Make NetworkLock non-static and less specific.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=126682871

library/src/main/java/com/google/android/exoplayer/upstream/PriorityDataSource.java

@@ -16,39 +16,51 @@
 package com.google.android.exoplayer.upstream;
 
 import com.google.android.exoplayer.util.Assertions;
+import com.google.android.exoplayer.util.PriorityTaskManager;
 
 import android.net.Uri;
 
 import java.io.IOException;
 
 /**
- * Allows {@link #open(DataSpec)} and {@link #read(byte[], int, int)} calls only if the specified
- * priority is the highest priority of any task. {@link NetworkLock.PriorityTooLowException} is
- * thrown when this condition does not hold.
+ * A {@link DataSource} that can be used as part of a task registered with a
+ * {@link PriorityTaskManager}.
+ * <p>
+ * Calls to {@link #open(DataSpec)} and {@link #read(byte[], int, int)} are allowed to proceed only
+ * if there are no higher priority tasks registered to the {@link PriorityTaskManager}. If there
+ * exists a higher priority task then {@link PriorityTaskManager.PriorityTooLowException} is thrown.
+ * <p>
+ * Instances of this class are intended to be used as parts of (possibly larger) tasks that are
+ * registered with the {@link PriorityTaskManager}, and hence do <em>not</em> register as tasks
+ * themselves.
  */
 public final class PriorityDataSource implements DataSource {
 
   private final DataSource upstream;
+  private final PriorityTaskManager priorityTaskManager;
   private final int priority;
 
   /**
-   * @param priority The priority of the source.
    * @param upstream The upstream {@link DataSource}.
+   * @param priorityTaskManager The priority manager to which the task is registered.
+   * @param priority The priority of the task.
    */
-  public PriorityDataSource(int priority, DataSource upstream) {
-    this.priority = priority;
+  public PriorityDataSource(DataSource upstream, PriorityTaskManager priorityTaskManager,
+      int priority) {
     this.upstream = Assertions.checkNotNull(upstream);
+    this.priorityTaskManager = Assertions.checkNotNull(priorityTaskManager);
+    this.priority = priority;
   }
 
   @Override
   public long open(DataSpec dataSpec) throws IOException {
-    NetworkLock.instance.proceedOrThrow(priority);
+    priorityTaskManager.proceedOrThrow(priority);
     return upstream.open(dataSpec);
   }
 
   @Override
   public int read(byte[] buffer, int offset, int max) throws IOException {
-    NetworkLock.instance.proceedOrThrow(priority);
+    priorityTaskManager.proceedOrThrow(priority);
     return upstream.read(buffer, offset, max);
   }
 

library/src/main/java/com/google/android/exoplayer/util/PriorityTaskManager.java

@@ -13,26 +13,24 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package com.google.android.exoplayer.upstream;
+package com.google.android.exoplayer.util;
 
 import java.io.IOException;
+import java.util.Collections;
 import java.util.PriorityQueue;
 
 /**
- * A network task prioritization mechanism.
+ * Allows tasks with associated priorities to control how they proceed relative to one another.
  * <p>
- * Manages different priority network tasks. A network task that wishes to have its priority
- * respected, and respect the priority of other tasks, should register itself with the lock prior
- * to making network requests. It should then call one of the lock's proceed methods frequently
- * during execution, so as to ensure that it continues only if it is the highest (or equally
- * highest) priority task.
- * <p>
- * Note that lower integer values correspond to higher priorities.
+ * A task should call {@link #add(int)} to register with the manager and {@link #remove(int)} to
+ * unregister. A registered task will prevent tasks of lower priority from proceeding, and should
+ * call {@link #proceed(int)}, {@link #proceedNonBlocking(int)} or {@link #proceedOrThrow(int)} each
+ * time it wishes to check whether it is itself allowed to proceed.
  */
-public final class NetworkLock {
+public final class PriorityTaskManager {
 
   /**
-   * Thrown when a task is attempts to proceed when it does not have the highest priority.
+   * Thrown when task attempts to proceed when another registered task has a higher priority.
    */
   public static class PriorityTooLowException extends IOException {
 
