<<<<<<<<<<<<<<<<<

io_select(prog_tools) Programming Tools io_select(prog_tools)

NAME

io_select -- multiple input source co-ordinator for all Lymb i/o.

DESCRIPTION

The io_select object allows LYMB to select input from a number of sources and take a particular action whenever input is available on a given source. This is done by registering callback actions or functions for specific file descriptors. There is an object/message interface for use within scripts as well as a function callback interface for efficient use within C code. If the "xt" class is present in the system, it uses xt's facilities for blocking on multiple sources to allow intrinsics timeouts to be processed in addition to i/o on real file or socket descriptors.

The lymb parser uses the io_select object to allow other input sources (such as X events) to be processed while it is waiting for input from the keyboard. In addition to keyboard input and X events, the io_select object is used for dispatching signal handlers, sending "read!" messages to network objects in auto_read mode, and processing incoming requests for netserver_filter objects and lymb_process objects (in server or slave mode).

SUPERCLASS

object

INSTANCE VARIABLES

None

MESSAGES

register_function(fd,func,data) Takes three arguments, an integer file descriptor, a function pointer, and an arbitrary data pointer. When input becomes available on the file descriptor, the corresponding function is called with the corresponding data pointer as an argument.

register_object:(fd,object_name,message) Takes three arguments, an integer file descriptor, an object name, and a message. When input becomes available on the file descriptor, the corresponding message is sent to the corresponding object.

unregister:(fd) Removes any callbacks associated with the file

descriptor

block_on:(fd) Waits for input to become available on the indicated file descriptor and then returns. While waiting, it dispatches callbacks for file descriptors that have been previously registered. This method should not be used to block on file descriptors that have previously been registered for callback. This message also implicitly dispatches X events. This message is used by the parser.

process_inputs! Dispatches callbacks for whatever file descritors currently have input available. It also implicitly dispatches X events. This message never blocks. This message is used by ui_scene and motif_scene to process input sources between ticks.

main_loop! If the application needs to do nothing other than process callbacks for previously registered descriptors, it may issue this message after setting up all necessary callbacks. This message never returns.

initialize Private message used internally before any other messages are sent. Performs some internal initialization consisting of detecting for presence of the "xt" class (and initializing that if present), determining the maximum number of file descriptors available to the process, and initializing the internal callback tables.

NOTES

If an end-of-file condition occurrs on a a registered file descriptor (or a file descriptor currently being blocked on), the io_select object will dispatch the appropriate callback (or return from the "block_on:" message) as if input were available on that file descriptor. This is due to the fact that under such a condition an attempt to read will not block. In the event of a registered descriptor, the client must, within the callback, detect this condition and unregister the descriptor. Otherwise, the callback will continue to be invoked.

EXAMPLE

This class will rarely be used by the end user. It will be used mainly by the classes mentioned above. The user may, on occasion, use the "register_object:" message, but there aren't any uses "typical" enough to serve as an example.