TweetFollow Us on Twitter

Distribute Processing
Volume Number:8
Issue Number:2
Column Tag:Jörg's Folder

Related Info: Apple Event Mgr

A Way to Distribute Processing

With today’s Apple Event technology, you could set up a distributed processor

By Jörg Langowski, MacTutor Regular Contributing Author

Note: Source code files accompanying article are located on MacTech CD-ROM or source code disks.

The example that I presented last month showed a very simple way to communicate between Fortran programs using the built-in Apple event handling of the Language Systems (LS) Fortran runtime system. Although the F_SendEvent routine can be used to send high-level events of class 'aevt' in a very simple way, its possibilities are limited. The event class can not be changed, and therefore you cannot declare your own suite of events with a new class identifier. Also, the only kind of parameter that you can add to an Apple event that you send with F_SendEvent is a filename, which identifies a file to be associated with the Apple event. This makes sense when you want to send an 'odoc' or 'pdoc' event, but the file remains the only way to send data with the Apple event.

On the other hand, the LS Fortran runtime system has Apple event handling built in, so you don’t have to take care to make the main event loop System 7-aware. This is the great advantage of LS Fortran when you are porting programs from other machines, and nevertheless want to add easily some System 7 goodies. Exchange of arbitrary types of data between programs on the same machine or over a network is certainly one of the more important features of System 7. So this time, I’ll show you how to create and send an arbitrary Apple event in LS Fortran. The event can contain data that will be processed by the receiving program and sent back when it’s done.

A math library server

When you look at a large computer installation with many workstations and mainframes coupled together through a network, you can’t avoid the impression that most of the time the workstations - at least when its users are engaged in non-productive activities such as sleeping, eating, editing programs or writing manuscripts - are doing nothing but sit there and wait for something to happen. The idle CPU time that accumulates in a place where tens or even hundreds of MacII - class machines are kept must be enormous. Why couldn’t that idle time be used by other machines to do CPU-intensive things like operations on large matrices? Even if any single node on the network is not any more powerful than the machine that needs the extra CPU power, one could split up operations into blocks that would be executed by different idle nodes on the network.

You can imagine the implications of such a system: for instance, a small process turning in the background of each MacII on the network and implementing, for example, the Linpack math library. The process would accept requests from other nodes for calculating matrix operations, do the calculations only during the time when really nothing else is happening (the user at the node should always have priority), and send the result back to the requesting node.

The CPU-intensive program that is executing on one node is responsible for splitting its operations into pieces that can be executed independently, sending out the requests for calculations, and reassembling the answers into one final result.

In this column, I won’t show you all the pieces that are necessary for building such a system - this would much exceed the scope of this column, and anyway, if I had everything done perfectly, I’d sell it and make lots of money. But we can look at a very simple example: a “server process” that accepts an array of real numbers, squares every element and sends back the resulting array, and a program that requests this service.

Setting up an Apple Event and sending it

We’ll define the Apple event first in which we are going to encapsulate our data. Let’s give it the class 'JLMT', and ID 'MULT' (why not). Certain data is always associated with any apple event: a target address descriptor that specifies where the event is going to be sent, a return ID that can be used by a program that sent several Apple events to find out who sent the reply, and a transaction ID. In addition, if you want to send data with the event, you have to add descriptors to it that specify that data.

In the example given below the setting up and sending of the event are done by the routine send_array. First of all, PPCBrowser is called to select the process to which we send the event (this is the routine that displays the dialog “Please select a program to link to:”). The information returned by PPCBrowser is then put into a target address descriptor which we created with AECreateDesc. We need this target address descriptor for creating the actual Apple event with AECreateAppleEvent. The other parameters after the event class, ID, and the target address are the return ID (here we specify that a unique return ID is generated automatically) and a transaction ID (the parameter kAnyTransactionID means that the event does not belong to any particular group of events which form a separate transaction).

