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/*
 * Copyright 2011 Software Freedom Conservancy.
 *
 *  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 org.openqa.selenium.support;

import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebDriverException;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;

/**
 * Multithreaded client code should use this to assert that it accesses webdriver in a
 * thread-safe manner.
 *
 * Wrap WebDriver instances as follows:
 *
 *  * WebDriver driver = ThreadGuard.protect(new FirefoxDriver());
 * 
 *
 * Threading issues related to incorrect client threading may have mysterious and hard to diagnose
 * errors. Using this wrapper prevents this category of errors. It is recommended for all
 * multithreaded usage. This class has no overhead of any importance.
 *
 */
public class ThreadGuard {

  public static WebDriver protect(WebDriver actualWebDriver) {
    WebDriverInvocationHandler invocationHandler = new WebDriverInvocationHandler(actualWebDriver);
    return (WebDriver) java.lang.reflect.Proxy
        .newProxyInstance(actualWebDriver.getClass().getClassLoader(),
                          getInterfaces(actualWebDriver),
                          invocationHandler);
  }

  private static Class[] getInterfaces(Object target) {
    Class base = target.getClass();
    Set interfaces = new HashSet();
    if (base.isInterface()) {
      interfaces.add(base);
    }
    while (base != null && !Object.class.equals(base)) {
      interfaces.addAll(Arrays.asList(base.getInterfaces()));
      base = base.getSuperclass();
    }
    return interfaces.toArray(new Class[interfaces.size()]);

  }

  static class WebDriverInvocationHandler implements InvocationHandler {

    private final long threadId;
    private final Object underlying;
    private final String threadName;


    public WebDriverInvocationHandler(Object underlyingWebDriver) {
      Thread thread = Thread.currentThread();
      this.threadId = thread.getId();
      this.threadName = thread.getName();
      this.underlying = underlyingWebDriver;
    }

    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
      try {
        if (Thread.currentThread().getId() != threadId) {
          Thread currentThread = Thread.currentThread();
          throw new WebDriverException(
              String.format("Thread safety error; this instance of WebDriver was constructed on " +
                            "thread %s (id %d) and is being accessed by thread %s (id %d)" +
                            "This is not permitted and *will* cause undefined behaviour",
                            threadName, threadId, currentThread.getName(), currentThread.getId()));
        }
        return invokeUnderlying(method, args);
      } catch (InvocationTargetException e) {
        throw e.getTargetException();
      }
    }

    protected Object invokeUnderlying(Method method, Object[] args)
        throws IllegalAccessException, InvocationTargetException {
      return method.invoke(underlying, args);
    }
  }

}