Colin Cross | 7bb052a | 2015-02-03 12:59:37 -0800 | [diff] [blame^] | 1 | // Copyright 2010 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 | package textproto |
| 6 | |
| 7 | import ( |
| 8 | "sync" |
| 9 | ) |
| 10 | |
| 11 | // A Pipeline manages a pipelined in-order request/response sequence. |
| 12 | // |
| 13 | // To use a Pipeline p to manage multiple clients on a connection, |
| 14 | // each client should run: |
| 15 | // |
| 16 | // id := p.Next() // take a number |
| 17 | // |
| 18 | // p.StartRequest(id) // wait for turn to send request |
| 19 | // «send request» |
| 20 | // p.EndRequest(id) // notify Pipeline that request is sent |
| 21 | // |
| 22 | // p.StartResponse(id) // wait for turn to read response |
| 23 | // «read response» |
| 24 | // p.EndResponse(id) // notify Pipeline that response is read |
| 25 | // |
| 26 | // A pipelined server can use the same calls to ensure that |
| 27 | // responses computed in parallel are written in the correct order. |
| 28 | type Pipeline struct { |
| 29 | mu sync.Mutex |
| 30 | id uint |
| 31 | request sequencer |
| 32 | response sequencer |
| 33 | } |
| 34 | |
| 35 | // Next returns the next id for a request/response pair. |
| 36 | func (p *Pipeline) Next() uint { |
| 37 | p.mu.Lock() |
| 38 | id := p.id |
| 39 | p.id++ |
| 40 | p.mu.Unlock() |
| 41 | return id |
| 42 | } |
| 43 | |
| 44 | // StartRequest blocks until it is time to send (or, if this is a server, receive) |
| 45 | // the request with the given id. |
| 46 | func (p *Pipeline) StartRequest(id uint) { |
| 47 | p.request.Start(id) |
| 48 | } |
| 49 | |
| 50 | // EndRequest notifies p that the request with the given id has been sent |
| 51 | // (or, if this is a server, received). |
| 52 | func (p *Pipeline) EndRequest(id uint) { |
| 53 | p.request.End(id) |
| 54 | } |
| 55 | |
| 56 | // StartResponse blocks until it is time to receive (or, if this is a server, send) |
| 57 | // the request with the given id. |
| 58 | func (p *Pipeline) StartResponse(id uint) { |
| 59 | p.response.Start(id) |
| 60 | } |
| 61 | |
| 62 | // EndResponse notifies p that the response with the given id has been received |
| 63 | // (or, if this is a server, sent). |
| 64 | func (p *Pipeline) EndResponse(id uint) { |
| 65 | p.response.End(id) |
| 66 | } |
| 67 | |
| 68 | // A sequencer schedules a sequence of numbered events that must |
| 69 | // happen in order, one after the other. The event numbering must start |
| 70 | // at 0 and increment without skipping. The event number wraps around |
| 71 | // safely as long as there are not 2^32 simultaneous events pending. |
| 72 | type sequencer struct { |
| 73 | mu sync.Mutex |
| 74 | id uint |
| 75 | wait map[uint]chan uint |
| 76 | } |
| 77 | |
| 78 | // Start waits until it is time for the event numbered id to begin. |
| 79 | // That is, except for the first event, it waits until End(id-1) has |
| 80 | // been called. |
| 81 | func (s *sequencer) Start(id uint) { |
| 82 | s.mu.Lock() |
| 83 | if s.id == id { |
| 84 | s.mu.Unlock() |
| 85 | return |
| 86 | } |
| 87 | c := make(chan uint) |
| 88 | if s.wait == nil { |
| 89 | s.wait = make(map[uint]chan uint) |
| 90 | } |
| 91 | s.wait[id] = c |
| 92 | s.mu.Unlock() |
| 93 | <-c |
| 94 | } |
| 95 | |
| 96 | // End notifies the sequencer that the event numbered id has completed, |
| 97 | // allowing it to schedule the event numbered id+1. It is a run-time error |
| 98 | // to call End with an id that is not the number of the active event. |
| 99 | func (s *sequencer) End(id uint) { |
| 100 | s.mu.Lock() |
| 101 | if s.id != id { |
| 102 | panic("out of sync") |
| 103 | } |
| 104 | id++ |
| 105 | s.id = id |
| 106 | if s.wait == nil { |
| 107 | s.wait = make(map[uint]chan uint) |
| 108 | } |
| 109 | c, ok := s.wait[id] |
| 110 | if ok { |
| 111 | delete(s.wait, id) |
| 112 | } |
| 113 | s.mu.Unlock() |
| 114 | if ok { |
| 115 | c <- 1 |
| 116 | } |
| 117 | } |