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1 | // 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 | ||
7 | package context | |
8 | ||
9 | import ( | |
10 | "context" // standard library's context, as of Go 1.7 | |
11 | "time" | |
12 | ) | |
13 | ||
14 | var ( | |
15 | todo = context.TODO() | |
16 | background = context.Background() | |
17 | ) | |
18 | ||
19 | // Canceled is the error returned by Context.Err when the context is canceled. | |
20 | var Canceled = context.Canceled | |
21 | ||
22 | // DeadlineExceeded is the error returned by Context.Err when the context's | |
23 | // deadline passes. | |
24 | var 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. | |
32 | func 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. | |
46 | func 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 | // } | |
61 | func 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. | |
70 | func WithValue(parent Context, key interface{}, val interface{}) Context { | |
71 | return context.WithValue(parent, key, val) | |
72 | } |