peridot/vendor/go.temporal.io/sdk/internal/context.go

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// The MIT License
//
// Copyright (c) 2020 Temporal Technologies Inc. All rights reserved.
//
// Copyright (c) 2020 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
import (
"fmt"
"sync"
"time"
enumspb "go.temporal.io/api/enums/v1"
)
// Context is a clone of context.Context with Done() returning Channel instead
// of native channel.
// A Context carries a deadline, a cancellation signal, and other values across
// API boundaries.
//
// Context's methods may be called by multiple goroutines simultaneously.
type Context interface {
// Deadline returns the time when work done on behalf of this context
// should be canceled. Deadline returns ok==false when no deadline is
// set. Successive calls to Deadline return the same results.
Deadline() (deadline time.Time, ok bool)
// Done returns a channel that's closed when work done on behalf of this
// context should be canceled. Done may return nil if this context can
// never be canceled. Successive calls to Done return the same value.
//
// WithCancel arranges for Done to be closed when cancel is called;
// WithDeadline arranges for Done to be closed when the deadline
// expires; WithTimeout arranges for Done to be closed when the timeout
// elapses.
//
// Done is provided for use in select statements:
//
// // Stream generates values with DoSomething and sends them to out
// // until DoSomething returns an error or ctx.Done is closed.
// func Stream(ctx Context, out Channel) (err error) {
// for {
// v, err := DoSomething(ctx)
// if err != nil {
// return err
// }
// s := NewSelector(ctx)
// s.AddReceive(ctx.Done(), func(v interface{}) { err = ctx.Err() })
// s.AddReceive(v, func(v interface{}, more bool) { out.Send(ctx, v) })
// s.Select(ctx)
// if err != nil {
// return err
// }
// }
// }
//
// See http://blog.golang.org/pipelines for more examples of how to use
// a Done channel for cancellation.
Done() Channel
// Err returns a non-nil error value after Done is closed. Err returns
// Canceled if the context was canceled or DeadlineExceeded if the
// context's deadline passed. No other values for Err are defined.
// After Done is closed, successive calls to Err return the same value.
Err() error
// Value returns the value associated with this context for key, or nil
// if no value is associated with key. Successive calls to Value with
// the same key returns the same result.
//
// Use context values only for request-scoped data that transits
// processes and API boundaries, not for passing optional parameters to
// functions.
//
// A key identifies a specific value in a Context. Functions that wish
// to store values in Context typically allocate a key in a global
// variable then use that key as the argument to context.WithValue and
// Context.Value. A key can be any type that supports equality;
// packages should define keys as an unexported type to avoid
// collisions.
//
// Packages that define a Context key should provide type-safe accessors
// for the values stores using that key:
//
// // Package user defines a User type that's stored in Contexts.
// package user
//
// import "context"
//
// // User is the type of value stored in the Contexts.
// type User struct {...}
//
// // key is an unexported type for keys defined in this package.
// // This prevents collisions with keys defined in other packages.
// type key int
//
// // userKey is the key for user.User values in Contexts. It is
// // unexported; clients use user.NewContext and user.FromContext
// // instead of using this key directly.
// var userKey key = 0
//
// // NewContext returns a new Context that carries value u.
// func NewContext(ctx context.Context, u *User) context.Context {
// return context.WithValue(ctx, userKey, u)
// }
//
// // FromContext returns the User value stored in ctx, if any.
// func FromContext(ctx context.Context) (*User, bool) {
// u, ok := ctx.Value(userKey).(*User)
// return u, ok
// }
Value(key interface{}) interface{}
}
// An emptyCtx is never canceled, has no values, and has no deadline. It is not
// struct{}, since vars of this type must have distinct addresses.
type emptyCtx int
func (*emptyCtx) Deadline() (deadline time.Time, ok bool) {
return
}
func (*emptyCtx) Done() Channel {
return nil
}
func (*emptyCtx) Err() error {
return nil
}
func (*emptyCtx) Value(_ interface{}) interface{} {
return nil
}
func (e *emptyCtx) String() string {
switch e {
case background:
return "context.Background"
case todo:
return "context.TODO"
}
return "unknown empty Context"
}
var (
background = new(emptyCtx)
todo = new(emptyCtx)
)
// Background returns a non-nil, empty Context. It is never canceled, has no
// values, and has no deadline
func Background() Context {
return background
}
// ErrCanceled is the error returned by Context.Err when the context is canceled.
var ErrCanceled = NewCanceledError()
// ErrDeadlineExceeded is the error returned by Context.Err when the context's
// deadline passes.
var ErrDeadlineExceeded = NewTimeoutError("deadline exceeded", enumspb.TIMEOUT_TYPE_SCHEDULE_TO_CLOSE, nil)
// A CancelFunc tells an operation to abandon its work.
