pthread trick works with gcc 3.x.x, but not with 4.x.x

at8 · #1 21-Apr-2008, 06:31

At may 2000 issue of the drJobbs journal was a cool trick to do posix threading with cpp.
Here is the original paper:

HTML Code:

http://www.lotn.org/~calkinsc/papers/cujthread.pdf

I used the trick at small simulation SW and it works just fine.
Recently I tried to use it again, but it does not compile any more. After few tries I found out that it still builds with gcc 3.x.x.

Apparently gcc 4.x.x. is more strict. What is the problem and how to solve it??

Comple attached example by: g++ -lpthread main.cpp
(@ pdf document above are the original examples)

CPP / C++ / C Code:

#include <pthread.h>
#include <iostream>
using namespace std;

class Thread {
protected:
   pthread_t _threadptr;
   void Run() {cout << "thread hello" << endl;}
public:
   friend void *thread_func(void *);
   void Create() { pthread_create(&_threadptr, NULL, thread_func, this); }
   ~Thread() { pthread_join(_threadptr, NULL); }
};

void *thread_func(void *p) {
   Thread *t=reinterpret_cast<Thread *>(p);
   if (t)
     t->Run();
   return 0;
}

int main() {
   Thread t;
   t.Create();
   cout << "main hello" << endl;
   return 0;
}

LuciWiz · #2 21-Apr-2008, 08:03

I don't have the environment available right now. Could you please post the error message(s)?

Thanks,
Lucian

at8 · #3 21-Apr-2008, 08:14

oops.

$ g++ -lpthread main1.cpp
main1.cpp: In member function ‘void Thread::Create()’:
main1.cpp:12: error: ‘thread_func’ was not declared in this scope
$

-antti

LuciWiz · #4 21-Apr-2008, 08:25

You probably just need to let the compiler know of the signature of the function before implementing the method in the class.
Try to either declare the prototype of thread_func prior to the Class definition, or to simply move the entire function implementation before the class.

A code similar to the one you posted compiles fine in Visual Studio, and I don't have the Standard handy, nor the time to search in the Behemoth.

davekw7x · #5 21-Apr-2008, 16:58

Quote:

Originally Posted by LuciWiz

...declare the prototype of thread_func prior to the Class definition

That works for me.

Quote:

Originally Posted by LuciWiz

... move the entire function implementation before the class.

That doesn't, since the function does its thing with the cast to pointer to Thread...

With g++ version 4.1.2 on my Centos 5.1 Linux platform, the following works:

CPP / C++ / C Code:

#include <pthread.h>
#include <iostream>
using namespace std;

void *thread_func(void *p);

class Thread {

.
.
.
 //Everything else as in the original post
.
.
.

Output:

Code:

$ g++ -Wall -W test_pthread.cpp -lpthread -o test_pthread
$ ./test_pthread 
main hello
thread hello

Regards,

Dave

at8 · #6 22-Apr-2008, 08:02

Great, thanks to all.
That was a a really trivial error that I made.
-a

LuciWiz · #7 23-Apr-2008, 07:57

Quote:

Originally Posted by davekw7x

That doesn't, since the function does its thing with the cast to pointer to Thread...

You are right. I wrote the suggestion without actually trying it out - sorry.

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pthread trick works with gcc 3.x.x, but not with 4.x.x

Re: pthread trick works with gcc 3.x.x, but not with 4.x.x

Re: pthread trick works with gcc 3.x.x, but not with 4.x.x

Re: pthread trick works with gcc 3.x.x, but not with 4.x.x

Re: pthread trick works with gcc 3.x.x, but not with 4.x.x

Re: pthread trick works with gcc 3.x.x, but not with 4.x.x

Re: pthread trick works with gcc 3.x.x, but not with 4.x.x