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Passing parameters in threads

Pages: 12
TwilightSpectre (1392)
No, it has to be posix threads. Win32 threads don't work last time I checked, hence the need for the winpthreads library. Make sure that you have a command line option enabled for -pthread as well, to enable threading. To do that, go into your Build Options, Compiler Options, Other Options and add it in.
htirwin (1208)
Ahh, it throws the same error as before, I have every setting like the picture you've shown me but it still doesn't work. I have windows, should I have chosen


Should work. You probably specified the wrong path or didn't choose the compiler for the project in build options.

Make sure that you have a command line option enabled for -pthread as well, to enable threading.


I didn't have to do this in my environment for some reason.
greenleaf800073 (475)
IT WORKS, THANK YOU!

NT3, your thing worked :D

htirwin:

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mingw32-g++.exe -Wall -fexceptions -g -std=c++11 -Wextra  -c "C:\Users\cocon_000\Desktop\C++\PrimeArgsThreading\main.cpp" -o obj\Debug\main.o
C:\Users\cocon_000\Desktop\C++\PrimeArgsThreading\main.cpp: In function 'int main()':
C:\Users\cocon_000\Desktop\C++\PrimeArgsThreading\main.cpp:66:5: error: cannot convert 'long unsigned int*' to 'void* const*' for argument '2' to 'DWORD WaitForMultipleObjects(DWORD, void* const*, BOOL, DWORD)'
C:\Users\cocon_000\Desktop\C++\PrimeArgsThreading\main.cpp: In function 'int main()':
C:\Users\cocon_000\Desktop\C++\PrimeArgsThreading\main.cpp:76:5: error: redefinition of 'int main()'
C:\Users\cocon_000\Desktop\ C++\PrimeArgsThreading\main.cpp:41:5: error: 'int main()' previously defined here
C:\Users\cocon_000\Desktop\C++\PrimeArgsThreading\main.cpp:104:5: error: cannot convert 'long unsigned int*' to 'void* const*' for argument '2' to 'DWORD WaitForMultipleObjects(DWORD, void* const*, BOOL, DWORD)'
Process terminated with status 1 (0 minute(s), 2 second(s))
4 error(s), 0 warning(s) (0 minute(s), 2 second(s))


Your example, I figured out that you need
#include <windows.h>

but now I'm getting these errors :/
Last edited on
TwilightSpectre (1392)
You'll need to manually cast them - AFAIK, it would work in C, but C++ removed those kinds of implicit casts to and from void*.
greenleaf800073 (475)
How do you cast an object? also, what's AFAIK?
TwilightSpectre (1392)
To cast an object, the easiest (C-Style) way is to do this:(type)parameter;. In this case:
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WaitForMultipleObjects(
    4,
    (void*)handles, // or reinterpret_cast<void*>(handles) for C++ way
    TRUE,
    INFINITE
);


AFAIK = As Far As I Know
greenleaf800073 (475)
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mingw32-g++.exe -Wall -fexceptions -pthread -g -std=c++11 -Wextra  -c "C:\Desktop\C++\PrimeArgsThreading\main.cpp" -o obj\Debug\main.o
C:\Desktop\C++\PrimeArgsThreading\main.cpp: In function 'int main()':
C:\Desktop\C++\PrimeArgsThreading\main.cpp:66:5: error: invalid conversion from 'void*' to 'void* const*' [-fpermissive]
In file included from c:\program files (x86)\codeblocks\mingw\bin\../lib/gcc/mingw32/4.7.1/../../../../include/windows.h:50:0,
                 from C:\Desktop\C++\PrimeArgsThreading\main.cpp:4:
c:\program files (x86)\codeblocks\mingw\bin\../lib/gcc/mingw32/4.7.1/../../../../include/winbase.h:2199:25: error:   initializing argument 2 of 'DWORD WaitForMultipleObjects(DWORD, void* const*, BOOL, DWORD)' [-fpermissive]
C:\Desktop\C++\PrimeArgsThreading\main.cpp: In function 'int main()':
C:\Desktop\C++\PrimeArgsThreading\main.cpp:76:5: error: redefinition of 'int main()'
C:\Users\cocon_000\Desktop\Daniel Pham's C++\PrimeArgsThreading\main.cpp:41:5: error: 'int main()' previously defined here
C:\Desktop\C++\PrimeArgsThreading\main.cpp:104:5: error: invalid conversion from 'void*' to 'void* const*' [-fpermissive]
In file included from c:\program files (x86)\codeblocks\mingw\bin\../lib/gcc/mingw32/4.7.1/../../../../include/windows.h:50:0,
                 from C:\Desktop\C++\PrimeArgsThreading\main.cpp:4:
c:\program files (x86)\codeblocks\mingw\bin\../lib/gcc/mingw32/4.7.1/../../../../include/winbase.h:2199:25: error:   initializing argument 2 of 'DWORD WaitForMultipleObjects(DWORD, void* const*, BOOL, DWORD)' [-fpermissive]
Process terminated with status 1 (0 minute(s), 0 second(s))
6 error(s), 0 warning(s) (0 minute(s), 0 second(s))


I get this now when I try casting the handles
NoXzema (699)
What do you think the errors mean?
greenleaf800073 (475)
:/ I think I can fix the 'void*' to 'void* const*' but... how do you fix 2 iterations of int main()?
htirwin (1208)
how do you fix 2 iterations of int main()?