After the Apple event is created, we can add data to it. We’ll add three parameters: the x and y dimensions of a 2-dimensional array, both 32-bit integers (type 'long'), and the array data itself, which is sent as an unformatted string of bytes (type 'text'). The array is actually of type real*4, but since only the length (in bytes) and pointer to the first element are required, we can use the 'text' type in the Apple event. The three parameters will also get names ('XDIM','YDIM' and 'ARRY') to identify them uniquely.

Having set up the Apple event, we can then send it to the process which does the calculation. On sending (with the AESend routine) we specify the address of the Apple event that we want to send (normal), a pointer to a reply Apple event structure where the reply will be received, and a parameter that specifies that we wish a reply that will be received through the normal event queue (kAEQueueReply), and that the receiving program doesn’t need to notify the user that the event was received (kAENeverInteract). We might also have specified kAEWaitReply here, in that case, the sending program would idle and yield the CPU to other programs on the same machine until the reply was received. Since we are planning to send out several Apple events to different processes for parallel processing without having to wait for a reply each time, we use the queue reply mode.

After sending the Apple event, send_array returns to the Fortran runtime system.

The server process

The Apple event is received by the second program in the example. The main program simply installs a handler for the JLMT / MULT Apple event (the routine get_array) and then drops into an idle loop. The Fortran output window is never activated.

The event handler will receive the Apple event and a pointer to a reply event. It extracts the data out of the received event, processed it and puts it into the reply, which is automagically sent back by the Apple event manager. Extracting parameters is done by the AEGetParamPtr routine, where you have to specify the address of the Apple event (of course), and the identifier and type of the parameter to extracted. You also have to provide a pointer to a space where the data can be stored. The routine returns the parameter, or an error if such a parameter does not exist.

Thus, we extract the x and y dimensions of the array into two 32 bit integers, calculate the array size, and extract the array data into a real*4 array. We then call the process_array routine, which squares every element and divides it by 10000, and then put the three parameters XDIM, YDIM and ARRY into the reply Apple event record using the routine AEPutParamPtr which is very analogous to AEGetParamPtr. When our event handler returns, the Apple event manager will send the reply Apple event back to the program that sent the original event.

Receiving the result

The reply event is of class 'aevt', ID 'ansr'. Since the main program called AESend with the kAEQueueReply parameter, we will receive the reply through the normal event loop. Therefore, we must install our own handler for a reply event, in our case the routine get_reply. In this routine we extract the XDIM, YDIM and ARRY parameters out of the reply, write a message to the output window that the reply was received and return. The processed array data can then be displayed with the show_array routine which is selected from a menu.

[I have forgotten to mention the array setup routine, also selected from a menu, which puts the initial data into the array, and the menu selection send array, which calls the send_array routine. You’ll already have discovered them.]

What is missing?

Of course, this example is far from the idea of the math routine server that I mentioned initially. Several things would have to be added to make distributed processing really work: First of all, all replies will have the same class and ID ('aevt'/'ansr'), and since you might have sent out several requests for calculations, you have to remember the question when you are getting an answer. This is what the return ID is good for -- by keeping a table of pending requests and their return IDs, a reply can be easily identified. Implementation is left as an exercise for the reader, as is the automatic identification and selection of available server processes on a large Appletalk internetwork. Error handling, too, is very rudimentary in the example; in practice, the program would have to be stable against wrong parameters, values out of range, missing parameters, and send back error messages with some meaningful content.

Anyway, I hope this example has given you an impression about the many things that can be done with Apple events. See you next month with more interesting things from the Fortran side and elsewhere.

