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Volume Number: | 5 | |
Issue Number: | 1 | |
Column Tag: | Forth Forum |
System Queues
By Jörg Langowski, MacTutor Editorial Board
Note: Source code files accompanying article are located on MacTech CD-ROM or source code disks.
“Looking at system queues”
The utility that I’m going to describe this month can be used to look at various queues of the Macintosh operating system. I was always curious to know what’s going on in the background of my machine while I’m working away; that’s how this example came to be. At the same time, the program contains another example of popup menus (for which the correct trap call has been added in Mach2.14), and how to use the userData field in the user variable area to display messages in a task window.
A number of queues are maintained by the Mac operating system; the example won’t list all of them, but some of the more important ones. Queues are linked lists of information blocks. Each block contains the address of the next list element in its first four bytes, a 16-bit number indicating the queue type in its next 2 bytes, and variable length information thereafter, as indicated below:
Fig.1: general structure of a Macintosh queue
The first element of a queue is called the queue header and the last one the queue tail. The queue tail has a link address of zero, meaning no more elements will follow. One can access the elements of a queue through a pointer to its header which is usually kept in a low memory global variable. For some of the queues the tail’s location is kept in another global variable for faster access.
The low memory addresses of the queues that our utility will display - vertical blanking queue, volume control block queue, drive queue, file system queue, event queue, deferred task queue and time manager queue - are defined at the beginning of the listing. (Since the address of the TM queue is not given in IM, I dug it out of a disassembly of the _InsTime trap.)
Structure of the program
We’ll set up a Mach 2 terminal task that contains the usual Apple, File and Edit menus (for desk accessories). The task window will contain a bar display for each queue which gives a visual indication of the size of the queue. The display bars are ‘click-sensitive’; when the mouse is clicked on one of them, a popup menu is displayed which shows the name of the queue. When this name is selected, a second window will be opened with information about the queue elements. That second window will disappear on a mouse click.
Inter-task communication in Mach2
I was happily hacking away on the example, got the rectangles drawn in the right places, the popup menus setup (note the slight difference in the interface that’s used here - built-in - from my code in MT V4#4), when I got a row of bad bombs trying to write text into a second window from the queue-monitoring task. Just ADDing a new window, then doing a _SetPort and using the Mach2 text I/O routines wouldn’t work at all. When it finally dawned on me what was I actually doing? The main task detects a mouse down in the content region of its window and calls the content handler (see listing) to find out which rectangle it has been clicked in, which menu to display, and to output the text in the second window. Now that is a totally trivial piece of code in a single task program like one would write in C or Pascal most of the time. In Mach2, things are different.
The mouse down event is not detected by the task that is supposed to handle it, but by the (in)famous I-O task, present in any Mach2 application. That task calls WaitNextEvent, detects which window the mouse was clicked in, and calls the event handler of the task that owns the window. So while we’re executing the event handler, we’re actually in the context of the I-O task! The standard Mach2 console output would be sent to the window associated with the I-O task. Unfortunately, there is no such window - therefore bomb.
The bottom line is that you can’t use the Forth text I-O routines from event handlers that are called through the I-O task. You have to rely on the means that Mach2 provides to do inter-task communication and make a terminal task do the text output.
Mach2 text output from event handlers
How is this achieved? The User area of a Mach2 task contains two locations, UserData and UserVector. When a non-zero value is stored in UserData, the routine pointed to by UserVector will be executed. So all we need to do is define a user vector handling routine, and have the content handler of the task store some message in UserData.
The content handler of our main window simply stores the menu ID of the selected popup menu in UserData. The user vector handler finds this menu ID (it gets passed on the stack), and calls the corresponding queue display routine.
The queue display routines use a second window, qInfo. In order to have the output appear in that window and not on top of our bar display, we have to change the task window pointer momentarily; this is done by storing the qInfo window pointer in the user variable taskWindowPointer, doing the output and later restoring the original pointer.
Queues displayed
The utility displays seven queues (and you can easily add more): vertical blanking, volume control block, drive, event, file system, deferred task, and time manager queues, in that order. The display bars are not labeled, but the popup menu will show you the name of the queue when you click on a bar.
