Close()             // Destroys all coroutines without waiting for their completion
		StackTrace() string // Stack trace of all coroutines owned by the Dispatcher instance
	}

	// Workflow is an interface that any workflow should implement.
	// Code of a workflow must be deterministic. It must use workflow.Channel, workflow.Selector, and workflow.Go instead of
	// native channels, select and go. It also must not use range operation over map as it is randomized by go runtime.
	// All time manipulation should use current time returned by GetTime(ctx) method.
	// Note that workflow.Context is used instead of context.Context to avoid use of raw channels.
	workflow interface {
		Execute(ctx Context, input []byte) (result []byte, err error)
	}

	sendCallback struct {
		value interface{}
		fn    func() bool // false indicates that callback didn't accept the value
	}

	receiveCallback struct {
		// false result means that callback didn't accept the value and it is still up for delivery
		fn func(v interface{}, more bool) bool
	}

	channelImpl struct {
		name            string                // human readable channel name
		size            int                   // Channel buffer size. 0 for non buffered.
		buffer          []interface{}         // buffered messages
		blockedSends    []*sendCallback       // puts waiting when buffer is full.
		blockedReceives []*receiveCallback    // receives waiting when no messages are available.
		closed          bool                  // true if channel is closed.
		recValue        *interface{}          // Used only while receiving value, this is used as pre-fetch buffer value from the channel.
		dataConverter   encoded.DataConverter // for decode data
	}

	// Single case statement of the Select
	selectCase struct {
		channel     *channelImpl                // Channel of this case.
		receiveFunc *func(c Channel, more bool) // function to call when channel has a message. nil for send case.

		sendFunc   *func()         // function to call when channel accepted a message. nil for receive case.
		sendValue  *interface{}    // value to send to the channel. Used only for send case.
		future     asyncFuture     // Used for future case
		futureFunc *func(f Future) // function to call when Future is ready
	}

	// Implements Selector interface
	selectorImpl struct {
		name        string
		cases       []*selectCase // cases that this select is comprised from
		defaultFunc *func()       // default case
	}

	// unblockFunc is passed evaluated by a coroutine yield. When it returns false the yield returns to a caller.
	// stackDepth is the depth of stack from the last blocking call relevant to user.
	// Used to truncate internal stack frames from thread stack.
	unblockFunc func(status string, stackDepth int) (keepBlocked bool)

	coroutineState struct {
		name         string
		dispatcher   *dispatcherImpl  // dispatcher this context belongs to
		aboutToBlock chan bool        // used to notify dispatcher that coroutine that owns this context is about to block
		unblock      chan unblockFunc // used to notify coroutine that it should continue executing.
		keptBlocked  bool             // true indicates that coroutine didn't make any progress since the last yield unblocking
		closed       bool             // indicates that owning coroutine has finished execution
		blocked      atomic.Bool
		panicError   *PanicError // non nil if coroutine had unhandled panic
	}

	dispatcherImpl struct {
		sequence         int
		channelSequence  int // used to name channels
		selectorSequence int // used to name channels
		coroutines       []*coroutineState
		executing        bool       // currently running ExecuteUntilAllBlocked. Used to avoid recursive calls to it.
		mutex            sync.Mutex // used to synchronize executing
		closed           bool
	}

	// The current timeout resolution implementation is in seconds and uses math.Ceil() as the duration. But is
	// subjected to change in the future.
	workflowOptions struct {
		taskListName                        *string
		executionStartToCloseTimeoutSeconds *int32
		taskStartToCloseTimeoutSeconds      *int32
		domain                              *string
		workflowID                          string
		childPolicy                         ChildWorkflowPolicy
		waitForCancellation                 bool
		signalChannels                      map[string]Channel
		queryHandlers                       map[string]func([]byte) ([]byte, error)
		workflowIDReusePolicy               WorkflowIDReusePolicy
		dataConverter                       encoded.DataConverter
	}

	executeWorkflowParams struct {
		workflowOptions
		workflowType *WorkflowType
		input        []byte
	}

	// decodeFutureImpl
	decodeFutureImpl struct {
		*futureImpl
		fn interface{}
	}

	childWorkflowFutureImpl struct {
		*decodeFutureImpl             // for child workflow result
		executionFuture   *futureImpl // for child workflow execution future
	}

	asyncFuture interface {
		Future
		// Used by selectorImpl
		// If Future is ready returns its value immediately.
		// If not registers callback which is called when it is ready.
		GetAsync(callback *receiveCallback) (v interface{}, ok bool, err error)

		// Used by selectorImpl
		RemoveReceiveCallback(callback *receiveCallback)

		// This future will added to list of dependency futures.
		ChainFuture(f Future)

		// Gets the current value and error.
		// Make sure this is called once the future is ready.
		GetValueAndError() (v interface{}, err error)

