CODEWITHSUNDEEP
c++functionwinapiprivatequeueuserworkitem
BenWestbrook
BenWestbrook

Reputation: 23

Calling Win32 QueueUserWorkItem() with a private member function

I am attempting to call a private member function (should not be available as public or protected) as a worker item with the Win32 function QueueUserWorkItem(). I know I've done this before and it was easy, but now I can't find that snippet, nor can I make bind() voodoo work. So for the purposes of this question the class is:

class Arbitrary {

    public:
        Arbitrary() ;
        ~Arbitrary() ;

        bool    UsefulPublicFunction(unsigned uParameter) ;

    protected:

    private:
        void    PrivateWorkItem(void* pVoid) ;
} ;

And inside UsefulPublicFunction() we might see:

LPTHREAD_START_ROUTINE pThreadStartRoutine ;
ULONG uFlags = 0 ;
void* pContext = nullptr ;

if (QueueUserWorkItem(pThreadStartRoutine, pContext, uFlags)) {
    //blah blah blah
}

Where I seem to go off in the weeds is with the assignment to pThreadStartRoutine with something like:

pThreadStartRoutine = std::bind<&Arbitrary::PrivateWorkItem, this, std::placeholders::_1> ;

I recognize that the signature for PrivateWorkItem probably should change to:

private:
    DWORD   WINAPI  PrivateWorkItem(void* pVoid) ;

Even with that change, no joy. VS2015 really hates the way I'm using bind().

What should my assignment to pThreadStartRoutine look like?

Upvotes: 2

Views: 904

Answers (2)

Harry Johnston
Harry Johnston

Reputation: 36318

This seems to work:

#include <Windows.h>

#include <stdio.h>

#include <functional>

using namespace std::placeholders;

class Arbitrary {

    public:

        bool UsefulPublicFunction(int uParameter);

    protected:

    private:
        typedef std::function<void (void)> CallbackType;
        static DWORD WINAPI ProcessWorkItem(void* pVoid);
        void PrivateWorkItem1(int arg1, int arg2);
        void PrivateWorkItem2(char * arg1);
};

void Arbitrary::PrivateWorkItem1(int arg1, int arg2)
{
    printf("Numbers are %u %u\n", arg1, arg2);
    return;
}

void Arbitrary::PrivateWorkItem2(char * arg1)
{
    printf("String is %s\n", arg1);
    return;
}

DWORD WINAPI Arbitrary::ProcessWorkItem(void* pVoid)
{
    CallbackType * callback = static_cast<CallbackType *>(pVoid);
    (*callback)();
    delete callback;
    return 0;
}

bool Arbitrary::UsefulPublicFunction(int param1)
{
    QueueUserWorkItem(&ProcessWorkItem, new CallbackType(std::bind(&Arbitrary::PrivateWorkItem1, this, param1, 7)), 0);

    QueueUserWorkItem(&ProcessWorkItem, new CallbackType(std::bind(&Arbitrary::PrivateWorkItem2, this, (char *)"This is my string")), 0);

    Sleep(1000);
    return true;
}

int main(int argc, char ** argv)
{
    Arbitrary x;

    x.UsefulPublicFunction(5);

    return 0;
}

Upvotes: 2

Remy Lebeau
Remy Lebeau

Reputation: 596592

Try something more like this instead:

class Arbitrary {

    public:
        Arbitrary() ;
        ~Arbitrary() ;

        bool UsefulPublicFunction(unsigned uParameter);

    protected:

    private:
        static DWORD WINAPI PrivateWorkItem(void* pVoid) ;
        void PrivateFunction();
} ;


DWORD WINAPI Arbitrary::PrivateWorkItem(void* pVoid)
{
    static_cast<Arbitrary*>(pVoid)->PrivateFunction();
    return 0;
}

...

if (QueueUserWorkItem(&PrivateWorkItem, this, 0)) {
    //blah blah blah
}

Upvotes: 1

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