Coding – LinuxJedi's /dev/null

Event Loops and NCurses

Yesterday I wrote a blog post talking about Event Loops, this was a pre-cursor to discussing where I am using them in an application I’m currently developing which uses NCurses at its core.

Unfortunately the application is an R&D project and is not public yet (still very early in development), but it is written in C, has a TUI front end and handles many windows and network connections simultaneously so I am using libuv heavily underneath. For this post I’ll be discussing the integration between libuv and NCurses.

Event Loop Programming: A Different Way of Thinking

The concept of event loops is not new in programming, but I think it is still a really important technique to learn. They allow a program to send a request for something and carry on doing things rather than waiting on things to happen. It is a great way of multi-tasking in a single thread but there are some gotchas to be aware of.

In this blog post I’ll give a short intro to event loops and how to get the most out of them.

Socket SO_REUSEPORT and Kernel Implementations

Way back when I was at NGINX I worked with several people on integrating a kernel patch for SO_REUSEPORT in Linux to work with NGINX for something I termed “socket sharding“. In hindsight I should have maybe called it “socket load balancing” but the term “sharding” has stuck with that option across the industry now. Whilst this option is a standard option in many *nix kernels it behaves very differently in them. So I thought I would note some details down in this blog post

Sanitizers, The Alternative To Valgrind

Valgrind is an incredibly powerful tool which helps find leaks, buffer overflows and many other things. Whilst being extremely powerful it can also be very slow. As an alternative there are little known tools that are available for Clang and GCC which can fulfil similar functions for your C / C++ applications but with much higher performance.

I’ve had several people ask me about the sanitizers recently and how to use them, so I’ll cover some basics here.

My Journey Learning The Go Programming Language

The key to learning anything new is finding a way to engage with the material. Some people learn by reading and some learn by doing. I typically fall into the latter half and I’ve typically been more successful in mentoring people who learn in a more hands-on way.

A recent Tweet I made led to a chat which somehow led to a famous Open Source developer getting me kickstarted into the world of developing in the Go Programming Language. This post tracks some of my journey for the last week (my first week of learning Go).

POSIX File Handling and Undefined Behaviour

Whilst porting code between Linux and macOS I have come across two issues which make assumptions about how something works but in reality different implementations of libc handle them differently. In this post I’ll talk about recent issues I faced with fopen() and fclose() in codebases.

Nested Variadic Functions in C

You may be familiar with variadic functions in C, these are basically functions that allow a variable number of parameters, they are normally written like this:

void my_print_func(const char *format, ...)
{
    va_list args;
    va_start(args, format);
    vprintf(format, args);
    va_end(args);
}

Obviously you can do more with them and they are very useful, but if you want to have one function calling another things can get complicated. This post explores the problem and a couple of ways of solving it.

Unicode 7 in CentOS 7 TUI Code

I’m in the middle of developing a project in C which uses NCurses and Unicode 7+ characters. This has been working out great in macOS and Fedora 31 where I have been doing most of my testing. But in CentOS I have been having big problems getting the characters to render. This post goes into why and how to fix it.

My Open Source projects that still live on

I have recently created a new library called libMariaS3 for a couple of teams at MariaDB which provides a simple C API to Amazon’s S3. This was created because we needed a library which could link to GPLv2 software and Amazon’s own library is Apache 2.0 licensed which is incompatible.

It is not a perfect code base because I had a very short amount of time to get the first release out but it was a very fun project to work on. It led me to take a quick look this morning at a couple of other things I have created in the past to see where they are at today.

Coding and decoding crash dump handlers

All software has bugs. Even if you could possibly write the perfect bug free software all the layers down have bugs. Even CPUs as can be seen with the recent Meltdown and Spectre bugs. This means unfortunately sometimes software will crash. When this happens it is useful to capture as much information as possible to try and stop it happening again.

One of the first things I did when coming back to work from the holiday break is code a new crash dump handler to be used in MariaDB ColumnStore. This will spit out a stack trace for the current thread into a file upon a crash. It is very useful for daemons to try and find the root cause of a problem without running through a debugger. Continue reading Coding and decoding crash dump handlers