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diff --git a/src/man/xcb-requests.3 b/src/man/xcb-requests.3 new file mode 100644 index 0000000..278bcff --- /dev/null +++ b/src/man/xcb-requests.3 @@ -0,0 +1,165 @@ +.TH xcb-requests 3 2011-12-11 "XCB" "XCB examples" +.ad l +.SH NAME +xcb-requests \- about request manpages +.SH DESCRIPTION +Every request in X11, like \fIMapWindow\fP, corresponds to a number of +functions and data structures in XCB. For \fIMapWindow\fP, XCB provides the +function \fIxcb_map_window\fP, which fills the \fIxcb_map_window_request_t\fP +data structure and writes that to the X11 connection. Since the \fIMapWindow\fP +request does not have a reply, this is the most simple case. + +.SH REPLIES + +Many requests have replies. For each reply, XCB provides at least a +corresponding data structure and a function to return a pointer to a filled +data structure. Let's take the \fIInternAtom\fP request as an example: XCB +provides the \fIxcb_intern_atom_reply_t\fP data structure and +\fIxcb_intern_atom_reply\fP function. For replies which are more complex (for +example lists, such as in \fIxcb_list_fonts\fP), accessor functions are +provided. + +.SH COOKIES + +XCB returns a cookie for each request you send. This is an XCB-specific data +structure containing the sequence number with which the request was sent to the +X11 server. To get any reply, you have to provide that cookie (so that XCB +knows which of the waiting replies you want). Here is an example to illustrate +the use of cookies: + +.nf +.sp +void my_example(xcb_connection *conn) { + xcb_intern_atom_cookie_t cookie; + xcb_intern_atom_reply_t *reply; + + cookie = xcb_intern_atom(conn, 0, strlen("_NET_WM_NAME"), "_NET_WM_NAME"); + /* ... do other work here if possible ... */ + if ((reply = xcb_intern_atom_reply(conn, cookie, NULL))) { + printf("The _NET_WM_NAME atom has ID %u\n", reply->atom); + } + free(reply); +} +.fi + +.SH CHECKED VS. UNCHECKED + +The checked and unchecked suffixes for functions determine which kind of error +handling is used for this specific request. + +For requests which have no reply (for example \fIxcb_map_window\fP), errors +will be delivered to the event loop (you will receive an X11 event of type 0 +when calling \fIxcb_poll_for_event\fP). +If you want to explicitly check for errors in a blocking fashion, call the +_checked version of the function (for example \fIxcb_map_window_checked\fP) and +use \fIxcb_request_check\fP. + +For requests which have a reply (for example \fIxcb_intern_atom\fP), errors +will be checked when calling the reply function. To get errors in the event +loop instead, use the _unchecked version of the function (for example +\fIxcb_intern_atom_unchecked\fP). + +Here is an example which illustrates the four different ways of handling errors: + +.nf +.sp +/* + * Request without a reply, handling errors in the event loop (default) + * + */ +void my_example(xcb_connection *conn, xcb_window_t window) { + /* This is a request without a reply. Errors will be delivered to the event + * loop. Getting an error to xcb_map_window most likely is a bug in our + * program, so we don't need to check for that in a blocking way. */ + xcb_map_window(conn, window); + + /* ... of course your event loop would not be in the same function ... */ + while ((event = xcb_wait_for_event(conn)) != NULL) { + if (event->response_type == 0) { + fprintf("Received X11 error %d\\n", error->error_code); + free(event); + continue; + } + + /* ... handle a normal event ... */ + } +} + +/* + * Request without a reply, handling errors directly + * + */ +void my_example(xcb_connection *conn, xcb_window_t deco, xcb_window_t window) { + /* A reparenting window manager wants to know whether a new window was + * successfully reparented. If not (because the window got destroyed + * already, for example), it does not make sense to map an empty window + * decoration at all, so we need to know this right now. */ + xcb_void_cookie_t cookie = xcb_reparent_window_checked(conn, window, + deco, 0, 0); + xcb_generic_error_t *error; + if ((error = xcb_request_check(conn, cookie))) { + fprintf(stderr, "Could not reparent the window\\n"); + free(error); + return; + } + + /* ... do window manager stuff here ... */ +} + +/* + * Request with a reply, handling errors directly (default) + * + */ +void my_example(xcb_connection *conn, xcb_window_t window) { + xcb_intern_atom_cookie_t cookie; + xcb_intern_atom_reply_t *reply; + xcb_generic_error_t *error; + + cookie = xcb_intern_atom(c, 0, strlen("_NET_WM_NAME"), "_NET_WM_NAME"); + /* ... do other work here if possible ... */ + if ((reply = xcb_intern_atom_reply(c, cookie, &error))) { + printf("The _NET_WM_NAME atom has ID %u\n", reply->atom); + free(reply); + } else { + fprintf(stderr, "X11 Error %d\\n", error->error_code); + free(error); + } +} + +/* + * Request with a reply, handling errors in the event loop + * + */ +void my_example(xcb_connection *conn, xcb_window_t window) { + xcb_intern_atom_cookie_t cookie; + xcb_intern_atom_reply_t *reply; + + cookie = xcb_intern_atom_unchecked(c, 0, strlen("_NET_WM_NAME"), + "_NET_WM_NAME"); + /* ... do other work here if possible ... */ + if ((reply = xcb_intern_atom_reply(c, cookie, NULL))) { + printf("The _NET_WM_NAME atom has ID %u\n", reply->atom); + free(reply); + } + + /* ... of course your event loop would not be in the same function ... */ + while ((event = xcb_wait_for_event(conn)) != NULL) { + if (event->response_type == 0) { + fprintf("Received X11 error %d\\n", error->error_code); + free(event); + continue; + } + + /* ... handle a normal event ... */ + } +} +.fi + +.SH SEE ALSO +.BR xcb_map_window (3), +.BR xcb_intern_atom (3), +.BR xcb_list_fonts (3), +.BR xcb_poll_for_event (3), +.BR xcb_request_check (3) +.SH AUTHOR +Michael Stapelberg <michael+xcb at stapelberg dot de> |