		Set(value interface{}, err error)
	}

	queryHandler struct {
		fn            interface{}
		queryType     string
		dataConverter encoded.DataConverter
	}
)

const (
	workflowEnvironmentContextKey = "workflowEnv"
	workflowResultContextKey      = "workflowResult"
	coroutinesContextKey          = "coroutines"
	workflowEnvOptionsContextKey  = "wfEnvOptions"
)

// Assert that structs do indeed implement the interfaces
var _ Channel = (*channelImpl)(nil)
var _ Selector = (*selectorImpl)(nil)
var _ dispatcher = (*dispatcherImpl)(nil)

var stackBuf [100000]byte

// Pointer to pointer to workflow result
func getWorkflowResultPointerPointer(ctx Context) **workflowResult {
	rpp := ctx.Value(workflowResultContextKey)
	if rpp == nil {
		panic("getWorkflowResultPointerPointer: Not a workflow context")
	}
	return rpp.(**workflowResult)
}

func getWorkflowEnvironment(ctx Context) workflowEnvironment {
	wc := ctx.Value(workflowEnvironmentContextKey)
	if wc == nil {
		panic("getWorkflowContext: Not a workflow context")
	}
	return wc.(workflowEnvironment)
}

func (f *futureImpl) Get(ctx Context, value interface{}) error {
	more := f.channel.Receive(ctx, nil)
	if more {
		panic("not closed")
	}
	if !f.ready {
		panic("not ready")
	}
	if f.err != nil || f.value == nil || value == nil {
		return f.err
	}
	rf := reflect.ValueOf(value)
	if rf.Type().Kind() != reflect.Ptr {
		return errors.New("value parameter is not a pointer")
	}
	fv := reflect.ValueOf(f.value)
	if fv.IsValid() {
		rf.Elem().Set(fv)
	}
	return f.err
}

// Used by selectorImpl
// If Future is ready returns its value immediately.
// If not registers callback which is called when it is ready.
func (f *futureImpl) GetAsync(callback *receiveCallback) (v interface{}, ok bool, err error) {
	_, _, more := f.channel.receiveAsyncImpl(callback)
	// Future uses Channel.Close to indicate that it is ready.
	// So more being true (channel is still open) indicates future is not ready.
	if more {
		return nil, false, nil
	}
	if !f.ready {
		panic("not ready")
	}
	return f.value, true, f.err
}

// RemoveReceiveCallback removes the callback from future's channel to avoid closure leak.
// Used by selectorImpl
func (f *futureImpl) RemoveReceiveCallback(callback *receiveCallback) {
	f.channel.removeReceiveCallback(callback)
}

func (f *futureImpl) IsReady() bool {
	return f.ready
}

func (f *futureImpl) Set(value interface{}, err error) {
	if f.ready {
		panic("already set")
	}
	f.value = value
	f.err = err
	f.ready = true
	f.channel.Close()
	for _, ch := range f.chained {
		ch.Set(f.value, f.err)
	}
}

func (f *futureImpl) SetValue(value interface{}) {
	if f.ready {
		panic("already set")
	}
	f.Set(value, nil)
}

func (f *futureImpl) SetError(err error) {
	if f.ready {
		panic("already set")
	}
	f.Set(nil, err)
}

func (f *futureImpl) Chain(future Future) {
	if f.ready {
		panic("already set")
	}

	ch, ok := future.(asyncFuture)
	if !ok {
		panic("cannot chain Future that wasn't created with workflow.NewFuture")
	}
	if !ch.IsReady() {
		ch.ChainFuture(f)
		return
	}
	val, err := ch.GetValueAndError()
	f.value = val
	f.err = err
	f.ready = true
	return
}

func (f *futureImpl) ChainFuture(future Future) {
	f.chained = append(f.chained, future.(asyncFuture))
}

func (f *futureImpl) GetValueAndError() (interface{}, error) {
	return f.value, f.err
}

func (f *childWorkflowFutureImpl) GetChildWorkflowExecution() Future {
	return f.executionFuture
}

func (f *childWorkflowFutureImpl) SignalChildWorkflow(ctx Context, signalName string, data interface{}) Future {
	var childExec WorkflowExecution
	if err := f.GetChildWorkflowExecution().Get(ctx, &childExec); err != nil {
		return f.GetChildWorkflowExecution()
	}

	childWorkflowOnly := true // this means we are targeting child workflow
	// below we use empty run ID indicating the current running one, in case child do continue-as-new
	return signalExternalWorkflow(ctx, childExec.ID, "", signalName, data, childWorkflowOnly)
}

func newWorkflowContext(env workflowEnvironment) Context {
	rootCtx := WithValue(background, workflowEnvironmentContextKey, env)
	var resultPtr *workflowResult
	rootCtx = WithValue(rootCtx, workflowResultContextKey, &resultPtr)

