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Old 11-26-2004, 09:05 AM   #1
msriram_linux
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Registered: Nov 2004
Posts: 19

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Process and thread PIDs


Hi!
I was referring to Advanced Linux Programming downloaded from net(Pearson Education).
While distinguishing between threads-implementation on GNU/Linux systems from other UNIX-like systems it says every invocation of pthread_create creates a new process to run it
and the following example to prove it:
-------------------------------------------------------------------
#include<pthread.h>
#include<stdio.h>
#include<unistd.h>

void* thread-function(void* arg)
{
fprintf(stderr,"\n---child thread pid is %d -----\n",getpid());
while(1);
return(NULL);
}

int main()
{
pthread_t thread;
pthread_create(&thread,NULL,&fun,NULL);
fprintf(stderr,"\n---Main thread pid is %d -----\n",getpid());
while(1);
return(0);
}
------------------------------------------------
The output is expected ot be the main and the child with different pid.
However while I run this program I get the same pid for the child and main.
I am using RED HAT-9,
The Kernel version is 2.4.20-8
Can someone point what is it.
Regards,
 
Old 11-26-2004, 11:21 AM   #2
indian
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Registered: Aug 2004
Posts: 137

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Hi Sriram , Do a thing man...In Main() put

wait(2);

before

fprintf(stderr,"\n---Main thread pid is %d -----\n",getpid());

and after

pthread_create(&thread,NULL,&fun,NULL);

And than see what output it is giving!!!

Regards,
 
Old 11-26-2004, 11:22 AM   #3
indian
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Registered: Aug 2004
Posts: 137

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and remove while loops........
 
Old 11-27-2004, 01:16 AM   #4
msriram_linux
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Registered: Nov 2004
Posts: 19

Original Poster
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Dear Indian
I tried that but it didn't work...there is no change in output.
Is there any material on this particular topic...
Regards,
 
Old 11-27-2004, 11:43 AM   #5
btmiller
Senior Member
 
Registered: May 2004
Location: In the DC 'burbs
Distribution: Arch, Scientific Linux, Debian, Ubuntu
Posts: 4,131

Rep: Reputation: 319Reputation: 319Reputation: 319Reputation: 319
This link ought to help you resolve your difficulty. Basically, recent versions of Linux actually return the thread group ID, not the thread ID, when you call getpid(2). So your correct that Linux has a 1-1 provesses-threads implementationm -- it's just hidden.
 
  


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