[vlc-devel] Re: CVS Commit (sam)

[Samuel Hocevar]

On Wed, Oct 16, 2002, cvs at videolan.org wrote:
>   * ./include/variables.h, ./src/misc/variables.c: implemented variable
>     callbacks.

   A few words about this. It's functional, but has severe limitations
for the moment, due to reentrancy issues. My advice until this is solved
is: do not call any var_* functions from a callback! And do not try to
acquire a mutex that may be waiting for a var_* function termination.

   Here is some sample code:

static int MyCallback( vlc_object_t *p_object, char const *psz_var,
                       vlc_value_t oldval, vlc_value_t newval, void *p_data )
{
    printf( "triggered! object=%p name=%s old=%i new=%i data=%p\n",
            p_object, psz_var, oldval.i_int, newval.i_int, p_data );

    return VLC_SUCCESS;
}

1. at some place an object does this (I used VLC_VAR_INTEGER as an example
   but it can be any other type):

    var_Create( p_object1, "glop", VLC_VAR_INTEGER );

2. at some other place we do this:

    var_AddCallback( p_object1, "glop", MyCallback, p_data );

    p_data can be any pointer; usually it's p_object2 (or whatever
   the object registering the callback is called). don't forget to
   call var_DelCallback with the same arguments to remove it when
   it is not needed anymore.

3. at some other place someone does this, which triggers the callback:

    vlc_value_t val;
    val.i_int = 12;
    var_Set( p_object1, "glop", val );

Have fun,
-- 
Sam.
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