[vdr] Re: vdr-1.3.17: thread issues with vdr-xine and vdr-osdteletext

[Klaus Schmidinger <Klaus.Schmidinger@cadsoft.de>]

Reinhard Nissl wrote:
> [ ... fixing thread handling ... ]
Somehow this is getting a little too complicated for my taste.
There's way too much locking and condvar stuff being introduced.

I suggest the attached patch against thread.[hc] of VDR 1.3.17.
The main changes here are that the child thread no longer
accesses childTid at all (it calls pthread_self() directly),
and the running state is stored in a simple boolean variable,
which requires no extensive locking since it is read/written
atomically. parentTid has been removed, since it was never actually
used.

Please take a look at this and let me know if you can find a
possible loophole there.

Klaus
--- thread.h	2004/10/24 11:00:32	1.24
+++ thread.h	2004/12/19 10:43:10
@@ -4,7 +4,7 @@
  * See the main source file 'vdr.c' for copyright information and
  * how to reach the author.
  *
- * $Id: thread.h 1.24 2004/10/24 11:00:32 kls Exp $
+ * $Id: thread.h 1.25 2004/11/26 13:33:26 kls Exp kls $
  */
 
 #ifndef __THREAD_H
@@ -73,7 +73,8 @@
 class cThread {
   friend class cThreadLock;
 private:
-  pthread_t parentTid, childTid;
+  bool running;
+  pthread_t childTid;
   cMutex mutex;
   char *description;
   static bool emergencyExitRequested;
--- thread.c	2004/11/20 16:21:14	1.37
+++ thread.c	2004/12/19 10:43:14
@@ -4,7 +4,7 @@
  * See the main source file 'vdr.c' for copyright information and
  * how to reach the author.
  *
- * $Id: thread.c 1.37 2004/11/20 16:21:14 kls Exp $
+ * $Id: thread.c 1.39 2004/11/26 14:16:07 kls Exp kls $
  */
 
 #include "thread.h"
@@ -197,7 +197,8 @@
 
 cThread::cThread(const char *Description)
 {
-  parentTid = childTid = 0;
+  running = false;
+  childTid = 0;
   description = NULL;
   SetDescription(Description);
 }
@@ -221,33 +222,35 @@
 
 void *cThread::StartThread(cThread *Thread)
 {
-  Thread->childTid = pthread_self();
   if (Thread->description)
-     dsyslog("%s thread started (pid=%d, tid=%ld)", Thread->description, getpid(), Thread->childTid);
+     dsyslog("%s thread started (pid=%d, tid=%ld)", Thread->description, getpid(), pthread_self());
   Thread->Action();
   if (Thread->description)
-     dsyslog("%s thread ended (pid=%d, tid=%ld)", Thread->description, getpid(), Thread->childTid);
-  Thread->childTid = 0;
+     dsyslog("%s thread ended (pid=%d, tid=%ld)", Thread->description, getpid(), pthread_self());
+  Thread->running = false;
   return NULL;
 }
 
 bool cThread::Start(void)
 {
-  Lock();
-  if (!childTid) {
-     parentTid = pthread_self();
-     pthread_t Tid;
-     pthread_create(&Tid, NULL, (void *(*) (void *))&StartThread, (void *)this);
-     pthread_detach(Tid); // auto-reap
-     pthread_setschedparam(Tid, SCHED_RR, 0);
+  if (!running) {
+     running = true;
+     if (pthread_create(&childTid, NULL, (void *(*) (void *))&StartThread, (void *)this) == 0) {
+        pthread_detach(childTid); // auto-reap
+        pthread_setschedparam(childTid, SCHED_RR, 0);
+        }
+     else {
+        LOG_ERROR;
+        running = false;
+        return false;
+        }
      }
-  Unlock();
-  return true; //XXX return value of pthread_create()???
+  return true;
 }
 
 bool cThread::Active(void)
 {
-  if (childTid) {
+  if (running) {
      //
      // Single UNIX Spec v2 says:
      //
@@ -262,6 +265,7 @@
         if (err != ESRCH)
            LOG_ERROR;
         childTid = 0;
+        running = false;
         }
      else
         return true;
@@ -271,21 +275,18 @@
 
 void cThread::Cancel(int WaitSeconds)
 {
-  if (childTid) {
+  if (running) {
      if (WaitSeconds > 0) {
         for (time_t t0 = time(NULL) + WaitSeconds; time(NULL) < t0; ) {
             if (!Active())
                return;
             cCondWait::SleepMs(10);
             }
-        esyslog("ERROR: thread %ld won't end (waited %d seconds) - cancelling it...", childTid, WaitSeconds);
-        }
-     Lock();
-     if (childTid) {
-        pthread_cancel(childTid);
-        childTid = 0;
+        esyslog("ERROR: thread %ld won't end (waited %d seconds) - canceling it...", childTid, WaitSeconds);
         }
-     Unlock();
+     pthread_cancel(childTid);
+     childTid = 0;
+     running = false;
      }
 }