| The Ultimate Business Machine Technology, business And, not least, about by: Bernard Teo
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Wed 16 Aug 2006 Do the math ... or when is 156.14 != 156.14 ?Category : Technology/maths.txt This is a Cash Disbursement voucher in Luca :
I have a rule that says you can't save a voucher unless the debits and credits balance. So, here we have $156.14 being paid out of a checking account, recorded against an equal $156.14 in expenses. Yet the Save button refuses to be enabled. What is going on here? Looking a bit closer at the objects : NSLog(@"vouAmount = %f", [vouAmount doubleValue]); we get : Luca[1046] vouAmount = 156.140000 It's as we would expect but it remains puzzling, so we zoom even closer : NSLog(@"vouAmount = %1.24f", [vouAmount doubleValue]); we get : Luca[1046] vouAmount = 156.140000000000014779288904 The vouAmount is taken straight off the object. The total column has a rounding function applied to it, but still it's just one line item, for simplicity's sake. So both items are off the expected figure of 156.14. They never balance. This happens only at certain values, not all the time. It happens because "real numbers" in digital computations are only a very close approximation to the mathematical concept of real numbers. The difference is infinitesimally small (my favourite expression in engineering school), but it's there all the same. It's what throws us off. This reminds me of that paradox of Zeno, of a foot race between Achilles and a tortoise. The tortoise is given a headstart, but picture Brad Pitt as Achilles, huffing and puffing, always covering half the distance to the tortoise, always gaining, but never quite reaching, because the half-distance keeps getting smaller, and smaller, and smaller, but never disappears. It's become infinitesimally small. The solution is to round both numbers before comparing them, even the one entered exactly as 156.14.. But we have to take care to do the rounding at lots of places, not just when the value is entered. For example, you do rounding when one value is multiplied by another. But what happens when you divide a dollar by three. You lose that last infinitesimally small fraction of a cent because computers work with discrete values, not a continuum. So, that's why building such systems, mundane though they seem, is hard. It's a craft. It's precision work. But it's not the kind that will win Apple Design Awards at WWDC. I'm fixing this in a Luca 2.2.2 release. But I have the rounding done all over the place. The art is to find a way to control this in just one spot in the application. What happens when I find a user whose currency system works with other than two decimal points? Is there such a thing? Mon 14 Aug 2006 6000 CustomersCategory : Commentary/6000Customers.txt I think we've crossed 6000 paid customers. I just read that the guys at Parallels sold 100,000 copies of their virtualisation software at $80 per copy. So 6000 pales into insignificance when compared with that. But I know it'll mean something to me if I do get to cross the 10,000 mark. Building a business one customer at a time. Is this too slow? Slow is when you're waiting for time to pass in Eternity. "To see a world in a grain of sand, I'm reading this book "Art and Physics - Parallel Visions in Space, Time & Light" by Leonard Shlain. If you've ever done physics in school and know enough to tell a Monet from a Manet, this may make interesting reading (in spite of the pretty bad reviews it's gotten at Amazon, but one man's meat is another man's poison and so on ...) DNS Enabler in GermanCategory : Technology/DNSEnablerDeutsch.txt Matthias Schmidt at Admilon contributed this German localisation of DNS Enabler 2.1, including the new Bonjour panel.