Example: Distributed processing with Apple Events in LS Fortran

!!M Inlines.f
!!G AEvent.finc
c
c
 program AEMenu

 implicit none
 
 external get_reply,send_array
 integer*2 err
 
 err = AEInstallEventHandler  
(%val('aevt'),%val('ansr'),%val(%loc(get_reply)), %val(int4(0)),%val(int2(0))) 

 
 if (err. ne. 0) then
 type *,'Error installing Apple event, result code = ',err
 end if

 call AddMenuItem ('AE menu', 'setup array', setup_array)
 call AddMenuItem ('AE menu', 'send array', send_array)
 call AddMenuItem ('AE menu', 'show array', show_array)
 
 end
 
 subroutine setup_array
 implicit none
 
 real*4 myarray(10000)
 integer xdim,ydim
 global xdim,ydim,myarray
 
 xdim = 10
 ydim = 15
 call setarray(myarray,xdim,ydim)
 
 return
 end

 subroutine setarray(array,xdim,ydim)
 integer xdim,ydim
 real*4 array(xdim,ydim)
 
 do i=1,xdim
 do j=1,ydim
 array(i,j) = 10000.*(i-1) + 1.*(j-1)
 end do
 end do
 
 return
 end

 subroutine show_array
 implicit none
 
 real*4 myarray(10000)
 integer xdim,ydim
 global xdim,ydim,myarray
 
 xdim = 10
 ydim = 15
 call display(myarray,xdim,ydim)
 
 return
 end

 subroutine display(array,xdim,ydim)
 integer xdim,ydim
 real*4 array(xdim,ydim)
 
 write (*,'(1x,10(1xf7.0))') ((array(i,j),i=1,xdim),j=1,ydim)
 
 return
 end

 subroutine send_array
 implicit none
 real*4 myarray(10000)
 integer xdim,ydim
 global xdim,ydim,myarray
 
 integer totalsize
 
 integer*2 err
 record /AppleEvent/ theAppleEvent,reply
 record /targetID/ target
 record /LocationNameRec/ myLocation
 record /PortInfoRec/ myPortInfo
 record /AEAddressDesc/ targetAddress
 
 err = PPCBrowser(%val(int4(0)),%val(int4(0)),
 1 %val(int2(0)),%ref(myLocation),
 2 %ref(myPortInfo),%val(int4(0)),%val(int4(0)))
 if (err .ne. 0) then
 type *,'PPC Browser: error ',err
 return
 end if
 
 target.location = myLocation
 target.name = myPortInfo.name
 
 type *,'Session ID = ',target.sessionid,
 1 ', target name = ',target.name.name
 
 err = AECreateDesc(%val(typeTargetID),
 1 %val(%loc(target)),%val(sizeof(target)),
 2 %ref(targetAddress))
 if (err .ne. 0) then
 type *,'AECreateDesc: error ',err
 return
 end if 
 
 err=AECreateAppleEvent(%val('JLMT'),%val('MULT'),
 1 %ref(targetAddress),
 2 %val(kAutoGenerateReturnID),
 3 %val(int4(kAnyTransactionID)),
 4 %ref(theAppleEvent))
 if (err .ne. 0) then
 type *,'AECreateAppleEvent: error ',err
 return
 end if 
 
 err = AEPutParamPtr(%ref(theAppleEvent),
 1 %val('XDIM'),%val(typeInteger),
 2 %val(%loc(xdim)),%val(sizeof(xdim)))
 if (err .ne. 0) then
 type *,'AEPutParamPtr: error ',err
 return
 end if 
 
 err = AEPutParamPtr(%ref(theAppleEvent),
 1 %val('YDIM'),%val(typeInteger),
 2 %val(%loc(ydim)),%val(sizeof(ydim)))
 if (err .ne. 0) then
 type *,'AEPutParamPtr: error ',err
 return
 end if 
 
 totalsize = xdim * ydim * 4
 
 err = AEPutParamPtr(%ref(theAppleEvent),
 1 %val('ARRY'),%val(typeChar),
 2 %val(%loc(myarray)),%val(totalsize))
 if (err .ne. 0) then
 type *,'AEPutParamPtr: error ',err
 return
 end if 
 
