From 335fa130635b463e9b5d8acce30178fd6d180d9a Mon Sep 17 00:00:00 2001
From: tonihei <tonihei@google.com>
Date: Fri, 24 Aug 2018 03:43:50 -0700
Subject: [PATCH] Use set-like behaviour for BaseDataSource listeners.

This prevents problems caused by unintended double-registration of the same
transfer listener.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=210078454
---
 .../google/android/exoplayer2/upstream/BaseDataSource.java  | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/library/core/src/main/java/com/google/android/exoplayer2/upstream/BaseDataSource.java b/library/core/src/main/java/com/google/android/exoplayer2/upstream/BaseDataSource.java
index 18a7dcea49..5ed2e33d2b 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/upstream/BaseDataSource.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/upstream/BaseDataSource.java
@@ -47,8 +47,10 @@ public abstract class BaseDataSource implements DataSource {
 
   @Override
   public final void addTransferListener(TransferListener transferListener) {
-    listeners.add(transferListener);
-    listenerCount++;
+    if (!listeners.contains(transferListener)) {
+      listeners.add(transferListener);
+      listenerCount++;
+    }
   }
 
   /**