Java2C#

Antonio Cisternino

Part IV

Outline

Exception handling (no throws clause) Advanced features:

"preprocessor“ unsafe code interoperability:

using C++ using COM Interop tlbimp/tlbexp using PInvoke

Introduction to BCL

Outline

Exception handling (no throws clause) Advanced features:

"preprocessor“ unsafe code interoperability:

using C++ using COM Interop tlbimp/tlbexp using PInvoke

Introduction to BCL

Exception handling

CLR and C# support exception handling Structure of exceptions is similar to Java There is no throws clause in C# Example of Exception Handling:

try { … } catch(XXXException) { … } finally { … }

Multiple catch clauses are allowed Finally block is executed either the try block

raises or not an exception

Common C# Exceptions

System.ArithmeticException System.ArrayTypeMismatchException System.IndexOutOfRangeException System.InvalidCastException System.MulticastNotSupportedException System.NullReferenceException System.OutOfMemoryException System.OverflowException System.StackOverflowException System.TypeInitializationException

Outline

Exception handling (no throws clause) Advanced features:

"preprocessor“ unsafe code interoperability:

using C++ using COM Interop tlbimp/tlbexp using PInvoke

Introduction to BCL

C# “preprocessor”

C# borrows from C++ the preprocessor syntax There isn’t a separate “preprocessor”: the tokenizer

implements it Preprocessor directives are less expressive than C++:

there are no macros! Supported directives are:

#define, #undef #if, #elif, #else, #endif #error, #warning #region, #endregion #line

Conditional compilation

#define DEBUGpublic class Stream { public void Write(string s) {#if DEBUG Console.WriteLine("Debug: " + s);#elif CONSOLE Console.WriteLine(s);#else label.Text = s;#endif }}#undef DEBUG

Warning: not pre!

class Hello { static void Main() { System.Console.WriteLine(@"Hello,#if Debug world#else Pisa#endif "); }} Output is the whole string with directives!

Other directives

Error and warning allow to detect inconsistencies in configuration at compile time

Region/endregion are directives that allow mark region of code with a label (after the region directive). Other programs will be responsible of their processing

Line directive helps code generators to associate C# code to source file (i.e. Yacc)

Conditional attribute

An important attribute is the Conditional attribute It can be specified only for methods If a method has such attribute its calls are included or

not depending if a symbol is defined where the call is made

Example:class Foo { [Conditional("Debug")] void Baz(); }…Foo f;f.Baz(); // Not included!#define Debugf.Baz(); // Included!

Unsafe code

The base model of C# is similar to Java: no MEMORY is present

BUT C# provides a special mode called unsafe that allow using pointers!

Unsafe code is not verifiable thus high privileges are required to run it

The pointer data type is very like C pointers and introduces memory in the model

Unsafe code is needed to support PInvoke mechanism Support from GC allows programs pinning of objects

Example

class Test { unsafe static void Main() { char* p = stackalloc char[256]; for (int i = 0; i < 256; i++) { p[i] = (char)i; } *p = 64; }}

Pinning objects!

unsafe class Test { static int x; int y; static void F(int* p) { *p = 1; } static void Main() { Test t = new Test(); int[] a = new int[10]; fixed (int* p = &x) F(p); fixed (int* p = &t.y) F(p); fixed (int* p = &a[0]) F(p); fixed (int* p = a) F(p); }}

Interoperability using VC++

Visual C++ compiler is able to generate code managed and unmanged that interacts at source level!

Crossing the barrier managed/unmanaged is simplified: write standard C++ classes that uses .lib and DLLs and little managed classes that act as wrappers

The compilers is in charge of separating the two environment and output the appropriate code

In order to support managed code C++ language has been extended syntactically

Example

#include <mscorlib.dll>using namespace System;class CppClass { public: CppClass() {} ~CppClass() {} void native_f() {} }; __gc class MClass { public: MClass() { m_pC = new CppClass(); } ~MClass() { delete m_pC; } void managed_f() { m_pC->native_f(); } private: CppClass * m_pC; };

Managed C++

To indicate which elements should be managed the keyword __gc is extensively used

Managed objects are pointer to managed classes labeled with __gc

Managed classes are annotated with __gc Other extensions are required to handle with

other features such as attributes Although it is great the ability of mixing

unmanagd and managed code the program becomes more difficult to read: managed objects aren’t equivalent to C++ ones!

