mirror of https://github.com/perkeep/perkeep.git
116 lines
2.6 KiB
Go
116 lines
2.6 KiB
Go
// +build appengine
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/*
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Copyright 2013 Google Inc.
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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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package appengine
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import (
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"sync"
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"appengine"
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)
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type ContextPool struct {
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mu sync.Mutex // guards live
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// Live HTTP requests
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live map[appengine.Context]*sync.WaitGroup
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}
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// HandlerBegin notes that the provided context is beginning and it can be
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// shared until HandlerEnd is called.
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func (p *ContextPool) HandlerBegin(c appengine.Context) {
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p.mu.Lock()
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defer p.mu.Unlock()
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if p.live == nil {
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p.live = make(map[appengine.Context]*sync.WaitGroup)
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}
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if _, ok := p.live[c]; ok {
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// dup; ignore.
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return
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}
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p.live[c] = new(sync.WaitGroup)
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}
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// HandlerEnd notes that the provided context is about to go out of service,
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// removes it from the pool of available contexts, and blocks until everybody
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// is done using it.
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func (p *ContextPool) HandlerEnd(c appengine.Context) {
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p.mu.Lock()
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wg := p.live[c]
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delete(p.live, c)
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p.mu.Unlock()
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if wg != nil {
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wg.Wait()
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}
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}
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// A ContextLoan is a superset of a Context, so can passed anywhere
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// that needs an appengine.Context.
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//
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// When done, Return it.
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type ContextLoan interface {
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appengine.Context
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// Return returns the Context to the pool.
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// Return must be called exactly once.
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Return()
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}
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// Get returns a valid App Engine context from some active HTTP request
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// which is guaranteed to stay valid. Be sure to return it.
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//
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// Typical use:
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// ctx := pool.Get()
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// defer ctx.Return()
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func (p *ContextPool) Get() ContextLoan {
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p.mu.Lock()
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defer p.mu.Unlock()
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// Pick a random active context. TODO: pick the "right" one,
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// using some TLS-like-guess/hack from runtume.Stacks.
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var c appengine.Context
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var wg *sync.WaitGroup
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for c, wg = range p.live {
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break
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}
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if c == nil {
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panic("ContextPool.Get called with no live HTTP requests")
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}
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wg.Add(1)
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cl := &contextLoan{Context: c, wg: wg}
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// TODO: set warning finalizer on this?
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return cl
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}
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type contextLoan struct {
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appengine.Context
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mu sync.Mutex
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wg *sync.WaitGroup
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}
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func (cl *contextLoan) Return() {
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cl.mu.Lock()
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defer cl.mu.Unlock()
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if cl.wg == nil {
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panic("Return called twice")
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}
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cl.wg.Done()
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cl.wg = nil
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}
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