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/*
* 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 com.android.inputmethod.research;
import java.util.LinkedList;
/**
* A buffer that holds a fixed number of LogUnits.
*
* LogUnits are added in and shifted out in temporal order. Only a subset of the LogUnits are
* actual words; the other LogUnits do not count toward the word limit. Once the buffer reaches
* capacity, adding another LogUnit that is a word evicts the oldest LogUnits out one at a time to
* stay under the capacity limit.
*
* This variant of a LogBuffer has a limited memory footprint because of its limited size. This
* makes it useful, for example, for recording a window of the user's most recent actions in case
* they want to report an observed error that they do not know how to reproduce.
*/
public class FixedLogBuffer extends LogBuffer {
/* package for test */ int mWordCapacity;
// The number of members of mLogUnits that are actual words.
private int mNumActualWords;
/**
* Create a new LogBuffer that can hold a fixed number of LogUnits that are words (and
* unlimited number of non-word LogUnits), and that outputs its result to a researchLog.
*
* @param wordCapacity maximum number of words
*/
public FixedLogBuffer(final int wordCapacity) {
super();
if (wordCapacity <= 0) {
throw new IllegalArgumentException("wordCapacity must be 1 or greater.");
}
mWordCapacity = wordCapacity;
mNumActualWords = 0;
}
protected int getNumActualWords() {
return mNumActualWords;
}
/**
* Adds a new LogUnit to the front of the LIFO queue, evicting existing LogUnit's
* (oldest first) if word capacity is reached.
*/
@Override
public void shiftIn(final LogUnit newLogUnit) {
if (newLogUnit.getWord() == null) {
// This LogUnit isn't a word, so it doesn't count toward the word-limit.
super.shiftIn(newLogUnit);
return;
}
if (mNumActualWords == mWordCapacity) {
shiftOutThroughFirstWord();
}
super.shiftIn(newLogUnit);
mNumActualWords++; // Must be a word, or we wouldn't be here.
}
@Override
public LogUnit unshiftIn() {
final LogUnit logUnit = super.unshiftIn();
if (logUnit != null && logUnit.hasWord()) {
mNumActualWords--;
}
return logUnit;
}
public void shiftOutThroughFirstWord() {
final LinkedList<LogUnit> logUnits = getLogUnits();
while (!logUnits.isEmpty()) {
final LogUnit logUnit = logUnits.removeFirst();
onShiftOut(logUnit);
if (logUnit.hasWord()) {
// Successfully shifted out a word-containing LogUnit and made space for the new
// LogUnit.
mNumActualWords--;
break;
}
}
}
/**
* Removes all LogUnits from the buffer without calling onShiftOut().
*/
@Override
public void clear() {
super.clear();
mNumActualWords = 0;
}
/**
* Called when a LogUnit is removed from the LogBuffer as a result of a shiftIn. LogUnits are
* removed in the order entered. This method is not called when shiftOut is called directly.
*
* Base class does nothing; subclasses may override if they want to record non-privacy sensitive
* events that fall off the end.
*/
protected void onShiftOut(final LogUnit logUnit) {
}
/**
* Called to deliberately remove the oldest LogUnit. Usually called when draining the
* LogBuffer.
*/
@Override
public LogUnit shiftOut() {
if (isEmpty()) {
return null;
}
final LogUnit logUnit = super.shiftOut();
if (logUnit.hasWord()) {
mNumActualWords--;
}
return logUnit;
}
}
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