** Basics
Q: Is Mono the same as Microsoft's .NET initiative?
A: It is not.
.NET is a company-wide initiative at Microsoft that
encompasses many different areas. The .NET development framework,
Passport, Biztalk, new server products, and anything that is
remotely connected to .NET gets the ".NET-stamping" treatment.
Some components of Microsoft's .NET initiative have been announced
and some others are in the works.
Mono is a project to implement several technologies developed by
Microsoft that have now been submitted to the ECMA Standards Body.
Q: What technologies are included in Mono?
A: Mono contains a number of components useful for building new
software:
* A Common Language Infrastructure (CLI) virtual
machine that contains a class loader, Just-in-time
compiler, and a garbage collecting runtime.
* A class library that can work with any language
which works on the CLR.
* A compiler for the C# language. In the future we
might work on other compilers that target the Common
Language Runtime.
Windows has compilers that target the
virtual machine from
a
number of languages: Managed C++, Java Script,
Eiffel, Component Pascal, APL, Cobol, Oberon, Perl,
Python, Scheme, Smalltalk, Standard ML, Haskell,
Mercury and Oberon.
The CLR and the Common Type System (CTS) enables applications and
libraries to be written in a number of languages. Classes and
methods created in one language can be used from a different
language.
This means for example that if you define a class to do algebraic
manipulation in C#, that class can be reused from any other
language that supports the CLI. You could create a class in C#,
subclass it in C++ and instantiate it in an Eiffel program.
A single object system, threading system, class libraries, and
garbage collection system can be shared across all these languages.
Q: Where can I find the specification for these technologies?
A: You can find the work-in-progress documentation from the T3G ECMA
group here:
http://www.dotnetexperts.com
Q: Will you implement the .NET Framework SDK class libraries?
A: Yes, we will be implementing the APIs of the .NET Framework SDK
class libraries.
Q: What does Mono stand for?
A: Mono is the word for `Monkey' in Spanish. We like monkeys.
It only means a number of other things: monochromatic (hence the
gray theme used in the Web site).
Q: When will you ship it?
A: We do not know when the code will be shipped. The more
contributions we get to the project, the sooner it will ship.
A rough estimate is that we might be able to run our C# compiler on
Linux by the end of the year. That means running the Windows
Executable generated by a Microsoft .NET compiler on the Linux
platform.
We expect that doing GUI applications will require more work on the
class libraries. That could take another six months.
Q: How can I contribute?
A: Check the contributing section.
Q: You guys should innovate instead of copying.
A: In this particular case, we see a clear advantage in the platform
and we are interested in using the features of the CLI on open source systems.
We have decided that we should spend our limited resources towards
implementing an existing specification instead of designing and
implementing our own.
Designing and implementing our own would be possible, but it doesn't make
sense to do that just because the specification comes from a
proprietary vendor.
** Ximian
Q: Why is Ximian working on .NET?
A: We are interested in providing the best tools for programmers to
develop applications for Free Operating Systems.
For more information, read the project rationale page.
Q: Will Ximian be able to take on a project of this size?
A: Ximian will not be able to taken on the whole project on its own.
Mono will be a free software/open source community project, that is
the only way we can hope to implement something of this size. You
can contribute to this effort.
Q: What pieces will Ximian be working on?
A: We will focus on building a development and execution
environment.
The idea is to get Mono to a state of that would allow
third parties to actually be able to use it real-world development.
Q: Why does Ximian even care?
A: We like the features that the CLI and its related technologies
bring to the table. An exciting addition to the developer toolkit.
The goal of Mono is to bring this technology to non-Windows
platforms (although we hope Mono will also run on Windows, for
debugging and comparative purposes).
** Licensing
Q: Will I be able to write proprietary applications that run with
Mono?
A: Yes. The licensing scheme is planned to allow proprietary
developers to write applications with Mono.
Q: What license is Mono on?
A: The C# Compiler is released under the terms of the GPL. The class
libraries will be under the LGPL or the GPL with a special
exception. The runtime libraries are under the LGPL.
