pthread_create problem

live_dont_exist · 04-24-2005, 05:22 AM

Hi Guys,
I'm trying to use threads and write soem code for TCP timers and seem to have got totlly stuck right at the start .It gives me a segmentation fault whenever I use pthread_create .Here's the code :-

Code:

#include <iostream>
#include <pthread.h>

using namespace std;

int store_ack_tid[20][20];
int i=0; int j=0;

void * dynamic_timer_calc(void *)
{
  cout<<"INSIDE DYNAMIC TIMER CALC"<<endl;
}

void start_timer(int storeack)
{
  int temp=0;
  cout<<"Storeack is "<<storeack<<endl;
  pthread_t tid;   /*=new pthread_t*/
  temp=pthread_create(&tid,NULL,dynamic_timer_calc,NULL);
  cout<<"Error code is "<<temp<<endl;
}

void send_segment()
{
  int seq=5;   // IN THE REAL CODE THIS WILL NOT BE THERE AS THE SEQ WILL ALREADY BE DEFINED
  cout<<"CODE FOR SENDING SEGMENT"<<endl;
  start_timer(seq);
}

int main()
{
  cout<<"inside main"<<endl;

  for (i=0; i<19; i++)
   for (j=0; j<19; j++)
     store_ack_tid[i][j]=0;

  send_segment();
  return 0;

Whenever I comment that code related to pthread it runs okay . I've tried running it with and without arguments and the result is the same.

Here's my system type :-
[root@LABPC02 timers]#
uname -a 19,3 All
Linux LABPC02 2.4.20-8 #1 Thu Mar 13 17:54:28 EST 2003 i686 i686 i386 GNU/Linux
[root@LABPC02 timers]#

Do try and see what's going wrong here. Any help/advice is appreciated.

Thnx
Arvind

live_dont_exist · 04-24-2005, 05:53 AM

Hey guys, never mind...I figured it out . I wasnt linking it up...so it should be
g++ -o timer -lpthread timer.cpp and it works properly . Iwasn't linking it previously.
Thnx for reading though.
Arvind

Ephracis · 04-24-2005, 05:56 AM

It should work. Make sure you link it with the pthread library after you have compiled it. With g++ you should use the -lpthread switch.

Hivemind · 04-24-2005, 06:06 AM

Yeah, I tried and it doesn't segfault. But here's one thing you might want to fix:

Code:

for (i=0; i<19; i++)
   for (j=0; j<19; j++)
     store_ack_tid[i][j]=0;

That block doesn't set all elements to zero, the condition must me < 20 for both i and j for that. And why on earth are i and j globals??
Anyway, if you want to set all elements to zero, simply do:

Code:

memset(store_ack_tid, 0, sizeof(store_ack_tid));

Include <cstring> for std::memset. And use it with care, if the array has decayed to a pointer after being passed to a function, sizeof() will return the size of an int*, not the array itself. But if it's global like in your case, it will work.

Hivemind · 04-24-2005, 06:12 AM

And, also, I would change the call to pthread_create() to something like:

Code:

int return_value = 0;
if((return_value = pthread_create(&tid,NULL,dynamic_timer_calc,NULL)) != 0)
     cerr << "pthread_create() failed." << endl; /* TODO: print error code and description */
  else
     cout << "pthread_create() was successful." << endl;

live_dont_exist · 04-24-2005, 06:21 AM

hey...it works guys...thnx a million 4 all your suggestions...will try all of them out...thnx ...will post back if I have other problems..
Thnx
Arvind