When a popup menu has been selected, a queue list is displayed in a second window. The first two columns are the element number and queue type for each list element. The remaining columns vary according to the queue displayed. For the VBL queue, the VBL procedure pointer, the tick count and the ‘phase’ are listed. The VCB queue gives the name of each mounted volume, its drive number, driver and volume reference numbers, total number of allocation blocks, allocation block size and free blocks. The drive queue will give the drive number, driver reference number, file system ID, total number of blocks, and the status of the drive (locked disk, disk inserted, single or double sided for floppies). The status information is kept in the four bytes preceding the queue element (see IM II-128).
The event queue listing contains the what, message, when, where, and modifiers fields of the event. However, I’m sorry to say that in this case the listing window is next to useless, because the list is always empty when it is displayed. I’ll let you think of a reason why. The bar display sometimes shows queued events, when the display window is brought to the front from a partially covered position (its activate and update events).
Since I never found any pending asynchronous file system requests, I could not test the display for the FS queue, so that display routine is empty, just like the deferred task display. The time manager queue list shows the procedure pointer and count field for each time manager task.
In my system (MacII, 80MB hard disk, 5 MB memory, Appletalk and file server installed) I found a total of 8 VBL tasks, 2 time manager tasks, 2 mounted volumes (hard disk and Alisashare volume), and, interestingly, 5 different drives. I could make sense of three drives (SCSI disk, floppy drive and Alisashare disk), and can guess that a fourth ‘drive’, with the same file system ID as the Alisashare volume, might have something to do with the server. The fifth entry, with a queue type of 3, file system ID of $43C, and driver reference number of zero, doesn’t make sense to me. If someone has something to say about that point I’d be happier.
Why?
The crucial question - what is this utility good for? Besides satisfying the general curiosity of a system hacker, one important thing that I can imagine it would be helpful in is the detection of - you guessed it - viruses. At least background routines that install VBL or time manager tasks to do their malicious job might be spotted a lot easier when the queue display suddenly starts changing.
I did not add information about working directory control blocks, but you may do so if you like. The working directory queue header pointer is at $372.
Mach2 news
Finally, Palo Alto Shipping has published a trap compiler that allows you to add new traps to the Mach2 system without writing assembly code. The code is freely accessible on the Mach2 GEnie roundtable, but for those of you who don’t have access to GEnie, I’m including it on the source code disk together with some trap fixes for version 2.14. Sorry we can’t print the complete code here because it is too long; also you’ll have a lot of glue code typed in and debugged before you have finished typing the trap compiler in by hand. I’ll nevertheless print a short extract of the description:
This utility allows you to define your own trap “glue.” Thus as new system traps become available, you will be able to define their high-level interface symbolically (without using assembly language). It will also allow you to define a substitute syntax to the CALL interface, in case you need to modify (fix?) one of the existing traps. Note that in the latter case, you do not actually change the existing CALL, you simply define a new syntax which can be used in place of the CALL sequence.
One might wonder whether it makes good sense to include a 2K utility in an application when all you need is a few trap calls (but, see my comments below). However, for casual use you might consider putting this code in your workspace, along with your commonly used constants, mach words, and other compiler utilities (that way they will always be available during your “experimental” sessions). If you are working on a serious application, I would suggest the following approach. Place all variables, mach words, and compiler utilities (such as this trap compiler) in a separate segment and when you finish your application use ResEdit to remove that very same segment from your finished application.
This will work because mach words, variables, and compiler utilities (such as this trap compiler) do NOT need to be in memory during the execution of the code which they produce. Generally speaking, any word which only produces in-line code, most immediate words, or any child word which does not reference its parent at run-time can safely be removed from a finished application. If you are really concerned about making the smallest possible applications, then this is a technique which you should always use (as a final step, when you are completely finished with your program). If it seems risky to remove a segment from a finished application, just remember that there is NO WAY you can run code in another segment if that segment has NO jump-table entries (i.e. if you can’t get to the code, why include it in your application?)
