Tracer.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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
 * <p>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p>
 * 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.
 */

import java.io.Closeable;
import java.util.*;

public final class Tracer implements Closeable {

    private static List<StackTraceElement> cut(final List<StackTraceElement> trace, final int depth) {
        List<StackTraceElement> filtered = trace.subList(2, trace.size());
        return filtered.size() > depth ? filtered.subList(0, depth) : filtered;
    }

    public static Tracer record(final int depth) {
        final List<StackTraceElement> trace = cut(Arrays.asList(Thread.currentThread().getStackTrace()), depth);
        final long millis = System.currentTimeMillis();
        return new Tracer(millis, trace);
    }

    private static final Map<List<StackTraceElement>, List<Long>> timings = new HashMap<>();

    private final long start;
    private final List<StackTraceElement> trace;

    private Tracer(long start, List<StackTraceElement> trace) {
        this.start = start;
        this.trace = trace;
    }

    @Override
    public void close() {
        final long millis = System.currentTimeMillis();
        synchronized (Tracer.timings) {
            final List<Long> times;
            if (!Tracer.timings.containsKey(this.trace)) {
                times = new LinkedList<>();
                Tracer.timings.put(this.trace, times);
            } else {
                times = Tracer.timings.get(this.trace);
            }
            times.add(millis - this.start);
        }
    }

    public static void print() {
        synchronized (Tracer.timings) {
            timings.entrySet().forEach(kv -> print(kv.getKey(), kv.getValue()));
        }
    }

    private static void print(final List<StackTraceElement> trace, final List<Long> times) {
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>");
        trace.forEach(tr -> System.out.println(tr.toString()));
        final long min = times.stream().mapToLong(Tracer::id).min().getAsLong();
        final long max = times.stream().mapToLong(Tracer::id).max().getAsLong();
        final double avg = times.stream().mapToLong(Tracer::id).average().getAsDouble();
        final int count = times.size();
        System.out.printf(Locale.US, "\tSUM: min/max/avg/cnt: %d/%d/%f/%d\n", min, max, avg, count);
        System.out.println("<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<");
    }

    private static <X> X id(X x) {
        return x;
    }
}