content: /*
   * Copyright (C) 2016 The Android Open Source Project
   *
   * 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 com.google.android.exoplayer2.util;
  
  /**
   * An interruptible condition variable. This class provides a number of benefits over {@link
   * android.os.ConditionVariable}:
   *
   * <ul>
   *   <li>Consistent use of ({@link Clock#elapsedRealtime()} for timing {@link #block(long)} timeout
   *       intervals. {@link android.os.ConditionVariable} used {@link System#currentTimeMillis()}
   *       prior to Android 10, which is not a correct clock to use for interval timing because it's
   *       not guaranteed to be monotonic.
   *   <li>Support for injecting a custom {@link Clock}.
   *   <li>The ability to query the variable's current state, by calling {@link #isOpen()}.
   *   <li>{@link #open()} and {@link #close()} return whether they changed the variable's state.
   * </ul>
   */
  public class ConditionVariable {
  
    private final Clock clock;
    private boolean isOpen;
  
    /** Creates an instance using {@link Clock#DEFAULT}. */
    public ConditionVariable() {
      this(Clock.DEFAULT);
    }
  
    /**
     * Creates an instance, which starts closed.
     *
     * @param clock The {@link Clock} whose {@link Clock#elapsedRealtime()} method is used to
     *     determine when {@link #block(long)} should time out.
     */
    public ConditionVariable(Clock clock) {
      this.clock = clock;
    }
  
    /**
     * Opens the condition and releases all threads that are blocked.
     *
     * @return True if the condition variable was opened. False if it was already open.
     */
    public synchronized boolean open() {
      if (isOpen) {
        return false;
      }
      isOpen = true;
      notifyAll();
      return true;
    }
  
    /**
     * Closes the condition.
     *
     * @return True if the condition variable was closed. False if it was already closed.
     */
    public synchronized boolean close() {
      boolean wasOpen = isOpen;
      isOpen = false;
      return wasOpen;
    }
  
    /**
     * Blocks until the condition is opened.
     *
     * @throws InterruptedException If the thread is interrupted.
     */
    public synchronized void block() throws InterruptedException {
      while (!isOpen) {
        wait();
      }
    }
  
    /**
     * Blocks until the condition is opened or until {@code timeoutMs} have passed.
     *
     * @param timeoutMs The maximum time to wait in milliseconds. If {@code timeoutMs <= 0} then the
     *     call will return immediately without blocking.
     * @return True if the condition was opened, false if the call returns because of the timeout.
     * @throws InterruptedException If the thread is interrupted.
     */
    public synchronized boolean block(long timeoutMs) throws InterruptedException {
      if (timeoutMs <= 0) {
        return isOpen;
      }
      long nowMs = clock.elapsedRealtime();
      long endMs = nowMs + timeoutMs;
      if (endMs < nowMs) {
        // timeoutMs is large enough for (nowMs + timeoutMs) to rollover. Block indefinitely.
        block();
      } else {
        while (!isOpen && nowMs < endMs) {
          wait(endMs - nowMs);
          nowMs = clock.elapsedRealtime();
        }
      }
      return isOpen;
    }
  
    /**
     * Blocks until the condition is open. Unlike {@link #block}, this method will continue to block
     * if the calling thread is interrupted. If the calling thread was interrupted then its {@link
     * Thread#isInterrupted() interrupted status} will be set when the method returns.
     */
    public synchronized void blockUninterruptible() {
      boolean wasInterrupted = false;
      while (!isOpen) {
        try {
          wait();
        } catch (InterruptedException e) {
          wasInterrupted = true;
        }
      }
      if (wasInterrupted) {
        // Restore the interrupted status.
        Thread.currentThread().interrupt();
      }
    }
  
    /** Returns whether the condition is opened. */
    public synchronized boolean isOpen() {
      return isOpen;
    }
  }
  