119 lines
3 KiB
Go
119 lines
3 KiB
Go
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// Copyright 2010 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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package textproto
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import (
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"sync"
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)
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// A Pipeline manages a pipelined in-order request/response sequence.
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//
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// To use a Pipeline p to manage multiple clients on a connection,
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// each client should run:
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//
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// id := p.Next() // take a number
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//
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// p.StartRequest(id) // wait for turn to send request
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// «send request»
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// p.EndRequest(id) // notify Pipeline that request is sent
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//
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// p.StartResponse(id) // wait for turn to read response
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// «read response»
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// p.EndResponse(id) // notify Pipeline that response is read
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//
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// A pipelined server can use the same calls to ensure that
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// responses computed in parallel are written in the correct order.
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type Pipeline struct {
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mu sync.Mutex
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id uint
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request sequencer
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response sequencer
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}
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// Next returns the next id for a request/response pair.
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func (p *Pipeline) Next() uint {
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p.mu.Lock()
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id := p.id
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p.id++
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p.mu.Unlock()
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return id
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}
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// StartRequest blocks until it is time to send (or, if this is a server, receive)
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// the request with the given id.
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func (p *Pipeline) StartRequest(id uint) {
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p.request.Start(id)
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}
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// EndRequest notifies p that the request with the given id has been sent
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// (or, if this is a server, received).
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func (p *Pipeline) EndRequest(id uint) {
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p.request.End(id)
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}
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// StartResponse blocks until it is time to receive (or, if this is a server, send)
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// the request with the given id.
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func (p *Pipeline) StartResponse(id uint) {
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p.response.Start(id)
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}
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// EndResponse notifies p that the response with the given id has been received
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// (or, if this is a server, sent).
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func (p *Pipeline) EndResponse(id uint) {
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p.response.End(id)
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}
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// A sequencer schedules a sequence of numbered events that must
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// happen in order, one after the other. The event numbering must start
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// at 0 and increment without skipping. The event number wraps around
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// safely as long as there are not 2^32 simultaneous events pending.
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type sequencer struct {
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mu sync.Mutex
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id uint
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wait map[uint]chan struct{}
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}
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// Start waits until it is time for the event numbered id to begin.
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// That is, except for the first event, it waits until End(id-1) has
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// been called.
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func (s *sequencer) Start(id uint) {
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s.mu.Lock()
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if s.id == id {
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s.mu.Unlock()
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return
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}
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c := make(chan struct{})
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if s.wait == nil {
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s.wait = make(map[uint]chan struct{})
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}
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s.wait[id] = c
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s.mu.Unlock()
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<-c
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}
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// End notifies the sequencer that the event numbered id has completed,
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// allowing it to schedule the event numbered id+1. It is a run-time error
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// to call End with an id that is not the number of the active event.
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func (s *sequencer) End(id uint) {
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s.mu.Lock()
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if s.id != id {
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s.mu.Unlock()
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panic("out of sync")
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}
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id++
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s.id = id
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if s.wait == nil {
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s.wait = make(map[uint]chan struct{})
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}
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c, ok := s.wait[id]
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if ok {
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delete(s.wait, id)
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}
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s.mu.Unlock()
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if ok {
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close(c)
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}
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}
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