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Rewrite QRingBuffer

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QRingBuffer is a fully inlined class used in many I/O classes.
So, it must be as fast and small as possible. To this end, a lot of
unnecessary special cases were replaced by generic structures.

Change-Id: Ic189ced3b200924da158ce511d69d324337d01b6
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
This commit is contained in:
Alex Trotsenko 2014-06-21 14:30:30 +03:00
parent 40705cb4c1
commit df4f334ad0
4 changed files with 297 additions and 189 deletions
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275
src/corelib/tools/qringbuffer_p.h
View File

@ -61,9 +61,9 @@ QT_BEGIN_NAMESPACE
class QRingBuffer
{
public:
explicit inline QRingBuffer(int growth = 4096) : basicBlockSize(growth) {
buffers << QByteArray();
clear();
explicit inline QRingBuffer(int growth = 4096) :
head(0), tail(0), tailBuffer(0), basicBlockSize(growth), bufferSize(0) {
buffers.append(QByteArray());
}
inline int nextDataBlockSize() const {
@ -78,115 +78,65 @@ public:
// the out-variable length will contain the amount of bytes readable
// from there, e.g. the amount still the same QByteArray
inline const char *readPointerAtPosition(qint64 pos, qint64 &length) const {
if (buffers.isEmpty()) {
length = 0;
return 0;
}
if (pos >= bufferSize) {
length = 0;
return 0;
}
// special case: it is in the first buffer
int nextDataBlockSizeValue = nextDataBlockSize();
if (pos < nextDataBlockSizeValue) {
length = nextDataBlockSizeValue - pos;
return buffers.at(0).constData() + head + pos;
}
// special case: we only had one buffer and tried to read over it
if (buffers.length() == 1) {
length = 0;
return 0;
}
// skip the first
pos -= nextDataBlockSizeValue;
// normal case: it is somewhere in the second to the-one-before-the-tailBuffer
for (int i = 1; i < tailBuffer; i++) {
if (pos >= buffers[i].size()) {
pos -= buffers[i].size();
continue;
if (pos >= 0) {
pos += head;
for (int i = 0; i < buffers.size(); ++i) {
length = (i == tailBuffer ? tail : buffers[i].size());
if (length > pos) {
length -= pos;
return buffers[i].constData() + pos;
}
pos -= length;
}
length = buffers[i].length() - pos;
return buffers[i].constData() + pos;
}
// it is in the tail buffer
length = tail - pos;
return buffers[tailBuffer].constData() + pos;
length = 0;
return 0;
}
inline void free(int bytes) {
bufferSize -= bytes;
if (bufferSize < 0)
bufferSize = 0;
while (bytes > 0) {
int blockSize = buffers.first().size() - head;
for (;;) {
int nextBlockSize = nextDataBlockSize();
if (bytes < nextBlockSize) {
head += bytes;
if (head == tail && tailBuffer == 0)
head = tail = 0;
break;
if (tailBuffer == 0 || blockSize > bytes) {
bufferSize -= bytes;
if (bufferSize <= 0)
clear(); // try to minify/squeeze us
else
head += bytes;
return;
}
bytes -= nextBlockSize;
if (buffers.count() == 1) {
if (buffers.at(0).size() != basicBlockSize)
buffers[0].resize(basicBlockSize);
head = tail = 0;
tailBuffer = 0;
break;
}
buffers.removeAt(0);
bufferSize -= blockSize;
bytes -= blockSize;
buffers.removeFirst();
--tailBuffer;
head = 0;
}
if (isEmpty())
clear(); // try to minify/squeeze us
}
inline char *reserve(int bytes) {
// if this is a fresh empty QRingBuffer
if (bufferSize == 0) {
buffers[0].resize(qMax(basicBlockSize, bytes));
bufferSize += bytes;
tail = bytes;
return buffers[tailBuffer].data();
if (bytes <= 0)
return 0;
// if need buffer reallocation
if (tail + bytes > buffers.last().size()) {
if (tail >= basicBlockSize) {
// shrink this buffer to its current size
buffers.last().resize(tail);
// create a new QByteArray
buffers.append(QByteArray());
++tailBuffer;
tail = 0;
}
buffers.last().resize(qMax(basicBlockSize, tail + bytes));
}
char *writePtr = buffers.last().data() + tail;
bufferSize += bytes;
// if there is already enough space, simply return.
if (tail + bytes <= buffers.at(tailBuffer).size()) {
char *writePtr = buffers[tailBuffer].data() + tail;
tail += bytes;
return writePtr;
}
// if our buffer isn't half full yet, simply resize it.
if (tail < buffers.at(tailBuffer).size() / 2) {
buffers[tailBuffer].resize(tail + bytes);
char *writePtr = buffers[tailBuffer].data() + tail;
tail += bytes;
return writePtr;
}
// shrink this buffer to its current size
buffers[tailBuffer].resize(tail);
// create a new QByteArray with the right size
buffers << QByteArray();
++tailBuffer;
buffers[tailBuffer].resize(qMax(basicBlockSize, bytes));
tail = bytes;
return buffers[tailBuffer].data();
tail += bytes;
return writePtr;
}
inline void truncate(int pos) {
@ -195,33 +145,22 @@ public:
}
inline void chop(int bytes) {
bufferSize -= bytes;
if (bufferSize < 0)
bufferSize = 0;
for (;;) {
// special case: head and tail are in the same buffer
if (tailBuffer == 0) {
tail -= bytes;
if (tail <= head)
tail = head = 0;
return;
}
if (bytes <= tail) {