 err = AESend(%ref(theAppleEvent),%ref(reply),
 1 %val(int4(kAEQueueReply+kAENeverInteract)),
 2 %val(kAENormalPriority),%val(int4(120)),
 3 %val(int4(0)),%val(int4(0)) )
 if (err .ne. 0) then
 type *,'AESend: error ',err
 return
 end if 
 
 type *,'Sent test array of size ',xdim*ydim

 return
 end

 integer*2 function get_reply(theAppleEvent,reply,
 1 %val(handlerRefCon))

 record /AppleEvent/ theAppleEvent
 record /AppleEvent/ reply
 integer*4 handlerRefCon
 
 real*4 myarray(10000)
 integer xdim,ydim
 global xdim,ydim,myarray
 
 integer totalsize
 
 err = AEGetParamPtr(%ref(theAppleEvent),
 1 %val('XDIM'),%val(typeInteger),returnedType,
 2 %val(%loc(xdim)),%val(sizeof(xdim)),actualSize)
 if (err .ne. 0) then
 type *,'AEGetParamPtr: error ',err
 goto 9999
 end if 
 
 err = AEGetParamPtr(%ref(theAppleEvent),
 1 %val('YDIM'),%val(typeInteger),returnedType,
 2 %val(%loc(ydim)),%val(sizeof(ydim)),actualSize)
 if (err .ne. 0) then
 type *,'AEGetParamPtr: error ',err
 goto 9999
 end if 
 
 totalsize = xdim * ydim * 4
 
 err = AEGetParamPtr(%ref(theAppleEvent),
 1 %val('ARRY'),%val(typeChar),returnedType,
 2 %val(%loc(myarray)),%val(totalsize),actualSize)
 if (err .ne. 0) then
 type *,'AEGetParamPtr: error ',err
 goto 9999
 end if 
 
 type *,'Reply received from server'
 
 get_reply = 0 ! noErr
 return

9999  get_reply = err
 return
 end



!!M Inlines.f
!!G AEvent.finc
c
c
 program Array_process

 implicit none
 
 external get_array
 integer*2 err
 
 err = AEInstallEventHandler(%val('JLMT'),%val('MULT'),
 1    %val(%loc(get_array)),%val(int4(0)),%val(int2(0))) 
 if (err. ne. 0) call alertbox
 1 ('Array_process: Apple Event install error')

 do while (.true.)
 call F_DoBackground
 end do
 
 end

 integer*2 function get_array(theAppleEvent,reply,
 1 %val(handlerRefCon))
 implicit none
 
 record /AppleEvent/ theAppleEvent
 record /AppleEvent/ reply
 integer*4 handlerRefCon
 
 integer*2 err
 integer*4 keywd,returnedType,actualSize
 
 real*4 myarray(10000)

 integer xdim,ydim
 global xdim,ydim,myarray
 
 integer totalsize
 
 err = AEGetParamPtr(%ref(theAppleEvent),
 1 %val('XDIM'),%val(typeInteger),returnedType,
 2 %val(%loc(xdim)),%val(sizeof(xdim)),actualSize)
 if (err .ne. 0) goto 9999
 
 err = AEGetParamPtr(%ref(theAppleEvent),
 1 %val('YDIM'),%val(typeInteger),returnedType,
 2 %val(%loc(ydim)),%val(sizeof(ydim)),actualSize)
 if (err .ne. 0) goto 9999
 
 totalsize = xdim * ydim * 4
 
 err = AEGetParamPtr(%ref(theAppleEvent),
 1 %val('ARRY'),%val(typeChar),returnedType,
 2 %val(%loc(myarray)),%val(totalsize),actualSize)
 if (err .ne. 0) goto 9999

cwe don't check whether actualSize = totalsize 
cand returnedType = typeChar.
c
cIn an actual application, such errors 
chave to be trapped, of course.
c
 call process_array(myarray,xdim,ydim)
 
