TLS 1.2 Comes to Mono: Update

Short version: the master branch of Mono now has support for TLS 1.2 out of the box. This means that SslStream now uses TLS 1.2, and uses of HttpWebRequest for HTTPS endpoints also uses TLS 1.2 on the desktop.

This brings TLS 1.2 to Mono on Unix/Linux in addition to Xamarin.{Mac,iOS,tvOS} which were already enabled to use TLS 1.2 via the native Apple TLS stack.

To use, install your fresh version of Mono, and then either run the btls-cert-sync command which will convert your existing list of trusted certificates to the new format (if you used cert-sync or mozroots in the past).

In Detail

The new version of Mono now embeds Google's Boring SSL as the TLS implementation to use.

Last year, you might remember that we completed a C# implementation of TLS 1.2. But we were afraid of releasing a TLS stack that had not been audited, that might contain exploitable holes, and that we did not have the cryptographic chops to ensure that the implementation was bullet proof.

So we decided that rather than ship a brand new TLS implementation we would use a TLS implementation that had been audited and was under active development.

So we picked Boring TLS, which is Google's fork of OpenSSL. This is the stack that powers Android and Google Chrome so we felt more comfortable using this implementation than a brand new implementation.

Linux Distributions

We are considering adding a --with-openssl-cert-directory= option to the configure script so that Linux distributions that package Mono could pass a directory that contains trusted root certificates in the format expected by OpenSSL.

Let us discuss the details in the

Posted on 30 Sep 2016 by Miguel de Icaza

Asset Previewer

Mobile developers are working with all kinds of graphics assets and until now, to preview them, we would use an external tool to browse them.

We have developed a plug-in for both Visual Studio and Xamarin Studio that will provide live previews of various assets right into the IDE. It works particularly well for UrhoSharp projects.

The previewer can display in the IDE previews of the following asset types.

  • Static Models (*.mdl files)
  • Materials, Skyboxes, Textures (*.dds)
  • Animations (*.ani)
  • 2D and 3D Particles (*.pex)
  • Urho Prefabs (*.xml if the XML is an Urho Prefab)
  • Scenes (*.xml if the XML is an Urho Scene)
  • SDF Fonts (*.sdf)
  • Post-process effects (*.xml if the XML is an Urho RenderPath)
  • Urho UI layouts (*.xml if the XML is an Urho UI).

For Visual Studio, just download the previwer from the Visual Studio Gallery.

For Xamarin Studio, go to Xamarin Studio > Add-ins go to the "Gallery" tab, and search for "Graphics asset previewer" and install.

Posted on 28 Jul 2016 by Miguel de Icaza

The Evolution of Interactive C#

The Early Days

Years ago, in 2008 we introduced an interactive C# shell, at the time a challenge was to adjust the syntax to be suitable for interactive use, to provide a usable decent command line editing API for .NET and to turn our compiler as a service into a tool that could provide code completion.

A few months later, we added a UI shell for this on Linux and used Gtk's text widget to add support for embedding rich content into the responses. It was able to render images inline with the responses:

This was inspired at the time by the work that Owen Taylor at Red Hat had done on Re-interact. You can still watch a screencast of what it looked like.

Like Owen, I added a plot command:

At the time, Re-interact took some ideas from IPython and it seems like they are both inspired to some extent by Mathematica's interactive window.

Re-interact in particular introduced a brilliant idea, which was that users could go back in history, edit the previous expressions and the entire buffer would be re-evaluated. This idea lives on in Apple's Playgrounds for Swift.

In the meantime, the IPython project grew and they added one of my favorite features: it was now possible to blend text, explanations and code into workbooks. You can see a sample of this here. For years, I have desired an IPython for C#.

The Xamarin Years

In the meantime, at Xamarin, we experimented with the idea of bringing sometehing like Re-interact/Playgrounds to Xamarin Studio and we shipped Sketches:

But while these were interesting for trying out ideas and learning C#, they are not very useful for day to day work. We found that what our developers needed was a full C# REPL that was connected to the application they were running on, so they could experiment with their UI live. This is when we introduced Xamarin's Inspector. We took the existing engine and changed the way you interacted with C#.