Since the LGPL is not suitable for embedded systems development, we
are also licensing the libraries under the GPL with the following exception:
If you link this library against your own program, then you do not
need to release the source code for that program. However, any
changes that you make to the library itself, or to any native
methods upon which the library relies, must be re-distributed in
accordance with the terms of the GPL.
This is similar in spirit to GNU
Classpath.
Q: But in Object Oriented Programming I need to subclass your library
functions, does that mean that I am making modifications to your
library and hence I would have to distribute my sources under the
LGPL?
A: No. Object Oriented Programming in the class library is a well
understood interface barrier, so you can actually develop
proprietary applications with the Mono libraries.
Q: Will you accept code under the XXX License?
A: If the XXX License is compatible with the license we use in that
specific piece of code, then yes. If you want to use the BSD license, make
sure you use the BSD license without the advertisement clause (The
`Ousterhout License').
** Mono and .NET
Q: If applications use Mono, does that mean that I have to pay a service fee?
A: No. Mono is not related to Microsoft's initiative of
software-as-a-service.
Q: If you implement .NET, will I depend on Microsoft Passport to run my software?
A: No. The .NET Framework is a runtime infrastructure and collection
of class libraries. Passport may be required to access certain web
services written for that framework, but only if the programmer
chooses Passport as the authentication mechanism.
Q: Is .NET just a bunch of marketing slogans?
A: Although the `.NET initiative' is still quite nebulous, The .NET Framework
has been available for some time. Mono is not an implementation of the .NET
initiative, just the development framework.
Q: What is a 100% .NET application?
A: A `100% .NET application' is one that only uses the APIs defined
under the System namespace and does not use PInvoke. These
applications would in theory run unmodified on Windows, Linux,
HP-UX, Solaris, MacOS X and others.
Q: But Microsoft will release a port of the real thing under the
`Shared Source' license, why bother with anything else?
A: The Shared Source implementation will not be usable for commercial
purposes. We are working towards an implementation that will grant
a number of rights to recipients: use for any purpose,
redistribution, modification, and redistribution of modifications.
This is what we call Free Software
** Passport
Q: Is this a free implementation of Passport?
A: No. Passport is part of Microsoft's Hailstorm initiative. Mono
is just a runtime, a compiler and a set of class libraries.
Q: Will the System.Web.Security.PassportIdentity class, mean
that my software will depend on Passport?
A: No. That just means that applications might use that API to
contact a Passport site.
As long as your application does not use Passport, you will not
need Passport.
It might even be possible to implement that class with
a set of dummy functions, or use an alternate Passport implementation.
We do not know at this time whether the Passport protocol is
documented and whether we will be able to talk to
passport.com
Q: But that must mean that you are tied to Passport!
A: All the contrary. The implementation could keep the interface (for
the sake of simplicity, lets say it implements the method `Login'
and `GetUserName').
We could implement `Login' and `GetUserName' by talking to XNS or
any other decentralized systems. Or any other system that the
industry standarizes on.
Q: What is your opinion?
A: You can read my personal opinion on
passport.
Q: Will Mono running on Linux make Passport available for Linux?
A: The Passport toolkit for Linux-based web servers is available from
Microsoft.
Again, Mono has nothing to do with Passport.
** Mono and Windows
Q: Will Mono allow me to run Microsoft Office on Linux?
A: No, it will not. Microsoft Office is a Windows application. To
run Windows applications on Intel Unix systems refer to the Wine Project
** GNOME
Q: How is this related to GNOME?
A: In a number of ways:
* Mono will use existing
components that have been developed for GNOME when it makes
sense. For example on X systems, we will use Gtk+ and
Libart to implement Winforms and the Drawing2D API.
For database access, we will use LibGDA (not really
depending on GNOME, but related to).
* This project was born out of the need of providing improved
tools for the GNOME community.
* We would like to add support to our CLR implementation to
deal with GObjects (in GNOME 1.x, they are called
GtkObjects), and allow Mono developers to provide GObjects
or use and extend existing GObjects.
Q: Has the GNOME Foundation or the GNOME team adopted Mono?
