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110 lines
4.0 KiB
110 lines
4.0 KiB
// Copyright 2014 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 !go1.9
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package context
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import "time"
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// A Context carries a deadline, a cancelation signal, and other values across
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// API boundaries.
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//
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// Context's methods may be called by multiple goroutines simultaneously.
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type Context interface {
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// Deadline returns the time when work done on behalf of this context
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// should be canceled. Deadline returns ok==false when no deadline is
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// set. Successive calls to Deadline return the same results.
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Deadline() (deadline time.Time, ok bool)
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// Done returns a channel that's closed when work done on behalf of this
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// context should be canceled. Done may return nil if this context can
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// never be canceled. Successive calls to Done return the same value.
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//
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// WithCancel arranges for Done to be closed when cancel is called;
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// WithDeadline arranges for Done to be closed when the deadline
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// expires; WithTimeout arranges for Done to be closed when the timeout
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// elapses.
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//
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// Done is provided for use in select statements:
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//
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// // Stream generates values with DoSomething and sends them to out
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// // until DoSomething returns an error or ctx.Done is closed.
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// func Stream(ctx context.Context, out chan<- Value) error {
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// for {
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// v, err := DoSomething(ctx)
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// if err != nil {
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// return err
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// }
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// select {
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// case <-ctx.Done():
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// return ctx.Err()
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// case out <- v:
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// }
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// }
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// }
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//
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// See http://blog.golang.org/pipelines for more examples of how to use
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// a Done channel for cancelation.
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Done() <-chan struct{}
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// Err returns a non-nil error value after Done is closed. Err returns
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// Canceled if the context was canceled or DeadlineExceeded if the
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// context's deadline passed. No other values for Err are defined.
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// After Done is closed, successive calls to Err return the same value.
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Err() error
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// Value returns the value associated with this context for key, or nil
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// if no value is associated with key. Successive calls to Value with
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// the same key returns the same result.
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//
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// Use context values only for request-scoped data that transits
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// processes and API boundaries, not for passing optional parameters to
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// functions.
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//
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// A key identifies a specific value in a Context. Functions that wish
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// to store values in Context typically allocate a key in a global
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// variable then use that key as the argument to context.WithValue and
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// Context.Value. A key can be any type that supports equality;
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// packages should define keys as an unexported type to avoid
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// collisions.
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//
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// Packages that define a Context key should provide type-safe accessors
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// for the values stores using that key:
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//
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// // Package user defines a User type that's stored in Contexts.
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// package user
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//
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// import "golang.org/x/net/context"
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//
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// // User is the type of value stored in the Contexts.
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// type User struct {...}
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//
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// // key is an unexported type for keys defined in this package.
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// // This prevents collisions with keys defined in other packages.
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// type key int
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//
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// // userKey is the key for user.User values in Contexts. It is
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// // unexported; clients use user.NewContext and user.FromContext
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// // instead of using this key directly.
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// var userKey key = 0
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//
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// // NewContext returns a new Context that carries value u.
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// func NewContext(ctx context.Context, u *User) context.Context {
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// return context.WithValue(ctx, userKey, u)
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// }
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//
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// // FromContext returns the User value stored in ctx, if any.
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// func FromContext(ctx context.Context) (*User, bool) {
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// u, ok := ctx.Value(userKey).(*User)
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// return u, ok
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// }
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Value(key interface{}) interface{}
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}
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// A CancelFunc tells an operation to abandon its work.
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// A CancelFunc does not wait for the work to stop.
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// After the first call, subsequent calls to a CancelFunc do nothing.
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type CancelFunc func()
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