Question

I have the following code and I make ps aux | grep myprogram in each step of the main() code of myprogram (name of the application I build).

At the beggining of the execution of myprogram, the ps aux | grep myprogram show only 1 time the myprogram in the list

after cancelling a thread that I created in the begging of the main(), the ps aux | grep myprogram show the myprogram twice and I expected to get only 1.

Could some one explain this behaviour? and how to return to the initial situation (only 1 myprogram)

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

pthread_t test_thread;

void *thread_test_run (void *v)
{
    int i=1;
    while(1)
    {
       printf("into thread %d\r\n",i);
       i++; 
       sleep(1);
    }
    return NULL
}

int main()
{
    // ps aux | grep myprogram  ---> show only 1 myprogram

    pthread_create(&test_thread, NULL, &thread_test_run, NULL);

    // ps aux | grep myprogram  ---> show  3 myprogram

    sleep (20);  


    pthread_cancel(test_thread);

    // ps aux | grep myprogram  ---> show 2 myprogram and I expected only 1 !!??

   // other function are called here...

    return 0;
}

EDIT

the libc used by the linux is libc-0.9.30.1.so

# ls -l /lib/| grep libc
-rwxr-xr-x    1 root     root        16390 Jul 11 14:04 ld-uClibc-0.9.30.1.so
lrwxrwxrwx    1 root     root           21 Jul 30 10:16 ld-uClibc.so.0 -> ld-uClibc-0.9.30.1.so
lrwxrwxrwx    1 root     root           21 Jul 30 10:16 libc.so.0 -> libuClibc-0.9.30.1.so
-rw-r--r--    1 root     root         8218 Jul 11 14:04 libcrypt-0.9.30.1.so
lrwxrwxrwx    1 root     root           20 Jul 30 10:16 libcrypt.so.0 -> libcrypt-0.9.30.1.so
-rw-r--r--    1 root     root       291983 Jul 11 14:04 libuClibc-0.9.30.1.so

Answer 1

I’ll assume you have some outdated glibc (version 2.2 or 2.3), which used the “linuxthreads” implementation of pthread.

In this older library one additional thread is created by the library for thread management; it can be created after first call to pthread_create; but it will sleep most time.

In newer linuxes there is glibc with NPTL (“Native posix thread library”) implementation. When it is used, you will not see threads in ps axu; use ps axum (with m) to see native threads. And NPTL not uses a management thread.

PS Check http://pauillac.inria.fr/~xleroy/linuxthreads/faq.html D.5 answer:

D.5: When I’m running a program that creates N threads, top or ps display N+2 processes that are running my program. What do all these processes correspond to?

Due to the general “one process per thread” model, there’s one process for the initial thread and N processes for the threads it created using pthread_create. That leaves one process unaccounted for. That extra process corresponds to the “thread manager” thread, a thread created internally by LinuxThreads to handle thread creation and thread termination. This extra thread is asleep most of the time.

PPS: Thanks, Mohamed KALLEL; thanks, mux: libc-0.9.30.1 is uClibc and seems that it uses same outdated linuxthreads implementation (which is known to be not fully posix-compatible). Here is changelog: http://web.archive.org/web/20070609171609/http://www.uclibc.org/downloads/Changelog

0.9.10 21 March 2002

Major new features:
o pthreads support (derived from glibc 2.1.3’s linuxthreads library)
by Stefan Soucek and Erik Andersen