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72 lines
2.8 KiB
Go
72 lines
2.8 KiB
Go
// Copyright 2016 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// +build go1.7
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package context
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import (
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"context" // standard library's context, as of Go 1.7
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"time"
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)
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var (
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todo = context.TODO()
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background = context.Background()
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)
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// Canceled is the error returned by Context.Err when the context is canceled.
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var Canceled = context.Canceled
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// DeadlineExceeded is the error returned by Context.Err when the context's
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// deadline passes.
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var DeadlineExceeded = context.DeadlineExceeded
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// WithCancel returns a copy of parent with a new Done channel. The returned
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// context's Done channel is closed when the returned cancel function is called
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// or when the parent context's Done channel is closed, whichever happens first.
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//
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// Canceling this context releases resources associated with it, so code should
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// call cancel as soon as the operations running in this Context complete.
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func WithCancel(parent Context) (ctx Context, cancel CancelFunc) {
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ctx, f := context.WithCancel(parent)
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return ctx, CancelFunc(f)
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}
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// WithDeadline returns a copy of the parent context with the deadline adjusted
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// to be no later than d. If the parent's deadline is already earlier than d,
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// WithDeadline(parent, d) is semantically equivalent to parent. The returned
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// context's Done channel is closed when the deadline expires, when the returned
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// cancel function is called, or when the parent context's Done channel is
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// closed, whichever happens first.
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//
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// Canceling this context releases resources associated with it, so code should
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// call cancel as soon as the operations running in this Context complete.
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func WithDeadline(parent Context, deadline time.Time) (Context, CancelFunc) {
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ctx, f := context.WithDeadline(parent, deadline)
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return ctx, CancelFunc(f)
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}
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// WithTimeout returns WithDeadline(parent, time.Now().Add(timeout)).
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//
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// Canceling this context releases resources associated with it, so code should
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// call cancel as soon as the operations running in this Context complete:
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//
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// func slowOperationWithTimeout(ctx context.Context) (Result, error) {
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// ctx, cancel := context.WithTimeout(ctx, 100*time.Millisecond)
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// defer cancel() // releases resources if slowOperation completes before timeout elapses
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// return slowOperation(ctx)
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// }
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func WithTimeout(parent Context, timeout time.Duration) (Context, CancelFunc) {
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return WithDeadline(parent, time.Now().Add(timeout))
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}
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// WithValue returns a copy of parent in which the value associated with key is
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// val.
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//
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// Use context Values only for request-scoped data that transits processes and
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// APIs, not for passing optional parameters to functions.
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func WithValue(parent Context, key interface{}, val interface{}) Context {
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return context.WithValue(parent, key, val)
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}
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