Improved thread locking in the ring buffer to avoid possible race conditions under heavy load

3 files changed, 40 insertions, 32 deletions

diff --git a/CONTRIBUTORS b/CONTRIBUTORS
index 88f997ce..bff993cf 100644
--- a/CONTRIBUTORS
+++ b/CONTRIBUTORS
@@ -157,6 +157,8 @@ Werner Fink <werner@suse.de>
  for helping to debug leftover 'zombie' processes when closing a pipe
  for making the Dolby Digital thread start only if the recording actually
  contains Dolby Digital data
+ for improving thread locking in the ring buffer to avoid possible race conditions
+ under heavy load
 
 Rolf Hakenes <hakenes@hippomi.de>
  for providing 'libdtv' and adapting the EIT mechanisms to it
diff --git a/HISTORY b/HISTORY
index e2d69225..49d94a05 100644
--- a/HISTORY
+++ b/HISTORY
@@ -1191,7 +1191,7 @@ Video Disk Recorder Revision History
   same name was manually deleted on a system with more than one video directory
   (thanks to Dirk Wiebel for reporting this one).
 
-2002-04-13: Version 1.0.1
+2002-04-19: Version 1.0.1
 
 - Added some DVB-T channels for Berlin (Germany) to channels.conf.terr (thanks to
   Andreas Roedl).
@@ -1204,3 +1204,5 @@ Video Disk Recorder Revision History
   any timers referencing a channel with a number higher than 102 should be
   checked and adapted if necessary (this only applies if you are using the default
   'channels.conf').
+- Improved thread locking in the ring buffer to avoid possible race conditions
+  under heavy load (thanks to Werner Fink).
diff --git a/ringbuffer.c b/ringbuffer.c
index 8b8420c1..88b515b4 100644
--- a/ringbuffer.c
+++ b/ringbuffer.c
@@ -7,7 +7,7 @@
  * Parts of this file were inspired by the 'ringbuffy.c' from the
  * LinuxDVB driver (see linuxtv.org).
  *
- * $Id: ringbuffer.c 1.5 2001/11/03 09:50:46 kls Exp $
+ * $Id: ringbuffer.c 1.6 2002/04/19 12:38:44 kls Exp $
  */
 
 #include "ringbuffer.h"
@@ -154,7 +154,6 @@ int cRingBufferLinear::Put(const uchar *Data, int Count)
      Lock();
      int rest = Size() - head;
      int diff = tail - head;
-     Unlock();
      int free = (diff > 0) ? diff - 1 : Size() + diff - 1;
      if (statistics) {
         int fill = Size() - free - 1 + Count;
@@ -167,22 +166,25 @@ int cRingBufferLinear::Put(const uchar *Data, int Count)
               dsyslog(LOG_INFO, "buffer usage: %d%%", percent);
            }
         }
-     if (free <= 0)
-        return 0;
-     if (free < Count)
-        Count = free;
-     if (Count > maxFill)
-        maxFill = Count;
-     if (Count >= rest) {
-        memcpy(buffer + head, Data, rest);
-        if (Count - rest)
-           memcpy(buffer, Data + rest, Count - rest);
-        head = Count - rest;
-        }
-     else {
-        memcpy(buffer + head, Data, Count);
-        head += Count;
+     if (free > 0) {
+        if (free < Count)
+           Count = free;
+        if (Count > maxFill)
+           maxFill = Count;
+        if (Count >= rest) {
+           memcpy(buffer + head, Data, rest);
+           if (Count - rest)
+              memcpy(buffer, Data + rest, Count - rest);
+           head = Count - rest;
+           }
+        else {
+           memcpy(buffer + head, Data, Count);
+           head += Count;
+           }
         }
+     else
+        Count = 0;
+     Unlock();
      }
   return Count;
 }
@@ -193,22 +195,24 @@ int cRingBufferLinear::Get(uchar *Data, int Count)
      Lock();
      int rest = Size() - tail;
      int diff = head - tail;
-     Unlock();
      int cont = (diff >= 0) ? diff : Size() + diff;
-     if (rest <= 0)
-        return 0;
-     if (cont < Count)
-        Count = cont;
-     if (Count >= rest) {
-        memcpy(Data, buffer + tail, rest);
-        if (Count - rest)
-           memcpy(Data + rest, buffer, Count - rest);
-        tail = Count - rest;
-        }
-     else {
-        memcpy(Data, buffer + tail, Count);
-        tail += Count;
+     if (rest > 0) {
+        if (cont < Count)
+           Count = cont;
+        if (Count >= rest) {
+           memcpy(Data, buffer + tail, rest);
+           if (Count - rest)
+              memcpy(Data + rest, buffer, Count - rest);
+           tail = Count - rest;
+           }
+        else {
+           memcpy(Data, buffer + tail, Count);
+           tail += Count;
+           }
         }
+     else
+        Count = 0;
+     Unlock();
      }
   return Count;
 }