Question

I want to test out using WaitForMultipleObjects, and to do so I want to start multiple threads, using a loop, each passing different ThreadArgs.

(Essentially just an array of five ThreadArgs, and five HANDLEs?)

When I try to create an array of either the struct, or the HANDLE, neither will work and I get the error ‘cannot allocate an array of constant size 0′ for both, and ”initializing’ : cannot convert from ‘HANDLE’ to ‘HANDLE []” for the latter.

Is an array the appropriate way to do this with regards to the struct? (Also, a note – it will have to remain a struct as it will contain six members eventually, I’m just trying to get it working in a simpler form at first, since adding these members should be very straightforward)

And I’d assume an array of Handles is the best way to do this, but how do I go about declaring one?

Thank you!

#include <windows.h>
#include <iostream> 
#include <process.h>


struct ThreadArgs 
{
    int id;
};

ThreadArgs args = {1}; 


unsigned int __stdcall MyThread(void *data)
{
    std::cout << "Hello World!\n"; 
    ThreadArgs *args = (ThreadArgs *) data; 

    std::cout << (*args).id;

    return 2;
}

int main()
{

    HANDLE hThread = (HANDLE) _beginthreadex(NULL, 0, MyThread, &args, 0, NULL); 

    WaitForSingleObject(hThread, INFINITE);


    while(true);

}

The above is my code currently.

I was trying to create an array of HANDLEs using –

HANDLE hThread[5]; 

Edit:

The error is on this line, when it is altered to be an array of HANDLE[5] –

HANDLE hThread[0] = (HANDLE) _beginthreadex(NULL, 0, MyThread, &args, 0, NULL); 

Answer 1

You need to use WaitForMultipleObjects and pass it an array of handles to wait for multiple threads to complete. See an example here.

#include <windows.h>
#include <iostream>
#include <vector>
using std::vector;
using std::cout;
using std::endl;

CRITICAL_SECTION cs;

struct ThreadArgs 
{
    int id;
};

VOID MyThread(void *data)
{
    EnterCriticalSection(&cs);
    ThreadArgs *args = (ThreadArgs*)data;
    cout << args->id << endl;
    LeaveCriticalSection(&cs);
}

int main()
{
    InitializeCriticalSection(&cs);

    vector <HANDLE> T;

    DWORD id;

    ThreadArgs args[5] = {1, 2, 3, 4, 5};

    for (int i = 0; i < 5; i++)
    {
        T.push_back(CreateThread(0, 0, (LPTHREAD_START_ROUTINE)MyThread, &args[i], 0, &id));
    }

    WaitForMultipleObjects(5, &T[0], TRUE, INFINITE);

    DeleteCriticalSection(&cs);
}