Subj : Re: passing an 'int' to a thread
To   : comp.programming.threads
From : doug
Date : Wed Jun 08 2005 09:32 am

Look for DGC below.

"Huub" <hdotvdotniekerkathccnetdotnl> wrote in message 
news:42a671a3$0$156$3a628fcd@reader2.nntp.hccnet.nl...
> You were right. The errors were due to a linking problem. And I made a 
> another mistake which I corrected. Now something is being passed, but it's 
> not the correct value. Could you tell me what is being passed: task_ids or 
> t?
>
> New code:
>
>
> #ifdef HAVE_CONFIG_H
> #include <config.h>
> #endif
>
> #include <iostream>
> #include <cstdlib>
> #include <memory>
> #include <pthread.h>
> #include <time.h>
> #include "ftapi/ftapi.h"
>
> using namespace std;
> using namespace ftapi;
>
>   // default interface connection
> string device("");
> ft_if_conn connection = FT_IC_LIB_USB;
> IfOutputs out;
> IfInputs inp;
>
> void *MotorDraad(void *threadid)
> {
>   int *id_ptr, task_id;
>   id_ptr = (int *)threadid;
>   task_id = *id_ptr;
>   cout << "Start MotorDraad" << endl;
>   time_t start;
>   time_t current;
>   time(&start);
>   try
>   {
>     auto_ptr<FtInterface> fti (ftGetIfFromFactory(device,
>   connection));
>   // Initialspeed = task_id
>     FtMotorSpeed mSpeed1(task_id);
>     cout << "Snelheid1 = " << task_id << endl;
>   // Initialspeed = task_id
>     FtMotorSpeed mSpeed2(task_id);
>     cout << "Snelheid2 = " << task_id << endl;
>   // enable all motor outputs
>     out.data[FT_MASTER]= 0xFF;
>   // M1: not moving
>     out.setMotorSpeed(FT_MASTER, FT_M1, mSpeed1);
>   // M2: forward with velocity 4
>     out.setMotorSpeed(FT_MASTER, FT_M2, mSpeed2);
>     while (difftime(current,start) < 5.0)
>     {
>       time(&current);
>       fti->writeAndReadAllData(out, inp);
>     }
>   }
>   // anything went wrong
>   catch (exception &x)
>     {
>       cout << x.what() << endl;
>     }
> }
>
>
> int main(int argc, char *argv[])
> {
>   cout << "Start fase 1" << endl;
>
>   pthread_t threads[1];
>   int *task_ids[1];
>   int rc, t;
>   t = 0;
>   int snelheid = 0;
>
>   cout << "1 Thread gedeclareerd" << endl;
>
>   cout << "fttestextension v0.4" << endl;
>
>   if (1 == argc)
>     {
>       /* leave device name as defined above, since no
> parameters given */
>     }
>   else if (((2 == argc) || (3 == argc)) &&
>    (string("-l")==(argv[1])))
>     {
>       if (3 == argc) device = argv[2];
>       connection = FT_IC_LIB_USB;
>     }
>   else if (((2 == argc) || (3 == argc)) &&
>    (string("-u")==(argv[1])))
>     {
>       if (3 == argc)
> {
>   device = argv[2];
> }
>       else
> {
>   device = "/dev/usb/robointerface0";
> }
>       connection = FT_IC_USB;
>     }
>   else
>     {
>       return EXIT_FAILURE;
>     }
>
>   // now let's go!
>   cout << "opening fischertechnik interface \"" << device << "\""
>        << endl;
>   task_ids[t] = (int *) malloc(sizeof(int));

You should be malloc'ing sizeof(int*) here.

>   *task_ids[t] = t;
>   while (snelheid != 8)
>     {
>       cin >> snelheid;
>       cout << "Aanmaken thread" << endl;
>       cout << "t = " << t << endl;
>       t = snelheid; // new piece of code

Here you assign a new value to t...

>       rc = pthread_create(&threads[t], NULL, MotorDraad,
>   (void *)task_ids[t]);
> //what is passed: task_ids or t?

Tha value passed is task_ids[t], which is an int pointer.  However, just 
above you assigned a new value to t, so you likely haven't set up 
task_ids[t].  So you're probably passing an uninitialised, unless you can 
guarantee that t is always zero.  (In which case, why are you reading it 
from cin [via snelheid]?)

>     }
>   pthread_exit(NULL);
>   return EXIT_SUCCESS;
> }
>
> // EOF
>
> Thank you for helping out.

Hope that helps.  Not sure, though.

.