The inspector was originally planned as a debugging aid, one that you could use to attach to a live Android/iOS/WPF process and use to examine:

We wrote several backends to provide some visual representation of the running app:

While Sketches used the IDE editing surface and a custom renderer view for results, with the Inspector we took a different route. Our interactive surface was an HTML canvas, and our results are rendered using HTML. This allowed us to do some pretty visualizations for results.

We have only started to explore what is possible in this space, and our last release included various data renderers. In particular, we added support for pretty printing collections and a handful of native Android and iOS results.

Up until now, we had been powered by Mono's C# compiler and while it has served us well for many years, it pales in comparison with the services that we could get out of Microsoft's Roslyn. Our code completion and error reporting were limited and the model did not translate too well to F#.

We recently switched the inspector to use Roslyn:

With this release, we ended up with an Inspector that can now be used either to debug/analyze a running app (very much like a web inspector), or one that can be used to experiment with APIs in the same spirit as other shells.


In the meantime, Frank Krueger took the iOS support that we introduced for the compiler as a service, and wrote Continuous, a plug-in for Xamarin Studio and Visual Studio that allowed developers to live-code. That is, instead of using this as a separate tool, you can modify your classes and methods live and have your application update as you change the code:

Frank also added support for evaluating values immediately, and showing some values in comments, similar in spirit to his Calca app for iOS:

The Glorious Future

But now that we have a powerful HTML rendering engine to display our results and we upgraded our compiler engine, we are ready to take our next steps.

One step will be to add more visualizers and rendering capabilties to our results in our Inspector.

The second step is to upgrade Sketches based on this work. We will be changing the Sketches UI to be closer to IPython, that is, the ability of creating workbooks that contain both rich HTML text along with live code.

To give you a taste of what is coming up on our next release, check out this screenshot:

Developers will still have a few options of richly interacting with C# and F#:

  • With our inspector experiment with APIs like they do with many other interactive shells, and to poke and modify running apps on a wide spectrum of environments.
  • With Frank Krueger's Continuous engine to see your changes live for your C# code.
  • With our revamped Sketches/workbook approach to use it for creating training, educational materials.
Posted on 17 Feb 2016 by Miguel de Icaza

Shared Projects or PCL?

My colleague Jason Smith has shared his views on what developers should use when trying to share code between projects. Should you go with a Shared Project or a Portable Class Library (PCL) in the world of Xamarin.Forms?

He hastily concludes that you should go with PCLs (pronounced Pickles).

For me, the PCL is just too cumbersome for most uses. It is like using a canon to kill a fly. It imposes too many limitations (limited API surface), forces you to jump through hoops to achieve some very basic tasks.

PCLs when paired with Nugets are unmatched. Frameworks and library authors should continue to deliver these, because they have a low adoption barrier and in general bring smiles and delight to their users.

But for application developers, I stand firmly on the opposite side of Jason.

I am a fan of simplicity. The simpler the technology, the easier it is for you to change things. And when you are building mobile applications chances are, you will want to make sweeping changes, make changes continously and these are just not compatible with the higher bar required by PCLs.

Jason does not like #if statements on his shared code. But this is not the norm, it is an exception. Not only it is an exception, but careful use of partial classes in C# make this a non issue.

Plugging a platform specific feature does not to use an #if block, all you have to do is isolate the functioanlity into a single method, and have each platform that consumes the code implement that one method. This elegant idea is the same elegant idea that makes the Linux kernel source code such a pleasure to use - specific features are plugged, not #ifdefed.

If you are an application developer, go with Shared Projects for your shared code. And now that we support this for F#, there is no reason to not adopt them.

Posted on 22 Jan 2016 by Miguel de Icaza

getline.cs update: Partying like it is 1992

Back in 2008, I wrote about getline.cs, a single-file command line editor for shell application. It included Emacs key bindings, history, customizable completion and incremental search. It is equivalent to GNU's readline library, except it is implemented in a single C# file.