Thanks, Matthias. Luca 2.2.1Category : Technology/Luca2dot2dot1.txt Over the weekend I've fixed some (rather embarrassing) user interface bugs with the last release of Luca, like buttons and text not sticking to their corners when windows get resized, or the default financial period not getting saved to preferences when the save-to-defaults button was pressed. Notifications also work better now, so when something happens in one window, e.g., when a voucher gets deleted, the totals showing on other windows will all get updated automatically. Also, I had some problems mapping date fields between SQLite and MySQL, especially handling NULL data types. These are handled better now. Things To Do 1. I need to improve the speed in which data is imported/exported between SQLite and MySQL. This is currently slow and still not robust enough to handle, e.g., three years worth of data without hanging. 2. I need to put in a button to let the user choose whether to drop a database before exporting the data. Currently it assumes you want to overwrite the destination database and tables in MySQL. Here is someone I know who's using Luca with MySQL now - Jan Steinman at VeggieVanGogh. 3. Need to handle the "last one cent" problem better, e.g., when a dollar is split three ways and you put them back again, you get 99 cents. Which account should get the last one cent so that the debits and credits always balance, no matter how often you go back and edit or rollback the data? This problem shows up when you're apportioning amounts to cost centres or when you're doing currency exchange gain/loss calculations. I don't think I've ever totally solved it while we were doing custom applications - once in a while, our user would find that she can't save the voucher because the accounts are out by one cent. In a custom application, we're on hand to guide the user to correct this manually. But not when it's going to be a "shrink-wrapped" application. So I've got to pin this down once and for all. 4. Tax handling on line items rather than on the consolidated total. 5. After all these I think I can move on to the invoicing module, a payroll module, or a time-billing module? Actually I have pieces of quite a lot of these in 4th Dimension code. I'm like a PC guy who just loves Macs. I do these PC things for PC-using companies but I want to use a Mac. I'm stuck between art and science, engineering and design, the PC and the Mac. Luca is a work-in-progress - for the Mac as The Ultimate Business Machine. Do keep the suggestions coming. Sat 12 Aug 2006 Luca 2.2 with MySQLCategory : Technology/Luca2dot2MySQL.txt I've released Luca 2.2 with support for storing the accounting data in a MySQL database. I've also written the import/export code to shuttle the data between SQLite and MySQL, and back. I realised then that I've got the basis of the code to do a "universal" SQL data converter, to shuttle data between any kind of SQL database. If I have time, I'll take a look at PostgreSQL or Oracle. (Now, look how richly endowed we all are on the Mac. Who would have thought?)
Luca is getting more stable now and working faster. There are probably a few more bugs lurking inside the system but I thought I'd better get this out as it's quite usable now, and I've made some improvements to the workflow and made several bug fixes. I hope that by the next release, I can be sure that Luca will be thoroughly reliable. I'm going to stress-test this release next. I've already seen where it's still breaking. But I've worked hard to get to this point and release it because I want this idea to take hold in people's minds - that you can really do a lot on the Mac. With this release, people who want to integrate an accounting system to the rest of the custom, say, PHP-based workflow that they've built can now do it. The database is open and you can flow your data onto it or get data out of it in ways that I cannot even anticipate now. And you can get at your accounting data even when you're half-way round the world. I've yet to put in the concurrency-handling code. But we've done this years ago while it was still a 4th Dimension-cum-Oracle-based system (though that would never have worked outside a local area network) and so I know we can do it. I'll get to the point one day when all these things - MailServe, WebMon, DNS Enabler, Luca, etc - will all come together and make sense as one seamless whole. I have an idea what that is but I can't yet explain, even to myself, what that means. I'm learning as I go. They say (actually it was Steve Jobs) that you shouldn't start a company just because you want to start a company. You start a company because nobody else believed in an idea and the only way you can get it out of your system (and keep from going crazy) is to go out and build it on your own. Wed 09 Aug 2006 DNS Enabler 2.1Category : Technology/DNSEnabler2dot1.txt I've released DNS Enabler 2.1.
It includes a Bonjour panel to allow DNS Enabler to be used as a configurator to enable wide-area discovery of Bonjour devices :
More information about the types of Bonjour services you can currently configure, and what you need to enter into the individual columns in the Bonjour panel, can be found at : http://www.dns-sd.org/ServiceTypes.html (DNS SRV (RFC 2782) Service Types). What DNS Enabler saves the user is the need to know the specific syntax to set up SRV and TXT records at the DNS server. All he needs to know is the Bonjour service type, e.g., _http._tcp for publicising web pages (that may be served even from local private networks - you can use the Port number field to publicise a different port other than 80 and port-map that incoming request to a specific local machine) and the domain that will serve that request. The service name is a label that will show up in the Bonjour menu in, say, Safari. And the TXT column contains the path to that specific web page. (The TXT column stores different things for different services. See the cited Bonjour reference). Stuart Cheshire may be showing this panel at work sometime in his Bonjour talk at WWDC on Thursday, 10th August, at 9.00 am (PST). PS : I've also added a button to populate the Forwarders field with the list of DNS servers that the user has set up in his Network Preferences. I've left the interface somewhat cluttered at the moment because I'm planning to add a couple more features in the next two weeks, and I'll clean up the interface then. Sun 30 Jul 2006 Upcoming UpdatesCategory : Technology/NewUpdatesEndJuly.txt I'm working on a couple of things. I'll be releasing a version of Luca Accounting soon that will work with MySQL. I just need to write the script that will allow the initial built-in SQLite data to be exported to MySQL.