A: Mono is too new to be adopted by those groups. We hope that the
tools that we will provide will be adopted by free software
programmers including the GNOME Foundation members and the GNOME
project generally.
Q: Should GNOME programmers switch over to Mono?
A: Mono will not be ready even within the next six months, and a
complete implementation is probably one year away.
We encourage GNOME developers to continue using the existing tools,
libraries and components. Improvements made to GNOME will have an
impact on Mono, as they will provide the "backend" for various
classes.
Q: Will Mono include compatibility with Bonobo components?
A: Yes, we will provide a set of classes for implementing and using
Bonobo components from within Mono.
Q: Does Mono replace Bonobo?
A: Bonobo is very focused on cross-application component reuse. Mono
will provide a Bonobo framework to allow you to develop Bonobo
components and use Bonobo components on Unix.
Mono should allow you to write Bonobo components more easily, just
like .NET on Windows allows you to export .NET components to COM.
** Mono and the Web
Q: Is Mono a way of running Java applets?
A: No.
** Web Services
Q: Is Mono just a new way of writing Web Services?
A: No.
Q: If this implements the SDK classes, will I be able to write and
execute .NET Web Services with this?
A: Yes, you will.
When the project is finished, you will be able to use the same
technologies that are available through the .NET Framework SDK on
Windows to write Web Services.
Q: What about Soup?
A: Soup is a library for GNOME applications to create SOAP server and
SOAP clients. You can browse the source code for soup using GNOME's Bonsai
Q: Can I use CORBA?
A: Yes. The CLI contains enough information about a class that
exposing it to other RPC systems (like CORBA) is really simple, and
does not even require support from an object.
We will be implementing CORBA interoperation as an extension to the
Mono classes so that we can integrate with Bonobo, just like
Microsoft provides COM interoperation classes and support
mechanisms.
Q: Can I serialize my objects to other things other than XML?
A: Yes, although the serializing tools have not yet been planned, and
you would probably have to implement them yourself.
** Development Tools
Q: Will it be possible to use the CLI features without using bytecodes
or the JIT?
A: Yes. The CLI engine will be made available as a shared library.
The garbage collection engine, the threading abstraction, the
object system, the dynamic type code system and the JIT will be
available for C developers to integreate with their applications if
they wish to do so.
Q: Will you have new development tools?
A: Hopefully Free Software enthusiasts will contribute tools to
improve the developer environment. These tools could be developed
initially using Microsoft implementation of the CLI and then
executed later with Mono.
** Mono and Java
Q: What about using Java? After all there are many languages that
target the Java VM.
A: You can get very good tools for doing Java development on free
systems right now. Red Hat has
contributed a GCC frontend for Java that can take
Java sources or Java byte codes and generate native executables; Transvirtual has implemented
Kaffe a JIT engine for Java;
Intel also has a Java VM called ORP.
The JVM is not designed to be a general purpose virtual machine.
The Common Intermediate Language (CIL), on the other hand, is
designed to be a target for a
wide variety of programming languages, and has a set of rules
designed to be optimal for JITers.
Q: What kind of rules make the Common Intermediate Language useful for
JITers?
A: The main rule is that the stack in the CLI is not a general purpose
stack. You are not allowed to use it for other purposes than
computing values and passing arguments to functions or return
values.
At any given call or return instruction, the types on the stack
have to be the same independently of the flow of execution of your
code.
Q: I heard that the CIL is ideal for JITing and not efficient for
interpreters, is this the case?
A: The CIL is better suited to be JITed than JVM byte codes, but you
can interpret them as trivially as you can interpret JVM byte
codes.
Q: Could Java target the CLI?
A: Yes, Java could target the CLI. We have details on a project that someone could take on to
make this happen.
** Extending Mono
Q: Would you allow other classes other than those in the
specification?
A: Yes. The Microsoft class collection is very big, but it is by no
means complete. It would be nice to have a port of `Camel' (the
Mail API used by Evolution inspired by Java Mail) for Mono
applications.
You might also want to look into implementing CORBA for Mono. Not
only because it would be useful, but because it sounds like a fun
thing to do, given the fact that the CLI is such a type rich
system.
