Posts relating to software development.
Morphing into MIG

Posted by cwright on 2020.04.09 @ 16:54

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When we last left off, we were able to cook up a service name of our choosing, and resolve it from a client. If we hooked up launchd stuff, we could also make it demand-launch (maybe that’s for another day). But we didn’t actually do anything with that resolution. There are several reasons for that, first, because actually crafting a message and sending/receiving it was covered by a prior article. But even more than that, there are actually a substantial number of design decisions around this task, and plowing ahead requires a lot of text.

I’ll start with the previous server/client, and flesh it out in small steps. In between the steps, I’ll outline design decisions, maybe some history, and pitfalls/sharp edges to be aware of. [more...]

Worked like a charm! Worked like a charm!

Posted by jstrecker on 2019.10.04 @ 22:03

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Recently a friend and fellow programmer asked me how I learn a new language or platform. I answered that I do it with specific task in mind. Basically, I bumble along googling every little step until I complete my task. But I forgot to tell her about the pitfall of this method… [more...]

Making a mach server

Posted by cwright on 2019.08.17 @ 14:23

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(This is a sort of simplified retelling of http://fdiv.net/2011/01/14/machportt-inter-process-communication with some added lore. You should probably start there.)

Much of the magic behind macOS and iOS (and all the derived xOSs - watch, appleTV, the stripped down versions in cables and touch bars and wherever else these things invariably end up) is performed with the assistance of other processes (including the kernel). Communicating between them is accomplished by various ways, but for macOS, the underlying mechanism is a client/server IPC mechanism powered by Mach, and the underlying currency is the mach port (mach_port_t). [more...]

Mirror, Mirror, or, Don't fly off the Handle

Posted by cwright on 2019.08.13 @ 10:12

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During my time at Apple, I dealt with a lot of rather low-level systems treachery. It’s poorly documented, even internally, and asking for help has roughly even odds on getting a passive aggressive non-answer.

The cool trick for today is creating a “memory object.” A memory object is one or more physical pages that are wrapped in a mach port. With this, you can pass the port to another process, who can map the pages, creating shared memory. Or you can map the pages again in your own address space, to create a mirror, or with different permissions so you can expose read-only pages at an interface boundary while still having the pages be writable at a different address. [more...]

Debugging childbed fever Debugging childbed fever

Posted by jstrecker on 2019.01.13 @ 12:15

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Vienna in the 1840s was a scary time and place to give birth. From 1840 to 1846, 7% of women who gave birth at the Vienna General Hospital died of a postpartum infection called childbed fever. One doctor at the hospital, Ignaz Semmelweis, made it his mission to stop the disease. His work saved hundreds of lives, contributed to the development of medical hygiene — and can teach us a few things about debugging. [more...]

“The never-ending notary nuisance,” or, “infinite loop at Infinite Loop” “The never-ending notary nuisance,” or, “infinite loop at Infinite Loop”

Posted by smokris on 2018.10.24 @ 21:11

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A couple weeks ago, Apple posted a note that says:

In an upcoming release of macOS, Gatekeeper will require Developer ID–signed software to be notarized by Apple.

Being a developer of Developer ID-signed (i.e., non-App-Store) software, I set out to vault Apple’s latest hurdle.

Xcode includes a command-line utility called altool that manages the notarization process. That seems appropriate since my app isn’t built using Xcode’s build system. [more...]

Tweaking Synology’s DNS Server For Great Justice

Posted by cwright on 2016.06.23 @ 23:05

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Years ago I purchased a Synology NAS (a DS1812+, if you must know). I also purchased some hard drives for it, and a 2GB stick of RAM (bringing its total up to 3GB). Under the hood it’s a dual-core Cedarview Atom x86 CPU, and it runs a Linux distro wherein the owner of the device also has root access (i.e., you own what you own, like in the good old days). It’s also got dual GB NICs, some USB ports, etc.

In addition to storing substantial slabs of data, you can install services on these devices, so in effect they’re more like mini servers than the NAS name might imply. It’s busybox-based though, so a lot of the normal Linux commands act weird or don’t have useful aliases (more, not less, only a subset of vi commands work, etc).

One of the services I opted to install was a DNS server, in the hopes that it would allow me to move some per-machine hosts file management stuff to it, and that our previously-rootless devices (read: iPads, iPhones, etc) would also be able to finally take advantage of a local caching name server with internal friendly names for devices that don’t participate in Bonjour. [more...]

Emulating "defer" in C, with Clang or GCC+Blocks Emulating "defer" in C, with Clang or GCC+Blocks

Posted by smokris on 2015.10.08 @ 23:24

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In the Go language (and now Apple’s Swift), there’s a new control-flow mechanism: defer.

When you tag a function call with the defer keyword, its execution is deferred until the end of the current scope. This makes it easy to construct an ad-hoc use of the RAII pattern — handy for placing resource initialization and finalization next to each other, to make it less likely that you’ll forget to finalize a resource.

I was curious whether it was possible to do something similar in C. It turns out it’s pretty straightforward. [more...]

LLVM generates code that generates code LLVM generates code that generates code

Posted by jstrecker on 2012.11.16 @ 14:53

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Back from last week’s LLVM developer’s meeting, I’d like to talk about one of my favorite features of LLVM .

LLVM is the compiler infrastructure that underlies Clang, Vuo, and many other projects. It’s a set of libraries to help you build compilers (and more). Among other things, LLVM provides a C++ API for generating LLVM Intermediate Representation (LLVM IR) code. LLVM IR is an assembly language for a hypothetical computer. LLVM IR code can be either interpreted or compiled down to native code.

So LLVM provides this C++ API for generating LLVM IR code — but it doesn’t stop there. LLVM can also generate C++ code that generates LLVM IR code. In other words, LLVM can literally write part of your compiler for you! [more...]

Kosada is Developing a Next-Generation Programming and Performance Environment for Multimedia Artists

Posted by jmcc on 2012.11.02 @ 22:48

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Kosada is developing Vuo, a next-generation visual programming environment. It will enable multimedia artists to create powerful real-time audiovisual projects, data visualizations, and apps — all without writing code.

With Vuo, non-programmers will be able to create their own multimedia software for interactive art and music performances, animations, visualizations, games, special effects, museum exhibits, kiosks and other artistic projects. Rather than writing code in a traditional computer language, the composer will drag and drop building blocks onto a canvas, connecting those blocks with cables to create the composition. Unlike most programming environments, artists will be able to interact with their Vuo compositions while they are running, allowing for live improvisation. [more...]

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