I recently updated getline.cs to add a popup-based completion and C# heuristics for when to automatically trigger code completion. This is what it looks like when using in Mono's C# REPL in the command line:

Posted on 14 Jan 2016 by Miguel de Icaza

Mono's Cooperative Mode for SGen GC

Mono's master tree now contains support for a new mode of operation for our garbage collector, we call this the cooperative mode. This is in contrast with the default mode of operation, the preemptive mode.

This mode is currently enabled by setting the MONO_ENABLE_COOP environment variable.

We implemented this new mode of operation to make it simpler to debug our GC, to have access to more data on the runtime during GC times and also to support certain platforms that do not provide the APIs that our preemptive system needed.

Behind Preemptive Mode

When we started building Mono back in 2001, we wanted to get something up and running very quickly. The idea was to have enough of a system running on Linux that we could have a fully self-hosting C# environment in a short period of time, and we managed to do this within eight months.

We were very lucky when it came to garbage collection that the fabulous Boehm GC existed. We were able to quickly add garbage collection to Mono, without having to think much about the problem.

Boehm is fabulous because it does not really require the cooperation of the runtime to work. It is a garbage collector that was originally designed to add garbage collection capabilities to programs written in C or C++. It performs garbage collection without much developer intervention. And it achieves this for existing code: multi-threaded, assembly-loving, low-level code.

Boehm GC is a thing of beauty.

Boehm achieves its magic by pulling some very sophisticated low-level tricks. For example, when it needs to perform a garbage collection it relies on various operating system facilities to stop all running threads, examine the stacks for all these threads to gather roots from the stack, perform the actual GC job then resume the operation of the program.

While Boehm is fantastic, in Mono, we had needs that would be better served with a custom garbage collector. One that was generational and reduced collection times. One fit more closely with .NET. It was then that we built the current GC for Mono: SGen.

SGen has grown by leaps and bounds and has been key in supporting many advanced scenarios on Android and iOS as well as being a higher performance and lower latency GC for Mono.

When we implemented SGen, we had to make some substantial changes to Mono's code generator. This was the first time that Mono's code generator had to coordinate with the GC.

SGen kept a key feature of Boehm: most running code was blissfully unaware that it could be stopped and resumed at any point.

This meant that we did not have to do too much work to integrate SGen into Mono [1]. There are two main downsides with this.

The first downside is that we still required the host platform to support some mechanism to stop, resume and inspect threads. This alone is pretty obnoxious and caused much grief to developers porting Mono to strange platforms.

The second downside is that code that runs during the collection is not really allowed to use many of the runtime APIs or primitives, because the collector might be running in parallel to the regular code. You can only use reentrant code.

This is a major handicap for development and debugging of the collector. One that is just too obnoxious to deal with and one that has wasted too much of our time.

Cooperative Mode

In the new cooperative mode, the generated code is instrumented to support voluntarily stopping execution

Conceptually, you can think of the generated code as one that basically checks on every back-branch, or every call site that the collector has requested for the thread to stop.

The supporting Mono runtime has been instrumented as well to deal with this scenario. This means that every API that is implemented in the C runtime has been audited to determine whether it can run in a finite amount of time, or if it is a blocking operation and adjusted to participate accordingly.

For methods that run in a finite amount of time, we just wait for them to return back to managed code, where we will stop.

For methods that might potentially block, we need to add some annotations that inform our GC that it is safe to assume that the thread is not running any mutating code. Consider the internal call that implements the CreateDirectory method. It now has been decorated with MONO_PREPARE_BLOCKING and MONO_FINISH_BLOCKING to delimit blocking code.

This means that threads do not stop right away as they used to, but they stop soon enough. And it turns out that soon enough is good enough.

This has a number of benefits. First, it allows us to support platforms that do not have enough system primitives to stop, resume and examine arbitrary threads. Those include things like the Windows Store, WatchOS and various gaming consoles.

But selfishly, the most important thing for us is that we will be able to treat the garbage collector code as something that is a first class citizen in the runtime: when the collector works, it will be running in such a state that accessing various runtime structures is fine (or even using any tasty C libraries that we choose to use).


