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Zack Williamse940c7a2019-08-21 14:25:39 -07001// Copyright 2016 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5// +build go1.7
6
7package context
8
9import (
10 "context" // standard library's context, as of Go 1.7
11 "time"
12)
13
14var (
15 todo = context.TODO()
16 background = context.Background()
17)
18
19// Canceled is the error returned by Context.Err when the context is canceled.
20var Canceled = context.Canceled
21
22// DeadlineExceeded is the error returned by Context.Err when the context's
23// deadline passes.
24var DeadlineExceeded = context.DeadlineExceeded
25
26// WithCancel returns a copy of parent with a new Done channel. The returned
27// context's Done channel is closed when the returned cancel function is called
28// or when the parent context's Done channel is closed, whichever happens first.
29//
30// Canceling this context releases resources associated with it, so code should
31// call cancel as soon as the operations running in this Context complete.
32func WithCancel(parent Context) (ctx Context, cancel CancelFunc) {
33 ctx, f := context.WithCancel(parent)
34 return ctx, CancelFunc(f)
35}
36
37// WithDeadline returns a copy of the parent context with the deadline adjusted
38// to be no later than d. If the parent's deadline is already earlier than d,
39// WithDeadline(parent, d) is semantically equivalent to parent. The returned
40// context's Done channel is closed when the deadline expires, when the returned
41// cancel function is called, or when the parent context's Done channel is
42// closed, whichever happens first.
43//
44// Canceling this context releases resources associated with it, so code should
45// call cancel as soon as the operations running in this Context complete.
46func WithDeadline(parent Context, deadline time.Time) (Context, CancelFunc) {
47 ctx, f := context.WithDeadline(parent, deadline)
48 return ctx, CancelFunc(f)
49}
50
51// WithTimeout returns WithDeadline(parent, time.Now().Add(timeout)).
52//
53// Canceling this context releases resources associated with it, so code should
54// call cancel as soon as the operations running in this Context complete:
55//
56// func slowOperationWithTimeout(ctx context.Context) (Result, error) {
57// ctx, cancel := context.WithTimeout(ctx, 100*time.Millisecond)
58// defer cancel() // releases resources if slowOperation completes before timeout elapses
59// return slowOperation(ctx)
60// }
61func WithTimeout(parent Context, timeout time.Duration) (Context, CancelFunc) {
62 return WithDeadline(parent, time.Now().Add(timeout))
63}
64
65// WithValue returns a copy of parent in which the value associated with key is
66// val.
67//
68// Use context Values only for request-scoped data that transits processes and
69// APIs, not for passing optional parameters to functions.
70func WithValue(parent Context, key interface{}, val interface{}) Context {
71 return context.WithValue(parent, key, val)
72}