tail -= bytes;
while (bytes > 0) {
if (tailBuffer == 0 || tail > bytes) {
bufferSize -= bytes;
if (bufferSize <= 0)
clear(); // try to minify/squeeze us
else
tail -= bytes;
return;
}
bufferSize -= tail;
bytes -= tail;
buffers.removeAt(tailBuffer);
buffers.removeLast();
--tailBuffer;
tail = buffers.at(tailBuffer).size();
tail = buffers.last().size();
}
if (isEmpty())
clear(); // try to minify/squeeze us
}
inline bool isEmpty() const {
@ -245,11 +184,11 @@ public:
--head;
if (head < 0) {
buffers.prepend(QByteArray());
buffers[0].resize(basicBlockSize);
buffers.first().resize(basicBlockSize);
head = basicBlockSize - 1;
++tailBuffer;
}
buffers[0][head] = c;
buffers.first()[head] = c;
++bufferSize;
}
@ -259,8 +198,7 @@ public:
inline void clear() {
buffers.erase(buffers.begin() + 1, buffers.end());
buffers[0].resize(0);
buffers[0].squeeze();
buffers.first().clear();
head = tail = 0;
tailBuffer = 0;
@ -269,47 +207,34 @@ public:
inline int indexOf(char c) const {
int index = 0;
int j = head;
for (int i = 0; i < buffers.size(); ++i) {
int start = 0;
int end = buffers.at(i).size();
const char *ptr = buffers[i].constData() + j;
j = index + (i == tailBuffer ? tail : buffers[i].size()) - j;
if (i == 0)
start = head;
if (i == tailBuffer)
end = tail;
const char *ptr = buffers.at(i).data() + start;
for (int j = start; j < end; ++j) {
while (index < j) {
if (*ptr++ == c)
return index;
++index;
}
j = 0;
}
return -1;
}
inline int indexOf(char c, int maxLength) const {
int index = 0;
int remain = qMin(size(), maxLength);
for (int i = 0; remain && i < buffers.size(); ++i) {
int start = 0;
int end = buffers.at(i).size();
int j = head;
for (int i = 0; index < maxLength && i < buffers.size(); ++i) {
const char *ptr = buffers[i].constData() + j;
j = qMin(index + (i == tailBuffer ? tail : buffers[i].size()) - j, maxLength);
if (i == 0)
start = head;
if (i == tailBuffer)
end = tail;
if (remain < end - start) {
end = start + remain;
remain = 0;
} else {
remain -= end - start;
}
const char *ptr = buffers.at(i).data() + start;
for (int j = start; j < end; ++j) {
while (index < j) {
if (*ptr++ == c)
return index;
++index;
}
j = 0;
}
return -1;
}
@ -318,10 +243,9 @@ public:
int bytesToRead = qMin(size(), maxLength);
int readSoFar = 0;
while (readSoFar < bytesToRead) {
const char *ptr = readPointer();
int bytesToReadFromThisBlock = qMin(bytesToRead - readSoFar, nextDataBlockSize());
if (data)
memcpy(data + readSoFar, ptr, bytesToReadFromThisBlock);
memcpy(data + readSoFar, readPointer(), bytesToReadFromThisBlock);
readSoFar += bytesToReadFromThisBlock;
free(bytesToReadFromThisBlock);
}
@ -333,37 +257,19 @@ public:
if (bufferSize == 0)
return QByteArray();
// multiple buffers, just take the first one
if (head == 0 && tailBuffer != 0) {
QByteArray qba = buffers.takeFirst();
--tailBuffer;
bufferSize -= qba.length();
return qba;
}
QByteArray qba(buffers.takeFirst());
// one buffer with good value for head. Just take it.
if (head == 0 && tailBuffer == 0) {
QByteArray qba = buffers.takeFirst();
qba.resize(tail);
buffers << QByteArray();
bufferSize = 0;
tail = 0;
return qba;
}
// Bad case: We have to memcpy.
// We can avoid by initializing the QRingBuffer with basicBlockSize of 0
// and only using this read() function.
QByteArray qba(readPointer(), nextDataBlockSize());
buffers.removeFirst();
head = 0;
qba.reserve(0); // avoid that resizing needlessly reallocates
if (tailBuffer == 0) {
buffers << QByteArray();
qba.resize(tail);
tail = 0;
buffers.append(QByteArray());
} else {
--tailBuffer;
}
bufferSize -= qba.length();
qba.remove(0, head); // does nothing if head is 0
head = 0;
bufferSize -= qba.size();
return qba;
}
@ -373,11 +279,11 @@ public:
buffers.last() = qba;
} else {
buffers.last().resize(tail);
buffers << qba;
buffers.append(qba);
++tailBuffer;
}
tail = qba.length();
bufferSize += qba.length();
tail = qba.size();
bufferSize += tail;
}
inline int skip(int length) {
@ -385,35 +291,26 @@ public:
}
inline int readLine(char *data, int maxLength) {
int index = indexOf('\n');
if (index == -1)
return read(data, maxLength);
if (maxLength <= 0)
if (!data || --maxLength <= 0)
return -1;
int readSoFar = 0;
while (readSoFar < index + 1 && readSoFar < maxLength - 1) {
int bytesToRead = qMin((index + 1) - readSoFar, nextDataBlockSize());
bytesToRead = qMin(bytesToRead, (maxLength - 1) - readSoFar);
memcpy(data + readSoFar, readPointer(), bytesToRead);
readSoFar += bytesToRead;
free(bytesToRead);
}
int i = indexOf('\n', maxLength);
i = read(data, i >= 0 ? (i + 1) : maxLength);
// Terminate it.
data[readSoFar] = '\0';
return readSoFar;
data[i] = '\0';
return i;
}
inline bool canReadLine() const {
return indexOf('\n') != -1;
return indexOf('\n') >= 0;
}
private:
QList<QByteArray> buffers;
int head, tail;
int tailBuffer; // always buffers.size() - 1
int basicBlockSize;
const int basicBlockSize;
int bufferSize;
};

