CountingIdlingResource.java

package com.google.android.apps.common.testing.ui.espresso.contrib;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;

import com.google.android.apps.common.testing.ui.espresso.IdlingResource;

import android.os.SystemClock;
import android.util.Log;

import java.util.concurrent.atomic.AtomicInteger;

/**
 * An implementation of {@link IdlingResource} that determines idleness by maintaining an internal
 * counter. When the counter is 0 - it is considered to be idle, when it is non-zero it is not
 * idle. This is very similar to the way a {@link java.util.concurrent.Semaphore} behaves.
 * <p>
 * The counter may be incremented or decremented from any thread. If it reaches an illogical state
 * (like counter less than zero) it will throw an IllegalStateException.
 * </p>
 * <p>
 * This class can then be used to wrap up operations that while in progress should block tests from
 * accessing the UI.
 * </p>
 *
 * <pre>
 * {@code
 *   public interface FooServer {
 *     public Foo newFoo();
 *     public void updateFoo(Foo foo);
 *   }
 *
 *   public DecoratedFooServer implements FooServer {
 *     private final FooServer realFooServer;
 *     private final CountingIdlingResource fooServerIdlingResource;
 *
 *     public DecoratedFooServer(FooServer realFooServer,
 *         CountingIdlingResource fooServerIdlingResource) {
 *       this.realFooServer = checkNotNull(realFooServer);
 *       this.fooServerIdlingResource = checkNotNull(fooServerIdlingResource);
 *     }
 *
 *     public Foo newFoo() {
 *       fooServerIdlingResource.increment();
 *       try {
 *         return realFooServer.newFoo();
 *       } finally {
 *         fooServerIdlingResource.decrement();
 *       }
 *     }
 *
 *     public void updateFoo(Foo foo) {
 *       fooServerIdlingResource.increment();
 *       try {
 *         realFooServer.updateFoo(foo);
 *       } finally {
 *         fooServerIdlingResource.decrement();
 *       }
 *     }
 *   }
 *   }
 *   </pre>
 *
 *   Then in your test setup:
 *   <pre>
 *   {@code
 *     public void setUp() throws Exception {
 *       super.setUp();
 *       FooServer realServer = FooApplication.getFooServer();
 *       CountingIdlingResource countingResource = new CountingIdlingResource("FooServerCalls");
 *       FooApplication.setFooServer(new DecoratedFooServer(realServer, countingResource));
 *       Espresso.registerIdlingResource(countingResource);
 *     }
 *   }
 *   </pre>
 *
 */
@SuppressWarnings("javadoc")
public final class CountingIdlingResource implements IdlingResource {
  private static final String TAG = "CountingIdlingResource";
  private final String resourceName;
  private final AtomicInteger counter = new AtomicInteger(0);
  private final boolean debugCounting;

  // written from main thread, read from any thread.
  private volatile ResourceCallback resourceCallback;

  // read/written from any thread - used for debugging messages.
  private volatile long becameBusyAt = 0;
  private volatile long becameIdleAt = 0;

  /**
   * Creates a CountingIdlingResource without debug tracing.
   *
   * @param resourceName the resource name this resource should report to Espresso.
   */
  public CountingIdlingResource(String resourceName) {
    this(resourceName, false);
  }

  /**
   * Creates a CountingIdlingResource.
   *
   * @param resourceName the resource name this resource should report to Espresso.
   * @param debugCounting if true increment & decrement calls will print trace information to logs.
   */
  public CountingIdlingResource(String resourceName, boolean debugCounting) {
    this.resourceName = checkNotNull(resourceName);
    this.debugCounting = debugCounting;
  }

  @Override
  public String getName() {
    return resourceName;
  }

  @Override
  public boolean isIdleNow() {
    return counter.get() == 0;
  }

  @Override
  public void registerIdleTransitionCallback(ResourceCallback resourceCallback) {
    this.resourceCallback = resourceCallback;
  }

  /**
   * Increments the count of in-flight transactions to the resource being monitored.
   *
   * This method can be called from any thread.
   */
  public void increment() {
    int counterVal = counter.getAndIncrement();
    if (0 == counterVal) {
      becameBusyAt = SystemClock.uptimeMillis();
    }

    if (debugCounting) {
      Log.i(TAG, "Resource: " + resourceName + " in-use-count incremented to: " + (counterVal + 1));
    }
  }

  /**
   * Decrements the count of in-flight transactions to the resource being monitored.
   *
   * If this operation results in the counter falling below 0 - an exception is raised.
   *
   * @throws IllegalStateException if the counter is below 0.
   */
  public void decrement() {
    int counterVal = counter.decrementAndGet();

    if (counterVal == 0) {
      // we've gone from non-zero to zero. That means we're idle now! Tell espresso.
      if (null != resourceCallback) {
        resourceCallback.onTransitionToIdle();
      }
      becameIdleAt = SystemClock.uptimeMillis();
    }

    if (debugCounting) {
      if (counterVal == 0) {
        Log.i(TAG, "Resource: " + resourceName + " went idle! (Time spent not idle: " +
            (becameIdleAt - becameBusyAt) + ")");
      } else {
        Log.i(TAG, "Resource: " + resourceName + " in-use-count decremented to: " + counterVal);
      }
    }
    checkState(counterVal > -1, "Counter has been corrupted!");
  }

  /**
   * Prints the current state of this resource to the logcat at info level.
   */
  public void dumpStateToLogs() {
    StringBuilder message = new StringBuilder("Resource: ")
        .append(resourceName)
        .append(" inflight transaction count: ")
        .append(counter.get());
    if (0 == becameBusyAt) {
      Log.i(TAG, message.append(" and has never been busy!").toString());
    } else {
      message.append(" and was last busy at: ")
          .append(becameBusyAt);
      if (0 == becameIdleAt) {
        Log.w(TAG, message.append(" AND NEVER WENT IDLE!").toString());
      } else {
        message.append(" and last went idle at: ")
            .append(becameIdleAt);
        Log.i(TAG, message.toString());
      }
    }
  }
}