Mach words, variables, and (most) compiler words don’t use or create jump-table entries. This same principle is why you never have to mark mach words or variables as GLOBAL (there is one exception, if you write a CODE word which explicitly states “JSR <mach word>” or “LEA <mach word>” then the defined instance of that <mach word> must be in memory at run-time. Thus if <mach word> exists in another segment, it will need to be marked GLOBAL (however, it’s always ok to say LEA <variable> or MOVE.L <variable>, thus variables “never” need to be marked as GLOBAL).
Waymen @ PASC
Thanks for that utility and the comments on segmentation.
Till next month.
Listing 1: System queue display \ mini task to display system queues \ © 1988 J. Langowski / MacTutor only forth also assembler also mac $160 constant vblqhdr $356 constant vcbqhdr $308 constant drvqhdr $14a constant evtqhdr $360 constant fsqhdr $d92 constant dtqhdr $b30 constant timevars $11c constant utablebase 72 user taskwindowpointer 92 user (type) 108 user taskmenubar 144 user uservector 148 user userdata 152 user content-hook 164 user goaway-hook 168 user update-hook 172 user activate-hook 2 CONSTANT Message 10 CONSTANT Where 14 CONSTANT Modifiers 1 CONSTANT ActivateMask 300 constant appleid 301 constant fileid 302 constant editid 152 CONSTANT WrefCon create rect1 20 w, 20 w, 90 w, 28 w, create rect2 20 w, 35 w, 90 w, 43 w, create rect3 20 w, 50 w, 90 w, 58 w, create rect4 20 w, 65 w, 90 w, 73 w, create rect5 20 w, 80 w, 90 w, 88 w, create rect6 20 w, 95 w, 90 w, 103 w, create rect7 20 w, 110 w, 90 w, 118 w, CREATE APPLESTRING 01 C, $14 C, NEW.MBAR queueBar NEW.MENU AppleMenu APPLESTRING AppleMenu TITLE 0 APPLEID AppleMenu BOUNDS “ About Queues ...;(-” AppleMenu ITEMS NEW.MENU FileMenu “ File” FileMenu TITLE 0 FileID FileMenu BOUNDS “ Quit” FileMenu ITEMS NEW.MENU EditMenu “ Edit” EditMenu TITLE 0 EDITID EditMenu BOUNDS “ (Undo/Z;(-;(Cut/K;(Copy/C;(Paste/V;(Clear” EditMenu ITEMS NEW.MENU vblmenu “ vbl” vblmenu TITLE -1 150 vblmenu BOUNDS “ VBL Tasks;(-” vblmenu ITEMS NEW.MENU vcbmenu “ vcb” vcbmenu TITLE -1 151 vcbmenu BOUNDS “ Vol contrl blks;(-” vcbmenu ITEMS NEW.MENU drvmenu “ drv” drvmenu TITLE -1 152 drvmenu BOUNDS “ Drives;(-” drvmenu ITEMS NEW.MENU evtmenu “ evt” evtmenu TITLE -1 153 evtmenu BOUNDS “ Events [???];(-” evtmenu ITEMS NEW.MENU fsmenu “ fs” fsmenu TITLE -1 154 fsmenu BOUNDS “ File System;(-” fsmenu ITEMS NEW.MENU dtmenu “ dt” dtmenu TITLE -1 155 dtmenu BOUNDS “ Def Tasks;(-” dtmenu ITEMS NEW.MENU tmmenu “ tm” tmmenu TITLE -1 156 tmmenu BOUNDS “ Time manager;(-” tmmenu ITEMS NEW.WINDOW SysQueue “ System Queues” SysQueue TITLE 250 50 350 250 SysQueue BOUNDS Rounded Visible CloseBox GrowBox SysQueue ITEMS NEW.WINDOW qInfo “ Queue Info” qInfo TITLE 50 50 250 500 qInfo BOUNDS NoGrow Invisible NoCloseBox NoGrowBox qInfo ITEMS 500 2000 terminal queues CODE unpack MOVE.L (A6),D0 CLR.L D1 MOVE.W D0,D1 CLR.W D0 SWAP.W D0 MOVE.L D0,(A6) MOVE.L D1,-(A6) RTS END-CODE MACH : beep ( n ) 0 do 1 call sysbeep loop ; : wait { #ticks | time -- } call tickcount #ticks + -> time begin pause call tickcount time > until ; : popup.select { menu pt | point -- menuID item# } pt -> point ^ point call localtoglobal menu @ point unpack 1 call popupmenuselect unpack ; : do.content { | pt -- } CALL FrontWindow CALL SetPort qInfo call HideWindow RUN-CONTENT EVENT-RECORD Where + @ -> pt ^ pt CALL GlobalToLocal 0 pt rect1 CALL PtInRect IF drop vblmenu THEN pt rect2 CALL PtInRect IF drop vcbmenu THEN pt rect3 CALL PtInRect IF drop drvmenu THEN pt rect4 CALL PtInRect IF drop evtmenu THEN pt rect5 CALL PtInRect IF drop fsmenu THEN pt rect6 CALL PtInRect IF drop dtmenu THEN pt rect7 CALL PtInRect IF drop tmmenu THEN ?dup IF ( rectangle was selected) pt popup.select IF ( popup selection was made ) ( menuID ) userData task-> queues ! THEN THEN ; : draw.rects rect1 call framerect rect2 call framerect rect3 call framerect rect4 call framerect rect5 call framerect rect6 call framerect rect7 call framerect ; : clr.rects rect1 call eraserect rect2 call eraserect rect3 call eraserect rect4 call eraserect rect5 call eraserect rect6 call eraserect rect7 call eraserect ; : blackBar { rect pixels | locBR locTL } rect ^ locTL 8 cmove ^ locBR w@ ( bottom ) pixels - ^ locTL w! ^ locTL call paintrect ; : #elems { qhdr | elems -- #.of.queue.elements } 0 -> elems 2 +> qhdr begin qhdr @ ?dup while -> qhdr 1 +> elems repeat elems ; : display.queues { | -- } clr.rects draw.rects rect1 vblqhdr #elems 4* blackBar rect2 vcbqhdr #elems 4* blackBar rect3 drvqhdr #elems 4* blackBar rect4 evtqhdr #elems 4* blackBar rect5 fsqhdr #elems 4* blackBar rect6 dtqhdr #elems 4* blackBar rect7 timevars @ 8 + #elems 4* blackBar ; : dsp.vbl { | qelemPtr n -- } cls qinfo “ Vertical Blanking Tasks” call SetWTitle .” ----------------------------------------------------------------” cr .” task# qtype ProcPtr Count Phase” cr .” ----------------------------------------------------------------” cr vblqhdr 2+ -> qelemptr 1 -> n begin qelemptr @ ?dup while -> qelemptr n 3 .r 3 spaces hex qelemptr 4 + w@ 5 .r space qelemptr 6 + @ 8 .r space qelemptr 10 + w@ 5 .r space qelemptr 12 + w@ 5 .r cr decimal 1 +> n repeat ; : dsp.vcb { | qelemPtr n -- } cls qinfo “ Volume Control Blocks” call SetWTitle .” --------------------------------------------------------------------------------------------------------------------------------------------------” cr .” vcb# qtype Volume name Drive dRef# vRef# #blks blksz free” cr .” --------------------------------------------------------------------------------------------------------------------------------------------------” cr vcbqhdr 2+ -> qelemptr 1 -> n begin qelemptr @ ?dup while -> qelemptr n 3 .r 3 spaces hex qelemptr 4 + w@ 5 .r space qelemptr 44 + count dup rot swap type 27 swap - spaces qelemptr 72 + w@ 5 .r space qelemptr 74 + w@ 5 .r space qelemptr 78 + w@ 5 .r space qelemptr 26 + w@ 5 .r space qelemptr 28 + @ 5 .r space qelemptr 42 + w@ 4 .r cr decimal 1 +> n repeat ; : dsp.drv { | qelemPtr n -- } cls qinfo “ Drives” call SetWTitle .” ------------------------------------------------------------------------------------------” cr .” drv# qtype Drive dRef# FSID #blks l dd ss” cr .” ------------------------------------------------------------------------------------------” cr