As of today, Mono's Coop engine can either be compiled in by default (by passing --with-cooperative-gc to configure), or by setting the MONO_ENABLE_COOP environment variable to any value.

We have used a precursor of Coop for about 18 months, and now we have a fully productized version of it on Mono master and we are looking for developers to try it out.

We are hoping to enable this by default next year. [1] Astute readers will notice that it still took years of development to make SGen the default collector in Mono.

Posted on 22 Dec 2015 by Miguel de Icaza

David Brooks, Op-Ed for All Trades, Master of None

I first heard about David Brooks' article criticizing Most Likely to Succeed from a Mom at school that told me it was a rebuttal to the movie, and I should check it out.

I nodded, but did not really expect the article to change my mind.

David Brooks is an all-terrain commentator which dispenses platitudes and opinions on a wide range of topics, usually with little depth or understanding. In my book, anyone that supported and amplified the very fishy evidence for going to war with Iraq has to go an extra mile to prove their worth - and he was specially gross when it came to it.

Considering that the best part about David Brook's writing is that they often prompt beautiful take downs from Matt Taibbi and that his columns have given rise to a cottage industry of bloggers that routinely point out just how wrong he is, my expectations were low.

Anyways, I did read the article.

While the tone of the article is a general disagreement with novel approaches to education, his prescription is bland and generic: you need some basic facts before you can build upon those facts and by doing this, you will become a wise person.

The question of course is just how many facts? Because it is one thing to know basic facts about our world like the fact that there are countries, and another one to memorize every date and place of a historic event.

But you won't find an answer to that on Brooks piece. If there is a case to be made to continue our traditional education and continue relying on tests to raise great kids, you will not find it here.

The only thing that transpires from the article is that he has not researched the subject - he is shooting from the hip. An action necessitated by the need to fill eight hundred words a short hour before lunch.

His contribution to the future of education brings as much intellectual curiosity as washing the dishes.

I rather not shove useless information into our kids. Instead we should fill their most previous years with joy and passion, and give them the tools to plot their own destinies. Raise curious, critical and confident kids.

Ones that when faced with a new problem opt for the more rewarding in-depth problem solving, one that will have them research, reach out to primary sources, and help us invent the future.

Hopefully we can change education and raise a happier, kinder and better generation of humans. The road to get there will be hard, and we need to empower the teachers and schools that want to bring this change.

"Most Likely to Succeed" represends Forward Motion, and helps us start this discussion, and David's opinions should be dismissed for what they are: a case of sloppy stop energy.

Do not miss Ted Dintersmith's response to the article, my favorite part:

I agree with Brooks that some, perhaps even many, gain knowledge and wisdom over time. We just don’t gain it in school. It comes when we’re fully immersed in our careers, when we do things, face setbacks, apply our learning, and evolve and progress. But that almost always comes after our formal education is over. I interview a LOT of recent college graduates and I’m not finding lots of knowledge and wisdom. Instead, I find lots of student debt, fear of failure, and formulaic thinking. And what do I rarely see? Passion, purpose, creativity, and audacity.

So, game on, David Brooks and others defending the 19th Century model of education.

Posted on 19 Oct 2015 by Miguel de Icaza

Roslyn in MonoDevelop/XamarinStudio

As promised, we now have a version of our IDE powered by Roslyn, Microsoft's open sourced C# compiler as a service

When we did the port we found various leaks in the IDE that were made worse by Roslyn, so we decided to take the time and fix those leaks, and optimize our use of Roslyn.

Next Steps

We want to get your feedback on how well it works and to let us know what problems you are running into. Once we feel that there are no regressions, we will make this part of the default IDE.

While Roslyn is very powerful, this power comes with a memory consumption price tag. The Roslyn edition of Xamarin Studio will use more memory.

We are working to reduce Roslyn's and Xamarin Studio memory usage in future versions.

