[Xcb] problem when getting replies

[Ian Osgood]

A difference between Xlib and the raw protocol is that Xlib hides the  
difference between predefined and custom atoms. The atoms "ATOM",  
"CARDINAL", "STRING", and "WINDOW" are predefined, so you must not  
intern them. That is probably why you get the segfault.

If you want to keep the code identical, you can use the XCBAtom  
library, include <xcb/xcb_atom.h> and call intern_atom_fast() and  
intern_atom_fast_reply() instead of xcb_intern_atom() and  
xcb_intern_atom_reply().

Ian

On Nov 11, 2006, at 7:21 AM, Vincent Torri wrote:

>
> Hey,
>
> I've finished to write ecore_xcb. But (always a but) it seg fault,  
> and I don't understand the reason. The code is the following:
>
> In a file, I define these variables and functions:
>
> #define ECORE_XCB_ATOMS_COUNT 8
> static xcb_intern_atom_cookie_t ecore_xcb_atom_init_cookies 
> [ECORE_XCB_ATOMS_COUNT];
>
> /* Atoms */
> EAPI Ecore_Xcb_Atom ECORE_XCB_ATOM_ATOM          = 0;
> EAPI Ecore_Xcb_Atom ECORE_XCB_ATOM_CARDINAL      = 0;
> EAPI Ecore_Xcb_Atom ECORE_XCB_ATOM_COMPOUND_TEXT = 0;
> EAPI Ecore_Xcb_Atom ECORE_XCB_ATOM_FILE_NAME     = 0;
> EAPI Ecore_Xcb_Atom ECORE_XCB_ATOM_STRING        = 0;
> EAPI Ecore_Xcb_Atom ECORE_XCB_ATOM_TEXT          = 0;
> EAPI Ecore_Xcb_Atom ECORE_XCB_ATOM_UTF8_STRING   = 0;
> EAPI Ecore_Xcb_Atom ECORE_XCB_ATOM_WINDOW        = 0;
>
> /* To avoid round trips, the initialization is separated in 2
>    functions: _ecore_xcb_atom_init and
>    _ecore_xcb_atom_init_finalize. The first one gets the cookies and
>    the second one gets the replies and set the atoms. */
>
> void
> _ecore_xcb_atom_init(void)
> {
>    const char *atom_names[ECORE_XCB_ATOMS_COUNT] = {
>      "ATOM",
>      "CARDINAL",
>      "COMPOUND_TEXT",
>      "FILE_NAME",
>      "STRING",
>      "TEXT",
>      "UTF8_STRING",
>      "WINDOW"
>    };
>    int         i;
>
>    for (i = 0; i < ECORE_XCB_ATOMS_COUNT; i++)
>      ecore_xcb_atom_init_cookies[i] = xcb_intern_atom_unchecked 
> (_ecore_xcb_conn, 0,
>
> strlen(atom_names[i]),
>
> atom_names[i]);
> }
>
> void
> _ecore_xcb_atom_init_finalize(void)
> {
>    xcb_intern_atom_reply_t *replies[ECORE_XCB_ATOMS_COUNT];
>    int                      i;
>
>    for (i = 0; i < ECORE_XCB_ATOMS_COUNT; i++)
>       replies[i] = xcb_intern_atom_reply(_ecore_xcb_conn,
>                                          ecore_xcb_atom_init_cookies 
> [i],
>                                          NULL);
>
>    ECORE_XCB_ATOM_ATOM          = replies[0]->atom;
>    ECORE_XCB_ATOM_CARDINAL      = replies[1]->atom;
>    ECORE_XCB_ATOM_COMPOUND_TEXT = replies[2]->atom;
>    ECORE_XCB_ATOM_FILE_NAME     = replies[3]->atom;
>    ECORE_XCB_ATOM_STRING        = replies[4]->atom;
>    ECORE_XCB_ATOM_TEXT          = replies[5]->atom;
>    ECORE_XCB_ATOM_UTF8_STRING   = replies[6]->atom;
>    ECORE_XCB_ATOM_WINDOW        = replies[7]->atom;
>
>    for (i = 0; i < ECORE_XCB_ATOMS_COUNT; i++)
>       free(replies[i]);
> }
>
>
> So it's not that complicated. I save the cookies in a global  
> variable and I set them in _ecore_xcb_atom_init. Later, I call  
> _ecore_xcb_atom_init_finalize to get the replies and to set the atoms.
>
> In another function (ecore_xcb_init, to name it), I use these  
> functions:
>
> {
>  /* I prefetch the extension data */
>   ...
>   ...
>
>  /* I 'initialize' the atoms */
>  _ecore_xcb_atom_init ();
>  /* other similar init functions */
>
>  /* I get the extension data */
>  ...
>  ...
>
>  /* I 'finalize' the init */
>  _ecore_xcb_atom_init_finalize();
>  /* other similar finalization functions, in the same order */
> }
>
> If I only keep the ecore_xcb_atom_init(_finalize) functions, and  
> not the others *init(_finalize) functions, no seg fault. If I add  
> the others, all the replies in ecore_xcb_atom_init_finalize are NULL.
>
> I'm certainly doing something wrong, but I don't know what.
>
> Does someone have an idea, please ?
>
> Vincent
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