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Delta Between Two Patch Sets: ssh/buffer.go

Issue 6207051: code review 6207051: go.crypto/ssh: introduce a circular buffer for chanReader (Closed)
Left Patch Set: diff -r d59e35c8940f https://code.google.com/p/go.crypto Created 11 years, 10 months ago
Right Patch Set: diff -r d59e35c8940f https://code.google.com/p/go.crypto Created 11 years, 10 months ago
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LEFTRIGHT
1 // Copyright 2012 The Go Authors. All rights reserved. 1 // Copyright 2012 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style 2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file. 3 // license that can be found in the LICENSE file.
4 4
5 package ssh 5 package ssh
6 6
7 import ( 7 import (
8 "io" 8 "io"
9 "sync" 9 "sync"
10 ) 10 )
11 11
12 // buffer provides a linked list buffer for data exchange 12 // buffer provides a linked list buffer for data exchange
13 // between producer and consumer. Theoretically the buffer is 13 // between producer and consumer. Theoretically the buffer is
14 // of unlimited capacity as it does no allocation of its own. 14 // of unlimited capacity as it does no allocation of its own.
15 type buffer struct { 15 type buffer struct {
16 » // protects concurrent access to head, tail and eof 16 » // protects concurrent access to head, tail and closed
agl1 2012/05/14 15:21:31 s/eof/closed/?
dfc 2012/05/15 01:12:58 Done.
17 *sync.Cond 17 *sync.Cond
18 18
19 head *element // the buffer that will be read first 19 head *element // the buffer that will be read first
20 tail *element // the buffer that will be read last 20 tail *element // the buffer that will be read last
21 21
22 closed bool 22 closed bool
23 } 23 }
24 24
25 // An element represents a single link in a linked list. 25 // An element represents a single link in a linked list.
26 type element struct { 26 type element struct {
27 buf []byte 27 buf []byte
28 next *element 28 next *element
29 } 29 }
30 30
31 // newBuffer returns an empty buffer that is not closed. 31 // newBuffer returns an empty buffer that is not closed.
32 func newBuffer() *buffer { 32 func newBuffer() *buffer {
33 e := new(element) 33 e := new(element)
34 b := &buffer{ 34 b := &buffer{
35 Cond: newCond(), 35 Cond: newCond(),
36 head: e, 36 head: e,
37 tail: e, 37 tail: e,
38 } 38 }
39 return b 39 return b
40 } 40 }
41 41
42 // write makes buf available for Read to receive. 42 // write makes buf available for Read to receive.
agl1 2012/05/14 15:21:31 this refers to `buf' but the argument is called 'b
dfc 2012/05/15 01:12:58 Sorry, i'm not sure what you mean, the receiver is
agl1 2012/05/15 15:30:07 Sorry, my brain fart.
43 // buf must not be modified after the call to write. 43 // buf must not be modified after the call to write.
44 func (b *buffer) write(buf []byte) { 44 func (b *buffer) write(buf []byte) {
45 b.Cond.L.Lock() 45 b.Cond.L.Lock()
46 defer b.Cond.L.Unlock() 46 defer b.Cond.L.Unlock()
47 e := &element{buf: buf} 47 e := &element{buf: buf}
48 b.tail.next = e 48 b.tail.next = e
49 b.tail = e 49 b.tail = e
50 b.Cond.Signal() 50 b.Cond.Signal()
51 } 51 }
52 52
53 // eof closes the buffer. Reads from the buffer once all· 53 // eof closes the buffer. Reads from the buffer once all·
54 // the data has been consumed wiil receive os.EOF. 54 // the data has been consumed will receive os.EOF.
55 func (b *buffer) eof() error { 55 func (b *buffer) eof() error {
56 b.Cond.L.Lock() 56 b.Cond.L.Lock()
57 defer b.Cond.L.Unlock() 57 defer b.Cond.L.Unlock()
58 b.closed = true 58 b.closed = true
59 b.Cond.Signal() 59 b.Cond.Signal()
60 return nil 60 return nil
61 } 61 }
62 62
63 // Read reads data from the internal buffer in buf.· 63 // Read reads data from the internal buffer in buf.·
agl1 2012/05/14 15:21:31 ditto about buf/b.
dfc 2012/05/15 01:12:58 See above. On 2012/05/14 15:21:31, agl1 wrote:
64 // Reads will block if not data is available, or until 64 // Reads will block if no data is available, or until
agl1 2012/05/14 15:21:31 s/not/no/
dfc 2012/05/15 01:12:58 Done.
65 // the buffer is closed. 65 // the buffer is closed.
66 func (b *buffer) Read(buf []byte) (n int, err error) { 66 func (b *buffer) Read(buf []byte) (n int, err error) {
67 b.Cond.L.Lock() 67 b.Cond.L.Lock()
68 defer b.Cond.L.Unlock() 68 defer b.Cond.L.Unlock()
69 » for { 69 » for len(buf) > 0 {
70 // if there is data in b.head, copy it 70 // if there is data in b.head, copy it
71 if len(b.head.buf) > 0 { 71 if len(b.head.buf) > 0 {
72 r := copy(buf, b.head.buf) 72 r := copy(buf, b.head.buf)
73 buf, b.head.buf = buf[r:], b.head.buf[r:] 73 buf, b.head.buf = buf[r:], b.head.buf[r:]
74 n += r 74 n += r
75 if len(buf) == 0 {
agl1 2012/05/14 15:21:31 I think it's very slightly nicer if the for loop h
dfc 2012/05/15 01:12:58 Thanks for the suggestion, it is nicer and the log
76 // dest full
77 break
78 }
79 continue 75 continue
80 } 76 }
81 // if there is a next buffer, make it the head 77 // if there is a next buffer, make it the head
82 if len(b.head.buf) == 0 && b.head != b.tail { 78 if len(b.head.buf) == 0 && b.head != b.tail {
83 b.head = b.head.next 79 b.head = b.head.next
84 continue 80 continue
85 } 81 }
86 » » // if at least one byte has been copied return 82 » » // if at least one byte has been copied, return
87 if n > 0 { 83 if n > 0 {
88 break 84 break
89 } 85 }
90 » » // out of buffers, wait for producer 86 » » // if nothing was read, and there is nothing outstanding
agl1 2012/05/14 15:21:31 this comment should be moved down to the Wait()?
dfc 2012/05/15 01:12:58 Done.
87 » » // check to see if the buffer is closed.
91 if b.closed { 88 if b.closed {
92 err = io.EOF 89 err = io.EOF
93 break 90 break
94 } 91 }
92 // out of buffers, wait for producer
95 b.Cond.Wait() 93 b.Cond.Wait()
96 } 94 }
97 return 95 return
98 } 96 }
LEFTRIGHT
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