@@ -42,67 +40,15 @@ public final class NetworkLock {
 
   }
 
-  public static final NetworkLock instance = new NetworkLock();
-
-  /**
-   * Priority for network tasks associated with media streaming.
-   */
-  public static final int STREAMING_PRIORITY = 0;
-  /**
-   * Priority for network tasks associated with background downloads.
-   */
-  public static final int DOWNLOAD_PRIORITY = 10;
-
   private final Object lock = new Object();
 
-  /** Guarded by {@link #lock}. */
+  // Guarded by lock.
   private final PriorityQueue<Integer> queue;
-
-  /** Guarded by {@link #lock}. */
   private int highestPriority;
 
-  private NetworkLock() {
-    queue = new PriorityQueue<>();
-    highestPriority = Integer.MAX_VALUE;
-  }
-
-  /**
-   * Blocks until the passed priority is the lowest one (i.e. highest priority).
-   *
-   * @param priority The priority of the task that would like to proceed.
-   */
-  public void proceed(int priority) throws InterruptedException {
-    synchronized (lock) {
-      while (highestPriority < priority) {
-        lock.wait();
-      }
-    }
-  }
-
-  /**
-   * A non-blocking variant of {@link #proceed(int)}.
-   *
-   * @param priority The priority of the task that would like to proceed.
-   * @return Whether the passed priority is allowed to proceed.
-   */
-  public boolean proceedNonBlocking(int priority) {
-    synchronized (lock) {
-      return highestPriority >= priority;
-    }
-  }
-
-  /**
-   * A throwing variant of {@link #proceed(int)}.
-   *
-   * @param priority The priority of the task that would like to proceed.
-   * @throws PriorityTooLowException If the passed priority is not high enough to proceed.
-   */
-  public void proceedOrThrow(int priority) throws PriorityTooLowException {
-    synchronized (lock) {
-      if (highestPriority < priority) {
-        throw new PriorityTooLowException(priority, highestPriority);
-      }
-    }
+  private PriorityTaskManager() {
+    queue = new PriorityQueue<>(10, Collections.reverseOrder());
+    highestPriority = Integer.MIN_VALUE;
   }
 
   /**
@@ -115,7 +61,47 @@ public final class NetworkLock {
   public void add(int priority) {
     synchronized (lock) {
       queue.add(priority);
-      highestPriority = Math.min(highestPriority, priority);
+      highestPriority = Math.max(highestPriority, priority);
+    }
+  }
+
+  /**
+   * Blocks until the task is allowed to proceed.
+   *
+   * @param priority The priority of the task.
+   * @throws InterruptedException If the thread is interrupted.
+   */
+  public void proceed(int priority) throws InterruptedException {
+    synchronized (lock) {
+      while (highestPriority != priority) {
+        lock.wait();
+      }
+    }
+  }
+
+  /**
+   * A non-blocking variant of {@link #proceed(int)}.
+   *
+   * @param priority The priority of the task.
+   * @return Whether the task is allowed to proceed.
+   */
+  public boolean proceedNonBlocking(int priority) {
+    synchronized (lock) {
+      return highestPriority == priority;
+    }
+  }
+
+  /**
+   * A throwing variant of {@link #proceed(int)}.
+   *
+   * @param priority The priority of the task.
+   * @throws PriorityTooLowException If the task is not allowed to proceed.
+   */
+  public void proceedOrThrow(int priority) throws PriorityTooLowException {
+    synchronized (lock) {
+      if (highestPriority != priority) {
+        throw new PriorityTooLowException(priority, highestPriority);
+      }
     }
   }
 
@@ -127,7 +113,7 @@ public final class NetworkLock {
   public void remove(int priority) {
     synchronized (lock) {
       queue.remove(priority);
-      highestPriority = queue.isEmpty() ? Integer.MAX_VALUE : queue.peek();
+      highestPriority = queue.isEmpty() ? Integer.MIN_VALUE : queue.peek();
       lock.notifyAll();
     }
   }