For more information on extending Mono, see our ideas page.
** Mono and portability
Q: Will Mono only work on Linux?
A: Currently, we are doing our work on Linux-based systems and
Windows. We do not expect many Linux-isms in the code, so it
should be easy to port Mono to other UNIX variants.
Q: What about Mono on non X-based systems?
A: Our main intention at Ximian is to be able to develop GNOME
applications with Mono, but if you are interested in providing a
port of the Winform classes to other platforms (frame buffer or
MacOS X for example), we would gladly integrate them, as long
they are under a Free Software License.
** Reusing existing Code
Q: What projects will you reuse or build upon?
A: We want to get Mono in the hands of programmers soon. We are
interested in reusing existing open source software.
Q: What about Intel's research JIT framework, ORP?
A: At this time, we are investigating whether we can use elements of
ORP for Mono. ORP is a research JIT engine that has a clear
defined API that splits the JIT from the GC system and the actual
byte code implementation. It is a research product.
Q: What about using GNU Lightning?
A: We are also researching GNU
Lightning.
** Ximian and Microsoft
Q: I read that Microsoft is helping out Ximian, is this true?
A: Initial contact between David Stutz and Miguel de Icaza happened.
It was a friendly conversation. Microsoft is interested in other
implementing .NET and are willing to help make the ECMA spec more
accurate for this purpose.
We were initially contacted by Sam Ruby at the ECMA TG3 committee
to discuss the same issue. And we are glad to have good contacts
to ask questions about the specs.
Q: Is Microsoft paying Ximian to do this?
A: No, we are doing this for purely selfish reasons. We are upgrading
our development platform to build better applications on Unix and other
systems.
Q: Do you fear that Microsoft will change the spec and render Mono useless?
A: No. Microsoft proved with the CLI and the C# language that it was
possible to create a powerful foundation for many languages to
interoperate. We will always have that.
Even if changes happened in the platform which were undocumented
(which is very unlikely), the existing platform has a value on its
own.
Miguel once explained its motivation for working on Mono to Dave
Winer, and his mail got posted here
Q: Didn't Miguel de Icaza say that `Unix Sucks'?
A: Yes, he did, as a catch phrase in his opening remark on the Ottawa
Linux Symposium. His talk focused on various ways to improve Unix.
There is a paper describing some ways to improve Unix at:
http://primates.ximian.com/~miguel/bongo-bong.html
Q: Didn't Ximian's Miguel work for Microsoft?
A: Actually, Nat Friedman (Ximian's co-founder) did work as an
intern for Microsoft for one summer but Miguel did not.
Q: Did Nat and Miguel meet at Microsoft?
A: They met online on the Linux IRC network; They met in person for
the first time in 1997.
** Mono and Microsoft
Q: How can you expect Mono to compete with Microsoft, wont this
require an effort too large?
A: You are right. Mono will never become a reality without the help
of other contributors. Ximian is a small company that can not
finish Mono alone. We will be working with members of the
community to deliver the product.
Q: Is Microsoft and Corel involved in the Mono implementation?
A: No, they are not.
Q: Are you writing Mono from the ECMA specs?
A: yes, we are writing them from the ECMA specs and the published
materials in print about .NET
Q: What happens if Microsoft `Embraces and Extends' the CLI standard
and keeps Mono out of the play?
A: There are various explanations to this question. The first one is
that the benefits that you can get from the CLI are going to be
there with or without `embracing and extending'. We might not be
able to run every .NET Windows application on Mono. But remember:
it was already easy for someone to just use PInvoke to tie their
application to Windows.
The bottom line is that the advantages of having a CLI runtime will
be with us, no matter if Microsoft forks their version to be
incompatible.
Q: What if Microsoft changes the interface, and all of a sudden
applications break?
A: If they change their released API, every application that was
developed against it will break.
That being said, Microsoft have a pretty good record of keeping
backwards binary compatibility.
** Acronyms
Q: What is the difference between CLR (Common Language Runtime) and
CLI (Common Language Infrastructure)?