	// Set default values for the workflow execution.
	wInfo := env.WorkflowInfo()
	rootCtx = WithWorkflowDomain(rootCtx, wInfo.Domain)
	rootCtx = WithWorkflowTaskList(rootCtx, wInfo.TaskListName)
	rootCtx = WithExecutionStartToCloseTimeout(rootCtx, time.Duration(wInfo.ExecutionStartToCloseTimeoutSeconds)*time.Second)
	rootCtx = WithWorkflowTaskStartToCloseTimeout(rootCtx, time.Duration(wInfo.TaskStartToCloseTimeoutSeconds)*time.Second)
	rootCtx = WithTaskList(rootCtx, wInfo.TaskListName)
	rootCtx = WithDataConverter(rootCtx, env.GetDataConverter())
	getActivityOptions(rootCtx).OriginalTaskListName = wInfo.TaskListName

	return rootCtx
}

func (d *syncWorkflowDefinition) Execute(env workflowEnvironment, input []byte) {
	dispatcher, rootCtx := newDispatcher(newWorkflowContext(env), func(ctx Context) {
		r := &workflowResult{}

		// We want to execute the user workflow definition from the first decision task started,
		// so they can see everything before that. Here we would have all initialization done, hence
		// we are yielding.
		state := getState(d.rootCtx)
		state.yield("yield before executing to setup state")

		r.workflowResult, r.error = d.workflow.Execute(d.rootCtx, input)
		rpp := getWorkflowResultPointerPointer(ctx)
		*rpp = r
	})
	d.rootCtx, d.cancel = WithCancel(rootCtx)
	d.dispatcher = dispatcher

	getWorkflowEnvironment(d.rootCtx).RegisterCancelHandler(func() {
		// It is ok to call this method multiple times.
		// it doesn't do anything new, the context remains cancelled.
		d.cancel()
	})

	getWorkflowEnvironment(d.rootCtx).RegisterSignalHandler(func(name string, result []byte) {
		eo := getWorkflowEnvOptions(d.rootCtx)
		// We don't want this code to be blocked ever, using sendAsync().
		ch := eo.getSignalChannel(d.rootCtx, name).(*channelImpl)
		ok := ch.SendAsync(result)
		if !ok {
			panic(fmt.Sprintf("Exceeded channel buffer size for signal: %v", name))
		}
	})

	getWorkflowEnvironment(d.rootCtx).RegisterQueryHandler(func(queryType string, queryArgs []byte) ([]byte, error) {
		eo := getWorkflowEnvOptions(d.rootCtx)
		handler, ok := eo.queryHandlers[queryType]
		if !ok {
			keys := []string{QueryTypeStackTrace}
			for k := range eo.queryHandlers {
				keys = append(keys, k)
			}
			return nil, fmt.Errorf("unknown queryType %v. KnownQueryTypes=%v", queryType, keys)
		}
		return handler(queryArgs)
	})
}

func (d *syncWorkflowDefinition) OnDecisionTaskStarted() {
	executeDispatcher(d.rootCtx, d.dispatcher)
}

func (d *syncWorkflowDefinition) StackTrace() string {
	return d.dispatcher.StackTrace()
}

func (d *syncWorkflowDefinition) Close() {
	if d.dispatcher != nil {
		d.dispatcher.Close()
	}
}

// NewDispatcher creates a new Dispatcher instance with a root coroutine function.
// Context passed to the root function is child of the passed rootCtx.
// This way rootCtx can be used to pass values to the coroutine code.
func newDispatcher(rootCtx Context, root func(ctx Context)) (*dispatcherImpl, Context) {
	result := &dispatcherImpl{}
	ctxWithState := result.newCoroutine(rootCtx, root)
	return result, ctxWithState
}

// executeDispatcher executed coroutines in the calling thread and calls workflow completion callbacks
// if root workflow function returned
func executeDispatcher(ctx Context, dispatcher dispatcher) {
	env := getWorkflowEnvironment(ctx)
	panicErr := dispatcher.ExecuteUntilAllBlocked()
	if panicErr != nil {
		env.Complete(nil, panicErr)
		return
	}

	rp := *getWorkflowResultPointerPointer(ctx)
	if rp == nil {
		// Result is not set, so workflow is still executing
		return
	}

	us := getWorkflowEnvOptions(ctx).getUnhandledSignals()
	if len(us) > 0 {
		env.GetLogger().Info("Workflow has unhandled signals", zap.Strings("SignalNames", us))
		env.GetMetricsScope().Counter(metrics.UnhandledSignalsCounter).Inc(1)
	}

	env.Complete(rp.workflowResult, rp.error)
}

// For troubleshooting stack pretty printing only.
// Set to true to see full stack trace that includes framework methods.
const disableCleanStackTraces = false