COM Interop

COM is the component technology used in Windows

COM allows any program sharing data and interacting with other unknown programs

The CLR itself is a COM component (and can be embedded in other applications!)

CLR supports COM interoperability in both directions: COM components can be seen as .NET objects and vice-versa

COM in one slide! COM components are set of interfaces that inherits from

IUnknown A set of rules guarantees a notion of identity of the

component instance An interface is just a table of pointers to methods Information about types and interfaces are defined using

IDL and stored in type libraries Components are packaged in DLLs and registered into

registry Interpreters may use IDispatch or typelibs to use COM

components It is efficient but difficult to use from languages and

prone to errors Common issues: DLLs, Registry, typelibs, and so on

Tlbimp and tlbexp

The runtime handle with most of the complexity of COM and in general is able to expose COM components into the runtime automagically

Marshalling and unmarshalling of standard types is handled by the runtime

Two utilities are available to cope with COM: tlbimp/tlbexp

Tlbimp builds an assembly that wraps a COM component

Tlbexp generates COM interfaces to CLR types

PInvoke C# provides a mechanism called PInvoke to simplify

interaction with native code Using attributes and the extern keyword to expose as a

method the function of a DLL Example:

[DllImport("kernel32.dll", CharSet=CharSet.Auto, SetLastError=true)]

public static unsafe extern IntPtr CreateFileMapping(

IntPtr hFile, void* lpAttributes, FileProtection flProtect, int dwMaximumSizeHigh, int dwMaximumSizeLow, string lpName);

The program could use its own data types to interact with the function and specific attributes help controlling the memory layout of types

Example: pointer wrapper

Goal: expose a file mapped in memory Steps:

Expose memory mapping functions into CLRWrite a type that represents a MM fileWrite a “pointer” type that exposes the

memory as an array of bytesCast operations help reading memory

depending on data types.

Examplepublic struct MapPtr { private unsafe byte* p; private unsafe byte* b; private unsafe byte* e;

public MapPtr(MapPtr p, int sz) { unsafe { Debug.Assert(p.e - p.p >= sz,

"Wrong window size!"); this.b = p.p; this.p = p.p; this.e = p.p + sz; }} internal unsafe MapPtr(byte* p,

byte* b, byte* e) { this.p = p; this.b = b; this.e = e; } public byte this[int pos] { get { unsafe { byte* np = p + pos; Debug.Assert(np >= b && np < e,

"Illegal access"); return *np; }}}

public static MapPtr operator+(MapPtr p, int i) {

unsafe { Debug.Assert(p.p + i <= p.e,

"Illegal access"); return new MapPtr(p.p + i, p.b,

p.e); }} public static long operator-(MapPtr

p, MapPtr q) { unsafe { return p.p - q.p; }} public static explicit operator

int(MapPtr p) { unsafe { return *((int*)p.p); }} public static explicit operator

long(MapPtr p) { unsafe { return *((long*)p.p); }} public static bool

operator==(MapPtr p, MapPtr q) { unsafe { return p.p == q.p; }} public static bool operator!

=(MapPtr p, MapPtr q) { unsafe { return p.p != q.p; }}}

Outline

Exception handling (no throws clause) Advanced features:

"preprocessor“ unsafe code interoperability:

using C++ using COM Interop tlbimp/tlbexp using PInvoke

Introduction to BCL

Introduction to BCL

BCL is organized in hierarchical namespaces System.* namespaces and classes are considered part

of the framework Only a subset of System has been standardized within

ECMA standards A reasonable implementation of .NET should implement

more than the standard subset of BCL Additional libraries are exposed through the namespace

Microsoft.* In the following slides a brief introduction to BCL

namespaces is provided: in most cases a separate course will be needed to explain the details!

