gtsocial-umbx

pre_go17.go (8136B)

---

 // Copyright 2014 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 //go:build !go1.7
 // +build !go1.7
 
 package context
 
 import (
 	"errors"
 	"fmt"
 	"sync"
 	"time"
 )
 
 // 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() <-chan struct{} {
 	return nil
 }
 
 func (*emptyCtx) Err() error {
 	return nil
 }
 
 func (*emptyCtx) Value(key 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)
 )
 
 // Canceled is the error returned by Context.Err when the context is canceled.
 var Canceled = errors.New("context canceled")
 
 // DeadlineExceeded is the error returned by Context.Err when the context's
 // deadline passes.
 var DeadlineExceeded = errors.New("context deadline exceeded")
 
 // 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, Canceled) }
 }
 
 // newCancelCtx returns an initialized cancelCtx.
 func newCancelCtx(parent Context) *cancelCtx {
 	return &cancelCtx{
 		Context: parent,
 		done:    make(chan struct{}),
 	}
 }
 
 // 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 {
 		p.mu.Lock()
 		if p.err != nil {
 			// parent has already been canceled
 			child.cancel(false, p.err)
 		} else {
 			if p.children == nil {
 				p.children = make(map[canceler]bool)
 			}
 			p.children[child] = true
 		}
 		p.mu.Unlock()
 	} else {
 		go func() {
 			select {
 			case <-parent.Done():
 				child.cancel(false, parent.Err())
 			case <-child.Done():
 			}
 		}()
 	}
 }
 
 // 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
 		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.mu.Lock()
 	if p.children != nil {
 		delete(p.children, child)
 	}
 	p.mu.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() <-chan struct{}
 }
 
 // A cancelCtx can be canceled. When canceled, it also cancels any children
 // that implement canceler.
 type cancelCtx struct {
 	Context
 
 	done chan struct{} // closed by the first cancel call.
 
 	mu       sync.Mutex
 	children map[canceler]bool // set to nil by the first cancel call
 	err      error             // set to non-nil by the first cancel call
 }
 
 func (c *cancelCtx) Done() <-chan struct{} {
 	return c.done
 }
 
 func (c *cancelCtx) Err() error {
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	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")
 	}
 	c.mu.Lock()
 	if c.err != nil {
 		c.mu.Unlock()
 		return // already canceled
 	}
 	c.err = err
 	close(c.done)
 	for child := range c.children {
 		// NOTE: acquiring the child's lock while holding parent's lock.
 		child.cancel(false, err)
 	}
 	c.children = nil
 	c.mu.Unlock()
 
 	if removeFromParent {
 		removeChild(c.Context, c)
 	}
 }
 
 // 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) }
 	}
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	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)
 	}
 	c.mu.Lock()
 	if c.timer != nil {
 		c.timer.Stop()
 		c.timer = nil
 	}
 	c.mu.Unlock()
 }
 
 // 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)
 }