You can't have two main functions.

Here is a working version. I know it's contrived, it's just for testing threading.


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#include <iostream>
#include <windows.h>
#include <process.h>
#include <cmath>
#include <chrono>
#include <ctime>

struct PrimeSumArgs {

    unsigned long long sum;
    unsigned start;
    unsigned end;
};

bool isMerssenePrime( int n ) {

    if ( n < 2 )
        return false;

    int sqrtn = std::sqrt( n );
    for ( unsigned i = 2; i <= sqrtn; ++i ) {
        if ( n % i == 0 )
            return false;
    }

    return !( (n+1) & n );
}

unsigned __stdcall primeSum( void* _args ) {

    PrimeSumArgs *args = static_cast < PrimeSumArgs* >( _args );

    for( unsigned i = args->start; i <= args->end; ++i ) {
        if ( isMerssenePrime( i ) )
            args->sum += i;
    }

    return 0;
}

int main() {

    const int NUM_THREADS = 32;

    unsigned lim;
    std::cout << "how far out?\n";
    std::cin >> lim;

    int workSize = lim / NUM_THREADS;

    PrimeSumArgs args[ NUM_THREADS ];

    for ( unsigned i = 0; i < NUM_THREADS; ++i ) {
        args[i].sum = 0;
        args[i].start = i*workSize;
        args[i].end = ( i == NUM_THREADS - 1 ) ? lim : (  i + 1 ) * workSize - 1;
    }

    HANDLE handles[ NUM_THREADS ];

    std::chrono::time_point<std::chrono::system_clock> start = std::chrono::system_clock::now();

    for ( unsigned i = 0; i < NUM_THREADS; ++i ) {
        handles[i] = reinterpret_cast < HANDLE > ( _beginthreadex (
            NULL,
            0,
            primeSum,
            static_cast< void* >( &args[i] ),
            0,
            NULL
        ) );
    }

    WaitForMultipleObjects(
        NUM_THREADS,
        handles,
        TRUE,
        INFINITE
    );

    unsigned long long sum = 0;
    for ( int i = 0; i < NUM_THREADS; ++i )
        sum += args[i].sum;

    std::cout << "The sum of Merssene primes from between 1 and " << lim << " is " << sum
        << std::endl
        << "the calcuation took "
        << std::chrono::duration< double >( std::chrono::system_clock::now() - start ).count()
        << " second using " << NUM_THREADS << " threads"
        << std::endl;
}

Last edited on
greenleaf800073 (475)
I'm getting errors for your fixed version, if I don't have #include <process.h>
I'll get

_beginthreadex() was not declared in this scope

if I have #include <process.h>

then I get these:

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mingw32-g++.exe -Wall -fexceptions -pthread -g -std=c++11 -Wextra  -c "C:\Users\cocon_000\Desktop\Daniel Pham's C++\PrimeArgsThreading\main.cpp" -o obj\Debug\main.o
C:\Users\cocon_000\Desktop\Daniel Pham's C++\PrimeArgsThreading\main.cpp: In function 'bool isMerssenePrime(int)':
C:\Users\cocon_000\Desktop\Daniel Pham's C++\PrimeArgsThreading\main.cpp:21:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
C:\Users\cocon_000\Desktop\Daniel Pham's C++\PrimeArgsThreading\main.cpp: In function 'int main()':
C:\Users\cocon_000\Desktop\Daniel Pham's C++\PrimeArgsThreading\main.cpp:53:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
C:\Users\cocon_000\Desktop\Daniel Pham's C++\PrimeArgsThreading\main.cpp:63:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
C:\Users\cocon_000\Desktop\Daniel Pham's C++\PrimeArgsThreading\main.cpp:71:9: error: invalid conversion from 'unsigned int (*)(void*)' to 'unsigned int (__attribute__((__stdcall__)) *)(void*)' [-fpermissive]
In file included from C:\Users\cocon_000\Desktop\Daniel Pham's C++\PrimeArgsThreading\main.cpp:3:0:
c:\program files (x86)\codeblocks\mingw\bin\../lib/gcc/mingw32/4.7.1/../../../../include/process.h:100:2: error:   initializing argument 3 of 'long unsigned int _beginthreadex(void*, unsigned int, unsigned int (__attribute__((__stdcall__)) *)(void*), void*, unsigned int, unsigned int*)' [-fpermissive]
Process terminated with status 1 (0 minute(s), 1 second(s))
2 error(s), 3 warning(s) (0 minute(s), 1 second(s))
htirwin (1208)
You have to change this,

unsigned primeSum( void* _args ) {

to

unsigned __stdcall primeSum( void* _args ) {

I was compiling with my mingw-builds compiler and for some reason it didn't throw any errors.
greenleaf800073 (475)
Thanks! it works now :D

now I just need to analyze how all of these work .-.
Last edited on
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Pages: 12