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Re: simple pthread

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  Re: simple pthread cerr <ron.eggler@gmail.com> - 2011-07-25 21:15 -0700
    Re: simple pthread Ian Collins <ian-news@hotmail.com> - 2011-07-26 16:45 +1200
      Re: simple pthread cerr <ron.eggler@gmail.com> - 2011-07-25 22:54 -0700
        Re: simple pthread Paul Brettschneider <paul.brettschneider@yahoo.fr> - 2011-07-26 08:09 +0200
          Re: simple pthread cerr <ron.eggler@gmail.com> - 2011-07-25 23:15 -0700
            Re: simple pthread Ian Collins <ian-news@hotmail.com> - 2011-07-26 19:41 +1200
            Re: simple pthread Paul Brettschneider <paul.brettschneider@yahoo.fr> - 2011-07-26 17:35 +0200

#8227 — Re: simple pthread

> This looks like a mixed up function declaration!

Yep, exactly right... :o
> 
> 
> int something = pthread_create(  );
> 
> A decent compiler should tell you that MyThread::PrintMsg is the wrong 
> function type for the function pointer parameter of pthread_create.

I'm using g++ and io got this now:
int MyThread::StartMe(void)
{
  pthread_create(&ThreadA, NULL, &MyThread::PrintMsg, void);
}
//-------------------------------------------------------------
and the compiler tells me:
$ g++ -o example example.cpp
example.cpp: In member function ‘int MyThread::StartMe()’:
example.cpp:42:55: error: expected primary-expression before ‘void’

what is a primary expression in this case? :o
Thanks,

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#8228

On 07/26/11 04:15 PM, cerr wrote:
>> This looks like a mixed up function declaration!
>
> Yep, exactly right... :o
>>
>>
>> int something = pthread_create(  );
>>
>> A decent compiler should tell you that MyThread::PrintMsg is the wrong
>> function type for the function pointer parameter of pthread_create.
>
> I'm using g++ and io got this now:
> int MyThread::StartMe(void)
> {
>    pthread_create(&ThreadA, NULL,&MyThread::PrintMsg, void);
> }
> //-------------------------------------------------------------
> and the compiler tells me:
> $ g++ -o example example.cpp
> example.cpp: In member function ‘int MyThread::StartMe()’:
> example.cpp:42:55: error: expected primary-expression before ‘void’
>
> what is a primary expression in this case? :o
> Thanks,

Firstly, please don't use the sociopathic "new" google interface, it 
ruins threading!.

It looks like you missed my other comments, go be back and check, 'void' 
isn't a valid parameter value and a member function isn't a valid thread 
function.

-- 
Ian Collins

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#8229

On Jul 25, 9:45 pm, Ian Collins <ian-n...@hotmail.com> wrote:
> On 07/26/11 04:15 PM, cerr wrote:
>
>
>
>
>
>
>
>
>
> >> This looks like a mixed up function declaration!
>
> > Yep, exactly right... :o
>
> >> int something = pthread_create(  );
>
> >> A decent compiler should tell you that MyThread::PrintMsg is the wrong
> >> function type for the function pointer parameter of pthread_create.
>
> > I'm using g++ and io got this now:
> > int MyThread::StartMe(void)
> > {
> >    pthread_create(&ThreadA, NULL,&MyThread::PrintMsg, void);
> > }
> > //-------------------------------------------------------------
> > and the compiler tells me:
> > $ g++ -o example example.cpp
> > example.cpp: In member function ‘int MyThread::StartMe()’:
> > example.cpp:42:55: error: expected primary-expression before ‘void’
>
> > what is a primary expression in this case? :o
> > Thanks,
>
> Firstly, please don't use the sociopathic "new" google interface, it
> ruins threading!.
Alright, switched back.. hopefully they'll fix that soon, I like the
new interface...
hoooooooooowever...
>
> It looks like you missed my other comments, go be back and check, 'void'
> isn't a valid parameter value and a member function isn't a valid thread
> function.

Alright, so how can I pass no parameter then, NULL or (void) NULL
don't work either...
So I cannot have a thread in a class? Alright then...would a different
class by okay or does it need to be global?

Thanks!

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#8230

cerr wrote:

>> It looks like you missed my other comments, go be back and check, 'void'
>> isn't a valid parameter value and a member function isn't a valid thread
>> function.
> 
> Alright, so how can I pass no parameter then, NULL or (void) NULL
> don't work either...
> So I cannot have a thread in a class? Alright then...would a different
> class by okay or does it need to be global?

It's probably not standards conformant, but under g++ you can use static 
member functions as argument to pthread_create. Pass this as the void* 
argument parameter. In the static member function reinterpret_cast<> to your 
class and call a real member function from this pointer.