120
tests/auto/corelib/tools/qringbuffer/tst_qringbuffer.cpp
View File

@ -54,7 +54,13 @@ private slots:
void sizeWhenEmpty();
void sizeWhenReservedAndChopped();
void sizeWhenReserved();
void free();
void reserveAndRead();
void chop();
void ungetChar();
void indexOf();
void appendAndRead();
void readLine();
};
void tst_QRingBuffer::sizeWhenReserved()
@ -180,6 +186,93 @@ void tst_QRingBuffer::readPointerAtPositionWriteRead()
QVERIFY(outData.buffer().startsWith(inData.buffer()));
}
void tst_QRingBuffer::free()
{
QRingBuffer ringBuffer;
// make three byte arrays with different sizes
ringBuffer.reserve(4096);
ringBuffer.reserve(2048);
ringBuffer.append(QByteArray("01234", 5));
ringBuffer.free(1);
QCOMPARE(ringBuffer.size(), 4095 + 2048 + 5);
ringBuffer.free(4096);
QCOMPARE(ringBuffer.size(), 2047 + 5);
ringBuffer.free(48);
ringBuffer.free(2000);
QCOMPARE(ringBuffer.size(), 4);
QVERIFY(memcmp(ringBuffer.readPointer(), "1234", 4) == 0);
}
void tst_QRingBuffer::reserveAndRead()
{
QRingBuffer ringBuffer;
// fill buffer with an arithmetic progression
for (int i = 1; i < 256; ++i) {
QByteArray ba(i, char(i));
char *ringPos = ringBuffer.reserve(i);
QVERIFY(ringPos);
memcpy(ringPos, ba.constData(), i);
}
// readback and check stored data
for (int i = 1; i < 256; ++i) {
QByteArray ba;
ba.resize(i);
int thisRead = ringBuffer.read(ba.data(), i);
QCOMPARE(thisRead, i);
QVERIFY(ba.count(char(i)) == i);
}
QVERIFY(ringBuffer.size() == 0);
}
void tst_QRingBuffer::chop()
{
QRingBuffer ringBuffer;
// make three byte arrays with different sizes
ringBuffer.append(QByteArray("01234", 5));
ringBuffer.reserve(2048);
ringBuffer.reserve(4096);
ringBuffer.chop(1);
QCOMPARE(ringBuffer.size(), 5 + 2048 + 4095);
ringBuffer.chop(4096);
QCOMPARE(ringBuffer.size(), 5 + 2047);
ringBuffer.chop(48);
ringBuffer.chop(2000);
QCOMPARE(ringBuffer.size(), 4);
QVERIFY(memcmp(ringBuffer.readPointer(), "0123", 4) == 0);
}
void tst_QRingBuffer::ungetChar()
{
QRingBuffer ringBuffer(16);
for (int i = 1; i < 32; ++i)
ringBuffer.putChar(char(i));
for (int i = 1; i < 31; ++i) {
int c = ringBuffer.getChar();
QVERIFY(c == 1);
ringBuffer.getChar();
ringBuffer.ungetChar(char(c)); // unget first char
}
QCOMPARE(ringBuffer.size(), 1);
}
void tst_QRingBuffer::indexOf()
{
QRingBuffer ringBuffer(16);
for (int i = 1; i < 256; ++i)
ringBuffer.putChar(char(i));
for (int i = 1; i < 256; ++i) {
int index = ringBuffer.indexOf(char(i));
QCOMPARE(i - 1, index);
QCOMPARE(index, ringBuffer.indexOf(char(i), i));
QVERIFY(ringBuffer.indexOf(char(i), i - 1) == -1); // test for absent char
}
}
void tst_QRingBuffer::appendAndRead()
{
QRingBuffer ringBuffer;
@ -195,5 +288,32 @@ void tst_QRingBuffer::appendAndRead()
QVERIFY(ringBuffer.read() == ba3);
}
void tst_QRingBuffer::readLine()
{
QRingBuffer ringBuffer;
QByteArray ba1("Hello world!\n", 13);
QByteArray ba2("\n", 1);
QByteArray ba3("Test string.", 12);
QByteArray ba4("0123456789", 10);
ringBuffer.append(ba1);
ringBuffer.append(ba2);
ringBuffer.append(ba3 + ba4 + ba2);
char stringBuf[102];
stringBuf[101] = 0; // non-crash terminator
QVERIFY(ringBuffer.readLine(stringBuf, sizeof(stringBuf) - 2) == ba1.size());
QVERIFY(QByteArray(stringBuf, strlen(stringBuf)) == ba1);
// check first empty string reading
stringBuf[0] = 0xFF;
QCOMPARE(ringBuffer.readLine(stringBuf, sizeof(stringBuf) - 2), ba2.size());
QVERIFY(stringBuf[0] == ba2[0]);
QVERIFY(ringBuffer.readLine(stringBuf, sizeof(stringBuf) - 2) == (ba3.size() + ba4.size()
+ ba2.size()));
QVERIFY(QByteArray(stringBuf, strlen(stringBuf)) == (ba3 + ba4 + ba2));
QVERIFY(ringBuffer.size() == 0);
}
QTEST_APPLESS_MAIN(tst_QRingBuffer)
#include "tst_qringbuffer.moc"