// A CancelFunc does not wait for the work to stop.
// After the first call, subsequent calls to a CancelFunc do nothing.
type CancelFunc func()
// WithCancel returns a copy of parent with a new Done channel. The returned
// context's Done channel is closed when the returned cancel function is called
// or when the parent context's Done channel is closed, whichever happens first.
//
// Canceling this context releases resources associated with it, so code should
// call cancel as soon as the operations running in this Context complete.
func WithCancel(parent Context) (ctx Context, cancel CancelFunc) {
c := newCancelCtx(parent)
propagateCancel(parent, c)
return c, func() { c.cancel(true, ErrCanceled) }
}
// NewDisconnectedContext returns a new context that won't propagate parent's cancellation to the new child context.
// One common use case is to do cleanup work after workflow is canceled.
// err := workflow.ExecuteActivity(ctx, ActivityFoo).Get(ctx, &activityFooResult)
// if err != nil && temporal.IsCanceledError(ctx.Err()) {
// // activity failed, and workflow context is canceled
// disconnectedCtx, _ := workflow.newDisconnectedContext(ctx);
// workflow.ExecuteActivity(disconnectedCtx, handleCancellationActivity).Get(disconnectedCtx, nil)
// return err // workflow return CanceledError
// }
func NewDisconnectedContext(parent Context) (ctx Context, cancel CancelFunc) {
c := newCancelCtx(parent)
return c, func() { c.cancel(true, ErrCanceled) }
}
// newCancelCtx returns an initialized cancelCtx.
func newCancelCtx(parent Context) *cancelCtx {
return &cancelCtx{
Context: parent,
done: NewNamedChannel(parent, "cancelCtx-done-channel"),
}
}
// propagateCancel arranges for child to be canceled when parent is.
func propagateCancel(parent Context, child canceler) {
if parent.Done() == nil {
return // parent is never canceled
}
if p, ok := parentCancelCtx(parent); ok {
if parentErr := p.Err(); parentErr != nil {
// parent has already been canceled
child.cancel(false, parentErr)
} else {
p.childrenLock.Lock()
if p.children == nil {
p.children = make(map[canceler]bool)
}
p.children[child] = true
p.childrenLock.Unlock()
}
} else {
go func() {
s := NewSelector(parent)
s.AddReceive(parent.Done(), func(c ReceiveChannel, more bool) {
child.cancel(false, parent.Err())
})
s.AddReceive(child.Done(), func(c ReceiveChannel, more bool) {})
s.Select(parent)
}()
}
}
// parentCancelCtx follows a chain of parent references until it finds a
// *cancelCtx. This function understands how each of the concrete types in this
// package represents its parent.
func parentCancelCtx(parent Context) (*cancelCtx, bool) {
for {
switch c := parent.(type) {
case *cancelCtx:
return c, true
// TODO: Uncomment once timer story is implemented
//case *timerCtx:
// return c.cancelCtx, true
case *valueCtx:
parent = c.Context
default:
return nil, false
}
}
}
// removeChild removes a context from its parent.
func removeChild(parent Context, child canceler) {
p, ok := parentCancelCtx(parent)
if !ok {
return
}
p.childrenLock.Lock()
if p.children != nil {
delete(p.children, child)
}
p.childrenLock.Unlock()
}
// A canceler is a context type that can be canceled directly. The
// implementations are *cancelCtx and *timerCtx.
type canceler interface {
cancel(removeFromParent bool, err error)
Done() Channel
}
// A cancelCtx can be canceled. When canceled, it also cancels any children
// that implement canceler.
type cancelCtx struct {
Context
done Channel // closed by the first cancel call.
children map[canceler]bool // set to nil by the first cancel call
childrenLock sync.Mutex
err error // set to non-nil by the first cancel call
errLock sync.RWMutex
}
func (c *cancelCtx) Done() Channel {
return c.done
}
func (c *cancelCtx) Err() error {
c.errLock.RLock()
defer c.errLock.RUnlock()
return c.err
}
func (c *cancelCtx) String() string {
return fmt.Sprintf("%v.WithCancel", c.Context)
}
// cancel closes c.done, cancels each of c's children, and, if
// removeFromParent is true, removes c from its parent's children.
