Subj : Re: passing an 'int' to a thread
To   : comp.programming.threads
From : doug
Date : Wed Jun 08 2005 09:37 am


Damn, I forgot the DGCs!

"doug" <noone@nowhere.co.uk> wrote in message 
news:n2ype.238581$Cq2.10303@fe2.news.blueyonder.co.uk...
> 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));
>

DGC

> 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
>

DGC

> 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?
>

DGC

> 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.
>

.