A: CLI is the specification of an execution system. The Microsoft
implementation of this specification is named CLR.
Unless we come up with our own acronym, we could just call ours
also CLR, just because it would do exactly the same thing the
Microsoft implementation does.
** Mono and GCC
Q: Should someone work on a GCC front-end to C#?
A: I would love if someone does, and we would love to help anyone that
takes on that task, but we do not have the time or expertise to
build a C# compiler with the GCC engine. I find it a lot more fun
personally to work on C# on a C# compiler, which has an intrinsic
beauty.
We can provide help and assistance to anyone who would like to work
on this task.
Q: Should someone make a GCC backend that will generate CIL images?
A: I would love to see a backend to GCC that generates CIL images. It
would provide a ton of free compilers that would generate CIL
code. This is something that people would want to look into
anyways for Windows interoperation in the future.
Again, we would love to provide help and assistance to anyone
interested in working in such a project.
Q: What about making a front-end to GCC that takes CIL images and
generates native code?
A: I would love to see this, specially since GCC supports this same
feature for Java Byte Codes. You could use the metadata library
from Mono to read the byte codes (ie, this would be your
"front-end") and generate the trees that get passed to the
optimizer.
Ideally our implementation of the CLI will be available as a shared
library that could be linked with your application as its runtime
support.
Again, we would love to provide help and assistance to anyone
interested in working in such a project.
Q: But would this work around the GPL in the GCC compiler and allow
people to work on non-free front-ends?
A: People can already do this by targeting the JVM byte codes (there
are about 130 compilers for various languages that target the JVM).
Q: Why are you writing a JIT engine instead of a front-end to GCC?
A: The JIT engine and runtime engine will be able to execute CIL
executables generated on Windows.
** Mono and Portability
Q: Will Mono work on other variants of Unix?
A: Yes. We do not expect to add any gratuitous incompatibilities.
Q: Will Mono run on Windows?
A: Hopefully yes. Currently some parts of Mono only run on Windows
(the C# compiler is a .NET executable) and other parts have only
been compiled on Linux, but work on Windows with Cygwin.
Q: Will Mono depend on GNOME?
A: It will depend only if you are using a particular assembly (for
example, for doing GUI applications). If you are just interested
in Mono for implementing a `Hello World Enterprise P2P Web
Service', you will not need any GNOME component.
** Performance
Q: How fast will be Mono?
A: We can not predict the future, but a conservative estimate is that
it would be at least `as fast as other JIT engines'.
Now, wishfully thinking I hope that we will ship various JITs with
Mono just like Microsoft has done. A fast JITer when maximum
performance is not needed, but fast load times are important; And
an optimizing JITer that would be slower at generating code but
produce more optimal output.
The CIL has some advantages over the Java byte code: it is really
an intermediate representation and there are a number of
restrictions on how you can emit CIL code that simplify creating
better JIT engines.
For example, on the CIL the stack is not really an abstraction
available for the code generator to use at will: it is just a way
of creating a postfix representation of the parsed tree. At any
given call point or return point, the contents of the stack are
expected to contain the same object types independently of how the
instructions was reached.
** Mono and Portable.NET
Q: What are the differences between Mono and Portable.NET?
A: Most of Mono is being written using C#, the only pieces written in
C are those who have to absolutely be built using C (The JIT
engine, the runtime, the interfaces to the garbage collection
system).
The C# compiler and the tools will become reusable C# components.
Portable.NET is building its components out of C pieces.
** Assorted questions
Q: You say that the CLI allows multiple languages to execute on the
same environment. Isn't this the purpose of CORBA?
A: The key difference between CORBA (and COM) and the CLI is that the
CLI allows "data-level interoperability" because every
language/component uses the same data layout and memory management.
This means you can operate directly upon the datatypes that someone
else provides, without having to go via their interfaces. It also
means you don't have to "marshall" (convert) parameters (data
layouts are the same, so you can just pass components directly) and
you don't have to worry about memory managment, because all
languages/components share the same garbage collector and address
space. This means much less copying and no need for reference
counting.