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Spock is a testing and specification framework for Java and Groovy applications. What makes it stand out from the crowd is its beautiful and highly expressive specification language. Thanks to its JUnit runner, Spock is compatible with most IDEs, build tools, and continuous integration servers. Spock is inspired from JUnit, jMock, RSpec, Groovy, Scala, Vulcans, and other fascinating life forms.

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/*
 * Copyright 2010 the original author or authors.
 *
 * 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
 *     https://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 spock.util.concurrent;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;

import org.spockframework.runtime.SpockTimeoutError;
import org.spockframework.util.ThreadSafe;
import org.spockframework.util.TimeUtil;

/**
 * A statically typed variable whose get() method will block until some other
 * thread has set a value with the set() method, or a timeout expires. Useful
 * for verifying state in an expect- or then-block that has been captured in
 * some other thread.
 *
 * Example:
 * 
 * // create object under specification
 * def machine = new Machine()
 *
 * def result = new BlockingVariable<WorkResult>
 *
 * // register async callback
 * machine.workDone >> { r ->
 *  result.set(r)
 * }
 *
 * when:
 * machine.start()
 *
 * then:
 * // blocks until workDone callback has set result, or a timeout expires
 * result.get() == WorkResult.OK
 *
 * cleanup:
 * // shut down all threads
 * machine?.shutdown()
 * 
 *
 * @param  the variable's type
 *
 * @author Peter Niederwieser
 */
@ThreadSafe
public class BlockingVariable {
  private final double timeout;

  private T value; // access guarded by valueReady
  private final CountDownLatch valueReady = new CountDownLatch(1);

  /**
   * Same as BlockingVariable(1).
   */
  public BlockingVariable() {
    this(1);
  }

  /**
   * Instantiates a BlockingVariable with the specified timeout in seconds.
   *
   * @param timeout the timeout (in seconds) for calls to get().
   */
  public BlockingVariable(double timeout) {
    this.timeout = timeout;
  }

  /**
   * Instantiates a BlockingVariable with the specified timeout.
   *
   * @param timeout the timeout for calls to get().
   * @param unit the time unit
   *
   * @deprecated use {@link #BlockingVariable(double)} instead
   */
  @Deprecated
  public BlockingVariable(int timeout, TimeUnit unit) {
    this(TimeUtil.toSeconds(timeout, unit));
  }

  /**
   * Returns the timeout (in seconds).
   *
   * @return the timeout (in seconds)
   */
  public double getTimeout() {
    return timeout;
  }

  /**
   * Blocks until a value has been set for this variable, or a timeout expires.
   *
   * @return the variable's value
   *
   * @throws InterruptedException if the calling thread is interrupted
   */
  public T get() throws InterruptedException {
    if (!valueReady.await((long) (timeout * 1000), TimeUnit.MILLISECONDS)) {
      String msg = String.format("BlockingVariable.get() timed out after %1.2f seconds", timeout);
      throw new SpockTimeoutError(timeout, msg);
    }
    return value;
  }

  /**
   * Sets a value for this variable. Wakes up all threads blocked in get().
   *
   * @param value the value to be set for this variable
   */
  public void set(T value) {
    this.value = value;
    valueReady.countDown();
  }
}