Window server session.

The session between the client and the window server can be used to mediate asynchronous events, for client interface control and for system control. A description of each of these capabilities is given below.

Mediating asynchronous events:

Primarily, the session mediates asynchronous events to the user. Three event streams are available: the standard event stream which all applications must use; the redraw event stream which must be used by all applications except those which exclusively use backed-up windows; and the priority key event stream which may be used for abort keys and the like for specialist applications.

All these events are mediated as standard asynchronous services. Typical window server client programs encapsulate each service they require in an active object whose RunL() identifies the event and calls the appropriate member function of a class associated with an application framework, or a window.

Client interface control:

The client's interface with the window server has several aspects, each of which is controlled through the window server session.

Flushing defines how requests to the window server are handled.

System control:

Many system-wide settings may be controlled through the window server session. Typically, these functions are only used by the system shell and its associated sessions/applications. They include: auto-repeat and double-click, querying all window groups in the system, setting the default shadow vector, setting the system pointer cursors, counting resources used by the window server (this is only useful for debugging checks), getting and setting the state of the modifier keys (for instance Shift and Ctrl), setting the window server background colour, getting and setting thresholds for window server generated pointer events.