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UK Laws Are Not 'Fit For Social Media Age'
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Hacked Crosswalks In Bay Area Play Deepfake-Style Messages From Tech Billionaires
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Meta Starts Using Data From EU Users To Train Its AI Models
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NATO Inks Deal With Palantir For Maven AI System
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VMware Revives Its Free ESXi Hypervisor
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EU Issues US-bound Staff With Burner Phones Over Spying Fears
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OpenAI Unveils Coding-Focused GPT-4.1 While Phasing Out GPT-4.5
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Apple Preparing Major iPadOS 19 Overhaul with Mac-like Features
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Librarians in UK Increasingly Asked To Remove Books
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Blue Origin Sends All-Female Crew To Edge of Space in Historic Flight
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Facebook Sought To 'Neutralize' Competitive Threats, FTC Argues As Landmark Antitrust Trial Begins
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Nvidia To Make AI Supercomputers in US for First Time
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Can AI Help Manage Nuclear Reactors?
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An Electric Racecar Drives Upside Down
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A Single Mortgage
We talked about singletons a bit last week. That reminded John of a story from the long ago dark ages where we didn't have always accessible mobile Internet access.
At the time, John worked for a bank. The bank, as all banks do, wanted to sell mortgages. This often meant sending an agent out to meet with customers face to face, and those agents needed to show the customer what their future would look like with that mortgage- payment calculations, and pretty little graphs about equity and interest.
Today, this would be a simple website, but again, reliable Internet access wasn't a thing. So they built a client side application. They tested the heck out of it, and it worked well. Sales agents were happy. Customers were happy. The bank itself was happy.
Time passed, as it has a way of doing, and the agents started clamoring for a mobile web version, that they could use on their phones. Now, the first thought was, "Wire it up to the backend!" but the backend they had was a mainframe, and there was a dearth of mainframe developers. And while the mainframe was the source of truth, and the one place where mortgages actually lived, building a mortgage calculator that could do pretty visualizations was far easier- and they already had one.
The client app was in .NET, and it was easy enough to wrap the mortgage calculation objects up in a web service. A quick round of testing of the service proved that it worked just as well as the old client app, and everyone was happy - for awhile.
Sometimes, agents would run a calculation and get absolute absurd results. Developers, putting in exactly the same values into their test environment wouldn't see the bad output. Testing the errors in production didn't help either- it usually worked just fine. There was a Heisenbug, but how could a simple math calculation that had already been tested and used for years have a Heisenbug?
Well, the calculation ran by simulation- it simply iteratively applied payments and interest to generate the entire history of the loan. And as it turns out, because the client application which started this whole thing only ever needed one instance of the calculator, someone had made it a singleton. And in their web environment, this singleton wasn't scoped to a single request, it was a true global object, which meant when simultaneous requests were getting processed, they'd step on each other and throw off the iteration. And testing didn't find it right away, because none of their tests were simulating the effect of multiple simultaneous users.
The fix was simple- stop being a singleton, and ensure every request got its own instance. But it's also a good example of misapplication of patterns- there was no need in the client app to enforce uniqueness via the singleton pattern. A calculator that holds state probably shouldn't be a singleton in the first place.
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After Meta Cheating Allegations, 'Unmodified' Llama 4 Maverick Model Tested - Ranks #32
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Three Million Child Deaths Linked To Drug Resistance, Study Shows
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