将函数指针传递给pthread_create（C）

Question

Here is a minimal example which illustrates my problem

test.c:

#include <stdio.h>
#include <pthread.h>

#define CORES 8

pthread_t threads [ CORES ];
int threadRet [ CORES ];

void foo ()
{
   printf ("BlahBlahBlah\n" );
}

void distribute ( void ( *f )() )
{
   int i;

   for ( i = 0; i < CORES; i++ )
   {
      threadRet [ i ] = pthread_create ( &threads [ i ], NULL, f, NULL );
   }
   for ( i = 0; i < CORES; i++ )
   {
      pthread_join ( threads [ i ], NULL );
   }
}

int main ()
{
   distribute ( &foo );
   return 0;
}

Vim/gcc output :

test.c:20|11| warning: passing argument 3 of ‘pthread_create’ from incompatible pointer type [enabled by default]
/usr/include/pthread.h:225|12| note: expected ‘void * (*)(void *)’ but argument is of type ‘void (*)()’

What * / & do I need to add/remove to pass foo to distribute which then passes it to a thread?

Answer 1

void *foo (void *x)
{
   printf ("BlahBlahBlah\n" );
}

void distribute ( void * (*f)(void *) ) {
  /* code */
}

should do the trick

because the prototype is:

extern int pthread_create (pthread_t *__restrict __newthread,
                           __const pthread_attr_t *__restrict __attr,
                           void *(*__start_routine) (void *),
                           void *__restrict __arg) __THROW __nonnull ((1, 3));

Answer 2

The minimum recommended changes are:

void *foo(void *unused)
{
    printf("BlahBlahBlah\n");
    return 0;
}

void distribute(void *(*f)(void *))
{
    ...as before...
}

The pthread_create() function wants a pointer to a function that takes a void * argument and returns a void * result (though you haven't got to that error yet). So, pass it a pointer to that type of function by making foo() into a function that takes a void * argument and returns a void * result. And, for what it's worth, you can almost certainly make foo() into a static function since it is unlikely you will call it directly from outside this file.

Answer 3

This page seems to explain it quite well: http://publib.boulder.ibm.com/infocenter/iseries/v5r3/index.jsp?topic=%2Fapis%2Fusers_14.htm ;

Often IBM documentation is very good, keep an eye on those ibm links when they show up ;).

So, apparently you need a function pointer taking a void pointer in its argument. Try

void distribute ( void *( *f )(void *) ) {...}

You will probably also need to change your definition of foo though. See the following tutorial for function pointers: http://www.cprogramming.com/tutorial/function-pointers.html . Note: I haven't tested it myself, so no guarantees whether it will work - but I hope it at least points you in the right directions ;).