shithub: libvpx

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ref: d45e55015e85897c4307959b5f9df94da5b41f33
parent: 18c902f8a416ae97de8143840234a416700a1e64
author: Frank Galligan <fgalligan@google.com>
date: Wed Sep 1 12:40:18 EDT 2010 

Fix rare deadlock before loop filter

There was an extremely rare deadlock that happened when one thread
was waiting to start the loop filter on frame n while the other
threads were starting to work on frame n+1.

Change-Id: Icc94f728b3b6663405435640d9a2996735ba19ef


--- a/vp8/decoder/threading.c
+++ b/vp8/decoder/threading.c
@@ -161,6 +161,8 @@
 
     while (1)
     {
+        int current_filter_level = 0;
+
         if (pbi->b_multithreaded_rd == 0)
             break;
 
@@ -279,6 +281,11 @@
                 }
             }
         }
+
+        // If |pbi->common.filter_level| is 0 the value can change in-between
+        // the sem_post and the check to call vp8_thread_loop_filter.
+        current_filter_level = pbi->common.filter_level;
+
         //  add this to each frame
         if ((mbrd->mb_row == pbi->common.mb_rows-1) || ((mbrd->mb_row == pbi->common.mb_rows-2) && (pbi->common.mb_rows % (pbi->decoding_thread_count+1))==1))
         {
@@ -286,7 +293,7 @@
             sem_post(&pbi->h_event_end_decoding);
         }
 
-        if ((pbi->b_multithreaded_lf) &&(pbi->common.filter_level))
+        if ((pbi->b_multithreaded_lf) && (current_filter_level))
             vp8_thread_loop_filter(pbi, mbrd, ithread);
 
     }