github.com/lianghucheng/zrddz@v0.0.0-20200923083010-c71f680932e2/src/golang.org/x/net/context/go17.go (about)

     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  }