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# 12.4 Managing the Event Queue

The following paragraphs describe CLX functions and macros used to:

- Put a new event on the event queue
- Discard the current event
- Return the current length of the event queue
- Gain exclusive access to the event queue for a client process

queue-event | display event-key &rest event-slots &key :append-p & allow-other-keys | Function

| display A display. event-key Specifies the type of event placed in the queue. event-slots Keyword-value pairs that describe the contents of an event. :append-p If true, the event is placed at the tail of the queue; otherwise, the event is placed at the head of the queue. Places an event of the type given by event-key into the event queue. When :append-p is true, the event is placed at the tail of the queue; otherwise, the event is placed at the head of the queue. The actual event-slots passed depend on the event type. The keyword symbols used for each event type are event slot names defined by the declare-event macro and are described in paragraph 12.12.8, Declaring Event Types.

discard-current-event | display | Function

| display A display. Discards the current event for the display. Returns nil when the event queue is empty; otherwise, returns t . This function provides extra flexibility for discarding events, but it should be used carefully; use event-cond instead, if possible. Typically, discard-current-event is called inside a handler function or a clause of an event-case form and is followed by another call to process-event, event-case , or event-cond. discarded-p Type boolean.

event-listen | display & optional (timeout 0) | Function

| display A display. timeout The number of seconds to wait for events. Returns the number of events queued locally. If the event queue is empty, event-listen waits for an event to arrive. If timeout is non-nil and no event arrives within the specified timeout interval (given in seconds), event-listen returns nil; if timeout is nil , event-listen will not return until an event arrives. event-count Type (or null integer).

with-event-queue | display &body body | Macro

| display A display. body Forms to execute. Executes the body in a critical region in which the executing client process has exclusive access to the event queue.

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