84
tests/benchmarks/corelib/tools/qringbuffer/main.cpp Normal file
View File

@ -0,0 +1,84 @@
/****************************************************************************
**
** Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies).
** Contact: http://www.qt-project.org/legal
**
** This file is part of the test suite of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and Digia. For licensing terms and
** conditions see http://qt.digia.com/licensing. For further information
** use the contact form at http://qt.digia.com/contact-us.
**
** GNU Lesser General Public License Usage
** Alternatively, this file may be used under the terms of the GNU Lesser
** General Public License version 2.1 as published by the Free Software
** Foundation and appearing in the file LICENSE.LGPL included in the
** packaging of this file. Please review the following information to
** ensure the GNU Lesser General Public License version 2.1 requirements
** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** In addition, as a special exception, Digia gives you certain additional
** rights. These rights are described in the Digia Qt LGPL Exception
** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU
** General Public License version 3.0 as published by the Free Software
** Foundation and appearing in the file LICENSE.GPL included in the
** packaging of this file. Please review the following information to
** ensure the GNU General Public License version 3.0 requirements will be
** met: http://www.gnu.org/copyleft/gpl.html.
**
**
** $QT_END_LICENSE$
**
****************************************************************************/
#include <private/qringbuffer_p.h>
#include <QByteArray>
#include <qtest.h>
class tst_qringbuffer : public QObject
{
Q_OBJECT
private slots:
void reserveAndRead();
void free();
};
void tst_qringbuffer::reserveAndRead()
{
QRingBuffer ringBuffer;
QBENCHMARK {
for (int i = 1; i < 256; ++i)
ringBuffer.reserve(i);
for (int i = 1; i < 256; ++i)
ringBuffer.read(0, i);
}
}
void tst_qringbuffer::free()
{
QRingBuffer ringBuffer;
QBENCHMARK {
ringBuffer.reserve(4096);
ringBuffer.reserve(2048);
ringBuffer.append(QByteArray("01234", 5));
ringBuffer.free(1);
ringBuffer.free(4096);
ringBuffer.free(48);
ringBuffer.free(2000);
}
}
QTEST_MAIN(tst_qringbuffer)
#include "main.moc"

7
tests/benchmarks/corelib/tools/qringbuffer/qringbuffer.pro Normal file
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@ -0,0 +1,7 @@
TEMPLATE = app
TARGET = tst_bench_qringbuffer
QT = core-private testlib
CONFIG += release
SOURCES += main.cpp