squid-smp: synchronization issue & solutions

Hello,

Since last few days i am analyzing squid code for smp support, I found
one big issue regarding debugs() function, It is very hard get rid of
this issue as it is appearing at almost everywhere in the code. So for
testing purpose i have disable the debug option in squid.conf as
follows

-------------------------------
debug_options 0,0
-------------------------------

Well this was only way, as did not want to spend time on this issue.....

Now concentrating on locking mechanism...

As OpenMP library is widely supported by almost all platforms and
compilers, I am inheriting locking mechanism from the same
Just include omp.h & compile code with -fopenmp option if using gcc,
Other may use similar thing on their platform, Well that is not a big
issue..

BUT, is it wise to take support from this library? Please discuss on
this issue....  I felt it is really easy to manage threads and
critical sections if we use OPENMP.

AS DISCUSSED BEFORE...... AND details available on
http://wiki.squid-cache.org/Features/SmpScale
I think, I have solved SOME critical section problems in existing squid code.

*****************AsyncCallQueue.cc*******************************

void AsyncCallQueue::schedule(AsyncCall::Pointer &call)
{

#pragma omp critical (AsyncCallQueueLock_c) // HERE IS THE LOCK
{
   if (theHead != NULL) { // append
       assert(!theTail->theNext);
       theTail->theNext = call;
       theTail = call;
   } else { // create queue from cratch
       theHead = theTail = call;
   }
}

//AND THEN

AsyncCallQueue::fireNext()
{
AsyncCall::Pointer call;
#pragma omp critical (AsyncCallQueueLock_c)  // SAME LOCK
{
       call = theHead;
   theHead = call->theNext;
   call->theNext = NULL;
   if (theTail == call)
       theTail = NULL;
}
       ....

}

ITS WORKING, AS SAME CRITICAL SECTIONS (i.e AsyncCallQueueLock_c) CAN
NOT BE CALLED SIMULTANEOUSLY
******************************************************************

Well in the same way following thing as appearing on
/Features/SmpScale are also locked( May be incompletely)

1. hash_link ---- LOCKED

2. dlink_list ---- LOCKED

3. ipcache, fqdncache  ---- LOCKED,

4. FD / fde handling ---WELL, SEEMS NOT CREATING PROBLEM, If any then
please discuss.

5. statistic counters --- NOT LOCKED ( I know this is very important,
But these are scattered all around squid code, Write now they may be
holding wrong values)

6. memory manager --- DID NOT FOLLOW

7. configuration objects --- DID NOT FOLLOW

AND FINALLY, Two sections in EventLoop.cc are separated and executed
in two threads simultaneously
as follows (#pragma lines added in existing code, no other changes)

**************EventLoop.cc****************

#pragma omp parallel sections //PARALLEL SECTIONS
{

  #pragma omp section   //THREAD-1
  {
       if (waitingEngine != NULL)
            checkEngine(waitingEngine, true);
       if (timeService != NULL)
             timeService->tick();
       checked = true;
  }

#pragma omp section //THREAD-2
 {
  while(1)
  {
      if ( lastRound == true) break;
      sawActivity = dispatchCalls();
      if (sawActivity)
          runOnceResult = false;
      if(checked == true) lastRound = true;
   }
 }
}
********************************

May need deep testing , but it is working......
am I on the right path ?

Thank you,

--
Mr. S. H. Malave
Computer Science & Engineering Department,
Walchand College of Engineering,Sangli.
sachinmalave_at_wce.org.in