1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
|
/*
* Copyright (C) 2012 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.drrickorang.loopback;
/**
* Non-blocking pipe where writer writes to the pipe using write() and read reads from the pipe
* using read(). Data in the pipe are stored in the short array "mBuffer".
* The write side of a pipe permits overruns; flow control is the caller's responsibility.
*/
public class PipeShort extends Pipe {
private int mFront; // writer's current position
private int mRear; // reader's current position
private final short mBuffer[]; // store that data in the pipe
private volatile int mVolatileRear; // used to keep rear synchronized
/**
* IMPORTANT: Since a signed integer is used to store mRear and mFront, their values should not
* exceed 2^31 - 1, or else overflows happens and the positions of read and mFront becomes
* incorrect.
*/
public PipeShort(int maxSamples) {
super(maxSamples);
mBuffer = new short[mMaxValues];
}
/**
* offset must be >= 0.
* count is maximum number of bytes to copy, and must be >= 0.
* offset + count must be <= buffer.length.
* Return actual number of shorts copied, which will be >= 0.
*/
public int write(short[] buffer, int offset, int count) {
// mask the upper bits to get the correct position in the pipe
int rear = mRear & (mMaxValues - 1);
int written = mMaxValues - rear;
if (written > count) {
written = count;
}
System.arraycopy(buffer, offset, mBuffer, rear, written);
if (rear + written == mMaxValues) {
if ((count -= written) > rear) {
count = rear;
}
if (count > 0) {
System.arraycopy(buffer, offset + written, mBuffer, 0, count);
written += count;
}
}
mRear += written;
mVolatileRear = mRear;
return written;
}
@Override
public int read(short[] buffer, int offset, int count) {
int avail = availableToRead();
if (avail <= 0) {
return avail;
}
// An overrun can occur from here on and be silently ignored,
// but it will be caught at next read()
if (count > avail) {
count = avail;
}
// mask the upper bits to get the correct position in the pipe
int front = mFront & (mMaxValues - 1);
int read = mMaxValues - front;
if (read > count) {
read = count;
}
// In particular, an overrun during the System.arraycopy will result in reading corrupt data
System.arraycopy(mBuffer, front, buffer, offset, read);
// We could re-read the rear pointer here to detect the corruption, but why bother?
if (front + read == mMaxValues) {
if ((count -= read) > front) {
count = front;
}
if (count > 0) {
System.arraycopy(mBuffer, 0, buffer, offset + read, count);
read += count;
}
}
mFront += read;
return read;
}
@Override
public int availableToRead() {
int rear = mVolatileRear;
int avail = rear - mFront;
if (avail > mMaxValues) {
// Discard 1/16 of the most recent data in pipe to avoid another overrun immediately
int oldFront = mFront;
mFront = rear - mMaxValues + (mMaxValues >> 4);
mSamplesOverrun += mFront - oldFront;
++mOverruns;
return OVERRUN;
}
return avail;
}
@Override
public void flush() {
mRear = mFront;
mVolatileRear = mFront;
}
}
|
