How create thread from float function?

mnm71 (80)
In my class I have a float function that should work always and return value to use it in other place, but I can't create thread for this float function
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 pthread_create(&th, NULL, getload, NULL);
	 pthread_join(th, NULL);
float data::getload(void *arg) {
       float util;
    while(condition)
     {

      sleep(1);
                }
 
    return util;

}



Last edited on
salem c (3700)
Leaving aside for the moment that pthread knows nothing about classes, your getload() would need to be a static function to be callable from pthread_create.

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pthread_create(&th, NULL, getload, NULL);
// wait around for a while
void *result;
pthread_join(th, &result);
float *answer = reinterpret_cast<float*> (result);
// use the answer
delete answer;


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void *data::getload(void *arg) {
    float util;
    while(condition)
    {
      sleep(1);
    }
 
    float *result = new float;
    *result = util;
    return reinterpret_cast<void*> (result);
}


If you can, use https://www.cplusplus.com/reference/thread/ instead.
mnm71 (80)
When the program received to this pthread_create(&th, NULL, getload, NULL); line
thread not running
Last edited on
salem c (3700)
Works for me.
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#include <iostream>
#include <iomanip>
#include <pthread.h>
using namespace std;

class data {
public:
  static void *getload(void* arg);
};

void *data::getload(void *arg) {
  cout << "In getload" << endl;
  float *result = new float;
  *result = 42;
  return reinterpret_cast<void*> (result);
}

int main ( ) {
  pthread_t th;
  pthread_create(&th, NULL, data::getload, NULL);
  // wait around for a while
  void *result;
  pthread_join(th, &result);
  float *answer = reinterpret_cast<float*> (result);
  cout << "Got " << *answer << endl;
  delete answer;
}

$ g++ foo.cpp -pthread
$ ./a.out 
In getload
Got 42

mnm71 (80)
When I define function in static, I get an error from line 3 : cannot call member function ‘bool data::get_times(size_t&, size_t&)’ without object 

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void* data::getload(void *arg) {

	for (size_t idle_time, total_time; get_times(idle_time, total_time); sleep(1)) { //while(true)
	        
                }
            float *result = new float;
            *result = util;
           return reinterpret_cast<void*> (result);
}
Last edited on
salem c (3700)
Well typically, you would use the arg for the thread to pass in the instance you want to use with your thread.
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#include <iostream>
#include <iomanip>
#include <pthread.h>
using namespace std;

class data {
public:
  static void *getload(void* arg);
  bool get_times(size_t idle_time, size_t total_time) {
    return true;
  }
};

void *data::getload(void *arg) {
  data *ptr = reinterpret_cast<data*> (arg);
  cout << "In getload" << endl;
  bool foo = ptr->get_times(0,0);
  float *result = new float;

  *result = 42;
  return reinterpret_cast<void*> (result);
}

int main ( ) {
  pthread_t th;
  data  something;
  pthread_create(&th, NULL, data::getload, &something);
  // wait around for a while
  void *result;
  pthread_join(th, &result);
  float *answer = reinterpret_cast<float*> (result);
  cout << "Got " << *answer << endl;
  delete answer;
}

mnm71 (80)
@salem c, Thanks for the help but I still have a problem, now the issue is thread is run but does not get sleep and the result is not returned, I think because of for/while(true) I should use pthread_detach(th);


Last edited on
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