 err = AEPutParamPtr(%ref(reply),%val('XDIM'),
 1 %val(typeInteger),%val(%loc(xdim)),
 2 %val(sizeof(xdim)))
 if (err .ne. 0) goto 9999
 
 err = AEPutParamPtr(%ref(reply),%val('YDIM'),
 1 %val(typeInteger),%val(%loc(ydim)),
 2 %val(sizeof(ydim)))
 if (err .ne. 0) goto 9999
 
 err = AEPutParamPtr(%ref(reply),%val('ARRY'),
 1 %val(typeChar),%val(%loc(myarray)),
 2 %val(totalsize))
 if (err .ne. 0) goto 9999
 
 get_array = 0 ! noErr
 return

9999  get_array = err
 return
 
 end


 subroutine process_array(array,xdim,ydim)
 integer xdim,ydim
 real*4 array(xdim,ydim)
 
 do i=1,xdim
 do j=1,ydim
 array(i,j) = array(i,j)*array(i,j)/10000.
 end do
 end do
 
 return
 end
 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Latest Forum Discussions

See All

Tokkun Studio unveils alpha trailer for...
We are back on the MMORPG news train, and this time it comes from the sort of international developers Tokkun Studio. They are based in France and Japan, so it counts. Anyway, semantics aside, they have released an alpha trailer for the upcoming... | Read more »
Win a host of exclusive in-game Honor of...
To celebrate its latest Jujutsu Kaisen crossover event, Honor of Kings is offering a bounty of login and achievement rewards kicking off the holiday season early. [Read more] | Read more »
Miraibo GO comes out swinging hard as it...
Having just launched what feels like yesterday, Dreamcube Studio is wasting no time adding events to their open-world survival Miraibo GO. Abyssal Souls arrives relatively in time for the spooky season and brings with it horrifying new partners to... | Read more »
Ditch the heavy binders and high price t...
As fun as the real-world equivalent and the very old Game Boy version are, the Pokemon Trading Card games have historically been received poorly on mobile. It is a very strange and confusing trend, but one that The Pokemon Company is determined to... | Read more »
Peace amongst mobile gamers is now shatt...
Some of the crazy folk tales from gaming have undoubtedly come from the EVE universe. Stories of spying, betrayal, and epic battles have entered history, and now the franchise expands as CCP Games launches EVE Galaxy Conquest, a free-to-play 4x... | Read more »
Lord of Nazarick, the turn-based RPG bas...
Crunchyroll and A PLUS JAPAN have just confirmed that Lord of Nazarick, their turn-based RPG based on the popular OVERLORD anime, is now available for iOS and Android. Starting today at 2PM CET, fans can download the game from Google Play and the... | Read more »
Digital Extremes' recent Devstream...
If you are anything like me you are impatiently waiting for Warframe: 1999 whilst simultaneously cursing the fact Excalibur Prime is permanently Vault locked. To keep us fed during our wait, Digital Extremes hosted a Double Devstream to dish out a... | Read more »
The Frozen Canvas adds a splash of colou...
It is time to grab your gloves and layer up, as Torchlight: Infinite is diving into the frozen tundra in its sixth season. The Frozen Canvas is a colourful new update that brings a stylish flair to the Netherrealm and puts creativity in the... | Read more »
Back When AOL WAS the Internet – The Tou...
In Episode 606 of The TouchArcade Show we kick things off talking about my plans for this weekend, which has resulted in this week’s show being a bit shorter than normal. We also go over some more updates on our Patreon situation, which has been... | Read more »
Creative Assembly's latest mobile p...
The Total War series has been slowly trickling onto mobile, which is a fantastic thing because most, if not all, of them are incredibly great fun. Creative Assembly's latest to get the Feral Interactive treatment into portable form is Total War:... | Read more »