Posted on 21 Sep 2015 by Miguel de Icaza

Mono and LLVM's BitCode

This past June, Apple announced that WatchOS 2 applications would have to be submitted using LLVM BitCode. The idea being that Apple could optimize your code as new optimizations are developed or new CPU features are introduced, and users would reap the benefits without requiring the developer to resubmit their applications.

BitCode is a serialized version of the low-level intermediate representation used by LLVM.

WatchOS 2 requires pure BitCode to be submitted. That is, BitCode that does not contain any machine code blobs. iOS supports mixed mode BitCode, that is, BitCode that contains both the LLVM intermediate representation code, and blobs of machine code.

While Mono has had an LLVM backend for a long time, generating pure BitCode posed a couple of challenges for us.

First, Mono's LLVM backend does not cover all the generated code. There were some corner cases that we handled with Mono's old code generator. Also, Mono uses hand-written assembly language code in various places (lots of small optimizations involving generics code sharing, method dispatch and other things like that). This poses a problem for WatchOS.

Secondly, Mono uses a modified version of LLVM that adds support for many .NET idioms. In particular, our changes to LLVM produce the necessary information to support .NET-style exception handling [1].

We spent the summer adapting Mono to produce Vanilla LLVM bitcode support. This includes the removal of our hand-tuned machine code, as well as devising a new system for exception handling that works in this context. Sadly, the exception handling is not as efficient as the one that we got with our modified LLVM.

Hopefully, we will be able to upstream our changes for better exception handling for .NET-like languages to LLVM in the future and get some of the performance back.


[1] Vanilla LLVM exception support requires exceptions to be explicit. In .NET some exceptions happen implicitly, for example, when dereferencing a null pointer, or dividing by zero.

Posted on 02 Sep 2015 by Miguel de Icaza

Xamarin Release Cycles

There are four major components of Xamarin's platform product: the Android SDK, the iOS SDK, our Xamarin Studio IDE and our Visual Studio extension.

In the past, we used to release each component independently, but last year we realized that developing and testing each component against the other ones was getting too expensive, too slow and introduced gratuitous errors.

So we switched to a new style of releases where all the components ship together at the same time. We call these cycles.

We have been tuning the cycle releases. We started with time-based releases on a monthly basis, with the idea that any part of the platform that wanted to be released could catch one of these cycles, or wait for the next cycle if they did not have anything ready.

While the theory was great, the internal dependencies of these components was difficult to break, so our cycles started taking longer and longer.

On top of the cycles, we would always prepare builds for new versions of Android and iOS, so we could do same-day releases of the stacks. These are developed against our current stable cycle release, and shipped when we need to.

We are now switching to feature-based releases. This means that we are now waiting for features to be stable, with long preview periods to ensure that no regressions are introduced.

Because feature based releases can take as long as it is needed to ship a feature, we have introduced Service Releases on top of our cycles.

Our Current Releases

To illustrate this scenario, let me show what our current platform looks like.

We released our Cycle 5 to coincide with the Build conference, back in April 29th. This was our last timed release (we call this C5).

Since then we have shipped three service releases which contain important bug fixes and minor features (C5-SR1, SR2 and SR3), with a fourth being cooked in the oven right now (C5-SR4)

During this time, we have issued parallel previews of Android M and iOS 9 support, those are always built on top of the latest stable cycle. Our next iOS 9 preview for example, will be based on the C5-SR4.

We just branched all of our products for the next upgrade to the platform, Cycle 6.

This is the cycle that is based on Mono 4.2.0 and which contains a major upgrade to our Visual Studio support for iOS and plenty of improvements to Xamarin Studio. I will cover some of my favorite features in Cycle 6 in future posts.

Posted on 01 Sep 2015 by Miguel de Icaza

State of TLS in Mono

This is an update on our efforts to upgrade the TLS stack in Mono.

You can skip to the summary at the end if you do not care about the sausage making details.

Currently, TLS is surfaced in a few places in the .NET APIs:

  • By the SslStream class, which is a general purpose class that can be used to turn any bidirectional stream into an TLS-powered stream. This class is what currently powers the web client in Mono.
  • By the HttpWebRequest class, which provides .NET's HTTP client. This in turn is the foundation for the modern HttpClient, both the WCF and WebServices stacks as well as the quick and dirty WebClient API.

