From 4fe51789578e92ca399de3dfaf8c5f5c808f59ae Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tim-Philipp=20M=C3=BCller?= <tim@centricular.com>
Date: Thu, 1 Feb 2018 19:25:49 +0000
Subject: [PATCH] appsrc: don't signal the GCond if no one is waiting on it

Performance optimisation: Keep track whenever the streaming
thread or the application thread are waiting on the GCond for
more space or new data, and only signal on the GCond if someone
is actually waiting. Avoids unnecessary syscalls and thus
context switches.
---
 gst-libs/gst/app/gstappsrc.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/gst-libs/gst/app/gstappsrc.c b/gst-libs/gst/app/gstappsrc.c
index a619925c2d..94ed6f7a90 100644
--- a/gst-libs/gst/app/gstappsrc.c
+++ b/gst-libs/gst/app/gstappsrc.c
@@ -101,11 +101,19 @@
 
 #include "gstappsrc.h"
 
+typedef enum
+{
+  NOONE_WAITING,
+  STREAM_WAITING,               /* streaming thread is waiting for application thread */
+  APP_WAITING,                  /* application thread is waiting for streaming thread */
+} GstAppSrcWaitStatus;
+
 struct _GstAppSrcPrivate
 {
   GCond cond;
   GMutex mutex;
   GstQueueArray *queue;
+  GstAppSrcWaitStatus wait_status;
 
   GstCaps *last_caps;
   GstCaps *current_caps;
@@ -569,6 +577,7 @@ gst_app_src_init (GstAppSrc * appsrc)
   g_mutex_init (&priv->mutex);
   g_cond_init (&priv->cond);
   priv->queue = gst_queue_array_new (16);
+  priv->wait_status = NOONE_WAITING;
 
   priv->size = DEFAULT_PROP_SIZE;
   priv->duration = DEFAULT_PROP_DURATION;
@@ -1233,7 +1242,8 @@ gst_app_src_create (GstBaseSrc * bsrc, guint64 offset, guint size,
         priv->offset += buf_size;
 
       /* signal that we removed an item */
-      g_cond_broadcast (&priv->cond);
+      if (priv->wait_status == APP_WAITING)
+        g_cond_broadcast (&priv->cond);
 
       /* see if we go lower than the empty-percent */
       if (priv->min_percent && priv->max_bytes) {
@@ -1267,7 +1277,9 @@ gst_app_src_create (GstBaseSrc * bsrc, guint64 offset, guint size,
       goto eos;
 
     /* nothing to return, wait a while for new data or flushing. */
+    priv->wait_status = STREAM_WAITING;
     g_cond_wait (&priv->cond, &priv->mutex);
+    priv->wait_status = NOONE_WAITING;
   }
   g_mutex_unlock (&priv->mutex);
   return ret;
@@ -1828,7 +1840,9 @@ gst_app_src_push_internal (GstAppSrc * appsrc, GstBuffer * buffer,
         GST_DEBUG_OBJECT (appsrc, "waiting for free space");
         /* we are filled, wait until a buffer gets popped or when we
          * flush. */
+        priv->wait_status = APP_WAITING;
         g_cond_wait (&priv->cond, &priv->mutex);
+        priv->wait_status = NOONE_WAITING;
       } else {
         /* no need to wait for free space, we just pump more data into the
          * queue hoping that the caller reacts to the enough-data signal and
@@ -1852,7 +1866,10 @@ gst_app_src_push_internal (GstAppSrc * appsrc, GstBuffer * buffer,
     gst_queue_array_push_tail (priv->queue, buffer);
     priv->queued_bytes += gst_buffer_get_size (buffer);
   }
-  g_cond_broadcast (&priv->cond);
+
+  if (priv->wait_status == STREAM_WAITING)
+    g_cond_broadcast (&priv->cond);
+
   g_mutex_unlock (&priv->mutex);
 
   return GST_FLOW_OK;