core/java/com/android/internal/util/LocalLog.java

/*
 * 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.internal.util;

import java.io.PrintWriter;
import java.util.ArrayList;

import android.util.Slog;

/**
 * Helper class for logging serious issues, which also keeps a small
 * snapshot of the logged events that can be printed later, such as part
 * of a system service's dumpsys output.
 * @hide
 */
public class LocalLog {
    private final String mTag;
    private final int mMaxLines = 20;
    private final ArrayList<String> mLines = new ArrayList<String>(mMaxLines);

    public LocalLog(String tag) {
        mTag = tag;
    }

    public void w(String msg) {
        synchronized (mLines) {
            Slog.w(mTag, msg);
            if (mLines.size() >= mMaxLines) {
                mLines.remove(0);
            }
            mLines.add(msg);
        }
    }

    public boolean dump(PrintWriter pw, String header, String prefix) {
        synchronized (mLines) {
            if (mLines.size() <= 0) {
                return false;
            }
            if (header != null) {
                pw.println(header);
            }
            for (int i=0; i<mLines.size(); i++) {
                if (prefix != null) {
                    pw.print(prefix);
                }
                pw.println(mLines.get(i));
            }
            return true;
        }
    }
}