HttpClient is in particular interesting, as it allows for different transports to be provided for it. The default implementation in .NET 4.5 and Mono today is to use an HttpWebRequest-based implementation. But on Windows 10, the implementation is replaced with one that uses WinRT's HTTP client.

Microsoft is encouraging developers to abandon HttpWebRequest and instead adopt HttpClient as it both async-friendly and can use the best available transport given on a specific platform. More on this in a second.

Mono's Managed TLS

Mono currently only supports TLS 1.0.

This is the stack that powers SslStream and HttpWebRequest.

Last year we started an effort to bring managed implementations of TLS 1.2 and TLS 1.1. Given how serious security has become and how many holes have been found in existing implementation, we built this with an extensive test suite to check for conformance and to avoid common exploits found in implementation mistakes of TLS. This effort is currently under development and you can see where it currently lives at mono-tls module.

This will give us complete TLS support for the entire stack, but this work is still going to take a few months to audit.

Platform Specific HttpClients

Most of the uses for TLS today is via the HTTP protocol, and not over custom TLS streams. This means that it is more important to get an HTTP client that supports a brand new TLS stack, than it is to provide the SslStream code.

We want to provide native HttpClient handlers for all of Mono's supported platforms: Android, iOS, Mac, Linux, BSD, Unix and Windows.

On iOS: Today Xamarin.iOS already ships a native handler, the CFNetworkHandler. This one is powered by Apple's CFNetwork stack. In recent years, Apple has improved their networking stack, and we now I strongly recommend using Paul Bett's fantastic ModernHttpClient which uses iOS' brand new NSUrlSession and uses OkHttp on Android.

On Android: in the short term, we recommend adopting ModernHttpClient from Paul Betts (bonus points: the same component works on iOS with no changes). In the long term, we will change the default handler to use the Android Java client.

In both cases, you end up with HTTP 2.0 capable clients for free.

But this still leaves Linux, Windows and other assorted operating systems without a regular transport.

For those platforms, we will be adopting the CoreFX handlers, which on Unix are powered by the libcurl library.

This still leaves HttpWebRequest and everything built on top of it running on top of our TLS stack.

Bringing Microsoft's SslStream and HttpWebRequest to Mono

While this is not really TLS related, we wanted to bring Microsoft's implementations of those two classes to Mono, as they would fix many odd corner cases in the API, and address limitations in our stack that do not exist in Microsoft's implementation.

But the code is tightly coupled to native Windows APIs which makes the adoption of this code difficult.

We have built an adaptation layer that will allow us to bring Microsoft's code and use Mono's Managed TLS implementation.

SslStream backends

Our original effort focused on a pure managed implementation of TLS because we want to ensure that the TLS stack would work on all available platforms in the same way. This also means that all of the .NET code that expects to control every knob of your secure connection to work (pinning certificates or validating your own chains for example).

That said, in many cases developers do not need this capabilities, and in fact, on Xamarin.iOS, we can not even provide the functionality, as the OS does not give users access to the certificate chains.

So we are going to be developing at least two separate SslStream implementations. For Apple systems, we will be implementing a version on top of Apple's SSL stack, and for other systems we will be developing an implementation on top of Amazon's new SSL library, or the popular OpenSSL variant of the day.

These have the advantage that we would not need to maintain the code, and we benefit from third parties doing all the hard security work and will be suitable for most uses.

For those rare uses that like to handle connections manually, you will have to wait for Mono's new TLS implementation to land.

In Summary

Android, Mac and iOS users can get the latest TLS for HTTP workloads using ModernHttpClient. Mac/iOS users can use the built-in CFNetworkHandler as well.

Soon: OpenSSL/AppleSSL based transports to be available in Mono (post Mono 4.2).

Soon: Advanced .NET SSL use case scenarios will be supported with Mono's new mono-tls stack

Soon: HttpWebRequest and SslStream stacks will be replaced in Mono with Microsoft's implementations.