If there's anybody who can't wait and want to try this out now, just let me know. It's still missing the concurrency handling that is needed for multi-user access (that's the next step), but this is going to make it possible for anyone to access his accounting data from anywhere in the world (if he so chooses), as well as make the database open to all sorts of custom integration. The second thing I'm working on is this :
This is experimental. It's an extension to DNS Enabler that will allow the user to configure the DNS server so that it'll also broadcast Bonjour services (that the user has happened to have set up) so that they can be discovered, browsed, and accessed from the wide-area network (rather than on just the local network). I may also add a couple more new features to the next DNS Enabler release that people have asked for (e.g., the ability to set the DNS server so that it doesn't do recursive lookups, and the ability to restrict the range of IP addresses that you allow lookups to be made from). So, lots of things to do. Thu 20 Jul 2006 Working around Workaround BonjourCategory : Technology/WorkingAroundWorkaround.txt I've updated both DNS Enabler (to 2.0.9) and MailServe (to 2.1.6) to handle the bug introduced by the OS X 10.4.7 update (that "Workaround Bonjour" thing) whereby the system would stall for about 60 seconds whenever a call is made to /bin/launchctl to start a launchdaemon (like BIND, Fetchmail, etc). I've changed DNS Enabler so that the Restart DNS button avoids calling launchctl, so that the only time you actually see the stall is when you first start the DNS service (be patient - it'll clear - and the DNS Server will still work correctly), and not when you stop the service, and especially not when you restart the service to make changes to your DNS data, which is pretty much what we do most of the time. I've done the same to the Restart Fetchmail button in MailServe, so that you don't get held up when you need to change Fetchmail parameters. It's important to note that this happens only on 10.4.7, and that the DNS and Fetchmail services (as well as Postfix, POP, IMAP, etc, i.e, anything started or enabled using launchctl) are all still launched correctly. Up to now, I've ascertained that this stall only happens when an application makes a call to the "/bin/launchctl load" comamnd (well, sometimes on launchctl unload, depending on the sequence of the calls you make). I believe this is probably an unfortunate side effect of the security-related changes Apple made to patch up the launchdaemon mechanism (launchd) in the 10.4.7 update. I've just installed a second broadband line to my home so that I can now do all the testing that I had wished I could do without interrupting service on my live server. I happened to use DNSUpdate and also Lingon just now and both of them stalled. Looked up the Console - and it's our friend, Workaround Bonjour. When is Apple going to fix this? As another aside - as I was posting this on the live server (from this second broadband line), I noticed that things had suddenly become rather sluggish on the live server. Guess what? - it's all the people coming over, via MacUpdate and Version Tracker, for DNS Enabler. So that's how my server feels like from outside. You never know when you're inside your own network. Sun 16 Jul 2006 MailServe 2.1.5 UpdateCategory : Technology/MailServe2dot1dot5.txt I've updated MailServe to 2.1.5, to make improvements to the way MailServe triggers Fetchmail. It was while working on Fetchmail that I realised Apple broke launchctl on 10.4.7, probably as a side effect of the security changes they were making to launchd. I've added a way to specify a global value for the Polling Interval (default 60 seconds) and the Time-out Interval (default 45 seconds but can be set to 0 for no time-out). Also the quotes around the * in the .fetchmailrc file (when Fetchmail is used in multi-drop mode) interfered with the multi-drop operations. This has been corrected in this release. (Thanks to Fergus McMenemie for showing me there was a problem.) The French localisation for MailServe has been updated by Joselyne Rochaud and Corentin Cras-Méneur, who also took the opportunity to update the French localisations for DNS Enabler, WebMon and Postfix Enabler. Fri 14 Jul 2006 Bonjour Mystery UpdateCategory : Technology/BonjourMysteryUpdate.txt I ended my last post with "I'm starting to hate this thing called Bonjour". Actually, I don't - hate Bonjour, that is. I've watched Stuart Cheshire's demo of Bonjour on Google Video a couple of months ago, and I've been looking forward to seeing if I can extend DNS Enabler to aid wide-area browsing/discovery of Bonjour services. I'm planning to update DNS Enabler, WebMon and MailServe, all in the latter part of the year, as soon as I can get a Luca Accounting version released that works with MySQL rather than just SQLite. I'm getting quite close to it. For more on Bonjour, see this, this, and this. So, I do think Bonjour's good and I'm just being ironical when I say I'm starting to hate it. But what I do hate is that