
DIRECTORY
Rope USING [ROPE],
ViewerClasses USING [Viewer],
ViewerEvents USING [EventProc, EventRegistration, ViewerEvent],
ViewerPrivate USING [Severity],
UserProfile USING [Boolean];

ViewerEventsImpl: CEDAR MONITOR
IMPORTS UserProfile
EXPORTS ViewerEvents, ViewerPrivate
= BEGIN

ROPE: TYPE = Rope.ROPE;
EventProcs: TYPE = LIST OF RECORD[proc: ViewerEvents.EventProc, filter: REF, before: BOOL];
ArrayEventProcs: TYPE = ARRAY ViewerEvents.ViewerEvent OF EventProcs;
eventProcs: REF ArrayEventProcs м NEW[ArrayEventProcs м ALL[NIL]];


Error: PUBLIC SIGNAL [severity: ViewerPrivate.Severity м fatal, msg: Rope.ROPE м NIL] = CODE;

UserErrorQuery: PUBLIC ENTRY PROC RETURNS [continue: BOOL м FALSE] = TRUSTED {
ENABLE UNWIND => NULL;
IF UserProfile.Boolean["Viewers.WorldSwapDebug", FALSE] THEN RETURN [FALSE];
};


RegisterEventProc: PUBLIC PROC [proc: ViewerEvents.EventProc, 
event: ViewerEvents.ViewerEvent, filter: REF м NIL, before: BOOL м TRUE]
RETURNS [ViewerEvents.EventRegistration м NIL] = {
IF proc # NIL THEN {
key: EventProcs м LIST[[proc, filter, before]];
innerRegister: ENTRY PROC = {
eventProcs[event] м CONS[[proc, filter, before], eventProcs[event]];
};
innerRegister[];
RETURN [key];
};
};

UnRegisterEventProc: PUBLIC ENTRY PROC
[proc: ViewerEvents.EventRegistration, event: ViewerEvents.ViewerEvent] = {
newHead: EventProcs м NIL;
newTail: EventProcs м NIL;
who: EventProcs м NIL;
WITH proc SELECT FROM
ep: EventProcs => {
IF ep.first.proc = NIL THEN RETURN;
who м ep;
};
ENDCASE => RETURN;
FOR each: EventProcs м eventProcs[event], each.rest WHILE each # NIL DO
IF who.first = each.first
THEN {
IF newTail # NIL THEN newTail.rest м each.rest ELSE newHead м each.rest;
who.first.proc м NIL; -- don't let this key be used again!
EXIT;
}
ELSE {
new: EventProcs м LIST[each.first];
IF newTail # NIL THEN newTail.rest м new ELSE newHead м new;
newTail м new;
};
ENDLOOP;
eventProcs[event] м newHead;
};

GetHead: ENTRY PROC [event: ViewerEvents.ViewerEvent] RETURNS [EventProcs] = INLINE {
RETURN [eventProcs[event]];
};

ProcessEvent: PUBLIC PROC [event: ViewerEvents.ViewerEvent, viewer: ViewerClasses.Viewer, before: BOOL] RETURNS [abort: BOOL м FALSE] = {
FOR l: EventProcs м GetHead[event], l.rest UNTIL l=NIL DO
IF l.first.before = before THEN {
filter: REF м l.first.filter;
IF filter = NIL OR filter = viewer OR (viewer # NIL AND filter = viewer.class.flavor) THEN {
proc: ViewerEvents.EventProc м l.first.proc;
IF proc # NIL THEN
abort м proc[viewer, event, before ! ABORTED => {abort м TRUE; EXIT}].abort;
IF abort THEN RETURN;
};
};
ENDLOOP;
};

END.
  f  
ViewerEventsImpl.mesa
Copyright ╙ 1985, 1986, 1987, 1991 by Xerox Corporation.  All rights reserved.
Russ Atkinson (RRA) March 2, 1987 8:29:47 pm PST
Michael Plass, January 26, 1987 8:56:01 pm PST
Doug Wyatt, June 10, 1987 4:34:04 pm PDT
Bier, November 30, 1988 1:02:00 pm PST
Christian Jacobi, October 25, 1991 3:58 pm PDT
Exports to ViewerPrivate
RRA: formerly used to query user as to whether or not to continue when an uncaught error occurs in a paint or TIP notification procedure (not currently used, perhaps this entire module should go away).
Exports to ViewerEvents
Monitorized CONS onto the head of the list.  We don't check for duplicates.  The key returned is a copy to avoid smashing the list in UnRegisterEventProc.
If the proc is unsafe to assign this will get the fault before we grab the monitor lock.
Copy the previous list without the given entry.  We copy this to avoid needing to monitorize ProcessEvent (who needs the hassle, after all).
We have found the registration (or its equivalent), so just splice out the entry and exit.  There is no need to copy any more, since the list is immutable.
We have not found the registration yet, so copy the list.
This guarantees that the sampling is atomic.
Notice that we do not have to monitorize this processing since the sampling of GetHead[event] is atomic and the list is never changed by smashing elements.
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