Price Scanner via MacPrices.net

Early Black Friday Deal: Apple’s newly upgrad...
Amazon has Apple 13″ MacBook Airs with M2 CPUs and 16GB of RAM on early Black Friday sale for $200 off MSRP, only $799. Their prices are the lowest currently available for these newly upgraded 13″ M2... Read more
13-inch 8GB M2 MacBook Airs for $749, $250 of...
Best Buy has Apple 13″ MacBook Airs with M2 CPUs and 8GB of RAM in stock and on sale on their online store for $250 off MSRP. Prices start at $749. Their prices are the lowest currently available for... Read more
Amazon is offering an early Black Friday $100...
Amazon is offering early Black Friday discounts on Apple’s new 2024 WiFi iPad minis ranging up to $100 off MSRP, each with free shipping. These are the lowest prices available for new minis anywhere... Read more
Price Drop! Clearance 14-inch M3 MacBook Pros...
Best Buy is offering a $500 discount on clearance 14″ M3 MacBook Pros on their online store this week with prices available starting at only $1099. Prices valid for online orders only, in-store... Read more
Apple AirPods Pro with USB-C on early Black F...
A couple of Apple retailers are offering $70 (28%) discounts on Apple’s AirPods Pro with USB-C (and hearing aid capabilities) this weekend. These are early AirPods Black Friday discounts if you’re... Read more
Price drop! 13-inch M3 MacBook Airs now avail...
With yesterday’s across-the-board MacBook Air upgrade to 16GB of RAM standard, Apple has dropped prices on clearance 13″ 8GB M3 MacBook Airs, Certified Refurbished, to a new low starting at only $829... Read more
Price drop! Apple 15-inch M3 MacBook Airs now...
With yesterday’s release of 15-inch M3 MacBook Airs with 16GB of RAM standard, Apple has dropped prices on clearance Certified Refurbished 15″ 8GB M3 MacBook Airs to a new low starting at only $999.... Read more
Apple has clearance 15-inch M2 MacBook Airs a...
Apple has clearance, Certified Refurbished, 15″ M2 MacBook Airs now available starting at $929 and ranging up to $410 off original MSRP. These are the cheapest 15″ MacBook Airs for sale today at... Read more
Apple drops prices on 13-inch M2 MacBook Airs...
Apple has dropped prices on 13″ M2 MacBook Airs to a new low of only $749 in their Certified Refurbished store. These are the cheapest M2-powered MacBooks for sale at Apple. Apple’s one-year warranty... Read more
Clearance 13-inch M1 MacBook Airs available a...
Apple has clearance 13″ M1 MacBook Airs, Certified Refurbished, now available for $679 for 8-Core CPU/7-Core GPU/256GB models. Apple’s one-year warranty is included, shipping is free, and each... Read more

Jobs Board

Seasonal Cashier - *Apple* Blossom Mall - J...
Seasonal Cashier - Apple Blossom Mall Location:Winchester, VA, United States (https://jobs.jcp.com/jobs/location/191170/winchester-va-united-states) - Apple Read more
Seasonal Fine Jewelry Commission Associate -...
…Fine Jewelry Commission Associate - Apple Blossom Mall Location:Winchester, VA, United States (https://jobs.jcp.com/jobs/location/191170/winchester-va-united-states) Read more
Seasonal Operations Associate - *Apple* Blo...
Seasonal Operations Associate - Apple Blossom Mall Location:Winchester, VA, United States (https://jobs.jcp.com/jobs/location/191170/winchester-va-united-states) - Read more
Hair Stylist - *Apple* Blossom Mall - JCPen...
Hair Stylist - Apple Blossom Mall Location:Winchester, VA, United States (https://jobs.jcp.com/jobs/location/191170/winchester-va-united-states) - Apple Blossom Read more
Cashier - *Apple* Blossom Mall - JCPenney (...
Cashier - Apple Blossom Mall Location:Winchester, VA, United States (https://jobs.jcp.com/jobs/location/191170/winchester-va-united-states) - Apple Blossom Mall Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.