func getState(ctx Context) *coroutineState {
	s := ctx.Value(coroutinesContextKey)
	if s == nil {
		panic("getState: not workflow context")
	}
	state := s.(*coroutineState)
	if !state.dispatcher.executing {
		panic(panicIllegalAccessCoroutinueState)
	}
	return state
}

func (c *channelImpl) Receive(ctx Context, valuePtr interface{}) (more bool) {
	state := getState(ctx)
	hasResult := false
	var result interface{}
	callback := &receiveCallback{
		fn: func(v interface{}, m bool) bool {
			result = v
			hasResult = true
			more = m
			return true
		},
	}
	v, ok, more := c.receiveAsyncImpl(callback)
	if ok || !more {
		c.assignValue(v, valuePtr)
		return more
	}
	for {
		if hasResult {
			state.unblocked()
			c.assignValue(result, valuePtr)
			return more
		}
		state.yield(fmt.Sprintf("blocked on %s.Receive", c.name))
	}
}

func (c *channelImpl) ReceiveAsync(valuePtr interface{}) (ok bool) {
	ok, _ = c.ReceiveAsyncWithMoreFlag(valuePtr)
	return ok
}

func (c *channelImpl) ReceiveAsyncWithMoreFlag(valuePtr interface{}) (ok bool, more bool) {
	v, ok, more := c.receiveAsyncImpl(nil)
	c.assignValue(v, valuePtr)
	return ok, more
}

// ok = true means that value was received
// more = true means that channel is not closed and more deliveries are possible
func (c *channelImpl) receiveAsyncImpl(callback *receiveCallback) (v interface{}, ok bool, more bool) {
	if c.recValue != nil {
		r := *c.recValue
		c.recValue = nil
		return r, true, true
	}
	if len(c.buffer) > 0 {
		r := c.buffer[0]
		c.buffer[0] = nil
		c.buffer = c.buffer[1:]
		return r, true, true
	}
	if c.closed {
		return nil, false, false
	}
	for len(c.blockedSends) > 0 {
		b := c.blockedSends[0]
		c.blockedSends[0] = nil
		c.blockedSends = c.blockedSends[1:]
		if b.fn() {
			return b.value, true, true
		}
	}
	if callback != nil {
		c.blockedReceives = append(c.blockedReceives, callback)
	}
	return nil, false, true
}

func (c *channelImpl) removeReceiveCallback(callback *receiveCallback) {
	for i, blockedCallback := range c.blockedReceives {
		if callback == blockedCallback {
			c.blockedReceives = append(c.blockedReceives[:i], c.blockedReceives[i+1:]...)
			break
		}
	}
}

func (c *channelImpl) removeSendCallback(callback *sendCallback) {
	for i, blockedCallback := range c.blockedSends {
		if callback == blockedCallback {
			c.blockedSends = append(c.blockedSends[:i], c.blockedSends[i+1:]...)
			break
		}
	}
}

func (c *channelImpl) Send(ctx Context, v interface{}) {
	state := getState(ctx)
	valueConsumed := false
	callback := &sendCallback{
		value: v,
		fn: func() bool {
			valueConsumed = true
			return true
		},
	}
	ok := c.sendAsyncImpl(v, callback)
	if ok {
		state.unblocked()
		return
	}
	for {
		// Check for closed in the loop as close can be called when send is blocked
		if c.closed {
			panic("Closed channel")
		}
		if valueConsumed {
			state.unblocked()
			return
		}
		state.yield(fmt.Sprintf("blocked on %s.Send", c.name))
	}
}

func (c *channelImpl) SendAsync(v interface{}) (ok bool) {
	return c.sendAsyncImpl(v, nil)
}

func (c *channelImpl) sendAsyncImpl(v interface{}, pair *sendCallback) (ok bool) {
	if c.closed {
		panic("Closed channel")
	}
	for len(c.blockedReceives) > 0 {
		blockedGet := c.blockedReceives[0].fn
		c.blockedReceives[0] = nil
		c.blockedReceives = c.blockedReceives[1:]
		// false from callback indicates that value wasn't consumed
		if blockedGet(v, true) {
			return true
		}
	}
	if len(c.buffer) < c.size {
		c.buffer = append(c.buffer, v)
		return true
	}
	if pair != nil {
		c.blockedSends = append(c.blockedSends, pair)
	}
	return false
}

func (c *channelImpl) Close() {
	c.closed = true
	for _, callback := range c.blockedReceives {
		callback.fn(nil, false)
	}
	// All blocked sends are going to panic
	for _, callback := range c.blockedSends {
		callback.fn()
	}
}

// Takes a value and assigns that 'to' value.
func (c *channelImpl) assignValue(from interface{}, to interface{}) {
	err := decodeAndAssignValue(c.dataConverter, from, to)
	if err != nil {
		panic(err)
	}
}

