Threads in Octave

[Przemek Klosowski]

We ran into a strange problem with pthreads in octave, while trying to
implement an Octave GUI framework. After having weird synchronization
errors, we have whittled it down to a short test case. A standalone
program works as expected: a new thread is created and starts executing,
and the original thread is distinguishable from the new one; the following
source code:

    #include <string>
    #include <strstream>

    #include <string.h>
    #include <stdlib.h>
    #include <unistd.h>
    #include <signal.h>
    #include <pthread.h>

    void *
    my_thread_process(void * null){
       while (1){
          cout << "testing\n";
          sleep(1);
       }
    }
    int 
    pthread_equal_rig(   pthread_t t1,  pthread_t t2) {
       int result;
       cout << "threads: " << (int) t1 << " " << (int) t2 ;
       result = pthread_equal(t1,t2);
       cout << " and the result is " << result << "\n";
       return result;
    }

    int
    main() {
       pthread_t       my_thread;
       pthread_create(&my_thread, NULL, my_thread_process, NULL);

       if(pthread_equal_rig(my_thread, pthread_self()))   cout << "Same 
threads!\n";
       else                                               cout << "Different 
threads!\n";
    }

when compiled with 'c++ -o test2 test2.c -lpthread' and run, outputs the 
following:

    % ./test2
    threads: 1026 1024 and the result is 0
    Different threads!
    testing

The same code implemented as Octave extension (Octave 2.1.33) runs,
but the main process doesn't seem to return the correct thread ID from
pthread_self(). Furthermore, we seem to have problems with thread
synchronization (cut out from the above source), which we suspect are
caused by confusion within the thread system.

The output in this case is:

    octave>  test
    threads: 1026 0 and the result is 1
    Same threads!

So, it appears that pthreads_self() is returning 0 instead of the
thread ID for the parent (octave) process.  The source code in this
case is almost exactly the same as the standalone code (see below)

So, did anyone play with Posix threads in Octave? Is our problem due
to a conflict between pthreads and octave, or are we doing something
wrong?

                        przemek klosowski, Ph.D. <address@hidden>  (301) 
975-6249
                        NIST Center for Neutron Research (bldg. 235), E111 
                        National Institute of Standards and Technology
                        Gaithersburg, MD 20899,      USA
                        .. and for spam extractors, FCC Commisioners' email is: 
                        
address@hidden,address@hidden,address@hidden,address@hidden
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800-843-5678





    #include <octave/config.h>
    #include <octave/oct-obj.h>
    #include <octave/parse.h>
    #include <octave/defun-dld.h>
    #include <octave/error.h>
    #include <octave/variables.h>
    #include <octave/sighandlers.h>
    #include <octave/mx-base.h>

    #include <string>
    #include <strstream>

    #include <string.h>
    #include <stdlib.h>
    #include <unistd.h>
    #include <signal.h>
    #include <pthread.h>

    #define TRUE  1
    #define FALSE 0

    void *
    my_thread_process(void * null){
       while (1){
          cout << "testing\n";
          sleep(1);
       }
    }
    int 
    pthread_equal_rig(   pthread_t t1,  pthread_t t2) {
       int result;
       cout << "threads: " << (int) t1 << " " << (int) t2 ;
       result = pthread_equal(t1,t2);
       cout << " and the result is " << result << "\n";
       return result;
    }

    DEFUN_DLD (test, args,, "test")
    {
       octave_value_list ret;

       pthread_t       my_thread;
       pthread_create(&my_thread, NULL, my_thread_process, NULL);

       if(pthread_equal_rig(my_thread, pthread_self()))        printf("Same 
threads!\n");
       else                                                    
printf("Different threads!\n");

       return ret;
    }



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