func (c *cancelCtx) cancel(removeFromParent bool, err error) {
if err == nil {
panic("context: internal error: missing cancel error")
}
// This can be called from separate goroutines concurrently, so we use the
// presence of the error under lock to prevent duplicate calls
c.errLock.Lock()
alreadyCancelled := c.err != nil
if !alreadyCancelled {
c.err = err
}
c.errLock.Unlock()
if alreadyCancelled {
return
}
c.done.Close()
c.childrenLock.Lock()
children := c.children
c.children = nil
c.childrenLock.Unlock()
for child := range children {
// NOTE: acquiring the child's lock while holding parent's lock.
child.cancel(false, err)
}
if removeFromParent {
removeChild(c.Context, c)
}
}
// Commented out until workflow time API is exposed.
// WithDeadline returns a copy of the parent context with the deadline adjusted
// to be no later than d. If the parent's deadline is already earlier than d,
// WithDeadline(parent, d) is semantically equivalent to parent. The returned
// context's Done channel is closed when the deadline expires, when the returned
// cancel function is called, or when the parent context's Done channel is
// closed, whichever happens first.
//
// Canceling this context releases resources associated with it, so code should
// call cancel as soon as the operations running in this Context complete.
//func WithDeadline(parent Context, deadline time.Time) (Context, CancelFunc) {
// if cur, ok := parent.Deadline(); ok && cur.Before(deadline) {
// // The current deadline is already sooner than the new one.
// return WithCancel(parent)
// }
// c := &timerCtx{
// cancelCtx: newCancelCtx(parent),
// deadline: deadline,
// }
// propagateCancel(parent, c)
// d := deadline.Sub(time.Now())
// if d <= 0 {
// c.cancel(true, DeadlineExceeded) // deadline has already passed
// return c, func() { c.cancel(true, Canceled) }
// }
// if c.err == nil {
// c.timer = time.AfterFunc(d, func() {
// c.cancel(true, DeadlineExceeded)
// })
// }
// return c, func() { c.cancel(true, Canceled) }
//}
//
//// A timerCtx carries a timer and a deadline. It embeds a cancelCtx to
//// implement Done and Err. It implements cancel by stopping its timer then
//// delegating to cancelCtx.cancel.
//type timerCtx struct {
// *cancelCtx
// timer *time.Timer // Under cancelCtx.mu.
//
// deadline time.Time
//}
//
//func (c *timerCtx) Deadline() (deadline time.Time, ok bool) {
// return c.deadline, true
//}
//
//func (c *timerCtx) String() string {
// return fmt.Sprintf("%v.WithDeadline(%s [%s])", c.cancelCtx.Context, c.deadline, c.deadline.Sub(time.Now()))
//}
//
//func (c *timerCtx) cancel(removeFromParent bool, err error) {
// c.cancelCtx.cancel(false, err)
// if removeFromParent {
// // Remove this timerCtx from its parent cancelCtx's children.
// removeChild(c.cancelCtx.Context, c)
// }
// if c.timer != nil {
// c.timer.Stop()
// c.timer = nil
// }
//}
//
// WithTimeout returns WithDeadline(parent, time.Now().Add(timeout)).
//
// Canceling this context releases resources associated with it, so code should
// call cancel as soon as the operations running in this Context complete:
//
// func slowOperationWithTimeout(ctx context.Context) (Result, error) {
// ctx, cancel := context.WithTimeout(ctx, 100*time.Millisecond)
// defer cancel() // releases resources if slowOperation completes before timeout elapses
// return slowOperation(ctx)
// }
//func WithTimeout(parent Context, timeout time.Duration) (Context, CancelFunc) {
// return WithDeadline(parent, time.Now().Add(timeout))
//}
// WithValue returns a copy of parent in which the value associated with key is
// val.
//
// Use context Values only for request-scoped data that transits processes and
// APIs, not for passing optional parameters to functions.
func WithValue(parent Context, key interface{}, val interface{}) Context {
return &valueCtx{parent, key, val}
}
// A valueCtx carries a key-value pair. It implements Value for that key and
// delegates all other calls to the embedded Context.
type valueCtx struct {
Context
key, val interface{}
}
func (c *valueCtx) String() string {
return fmt.Sprintf("%v.WithValue(%#v, %#v)", c.Context, c.key, c.val)
}
func (c *valueCtx) Value(key interface{}) interface{} {
if c.key == key {
return c.val
}
return c.Context.Value(key)
}