Namespace System

Is the core namespace Many types are just exposed by EE It is like java.lang.* but more richer Relevant classes are

System.Activator System.Type System.AppDomain System.Attribute System.Environment (Cmd line args, variables and other info) System.GC System.Math System.Object System.Random Base value types (System.{ Byte, Int16, Int32, … })

Namespace System

Note that threads are not included in System namespace Threading is subject of System.Threading namespace Loading mechanism is exposed through

System.Activator class The class is sealed and classes cannot be derived from

it AppDomain exposes the bound of the managed code:

many AppDomains may share the same process (and EE) but are separated

In particular types are loaded per-AppDomain Activator + AppDomain + Assembly.LoadFrom ~= Java

class loader

Namespaces

System.CodeDom: an abstraction to support DOM representing code and compiler writing

System.Collections: container classes to manipulate collection of objects (Hashtable, SortedList, …)

System.ComponentModel: base abstraction for a component model

System.Configuration: classes to support reading of XML configuration files

System.Data namespace

System.Data: under this namespace are implemented the classes of ADO.NET architecture

ADO.NET reflects the experience of Microsoft with DB interfaces: it is a flexible framework that really improves ADODB and ODBC

The architecture consists in having a set of provider (.NET assemblies)

The interface is far better than JDBC provided with Java: relation among tables and other constraints are exposed as objects

A set of interfaces allows providers to extend the architecture

Namespaces

System.Diagnostics: contains classes to support interaction with OS logging system: event logs, process management, counter handling Debug class supports assertions and debug output!

System.Drawing: this namespace exposes classes for 2D graphics. The Graphics class contains base primitives (also sophisticated

ones such as Bezier curves) other classes support managing of images and other drawing

elements Text and Printing namespaces take care of corresponding

drawing support

Namespaces

System.Globalization: contains classes to support localization of software. MS has great experience in supporting different locales and the namespace reflects such experience.

System.IO: this namespace exposes IO management. The namespace is less stream oriented than Java although there are binary and character streams

System.IO.IsolatedStorage: support reading and writing in stores with code less trusted

System.Management: exposes WMI interface

Namespaces

System.Messaging: exposes messaging abstraction over the net

System.Net: contains high level classes to interact with TCP/IP. Sockets are exposed in System.Net.Sockets

System.Reflection: contains reflection classes. Emit namespace contains classes to generate managed programs

System.Resources: supports access to locale dependent resources

System.Runtime

Namespaces under System.Runtime exposes features of the runtime: CompilerServices: support for compiler writers InteropServices: important namespace that supports

interoperability services (i.e. COM) Remoting: architecture to support distributed objects.

Note that remoting is supported by CLR and not implemented on top of it!

Serialization: complex architecture to support serialization of objects allowing programs to customize serialization format

Namespaces

System.Security: contains classes to manage security

System.ServiceProcess: contains support for implementing easily Windows services!!!

System.Text: supports encodings and the StringBuilder to manipulate efficiently strings

System.Text.RegularExpressions: support for perl-like regular expressions. There is a compiler to generate IL for specialized expressions written using System.Reflection.Emit.

Namespaces

System.Threading: exposes Thread related types Synchronization is more rich than JavaMultiple synchronization objects are provided:

event, mutex, monitor, interlock System.Timers: support for timers System.Web: huge amount of classes to

support Web applications

System.Web

Two are the main technologies behind Web namespace: Web services ASP.NET

Web services are simply method exposed through an XML-based protocol called SOAP (W3C). The runtime together with IIS is able to expose type’s methods labeled with appropriate attributes as Web services

ASP.NET is an attempt to support Web application development offering to the programmer an abstraction that makes a Web application similar to a Windows application. WebForms are a set of “Web controls” that represents remote graphic

elements Events are dispatched through HTTP and the programming style may

lead very inefficient programs due to event handling!

Windows Forms and XML

System.Windows.Forms: this namespace contains support for building GUI applications. Its structure recalls java.awt although there are significant

differences. Example: a different layout mechanism is used

System.XML is the namespace devoted to XML standards. The following standards are supported: XML Dom XML reader (Sax-like approach) XML Schema XPath XSL and XSLT

Next lecture

Visual Studio environment example: using DirectX from C#. example: Web services Framework SDK tools: gac, csc, ildasm Assembly & co.