Workaround Error and the hanging that accompanies it. Stuart Cheshire tells me that the error has nothing to do with Bonjour, which is reasonable considering that you get the error even when you disable Bonjour. "The person who wrote the code that logs that message thought the problem it's reporting might be something related to Bonjour, but it's not." So, Bonjour gets a bad rep and I'm sorry I added to it. But we're not anywhere nearer finding an answer to the mystery. I hope Apple hurries up and solves it. I'm seeing a lot of people hitting these pages from Google, searching for Bonjour+Workaround, and not just from MacFixIt (who's just linked to it). So, from just a trickle a week ago, there are now a lot of people wondering how this came to insinuate itself into our systems since 10.4.7. It's an Apple bug and I've given up thinking there's anything I can do about it. Since DNS Enabler, MailServe and Postfix Enabler continue to work, though a bit hobbled on 10.4.7 and only on 10.4.7, I'm going back to working on Luca. Tue 04 Jul 2006 Bonjour MysteryCategory : Technology/BonjourMystery.txt The 10.4.7 "launchctl load / Bonjour Workaround Error" mystery deepens. I've been searching for an answer for hours. Nothing turns up from a Google search and I wonder who else is affected by it. Launchctl is used to turn or off the network-related daemons, like Bind, Fetchmail, Postfix, POP, IMAP, and even the Bonjour (previously known as Rendezvous) service itself. I've turned off Bonjour (not that I want to, because it's built so closely into the fabric of Mac OS X, e.g., BBedit crashed as soon as I turned off Bonjour), to see if it'll stop the workaround error from occuring. But no change, it still does. Even reloading Bonjour will throw up the "Workaround Bonjour: Unknown Error" as shown below :
So, in 10.4.7, Workaround Bonjour occurs every time a call to /bin/launchctl is made, no matter which services are launched. And it affects both PPC and Intel Macs updated to 10.4.7. The thing is, the launchctl command actually succeeds and completes. But it'll be followed by the Workaround Bonjour command(?) which executes and then just hangs there. Where did that come from? That's the big question. From the point of view of a user using DNS Enabler, or trying to enable Postfix, IMAP, POP or Fetchmail (as opposed to just restarting Postfix, POP or IMAP), he'll see the progress indicator spin for a long time, until the application decides to time out and return control to the user. Actually all the services have completed successfully - if the user has the patience to wait for a minute or so - and all the Postfix, DNS, POP, IMAP, Fetchmail services would have been set up correctly, even before the Bonjour Workaround Error hang-up occur. But watching the progress indicator spin for a minute or so, I'm sure the user would (reasonably) feel that something has gone wrong. Wait is what the user should do, because the Bonjour Workaround would eventually time out. Remember this only came with 10.4.7. And the services, once enabled, will work correctly as usual, even across reboots. It's just that the "enabling" process will seem to take longer (when it used to take a mere few seconds). So, don't be in a hurry to update your server. Wait for things to be fixed. Conversely, that's why I do the updates as soon as they appear - it's better that I know before I'm swamped with mail from the users. The search continues. I'm starting to hate this thing called Bonjour. As an aside, I'm learning to appreciate how having a weblog helps in a situation like this. It's a low-overhead communications tool, to keep the communications channel open, for when the time is better spent searching for solutions. I say this because I've often wondered what a weblog is worth - surely it's not meant to be a diary because who cares what I think or do? - surely there's got to be a more potent use. Mon 03 Jul 2006 Bonjour Error in 10.4.7Category : Technology/BonjourError.txt This snippet from my Terminal session shows when the Bonjour error occurs, when I try to restart Fetchmail :
The problem is at the "launchctl" line, which launches the Fetchmail launchdaemon (which is also used to launch the BIND launchdaemon and that's why DNS Enabler is also affected). The launchctl command executes and returns quickly, as it is expected to, but after that we get the "Workaround Bonjour: Unknown error: 0" line, which hangs indefinitely until both MailServe and Enabler give up and return control to the user. In both cases, Fetchmail and DNS services are launched correctly, but the user thinks that the system hangs because the progress indicator spins for a very long time before control is returned to the user. So the question is : why did this Bonjour thing appear in 10.4.7 and how do we get rid of it? Read more ... |
Mac@Work
Services running on this server, a Mac Mini running Mac OS X 10.9.2 Mavericks:
all set up using MailServe, WebMon, DNS Enabler, DNS Agent, VPN Enabler, Liya and our SQL installers, all on Mavericks. |
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