// initialYield called at the beginning of the coroutine execution
// stackDepth is the depth of top of the stack to omit when stack trace is generated
// to hide frames internal to the framework.
func (s *coroutineState) initialYield(stackDepth int, status string) {
	if s.blocked.Swap(true) {
		panic("trying to block on coroutine which is already blocked, most likely a wrong Context is used to do blocking" +
			" call (like Future.Get() or Channel.Receive()")
	}
	keepBlocked := true
	for keepBlocked {
		f := <-s.unblock
		keepBlocked = f(status, stackDepth+1)
	}
	s.blocked.Swap(false)
}

// yield indicates that coroutine cannot make progress and should sleep
// this call blocks
func (s *coroutineState) yield(status string) {
	s.aboutToBlock <- true
	s.initialYield(3, status) // omit three levels of stack. To adjust change to 0 and count the lines to remove.
	s.keptBlocked = true
}

func getStackTrace(coroutineName, status string, stackDepth int) string {
	top := fmt.Sprintf("coroutine %s [%s]:", coroutineName, status)
	// Omit top stackDepth frames + top status line.
	// Omit bottom two frames which is wrapping of coroutine in a goroutine.
	return getStackTraceRaw(top, stackDepth*2+1, 4)
}

func getStackTraceRaw(top string, omitTop, omitBottom int) string {
	stack := stackBuf[:runtime.Stack(stackBuf[:], false)]
	rawStack := fmt.Sprintf("%s", strings.TrimRightFunc(string(stack), unicode.IsSpace))
	if disableCleanStackTraces {
		return rawStack
	}
	lines := strings.Split(rawStack, "\n")
	lines = lines[omitTop : len(lines)-omitBottom]
	lines = append([]string{top}, lines...)
	return strings.Join(lines, "\n")
}

// unblocked is called by coroutine to indicate that since the last time yield was unblocked channel or select
// where unblocked versus calling yield again after checking their condition
func (s *coroutineState) unblocked() {
	s.keptBlocked = false
}

func (s *coroutineState) call() {
	s.unblock <- func(status string, stackDepth int) bool {
		return false // unblock
	}
	<-s.aboutToBlock
}

func (s *coroutineState) close() {
	s.closed = true
	s.aboutToBlock <- true
}

func (s *coroutineState) exit() {
	if !s.closed {
		s.unblock <- func(status string, stackDepth int) bool {
			runtime.Goexit()
			return true
		}
	}
}

func (s *coroutineState) stackTrace() string {
	if s.closed {
		return ""
	}
	stackCh := make(chan string, 1)
	s.unblock <- func(status string, stackDepth int) bool {
		stackCh <- getStackTrace(s.name, status, stackDepth+2)
		return true
	}
	return <-stackCh
}

func (d *dispatcherImpl) newCoroutine(ctx Context, f func(ctx Context)) Context {
	return d.newNamedCoroutine(ctx, fmt.Sprintf("%v", d.sequence+1), f)
}

func (d *dispatcherImpl) newNamedCoroutine(ctx Context, name string, f func(ctx Context)) Context {
	state := d.newState(name)
	spawned := WithValue(ctx, coroutinesContextKey, state)
	go func(crt *coroutineState) {
		defer crt.close()
		defer func() {
			if r := recover(); r != nil {
				st := getStackTrace(name, "panic", 4)
				crt.panicError = newPanicError(r, st)
			}
		}()
		crt.initialYield(1, "")
		f(spawned)
	}(state)
	return spawned
}

func (d *dispatcherImpl) newState(name string) *coroutineState {
	c := &coroutineState{
		name:         name,
		dispatcher:   d,
		aboutToBlock: make(chan bool, 1),
		unblock:      make(chan unblockFunc),
	}
	d.sequence++
	d.coroutines = append(d.coroutines, c)
	return c
}

func (d *dispatcherImpl) ExecuteUntilAllBlocked() (err *PanicError) {
	d.mutex.Lock()
	if d.closed {
		panic("dispatcher is closed")
	}
	if d.executing {
		panic("call to ExecuteUntilAllBlocked (possibly from a coroutine) while it is already running")
	}
	d.executing = true
	d.mutex.Unlock()
	defer func() { d.executing = false }()
	allBlocked := false
	// Keep executing until at least one goroutine made some progress
	for !allBlocked {
		// Give every coroutine chance to execute removing closed ones
		allBlocked = true
		lastSequence := d.sequence
		for i := 0; i < len(d.coroutines); i++ {
			c := d.coroutines[i]
			if !c.closed {
				// TODO: Support handling of panic in a coroutine by dispatcher.
				// TODO: Dump all outstanding coroutines if one of them panics
				c.call()
			}
			// c.call() can close the context so check again
			if c.closed {
				// remove the closed one from the slice
				d.coroutines = append(d.coroutines[:i],
					d.coroutines[i+1:]...)
				i--
				if c.panicError != nil {
					return c.panicError
				}
				allBlocked = false

