asked on

Why am i getting an error hete in the pthread_create()?

I am trying to create a C++ thread class by wrapping the C pthreads.

--Pthread.h file

class Pthread
{
public:
Pthread( pthread_attr_t* attr, void *arg);
Pthread();
virtual ~Pthread();
int create();
void join();
void exit();

private:
void* run(void *threadid);

pthread_t mPthread;
pthread_attr_t *mAttributes;
void *mArguments;
};

Then in my C++ .hh file I say this...

Pthread::Pthread( pthread_attr_t* attr, void *args)
{
mAttributes = attr;
mArguments = args;
}

Pthread::Pthread()
{
}

Pthread::~Pthread()
{
}

int Pthread::create()
{
return pthread_create( &mPthread, NULL, run, mArguments);

}

void Pthread::join()
{
pthread_join( mPthread, NULL);
}

void Pthread::exit()
{
int ex = 1;
pthread_exit(&ex);
}

void* Pthread::run(void *threadid)
{
return NULL;
}
}

int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
void *(*start_routine)(void*), void *arg);

-prain

I am getting an error in line:

return pthread_create( &mPthread, NULL, run, mArguments);

in my function create()

The pthread_create in 'C' <phread.h> has the prototype.

Zoppo

Hi prain,

the problem is you're passing a none-static member function, but pthread_create expects a global (or static member) function.

ZOPPO

prain

ASKER

I changed the function to status like this:

static void* Pthread::run(void *threadid){}

(also in .h file). But I am getting this error....

Pthread.cpp:51: error: cannot declare member function ‘static void* Sst::Pthread::run(void*)’ to have static linkage

Does this mean that I cannot have the function I want o execute for the thread inside the class?

Zoppo

Yes, that's correct. The problem simply is that to be able to use a function pointer to a member function you need to have an object too. It's not possible to call a member function without an object.

IMO you have two possibilities:

1. Implement run as static function and pass a pointer to an object as argument (maybe you have to implement a class/struct if you need to pass other data, i.e. threadId). Then from the none-static member simply call that static function and pass this ass argument, i.e.:

static run( PThread* pThis )
{
pThis->run();
}

int Pthread::create()
{
return pthread_create( &mPthread, NULL, run, this );
}

2. If it's ok for you to use boost library () use some existing thread implementation like boost::thread - i.e. here you can see a sample how this is used: http://blog.emptycrate.com/node/277

ZOPPO

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Zoppo

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prain

ASKER

Ok. Complilation is working good. But I do not get the line

return static_cast< PThread* >( pThis )->run();

Do not understand why a point of the same function is returned after static_cast.

Can you pl. explain.

Zoppo

It's not the same function run which is called here, it's the none-static void* PThread::run() member function called against the PThread object pointed to by pThis. The cast is needed since pThis is a void pointer.

SOLUTION

sarabande

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sarabande

start function should have been like

if (!pthread_create(&mPthread, NULL, Pthread::threadRun, this))
     return false;
return true;

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prain

ASKER

In this simple example, I expected the print statement Running..... priinting for ever.
But it is not hapenning. BTW I am working in a UNIX env.
--Thread.hh
class Thread
{
public:

Thread();
virtual ~Thread();
void initialize();
bool isRunning() const;

private :

static void* threadRun(void * pThis);
void run();

pthread_t mThread;
bool mIsRunning;
};

--Thread.cpp
#include "Thread.hh"
#include <pthread.h>
Thread::Thread()
{
}

Thread::~Thread()
{
}

void Thread::initialize()
{
// Create thread attribute
pthread_attr_t attr;
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);

// Create thread
int rc = pthread_create(&mThread, &attr, &Thread::threadRun, (void*) this);

// Destroy thread attribute
pthread_attr_destroy(&attr);
// check return code form thread create - this should throw exception
if (rc != 0) {
std::cout << "pthread_create failed" << std::endl;
}

}

bool Thread::isRunning() const {
return mIsRunning;
}

void* Thread::threadRun(void * pThis)
{
Thread* tThis = (Thread*) pThis;
tThis->run();
}

void Thread::run() {

mIsRunning = true;

while (1) {
std::cout << "Running...." << std::endl;
}
}

--Test Main
#include "Thread.hh"
#include <iostream>

// Main Function
int main ( int argc, int argv[] )
{
Sst::Thread* aThread = new Sst::Thread();
aThread->initialize();

return 0;
}

sarabande

you would need a loop in the main function as well cause if the main thread exits the worker thread would terminate either.

put a little sleep in all endless loops to let some cpu for other processes.

Sara

prain

ASKER

Just thinking, doesn't the master (parent) thread must wait until the worker thread finishes?

sarabande

you could do so by calling pthread_join after create (if i remember rightly). but the normal thing is that both threads run parallel such that you have real multi-tasking. or said differently: it makes not much sense to run a thread if other thread waits. then a simple call of the thread function is much easier.

Sara

sarabande

instead of an infinite loop you could wait for user input (std::cin) or do a peek on std::cin. that way your program keeps responsive and the user could quit. in case of a user quit you would set a stopflag of your class object and wait until the thread has terminated. the thread would check periodically whether the stopflag is set and would terminate (break the infinite loop). that way the thread would be gently stopped and not killed what could make a difference if the thread uses resources which should be orderly freed.

Sara

prain

ASKER

Thanks guys.
I have another quesiton opened in boost:threads. Finally our company decided to go with
boost.

prain