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debuggers02

Have you ever wonder what happens when you create and use breakpoints in .NET? Here’s a little picture that answers that question (if you don’t like the font, you have a different version at the bottom).

We have the main actors here as follows:

  • .NET Application – our regular .NET application that we want to debug. Methods, as provided by the compiler in the Intermediate Language form (IL) are Just-in-Time compiled to a native code when called. So, imagine our “e8 50 ff ff” represents an example binary code of a line we want to debug (no matter what it does now)
  • Debugger Runtime Control Thread (hereinafter referred to as Debugger RC Thread) – it is a special thread inside every .NET process for debugging purposes and serves as a bridge between the CLR and an external debugger. It consists of a so-called “debugger loop”, listening on events coming from the Debug Port (supported by the OS). Please note that in case of native debugging, such a special thread is typically injected into the debuggee process. But we don’t need to do that here, as .NET runtime provides it. And moreover, this thread understand the CLR data structures, so it is able to cooperate with JIT and so.
  • external Debugger – it is our external process that we cooperate with. Imagine it as a tooling part of Visual Studio or other IDE you use. It is using a set of COM objects that are able to communicate via Inter-process communication (IPC) mechanism with Debugger Runtime Control Thread.

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logo-thinkific

Testing shows the presence of errors in a product, but “cannot prove that there are no defects” – you probably know that quote. I remember so many hours spent on debugging those little, mean bugs hidding deeply in the code edge cases. But what’s worse, I remember even more hours trying to understand and reproduce an error that happens only in production environment. Here’s the first top 5 most popular issues I’ve met during last years:

  • app hangs due to deadlocks (in the app or external library)
  • memory issues like memory leaks, long GC pauses or high CPU usage due to the GC
  • swallowed exception preventing some logic, with no logs available
  • threading issues like thread-pool starvation
  • intermittent errors due to the resources shortage, like running out of sockets or file handles

BTW. And what’s yours top 5?

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Tune screenshot

I would like to present you a new tool I’ve started to work on recently. I’ve called it The Ultimate .NET Experiment (Tune) as its purpose is to learn .NET internals and performance tuning by experiments with C# code. As it is currently in very early 0.2 version, it can be treated as Proof Of Concept with many, many features still missing. But it is usable enough to have some fun with it already.

The main way of working with this tool is as follows:

  • write a sample, valid C# script which contains at least one class with public method taking a single string parameter. It will be executed by hitting Run button. This script can contain as many additional methods and classes as you wish. Just remember that first public method from the first public class will be executed (with single parameter taken from the input box below the script). You may also choose whether you want to build in Debug or Release mode (note: currently it is only x64 bit compilation).
  • after clicking Run button, the script will be compiled and executed. Additionally, it will be decompiled both to IL (Intermediate Language) and assembly code in the corresponding tab.
  • all the time Tune is running (including time during script execution) a graph with GC data is being drawn. It shows information about generation sizes and GC occurrences (as vertical lines with the number below showing which generation has been triggered).

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Zero Garbage Collector on .NET Core

Starting from .NET Core 2.0 coupling between Garbage Collector and the Execution Engine itself have been loosened. Prior to this version, the Garbage Collector code was pretty much tangled with the rest of the CoreCLR code. However, Local GC initiative in version 2.0 is already mature enough to start using it. The purpose of the exercise we are going to do is to prepare Zero Garbage Collector that replaces the default one.

Zero Garbage Collector is the simplest possible implementation that in fact does almost nothing. It only allows you to allocate objects, because this is obviously required by the Execution Engine. Created objects are never automatically deleted and theoretically, no longer needed memory is never reclaimed. Why one would be interested in such a simple GC implementation? There are at least two reasons:Continue reading

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Trace Compass

.NET Core on Linux is still very fresh in 2017. First production deployments are just beginning to emerge. Consequently, development on this platform is only beginning to show up. There is a lack of knowledge and good practices related to virtually every aspect of the existence of this environment. One of them is monitoring and diagnostic aspect. How can we monitor and analyze the health of our application?

The easiest way of getting tracing data is by using official perfcollect bash script and then using Perfview on Windows to analyze this recorded data. This approach has some drawbacks. The main one is are fairly limited analysis results available in PerfView. The second, less burdensome, is the need for Windows to… analyze Linux data. Recently Sasha Goldstein has created a lot of valuable material on this subject and I invite you to review the list posted at the end of this post.

I would like to present another diagnostic option here. This is using the free Eclipse Trace Compass tool. Continue reading