Source: go17.go in package golang.org/x/net/context

go:build go1.7 +build go1.7


package context

import (
	"context" // standard library's context, as of Go 1.7
	"time"
)

var (
	todo       = context.TODO()
	background = context.Background()
)

Canceled is the error returned by Context.Err when the context is canceled.

var Canceled = context.Canceled

DeadlineExceeded is the error returned by Context.Err when the context's deadline passes.

var DeadlineExceeded = context.DeadlineExceeded

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) {
	ctx, f := context.WithCancel(parent)
	return ctx, CancelFunc(f)
}

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) {
	ctx, f := context.WithDeadline(parent, deadline)
	return ctx, CancelFunc(f)
}

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 context.WithValue(parent, key, val)