You could for example implement this in a Thread-class with a pure virtual 
doit() function.

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#8231

On Jul 25, 11:09 pm, Paul Brettschneider
<paul.brettschnei...@yahoo.fr> wrote:
> cerr wrote:
> >> It looks like you missed my other comments, go be back and check, 'void'
> >> isn't a valid parameter value and a member function isn't a valid thread
> >> function.
>
> > Alright, so how can I pass no parameter then, NULL or (void) NULL
> > don't work either...
> > So I cannot have a thread in a class? Alright then...would a different
> > class by okay or does it need to be global?
>
> It's probably not standards conformant, but under g++ you can use static
> member functions as argument to pthread_create. Pass this as the void*
> argument parameter. In the static member function reinterpret_cast<> to your
> class and call a real member function from this pointer.
>
> You could for example implement this in a Thread-class with a pure virtual
> doit() function.
Alright, I wanna stick with standard c++ for this. But i'm still not
sure how
I can have the argument being void....anyone?

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#8236

On 07/26/11 06:15 PM, cerr wrote:
> On Jul 25, 11:09 pm, Paul Brettschneider
> <paul.brettschnei...@yahoo.fr>  wrote:
>> cerr wrote:
>>>> It looks like you missed my other comments, go be back and check, 'void'
>>>> isn't a valid parameter value and a member function isn't a valid thread
>>>> function.
>>
>>> Alright, so how can I pass no parameter then, NULL or (void) NULL
>>> don't work either...
>>> So I cannot have a thread in a class? Alright then...would a different
>>> class by okay or does it need to be global?
>>
>> It's probably not standards conformant, but under g++ you can use static
>> member functions as argument to pthread_create. Pass this as the void*
>> argument parameter. In the static member function reinterpret_cast<>  to your
>> class and call a real member function from this pointer.
>>
>> You could for example implement this in a Thread-class with a pure virtual
>> doit() function.
> Alright, I wanna stick with standard c++ for this. But i'm still not
> sure how
> I can have the argument being void....anyone?

The parameter type is void*, not void.  Pass NULL.

-- 
Ian Collins

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#8260

cerr wrote:

> On Jul 25, 11:09 pm, Paul Brettschneider
> <paul.brettschnei...@yahoo.fr> wrote:
>> cerr wrote:
>> >> It looks like you missed my other comments, go be back and check,
>> >> 'void' isn't a valid parameter value and a member function isn't a
>> >> valid thread function.
>>
>> > Alright, so how can I pass no parameter then, NULL or (void) NULL
>> > don't work either...
>> > So I cannot have a thread in a class? Alright then...would a different
>> > class by okay or does it need to be global?
>>
>> It's probably not standards conformant, but under g++ you can use static
>> member functions as argument to pthread_create. Pass this as the void*
>> argument parameter. In the static member function reinterpret_cast<> to
>> your class and call a real member function from this pointer.
>>
>> You could for example implement this in a Thread-class with a pure
>> virtual doit() function.
> Alright, I wanna stick with standard c++ for this. But i'm still not
> sure how
> I can have the argument being void....anyone?

pthread_* is not standard C++ anyway, so why bother? If you want to be 
conformant, I guess(!) that you will have to use a trampoline function 
declared extern "C". You need the arg parameter for passing the pointer to 
your object.

See for example this quickly hacked together piece of code (probably full of 
"UB", but seems to compile and produce the expected unpredictable results):

#include <pthread.h>
#include <unistd.h>
#include <iostream>

// Forward declaration
extern "C" {
void *trampoline(void *arg);
}

class Thread
{
        friend void *trampoline(void *arg);
protected:
        virtual void event_loop() = 0;
public:
        pthread_t threadid;
        void start();
        void join();
};

extern "C" {
void *trampoline(void *arg)
{
        Thread *thread = static_cast<Thread *>(arg);
        thread->event_loop();
        return NULL;
}
}

void Thread::start()
{
        pthread_create(&threadid, NULL, &trampoline, this);
}

void Thread::join()
{
        pthread_join(threadid, NULL);
}

//-------------------------------------
class MyThread : public Thread {
        void event_loop();
};

void MyThread::event_loop()
{
        std::cout << "Hello\n";
}

//-------------------------------------
int main()
{
        MyThread thread;
        thread.start();
        std::cout << "Thread id is/was " << thread.threadid << '\n';
        thread.join();
}



$ g++ -Wall -O3 -lpthread thread.C
$ ./a.out
Thread id is/was 3078568816
Hello
$ ./a.out
Thread id is/was Hello
3078990704

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