Posted on 27 Aug 2015 by Miguel de Icaza

Roslyn and Mono

Hello Internet! I wanted to share some updates of Roslyn and Mono.

We have been working towards using Roslyn in two scenarios. As the compiler you get when you use Mono, and as the engine that powers code completion and refactoring in the IDE.

This post is a status update on the work that we have been doing here.

Roslyn on MonoDevelop/XamarinStudio

For the past year, we have been working on replacing the IDE's engine that gives us code completion, refactoring capabilities and formatting capabilities with one powered by Roslyn.

The current engine is powered by a combination of NRefactory and the Mono C# compiler. It is not as powerful, comprehensive or reliable as Roslyn.

Feature-wise, we completed the effort, and we now have a Roslyn-powered branch that uses Roslyn for code completion, refactoring, suggestions and code formatting.

In addition, we ported most of the refactoring capabilities from NRefactory to work on top of Roslyn. These were quite significant. Visual Studio users can try them out by installing the Refactoring Essentials for Visual Studio extension.

While our Roslyn branch is working great and is a pleasure to use, it also consumes more memory and by extension, runs a little slower. This is not Roslyn's fault, but the side effects of leaks and limitations in our code.

Our original plan was to release this for our September release (what we internally call "Cycle 6"), but we decided to pull the feature out from the release to give us time to fix the leaks that affected the Roslyn engine and tune the performance of Roslyn running on Mono.

Our revisited plan is to ship an update to our tooling in Cycle 6 (the regular feature update) but without Roslyn. In parallel, we will ship a Roslyn-enabled preview of MonoDevelop/XamarinStudio. This will give us time to collect your feedback on performance and memory usage regressions, and time to fix the issues before we make Roslyn the default.

Roslyn as a Compiler in Mono

One of the major roadblocks for the adoption of Roslyn in Mono was the requirement to generate debugging information that Mono could consume on Unix (the other one is that our C# batch compiler is still faster than Roslyn).

The initial Roslyn release only had support for generating debug information through a proprietary/native library on Windows, which meant that while Roslyn could be used to compile code on Unix, the result would not contain any debug information - this prevented Roslyn from being useful for most compilation uses.

Recently, Roslyn got support for Portable Program Database (PPDB) files. This is a fully documented, open, compact and efficient format for storing debug information.

Mono's master release contains now support for using PPDB files as its debug information. This means that Roslyn can produce debug information that Mono can consume.

That said, we still need more work in the Mono ecosystem to fully support PPDB files. The Cecil library is used extensively to manipulate IL images as well as their associated debug information. Our Reflection.Emit implementation will need to get a backend to generate PPDBs (for third party compilers, dynamic code generators) and support in IKVM to produce PPDB files (this is used by Mono's C# compiler and other third party compilers).

Additionally, many features in Roslyn surfaced bloat and bugs in Mono's class libraries. We have been fixing those bugs (and in many cases, the bugs have gone away by replacing Mono's implementation with implementations from Microsoft's Reference Source).

Posted on 21 Jul 2015 by Miguel de Icaza

In Defense of the Selfie Stick

From the sophisticated opinion of the trendsetters to Forbes, the Selfie Stick is the recipient of scorn and ridicule.

One of the popular arguments against the Selfie Stick is that you should build the courage to ask a stranger to take a picture of you or your group.

This poses three problems.

First, the courage/imposition problem. Asking a stranger in the street assumes that you will find such a volunteer.

Further, it assumes that the volunteer will have the patience to wait for the perfect shot ("wait, I want the waves breaking" or "Try to get the sign, just on top of me"). And that the volunteer will have the patience to show you the result and take another picture.

Often, the selfista that has amassed the courage to approach a stranger on the street, out of politeness, will just accept the shot as taken. Good or bad.

Except for a few of you (I am looking at you Patrick), most people feel uncomfortable imposing something out of the blue on a stranger.

And out of shyness, will not ask a second stranger for a better shot as long as the first one is within earshot.

