src/main/java/org/cloudera/htrace/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
 *
 *     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.cloudera.htrace;

import java.lang.management.ManagementFactory;
import java.security.SecureRandom;
import java.util.List;
import java.util.Random;
import java.util.concurrent.CopyOnWriteArrayList;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.cloudera.htrace.impl.NullSpan;
import org.cloudera.htrace.impl.ProcessRootMilliSpan;

/**
 * A Tracer provides the implementation for collecting and distributing Spans
 * within a process.
 */
public class Tracer {
  public static final Log LOG = LogFactory.getLog(Tracer.class);
  private final static Random random = new SecureRandom();
  private final List<SpanReceiver> receivers = new CopyOnWriteArrayList<SpanReceiver>();
  private static final ThreadLocal<Span> currentTrace = new ThreadLocal<Span>() {
    @Override
    protected Span initialValue() {
      return NullSpan.getInstance();
    }
  };
  public static final TraceInfo DONT_TRACE = new TraceInfo(-1, -1);
  protected static String processId = null;

  private static Tracer instance = null;

  synchronized protected static Tracer getInstance() {
    if (instance == null) {
      instance = new Tracer();
    }
    return instance;
  }

  protected static TraceInfo traceInfo() {
    Span span = currentTrace.get();
    if (!span.equals(NullSpan.getInstance())) {
      return new TraceInfo(span.getTraceId(), span.getSpanId());
    }
    return DONT_TRACE;
  }

  protected Span on(String description) {
    Span parent = currentTrace.get();
    Span root;
    if (parent.equals(NullSpan.getInstance())) {
      root = new ProcessRootMilliSpan(description, random.nextLong(),
          random.nextLong(), Span.ROOT_SPAN_ID, getProcessId());
    } else {
      root = parent.child(description);
    }
    return setCurrentSpan(root);
  }

  protected boolean isTracing() {
    return !currentTrace.get().equals(NullSpan.getInstance());
  }

  protected Span currentTrace() {
    return currentTrace.get();
  }

  protected void deliver(Span span) {
    for (SpanReceiver receiver : receivers) {
      receiver.receiveSpan(span);
    }
  }

  protected void addReceiver(SpanReceiver receiver) {
    receivers.add(receiver);
  }

  protected void removeReceiver(SpanReceiver receiver) {
    receivers.remove(receiver);
  }

  protected Span setCurrentSpan(Span span) {
    if (span != null) {
      currentTrace.set(span);
    }
    return span;
  }
  
  protected void clearTraceStack() {
    while (isTracing()) {
      pop(currentTrace());
    }
  }

  protected void pop(Span span) {
    if (span != null) {
      if (!span.equals(currentTrace())
          && !currentTrace().equals(NullSpan.getInstance())) {
        LOG.warn("Stopped span: " + span
            + " that was not the current span. Current span is: "
            + currentTrace());
      }
      deliver(span);
      Span parent = span.getParent();
      currentTrace.set(parent != null ? parent : NullSpan.getInstance());
    } else {
      currentTrace.set(NullSpan.getInstance());
    }
  }

  protected int numReceivers() {
    return receivers.size();
  }

  static String getProcessId() {
    if (processId == null) {
      String mxBeanName = ManagementFactory.getRuntimeMXBean().getName();
      String cmdLine = System.getProperty("sun.java.command");
      if (cmdLine != null && !cmdLine.isEmpty()) {
        String fullClassName = cmdLine.split("\\s+")[0];
        String[] classParts = fullClassName.split("\\.");
        cmdLine = classParts[classParts.length - 1];
      }

      processId = cmdLine + " (" + mxBeanName + ")";
    }
    return processId;
  }
}