mirror of https://github.com/perkeep/perkeep.git
84 lines
1.9 KiB
Go
84 lines
1.9 KiB
Go
/*
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Copyright 2013 The Camlistore Authors
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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// Packaage context provides a Context type to propagate state and cancellation
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// information.
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package context
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import (
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"errors"
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"sync"
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)
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// ErrCanceled may be returned by code when it receives from a Context.Done channel.
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var ErrCanceled = errors.New("canceled")
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// TODO returns a dummy context. It's a signal that the caller code is not yet correct,
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// and needs its own context to propagate.
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func TODO() *Context {
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return nil
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}
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// A Context is carries state and cancellation information between calls.
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// A nil Context pointer is valid, for now.
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type Context struct {
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cancelOnce sync.Once
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done chan struct{}
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}
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func New() *Context {
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return &Context{
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done: make(chan struct{}),
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}
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}
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// New returns a child context attached to the receiver parent context c.
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// The returned context is done when the parent is done, but the returned child
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// context can be canceled indepedently without affecting the parent.
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func (c *Context) New() *Context {
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subc := New()
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if c == nil {
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return subc
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}
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go func() {
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<-c.Done()
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subc.Cancel()
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}()
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return subc
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}
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// Done returns a channel that is closed when the Context is cancelled
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// or finished.
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func (c *Context) Done() <-chan struct{} {
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if c == nil {
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return nil
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}
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return c.done
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}
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func (c *Context) Cancel() {
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if c == nil {
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return
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}
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c.cancelOnce.Do(c.cancel)
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}
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func (c *Context) cancel() {
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if c.done != nil {
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close(c.done)
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}
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}
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