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 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} 73