			} else {
				allBlocked = allBlocked && (c.keptBlocked || c.closed)
			}
		}
		// Set allBlocked to false if new coroutines where created
		allBlocked = allBlocked && lastSequence == d.sequence
		if len(d.coroutines) == 0 {
			break
		}
	}
	return nil
}

func (d *dispatcherImpl) IsDone() bool {
	return len(d.coroutines) == 0
}

func (d *dispatcherImpl) Close() {
	d.mutex.Lock()
	if d.closed {
		d.mutex.Unlock()
		return
	}
	d.closed = true
	d.mutex.Unlock()
	for i := 0; i < len(d.coroutines); i++ {
		c := d.coroutines[i]
		if !c.closed {
			c.exit()
		}
	}
}

func (d *dispatcherImpl) StackTrace() string {
	var result string
	for i := 0; i < len(d.coroutines); i++ {
		c := d.coroutines[i]
		if !c.closed {
			if len(result) > 0 {
				result += "\n\n"
			}
			result += c.stackTrace()
		}
	}
	return result
}

func (s *selectorImpl) AddReceive(c Channel, f func(c Channel, more bool)) Selector {
	s.cases = append(s.cases, &selectCase{channel: c.(*channelImpl), receiveFunc: &f})
	return s
}

func (s *selectorImpl) AddSend(c Channel, v interface{}, f func()) Selector {
	s.cases = append(s.cases, &selectCase{channel: c.(*channelImpl), sendFunc: &f, sendValue: &v})
	return s
}

func (s *selectorImpl) AddFuture(future Future, f func(future Future)) Selector {
	asyncF, ok := future.(asyncFuture)
	if !ok {
		panic("cannot chain Future that wasn't created with workflow.NewFuture")
	}
	s.cases = append(s.cases, &selectCase{future: asyncF, futureFunc: &f})
	return s
}

func (s *selectorImpl) AddDefault(f func()) {
	s.defaultFunc = &f
}

func (s *selectorImpl) Select(ctx Context) {
	state := getState(ctx)
	var readyBranch func()
	var cleanups []func()
	defer func() {
		for _, c := range cleanups {
			c()
		}
	}()

	for _, pair := range s.cases {
		if pair.receiveFunc != nil {
			f := *pair.receiveFunc
			c := pair.channel
			callback := &receiveCallback{
				fn: func(v interface{}, more bool) bool {
					if readyBranch != nil {
						return false
					}
					readyBranch = func() {
						c.recValue = &v
						f(c, more)
					}
					return true
				},
			}
			v, ok, more := c.receiveAsyncImpl(callback)
			if ok || !more {
				// Select() returns in this case/branch. The callback won't be called for this case. However, callback
				// will be called for previous cases/branches. We should set readyBranch so that when other case/branch
				// become ready they won't consume the value for this Select() call.
				readyBranch = func() {
				}
				c.recValue = &v
				f(c, more)
				return
			}
			// callback closure is added to channel's blockedReceives, we need to clean it up to avoid closure leak
			cleanups = append(cleanups, func() {
				c.removeReceiveCallback(callback)
			})
		} else if pair.sendFunc != nil {
			f := *pair.sendFunc
			c := pair.channel
			callback := &sendCallback{
				value: *pair.sendValue,
				fn: func() bool {
					if readyBranch != nil {
						return false
					}
					readyBranch = func() {
						f()
					}
					return true
				},
			}
			ok := c.sendAsyncImpl(*pair.sendValue, callback)
			if ok {
				// Select() returns in this case/branch. The callback won't be called for this case. However, callback
				// will be called for previous cases/branches. We should set readyBranch so that when other case/branch
				// become ready they won't consume the value for this Select() call.
				readyBranch = func() {
				}
				f()
				return
			}
			// callback closure is added to channel's blockedSends, we need to clean it up to avoid closure leak
			cleanups = append(cleanups, func() {
				c.removeSendCallback(callback)
			})
		} else if pair.futureFunc != nil {
			p := pair
			f := *p.futureFunc
			callback := &receiveCallback{
				fn: func(v interface{}, more bool) bool {
					if readyBranch != nil {
						return false
					}
					readyBranch = func() {
						p.futureFunc = nil
						f(p.future)
					}
					return true
				},
			}

			_, ok, _ := p.future.GetAsync(callback)
			if ok {
				// Select() returns in this case/branch. The callback won't be called for this case. However, callback
				// will be called for previous cases/branches. We should set readyBranch so that when other case/branch
				// become ready they won't consume the value for this Select() call.
				readyBranch = func() {
				}
				p.futureFunc = nil
				f(p.future)
				return
			}
			// callback closure is added to future's channel's blockedReceives, need to clean up to avoid leak
			cleanups = append(cleanups, func() {
				p.future.RemoveReceiveCallback(callback)
			})
		}
	}
	if s.defaultFunc != nil {
		f := *s.defaultFunc
		f()
		return
	}
	for {
		if readyBranch != nil {
			readyBranch()
			state.unblocked()
			return
		}
		state.yield(fmt.Sprintf("blocked on %s.Select", s.name))
	}
}

