从Java到C ++的线程

Question

I have this Kevin class that implements runnable on JAVA and this KevinThreads class that create thread objects based on the Kevin instances and run it.

public class KevinThreads{



    public static void main(String[] args){
        if(args.length!=2)
        {
            System.err.println("Usage: KevinThreads.java (1st param) (2nd param)");
            System.err.println("1st param: specifies the number of threads to be executed");
            System.err.println("2nd param: specifies the state of execution. 1=MUTEX,2=NON-MUTEX");
            return;
        }
        int number_of_threads = Integer.parseInt(args[0]);
        int thread_mode = Integer.parseInt(args[1]);
        for(int i=0;i<number_of_threads;i++){
        new Thread(new Kevin(i+1,thread_mode)).start();
        }

    }

}

I am now trying to replicate this logic to C++ with pthread. What I've done so far is I have a Kevin class

#include <iostream>
#include <time.h>
#include <pthread.h>
using namespace std;

class Kevin
{
public:
    Kevin();
    void Speak(int value);
};

Kevin::Kevin()
{
    cout << "new instance of Kevin is created";
}

void Kevin::Speak(int value)
{
    cerr << "Name: Kevin\n" << value << "Seconds since epoch:" << time(0) << "\nThread id:" << pthread_self() << endl;
}

and a main.cc that somewhat similar to KevinThreads

#include <iostream>
#include <pthread.h>
#include "Kevin.cc"
using namespace std;

int main(int argc, char *argv[])
{
    Kevin kevin1;
    int status;
    // creating thread objects
    pthread_t thrd_1;
    pthread_t thrd_2;
    // create thread
    pthread_create(&thrd_1,NULL,kevin1.Speak(1),(void *)0); //14
    pthread_create(&thrd_2,NULL,kevin1.Speak(2),(void *)0); //15
    pthread_join(thrd_1, (void **)&status);
    pthread_join(thrd_2, (void **)&status);
    system("PAUSE");
    return EXIT_SUCCESS;
}

however, it does not compile and gave me "Invalid use of void expression at main:14,15". I'm new to the C++ syntax, what does that error even mean? I've tried changing (void *)0 to NULL, and I'm pretty sure the return type of kevin1.Speak() is not the problem that caused this. Any idea?

Answer 1

Your kevin1.Speak is a function - pthread_create wants the memory address of the function so instead of passing the actual function kevin.Speak(1) pass the memory address of the function &kevin.speak

as for passing a value to the thread follow this format

long t;

t = 1; //value to pass

pthread_create( &thread, NULL, function, (void*)t);

here is a full example with added functions for your class

#include <iostream>
#include <time.h>
#include <pthread.h>
using namespace std;


class Kevin
{
public:
    Kevin(){
    cout << "new instance of Kevin is created";
}
    void Speak(int value){
    cerr << "Name: Kevin\n" << value << "Seconds since epoch:" << time(0) << "\nThread id:" << pthread_self() << endl;
}
};
Kevin kevin1;

void *kevinSpeaker1(void*)
{
    kevin1.Speak(2);
}
void *kevinSpeaker2(void*)
{
    kevin1.Speak(1);
}

int main(int argc, char *argv[])
{

    int status;
    // creating thread objects
    pthread_t thrd_1;
    pthread_t thrd_2;
    // create thread
    pthread_create(&thrd_1,NULL,&kevinSpeaker1,(void *)0); //14
    pthread_create(&thrd_2,NULL,&kevinSpeaker2,(void *)0); //15
    pthread_join(thrd_1, (void **)&status);
    pthread_join(thrd_2, (void **)&status);
    system("PAUSE");
    return EXIT_SUCCESS;
}

Answer 2

member function can not be directly used as callback function, and it should be a funciton address ,not the return value of a function call

you can not include a cc file #include "Kevin.cc"

try this piece of code

#include <iostream>
#include <time.h>
#include <pthread.h>
using namespace std;

class Kevin
{
  public:
        Kevin();
        static void* Speak(void* value);
};

Kevin::Kevin()
{
      cout << "new instance of Kevin is created";
}

void* Kevin::Speak(void* value)
{
      cout << "Name: Kevin\n" << *((int*)value) << "  Seconds since epoch:" << "\nThread id:" << pthread_self() << endl;
}

int main(int argc, char *argv[])
{
      Kevin kevin1;
      int status;
      pthread_t thrd_1;
      pthread_t thrd_2;
      int i = 1;
      int j = 2;
      pthread_create(&thrd_1,NULL,Kevin::Speak,(void *)&i); //14
      pthread_create(&thrd_2,NULL,Kevin::Speak,(void *)&j); //15
      pthread_join(thrd_1, (void **)&status);
      pthread_join(thrd_2, (void **)&status);
      system("PAUSE");
      return EXIT_SUCCESS;
}

compile command g++ -o main main.cc -lpthread it outputs:

new instance of Kevin is createdName: Kevin
1  Seconds since epoch:
Thread id:3083348896
Name: Kevin
2  Seconds since epoch:
Thread id:3074960288