Editing XHB (section)

=== Basic XHB notions ===

XHB has been created to eliminate the need for programs to actually implement the X protocol layer. This library gives a program a very low-level access to any X server. Since the protocol is standardized, a client using any implementation of XHB may talk with any X server (the same occurs for Xlib, of course). We now give a brief description of the basic XHB notions. They will be detailed later.

* The X server connection which abstracts request and reply queues.
* Requests and replies which are the means of communicating between X server and client.
* The graphics context which holds the current state of graphics variables (what foreground and background colors to use, what font to use when drawing some text, etc.). Actually, this is how we reduce bandwidth consumption.
* Events with additional information (e.g., position on the screen where event was generated, mouse button associated with the event, etc.).

What is really interesting here, is that XHB is non-blocking (asynchronous). That is, it doesn't force you to wait for reply on your request. When sending a request, XHB returns immediately (with a cookie, "a promise"), even if the reply is not yet available; while Xlib, for instance, locks your program waiting for X server to reply. This can be very slow (and it is, in fact).

Note that [[Lazy evaluation]] is good at hiding latency of this sort.