// NewWorkflowDefinition creates a WorkflowDefinition from a Workflow
func newWorkflowDefinition(workflow workflow) workflowDefinition {
	return &syncWorkflowDefinition{workflow: workflow}
}

func getValidatedWorkflowFunction(workflowFunc interface{}, args []interface{}, dataConverter encoded.DataConverter) (*WorkflowType, []byte, error) {
	fnName := ""
	fType := reflect.TypeOf(workflowFunc)
	switch getKind(fType) {
	case reflect.String:
		fnName = reflect.ValueOf(workflowFunc).String()

	case reflect.Func:
		if err := validateFunctionArgs(workflowFunc, args, true); err != nil {
			return nil, nil, err
		}
		fnName = getFunctionName(workflowFunc)
		if alias, ok := getHostEnvironment().getWorkflowAlias(fnName); ok {
			fnName = alias
		}

	default:
		return nil, nil, fmt.Errorf(
			"Invalid type 'workflowFunc' parameter provided, it can be either worker function or name of the worker type: %v",
			workflowFunc)
	}

	if dataConverter == nil {
		dataConverter = newDefaultDataConverter()
	}
	input, err := encodeArgs(dataConverter, args)
	if err != nil {
		return nil, nil, err
	}
	return &WorkflowType{Name: fnName}, input, nil
}

func getValidatedWorkflowOptions(ctx Context) (*workflowOptions, error) {
	p := getWorkflowEnvOptions(ctx)
	if p == nil {
		// We need task list as a compulsory parameter. This can be removed after registration
		return nil, errWorkflowOptionBadRequest
	}
	info := GetWorkflowInfo(ctx)
	if p.domain == nil || *p.domain == "" {
		// default to use current workflow's domain
		p.domain = common.StringPtr(info.Domain)
	}
	if p.taskListName == nil || *p.taskListName == "" {
		// default to use current workflow's task list
		p.taskListName = common.StringPtr(info.TaskListName)
	}
	if p.taskStartToCloseTimeoutSeconds == nil || *p.taskStartToCloseTimeoutSeconds < 0 {
		return nil, errors.New("missing or negative DecisionTaskStartToCloseTimeout")
	}
	if *p.taskStartToCloseTimeoutSeconds == 0 {
		p.taskStartToCloseTimeoutSeconds = common.Int32Ptr(defaultDecisionTaskTimeoutInSecs)
	}
	if p.executionStartToCloseTimeoutSeconds == nil || *p.executionStartToCloseTimeoutSeconds <= 0 {
		return nil, errors.New("missing or invalid ExecutionStartToCloseTimeout")
	}

	return p, nil
}

func getWorkflowEnvOptions(ctx Context) *workflowOptions {
	options := ctx.Value(workflowEnvOptionsContextKey)
	if options != nil {
		return options.(*workflowOptions)
	}
	return nil
}

func setWorkflowEnvOptionsIfNotExist(ctx Context) Context {
	options := getWorkflowEnvOptions(ctx)
	var newOptions workflowOptions
	if options != nil {
		newOptions = *options
	} else {
		newOptions.signalChannels = make(map[string]Channel)
		newOptions.queryHandlers = make(map[string]func([]byte) ([]byte, error))
	}
	if newOptions.dataConverter == nil {
		newOptions.dataConverter = newDefaultDataConverter()
	}
	return WithValue(ctx, workflowEnvOptionsContextKey, &newOptions)
}

func getDataConverterFromWorkflowContext(ctx Context) encoded.DataConverter {
	options := getWorkflowEnvOptions(ctx)
	if options == nil || options.dataConverter == nil {
		return newDefaultDataConverter()
	}
	return options.dataConverter
}

// getSignalChannel finds the assosciated channel for the signal.
func (w *workflowOptions) getSignalChannel(ctx Context, signalName string) Channel {
	if ch, ok := w.signalChannels[signalName]; ok {
		return ch
	}
	ch := NewBufferedChannel(ctx, defaultSignalChannelSize)
	w.signalChannels[signalName] = ch
	return ch
}

