From 77c63511d8809f7785328138e7e3a50303302730 Mon Sep 17 00:00:00 2001
From: Max Kellermann <max@duempel.org>
Date: Wed, 6 Nov 2013 23:30:29 +0100
Subject: [PATCH] PlayerThread: reduce the number of DecoderThread wakeups

After the number of decoded chunks has fallen below the threshold, the
PlayerThread woke up the DecoderThread over and over.  This commit
adds a boolean flag that avoids these duplicate wakeups, and thus
reduces the number of system calls.
---
 src/PlayerThread.cxx | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/src/PlayerThread.cxx b/src/PlayerThread.cxx
index e2e3ee3a4..cb3d6a9a4 100644
--- a/src/PlayerThread.cxx
+++ b/src/PlayerThread.cxx
@@ -68,6 +68,12 @@ class Player {
 	 */
 	bool decoder_starting;
 
+	/**
+	 * Did we wake up the DecoderThread recently?  This avoids
+	 * duplicate wakeup calls.
+	 */
+	bool decoder_woken;
+
 	/**
 	 * is the player paused?
 	 */
@@ -133,6 +139,7 @@ public:
 		:pc(_pc), dc(_dc), buffer(_buffer),
 		 buffering(true),
 		 decoder_starting(false),
+		 decoder_woken(false),
 		 paused(false),
 		 queued(true),
 		 output_open(false),
@@ -861,8 +868,13 @@ Player::PlayNextChunk()
 	pc.Lock();
 	if (!dc.IsIdle() &&
 	    dc.pipe->GetSize() <= (pc.buffered_before_play +
-				   buffer.GetSize() * 3) / 4)
-		dc.Signal();
+				   buffer.GetSize() * 3) / 4) {
+		if (!decoder_woken) {
+			decoder_woken = true;
+			dc.Signal();
+		}
+	} else
+		decoder_woken = false;
 	pc.Unlock();
 
 	return true;