drvqhdr 2+ -> qelemptr 1 -> n begin qelemptr @ ?dup while -> qelemptr n 3 .r 3 spaces hex qelemptr 4 + w@ 5 .r space qelemptr 6 + w@ 5 .r space qelemptr 8 + w@ 5 .r space qelemptr 10 + w@ 4 .r space qelemptr 12 + w@ qelemptr 4 + w@ 1 = IF qelemptr 14 + w@ 65536 * + THEN 8 .r space qelemptr 4- c@ $80 AND IF ascii y emit ELSE ascii n emit THEN space qelemptr 3- c@ 2 .r 2 spaces qelemptr 1- c@ $80 AND IF ascii n emit ELSE ascii y emit THEN cr decimal 1 +> n repeat ; : dsp.evt { | qelemPtr n -- } cls qinfo “ Queued Events” call SetWTitle .” ------------------------------------------------------------------------------------------------” cr .” drv# qtype What Message When Where Mods” cr .” ------------------------------------------------------------------------------------------------” cr evtqhdr 2+ -> qelemptr 1 -> n begin qelemptr @ ?dup while -> qelemptr n 3 .r 3 spaces hex qelemptr 4 + w@ 5 .r space qelemptr 6 + w@ 5 .r space qelemptr 8 + @ 8 .r space qelemptr 12 + @ 8 .r space qelemptr 16 + @ 8 .r space qelemptr 20 + w@ 4 .r cr decimal 1 +> n repeat ; : dsp.fs cls qinfo “ File System Requests” call SetWTitle ; : dsp.dt cls qinfo “ Deferred Tasks” call SetWTitle ; : dsp.tm { | qelemPtr n -- } cls qinfo “ Time manager” call SetWTitle .” ----------------------------------------------------” cr .” task# qtype ProcPtr Count” cr .” ----------------------------------------------------” cr timeVars @ 10 + -> qelemptr 1 -> n begin qelemptr @ ?dup while -> qelemptr n 3 .r 3 spaces hex qelemptr 4 + w@ 5 .r space qelemptr 6 + @ 8 .r space qelemptr 10 + w@ 5 .r cr decimal 1 +> n repeat ; : do.user qInfo dup call showwindow call selectwindow qInfo taskwindowpointer ! ( menuID ) CASE 150 OF dsp.vbl ENDOF 151 OF dsp.vcb ENDOF 152 OF dsp.drv ENDOF 153 OF dsp.evt ENDOF 154 OF dsp.fs ENDOF 155 OF dsp.dt ENDOF 156 OF dsp.tm ENDOF ENDCASE SysQueue taskwindowpointer ! ; : do.update { | pt -- } sysQueue call setport draw.rects run-update ; : do.activate event-record modifiers + w@ 1 AND \ Activate event? IF call DrawMenuBar ELSE THEN ; : do.close bye ; : INIT-MBAR queueBar ADD queueBar APPLEMENU ADD APPLEMENU @ ascii DRVR CALL ADDRESMENU queueBar FileMenu ADD queueBar EditMenu ADD queueBar vblmenu add queueBar vcbmenu add queueBar drvmenu add queueBar evtmenu add queueBar fsmenu add queueBar dtmenu add queueBar tmmenu add ; : DO-APPLE { item# | [ 32 lallot ] daName -- } item# 1 = IF3 beep ELSE AppleMenu @ item# ^ DAName CALL GetItem ^ DAName CALL OpenDeskAcc DROP THEN ; : do-file drop bye ; : MBAR-HANDLER ( item# menuID - ) CASE APPLEID OF DO-APPLE ENDOF FILEID OF DO-FILE ENDOF drop ENDCASE 0 CALL HILITEMENU ; : go.queue { | mb -- } activate [‘] do.content content-hook ! [‘] do.update update-hook ! [‘] mbar-handler menu-vector ! [‘] do.activate activate-hook ! [‘] do.close goaway-hook ! [‘] do.user uservector ! begin pause sysQueue call setport display.queues 60 wait again ; : start SysQueue add QInfo add SysQueue queues build SysQueue WRefCon + @ QInfo WRefCon + ! SysQueue dup call selectwindow call setport init-mbar queueBar queues mbar>task queues go.queue ;
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