// getUnhandledSignals checks if there are any signal channels that have data to be consumed.
func (w *workflowOptions) getUnhandledSignals() []string {
	unhandledSignals := []string{}
	for k, c := range w.signalChannels {
		ch := c.(*channelImpl)
		v, ok, _ := ch.receiveAsyncImpl(nil)
		if ok {
			unhandledSignals = append(unhandledSignals, k)
			ch.recValue = &v
		}
	}
	return unhandledSignals
}

func (d *decodeFutureImpl) Get(ctx Context, value interface{}) error {
	more := d.futureImpl.channel.Receive(ctx, nil)
	if more {
		panic("not closed")
	}
	if !d.futureImpl.ready {
		panic("not ready")
	}
	if d.futureImpl.err != nil || d.futureImpl.value == nil || value == nil {
		return d.futureImpl.err
	}
	rf := reflect.ValueOf(value)
	if rf.Type().Kind() != reflect.Ptr {
		return errors.New("value parameter is not a pointer")
	}

	err := deSerializeFunctionResult(d.fn, d.futureImpl.value.([]byte), value, getDataConverterFromWorkflowContext(ctx))
	if err != nil {
		return err
	}
	return d.futureImpl.err
}

func (p ChildWorkflowPolicy) toThriftChildPolicyPtr() *shared.ChildPolicy {
	var childPolicy shared.ChildPolicy
	switch p {
	case ChildWorkflowPolicyTerminate:
		childPolicy = shared.ChildPolicyTerminate
	case ChildWorkflowPolicyRequestCancel:
		childPolicy = shared.ChildPolicyRequestCancel
	case ChildWorkflowPolicyAbandon:
		childPolicy = shared.ChildPolicyAbandon
	default:
		panic(fmt.Sprintf("unknown child policy %v", p))
	}
	return &childPolicy
}

// newDecodeFuture creates a new future as well as associated Settable that is used to set its value.
// fn - the decoded value needs to be validated against a function.
func newDecodeFuture(ctx Context, fn interface{}) (Future, Settable) {
	impl := &decodeFutureImpl{
		&futureImpl{channel: NewChannel(ctx).(*channelImpl)}, fn}
	return impl, impl
}

// setQueryHandler sets query handler for given queryType.
func setQueryHandler(ctx Context, queryType string, handler interface{}) error {
	qh := &queryHandler{fn: handler, queryType: queryType, dataConverter: getDataConverterFromWorkflowContext(ctx)}
	err := qh.validateHandlerFn()
	if err != nil {
		return err
	}

	getWorkflowEnvOptions(ctx).queryHandlers[queryType] = qh.execute
	return nil
}

func (h *queryHandler) validateHandlerFn() error {
	fnType := reflect.TypeOf(h.fn)
	if fnType.Kind() != reflect.Func {
		return fmt.Errorf("query handler must be function but was %s", fnType.Kind())
	}

	if fnType.NumOut() != 2 {
		return fmt.Errorf(
			"query handler must return 2 values (serializable result and error), but found %d return values", fnType.NumOut(),
		)
	}

	if !isValidResultType(fnType.Out(0)) {
		return fmt.Errorf(
			"first return value of query handler must be serializable but found: %v", fnType.Out(0).Kind(),
		)
	}
	if !isError(fnType.Out(1)) {
		return fmt.Errorf(
			"second return value of query handler must be error but found %v", fnType.Out(fnType.NumOut()-1).Kind(),
		)
	}
	return nil
}

func (h *queryHandler) execute(input []byte) (result []byte, err error) {
	// if query handler panic, convert it to error
	defer func() {
		if p := recover(); p != nil {
			result = nil
			st := getStackTraceRaw("query handler [panic]:", 7, 0)
			if p == panicIllegalAccessCoroutinueState {
				// query handler code try to access workflow functions outside of workflow context, make error message
				// more descriptive and clear.
				p = "query handler must not use cadence context to do things like workflow.NewChannel(), " +
					"workflow.Go() or to call any workflow blocking functions like Channel.Get() or Future.Get()"
			}
			err = fmt.Errorf("query handler panic: %v, stack trace: %v", p, st)
		}
	}()

	fnType := reflect.TypeOf(h.fn)
	args := []reflect.Value{}

	if fnType.NumIn() == 1 && isTypeByteSlice(fnType.In(0)) {
		args = append(args, reflect.ValueOf(input))
	} else {
		decoded, err := decodeArgs(h.dataConverter, fnType, input)
		if err != nil {
			return nil, fmt.Errorf("unable to decode the input for queryType: %v, with error: %v", h.queryType, err)
		}
		args = append(args, decoded...)
	}

	// invoke the query handler with arguments.
	fnValue := reflect.ValueOf(h.fn)
	retValues := fnValue.Call(args)

	// we already verified (in validateHandlerFn()) that the query handler returns 2 values
	retValue := retValues[0]
	if retValue.Kind() != reflect.Ptr || !retValue.IsNil() {
		result, err = encodeArg(h.dataConverter, retValue.Interface())
		if err != nil {
			return nil, err
		}
	}

	errValue := retValues[1]
	if errValue.IsNil() {
		return result, nil
	}
	err, ok := errValue.Interface().(error)
	if !ok {
		return nil, fmt.Errorf("failed to parse error result as it is not of error interface: %v", errValue)
	}
	return result, err
}