Page:Xlib - C Language X Interface.pdf/34

 To track internal connections for a display, use XAddConnectionWatch.

The XAddConnectionWatch function registers a procedure to be called each time Xlib opens or closes an internal connection for the specified display. The procedure is passed the display, the specified client_data, the file descriptor for the connection, a Boolean indicating whether the connection is being opened or closed, and a pointer to a location for private watch data. If opening is True, the procedure can store a pointer to private data in the location pointed to by watch_data; when the procedure is later called for this same connection and opening is False, the location pointed to by watch_data will hold this same private data pointer.

This function can be called at any time after a display is opened. If internal connections already exist, the registered procedure will immediately be called for each of them, before XAddConnectionWatch returns. XAddConnectionWatch returns a nonzero status if the procedure is successfully registered; otherwise, it returns zero.

The registered procedure should not call any Xlib functions. If the procedure directly or indirectly causes the state of internal connections or watch procedures to change, the result is not defined. If Xlib has been initialized for threads, the procedure is called with the display locked and the result of a call by the procedure to any Xlib function that locks the display is not defined unless the executing thread has externally locked the display using XLockDisplay.

To stop tracking internal connections for a display, use XRemoveConnectionWatch.

The XRemoveConnectionWatch function removes a previously registered connection watch procedure. The client_data must match the client_data used when the procedure was initially