** Basics
Q: What is Mono exactly?
A: The Mono Project is a community initiative to develop an open
source, Linux-based version of the Microsoft.NET development
platform. Its objective is to enable Linux developers to build and
deploy cross platform .NET Applications. The project will
implement various technologies developed by Microsoft that have now
been submitted to the ECMA for standardization.
Q: Is Mono a .NET implementation?
A: No. Microsoft.Net is a broad, company-wide effort that ranges from
development tools to end user applications. Some components of
this initiative have been announced and some others are in the
works.
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 collection of different languages that
target the byte code
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: It is premature to target a shipdate for the code. While we anticipate
availability in the middle of next year, the more contributions we
get to the project, the sooner it will ship.
Q: How can I contribute?
A: Check the contributing section.
Q: Aren't you just copying someone else's work?
A: We are interested in providing the best tools for programmers to
develop applications for Free Operating Systems. We also want to help
provide the interoperability that will allow those systems to fit in
with other standards.
Please read the Mono
Project white paper on Ximian site] for more background and the
rationale for the project.
** The Ximian role in the Mono Project
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 cannot and will not be able to take on the whole project on
its own. Ximian is spearheading the effort and providing a call to
action. Mono will be a free software/open source community
project; that is the only way to implement something of this
size. Visit the contributing page
on this site to learn more about what you can do.
Q: What pieces will Ximian be working on?
A: We will devote most of our resources to work on the pieces which are
on the critical path to release 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.
** Relationship with GNOME
Q: How is this related to GNOME?
A: In a number of ways. This project was born out of the need of
providing improved tools for the GNOME community, and will use
existing components that have been developed for GNOME when they
are available. For example, we plan to use Gtk+ and Libart to
implement Winforms and the Drawing2D API and are considering
GObject support.
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 now?
A: It is still far to early for discussions of "switching over." No
pieces of Mono will be ready within the next six months, and a
complete implementation is roughly 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 would be the "backend" for various classes.
Q: Will Mono include compatibility with Bonobo components? What is the
relationship between Mono and Bonobo?
A: Yes, we will provide a set of classes for implementing and using
Bonobo components from within Mono. 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 Microsoft: .NET, Hailstorm, and Passport
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. It is going to provide an open source,
Linux-based version of the Microsoft.NET development platform. Its
objective is to enable Linux developers to build and deploy cross
platform .NET Applications.
Q: Is the Mono Project is related to the Microsoft Hailstorm effort? Is
Ximian endorsing Hailstorm?
A: No. The Mono Project is focused on providing a compatible set of
tools for the Microsoft.NET development platform. It does not
address, require, or otherwise endorse the MS Passport-based
Hailstorm single sign-on system that is part of Windows XP and
other services.
Q: If you implement .NET, will I depend on Microsoft Passport to run my software?
A: No. MS Passport is unrelated to running .NET compatible applications
produced with the Mono tools. The only thing you will need is a
just-in-time compiler (JIT).
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: If Microsoft will release a port of their .NET platform under the
`Shared Source' license, why should I bother with anything else?
A: The Shared Source implementation will be expensive and its uses
will be tightly restricted, especially for commercial use. We are
working towards an implementation that will grant a number of
important rights to recipients: use for any purpose,
redistribution, modification, and redistribution of modifications.
This is what we call Free Software
Q: Is Mono 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. Applications may use that API to contact a Passport site, but
are not required to do so.
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: Will Mono running on Linux make Passport available for Linux?
A: No. However, the Passport toolkit for Linux-based web servers is available from
Microsoft.
** 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.
** 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
learn more about running Windows applications on Intel Unix systems
refer to the Wine Project.
** Web Services
Q: Is Mono just a new way of writing Web Services?
A: No.
Q: If Mono implements the SDK classes, will I be able to write and
execute .NET Web Services with it?
A: Yes. 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? Can I use Soup without Mono?
A: Soup is a library for GNOME applications to create SOAP servers and
SOAP clients, and can be used without Mono. 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 and Issues
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: With any luck, Free Software enthusiasts will contribute tools to
improve the developer environment. These tools could be developed
initially using the Microsoft implementation of the CLI and then
executed later with Mono.
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: Is it true that the CIL is ideal for JITing and not efficient for
interpreters?
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.
** Mono and Java
Q: Why don't you use 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: 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.
Q: Will Mono run on Windows?
A: We hope so. 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 components.
** 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: Is Microsoft helping Ximian with this project?
A: Not exactly. Ximian CTO Miguel de Icaza had a friendly
conversation with Microsoft software architect David Stutz, but
that's about the extent of the contact.
Microsoft is interested in other implementations of .NET and are
willing to help make the ECMA spec more accurate for this purpose.
Ximian representatives have also spoken with Sam Ruby at the ECMA
TG3 committee to discuss the same issues.
Q: Is Microsoft paying Ximian to do this?
A: No.
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,
the existing platform would a value on its own.
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 then again,
it was already easy for someone to just use PInvoke to tie their
application to Windows.
Q: Are 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.
** 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: Are you working on a GCC front-end to C#?
A: We are seeking volunteers for this task. Visit the contributing section if
you'd like to work on this task.
Q: How about a GCC backend that will generate CIL images?
A: That would be great: it could provide a ton of free compilers that
would generate CIL code. This is something that people would want
to look into anyway for Windows interoperation in the future.
Visit the contributing section if
you'd like to work on this task.
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.
Visit the contributing section if
you'd like to work on this task.
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.
** Performance
Q: How fast will Mono be?
A: We can not predict the future, but a conservative estimate is that
it would be at least `as fast as other JIT engines'.
We would like to ship various JIT engines with Mono, just like
Microsoft has done with their .NET development platform. We could
provide a faster, JIT for fast load times but lower performance,
and an and an optimizing JIT 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.
** 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 or licenses are you using for the Mono Project?
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: Can I subclass objects within the LGPL licensed Mono code and still release
the resulting software under a closed license?
A: Yes. Object Oriented Programming in the class library is a well
understood interface barrier, and subclassing does not "count" as a
modification, so you may develop proprietary applications with the
Mono libraries.
Q: I would like to contribute code to Mono under a particular
license. What licenses will you accept?
A: We will have to evaluate the licenses for compatibility first,
but as a general rule, we will accept all GPL and LGPL-compatible
licenses. If you want to use the BSD
license, make sure you use the BSD license without the
advertisement clause (The `Ousterhout License').
** 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.