I know this.

Second, you might fear for the stranger to either take your precious iPhone 6+ and run, or even worse, that he might sweat all over your beautiful phone and you might need to disinfect it.

Do not pretend like you do not care about this, because I know you do.

Third, and most important, we have the legal aspect.

When you ask someone to take a picture of you, technically, they are the photographer, and they own the copyright of your picture.

This means that they own the rights to the picture and are entitled to copyright protection. The photographer, and, not you, gets to decide on the terms to distribute, redistribute, publish or share the picture with others. Including making copies of it, or most every other thing that you might want to do with those pictures.

You need to explicitly get a license from them, or purchase the rights. Otherwise, ten years from now, you may find yourself facing a copyright lawsuit.

All of a sudden, your backpacking adventure in Europe requires you to pack a stack of legal contracts.

Now your exchange goes from "Can you take a picture of us?" to "Can you take a picture of us, making sure that the church is on the top right corner, and also, I am going to need you to sign this paper".

Using a Selfie Stick may feel awkward, but just like a condom, when properly used, it is the best protection against unwanted surprises.

Posted on 22 Jan 2015 by Miguel de Icaza

.NET Foundation: Advisory Council

Do you know of someone that would like to participate in the .NET foundation, as part of the .NET Foundation Advisory Council?

Check the discussion where we are discussing the role of the Advisory Council.

Posted on 01 Dec 2014 by Miguel de Icaza

Microsoft Open Sources .NET and Mono

Today, Scott Guthrie announced that Microsoft is open sourcing .NET. This is a momentous occasion, and one that I have advocated for many years.

.NET is being open sourced under the MIT license. Not only is the code being released under this very permissive license, but Microsoft is providing a patent promise to ensure that .NET will get the adoption it deserves.

The code is being hosted at the .NET Foundation's github repository.

This patent promise addresses the historical concerns that the open source, Unix and free software communities have raised over the years.

.NET Components

There are three components being open sourced: the .NET Framework Libraries, .NET Core Framework Libraries and the RyuJit VM. More details below.

.NET Framework Class Libraries

These are the class libraries that power the .NET framework as it ships on windows. The ones that Mono has historically implemented in an open source fashion.

The code is available today from Mono will be able to use as much a it wants from this project.

We have a project underway that already does this. We are replacing chunks of Mono code that was either incomplete, buggy, or not as fully featured as it should be with Microsoft's code.

We will be checking the code into by the end of the week (I am currently in NY celebrating :-)

Microsoft has stated that they do not currently plan on taking patches back or engaging into a full open source community style development of this code base, as the requirements for backwards compatibility on Windows are very high.

.NET Core

The .NET Core is a redesigned version of .NET that is based on the simplified version of the class libraries as well as a design that allows for .NET to be incorporated into applications.

Those of you familiar with the PCL 2.0 contract assemblies have a good idea of what these assemblies will look like.

This effort is being hosted at and is an effort where Microsoft will fully engage with the community to evolve, develop and improve the class libraries.

Today, they released the first few components to github; the plan is for the rest of the redesigned frameworks to be checked in here in the next few months.

Xamarin and the Mono project will be contributing to the efforts to bring .NET to Mac, Unix, Linux and other platforms. We will do this as Microsoft open sources more pieces of .NET Core, including RyuJIT.

Next Steps

Like we did in the past with .NET code that Microsoft open sourced, and like we did with Roslyn, we are going to be integrating this code into Mono and Xamarin's products.

Later this week, expect updated versions of the Mono project roadmap and a list of tasks that need to be completed to integrate the Microsoft .NET Framework code into Mono.

Longer term, we will make the Mono virtual machine support the new .NET Core deployment model as well as the new VM/class library interface

We are going to be moving the .NET Core discussions over to the .NET Foundation Forums.

With the Mono project, we have spent 14 years working on open source .NET. Having Microsoft release .NET and issue a patent covenant will ensure that we can all cooperate and build a more vibrant, richer, and larger .NET community.

Posted on 12 Nov 2014 by Miguel de Icaza
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