NTP Software Jan 2012 Monthly Meeting IPC Presentation

Interprocess Communication

(IPC)For Windows

Muhamad Hesham9-JAN-2012

Agenda

• Choosing IPC method criteria

• Windows provided IPC mechanisms

• Pipes

• Mailslots

Choosing IPC Method Criteria

• Communication Scope

Local or over Networks ?



• Communicating parties compatibility

16-bit Windows, UNIX, etc…




• Locating the other party

User driven or implicitly ?





• Performance requirements

All IPC methods have performance overhead! But …





• Performance requirements

• Application type

GUI, console, windows service, etc…

Windows Provided IPC Mechanisms

• Clipboard

• Data Copy

• File Mapping

• RPC

• Windows Sockets

• Pipes

• Mailslots

• And others

OMG! Did MS test all these?!


• Clipboard• Data Copy

• File Mapping

• RPC

• Windows Sockets

• Pipes

• Mailslots

• All applications have access to the clipboard

• User-driven method used in: Cut, Copy and Paste operations


• Clipboard

• Data Copy• File Mapping

• RPC

• Windows Sockets

• Pipes

• Mailslots

Use WM_COPYDATA message to pass data to another application.

The following structure is passed to the received application as read-only data:

typedef struct tagCOPYDATASTRUCT { ULONG_PTR dwData;

DWORD cbData;

PVOID lpData;

} COPYDATASTRUCT, *PCOPYDATASTRUCT;


• Clipboard

• Data Copy• File Mapping

• RPC

• Windows Sockets

• Pipes

• Mailslots

Sender A:

COPYDATASTRUCT myCopyData;

// Initialize myCopyData

SendMessage( hwndOther, WM_COPYDATA, (WPARAM)(HWND) hwndSelf, (LPARAM) (LPVOID) &myCopyData);

Receiver B:

case WM_COPYDATA:

pMyCopyData = (PCOPYDATASTRUCT)lParam;

switch(pMyCopyData->dwData)

{

case ID_FOO: Foo(pMyCopyData->lpData);

…

}


• Clipboard

• Data Copy

• File Mapping• RPC

• Windows Sockets

• Pipes

• Mailslots

Four possible methods of implementing a program to reverse the order of all the bytes in a file:

Method 1: One File, One Buffer

Method 2: Two Files, One Buffer

Method 3: One File, Two Buffers

Method 4: …


• Clipboard

• Data Copy


• Windows Sockets

• Pipes

• Mailslots

Implementing a program to reverse the order of all the bytes in a file:




Method 4: One File, Zero Buffers


• Clipboard

• Data Copy


• Windows Sockets

• Pipes

• Mailslots

Implementing a program to reverse the order of all the bytes in a file:




Method 4: One File, Zero Buffers

Simply call _tcsrev to reverse the data in the file because it is usable simply as an in-memory text string!!

Power of Memory-Mapped Files


• Clipboard

• Data Copy


• Windows Sockets

• Pipes

• Mailslots

C:\Data.file

Map View

LPTSTR szBuffer;

szBuffer = // Create Map View_tcsrev(szBuffer);// Close Map View

Windows Memory Manager

szBuffer

….

….


• Clipboard

• Data Copy

• File Mapping

• RPC• Windows Sockets

• Pipes

• Mailslots

RPC Cycle

Developed as an extension to OSF RPC


• Clipboard

• Data Copy

• File Mapping

• RPC

• Windows Sockets• Pipes

• Mailslots

• Protocol-independent interface

• Based on the sockets first popularized by Berkeley Software Distribution (BSD) (UNIX).

Anonymous Pipes - Properties

• Unidirectional (2 handles: read-only and write-only)

2 instances to the same pipe with different access rights



• Byte-stream oriented

Useful for character-based data transfer




• Narrow scope (related processes)

Since it is unnamed, only its handle can be shared





• Implemented with Named Pipes

Can be treated as a named pipe





• Implemented with Named Pipes

• Asynchronous I/O NOT supported

ReadFile/WriteFile OVERLAPPED structure is ignored

Anonymous Pipes - CreatePipe

• Use ReadFile/WriteFile to communicate over the pipe

• Read operation block if buffer empty

• Write operation block if buffer full

• Write operation does not return until the buffer is Read

Anonymous Pipes

I/O redirection using anonymous pipes

Named Pipes - Big Picture

Clients and Servers using Named Pipes

Named Pipes - Properties

• Bidirectional (1 handle for read and write)

Read and Write using the same handle simultaneously



• Message and Byte-stream oriented

A very big advantage over anonymous pipes




• Networked and local

Pipe operations are transparent to user




• Networked and local

• Asynchronous I/O supported

Can perform asynchronous pipe read, write and connect

Named Pipes - CreateNamedPipe

• \\[servername]\pipe\[pipename]

• User provided buffer sizes is advisory

• Buffer sizes considerations and downsides

• Client connects using CreateFile or CalledNamedPipe

Named Pipes - Server/Client Sync

Server/Client race conditions can happen

Server says:

Client says:

Named Pipes - Connection Sequence

Multithreaded pipe server use multi pipe instances

Single-Threaded Pipe Server says:

Named Pipes - Connection Sequence

Clients can use Mailslots to locate server pipes

Client says:

Mailslots- Big Picture

Multiple writers single reader model

Send@ \\*\mailslot\mhesham

Maislot Client C (Writer)

Maislot Server (Reader)

Maislot Client A (Writer)

Maislot Client B (Writer)

Mailslots - Properties

• Unidirectional

One way communication line, i.e Broadcasting


• Bidirectional

• Multiple readers/writers capable

Typically, one writer many readers and vice versa


• Bidirectional


• No reception confirmation

Writers do not hear from the readers any response


• Bidirectional



• Can be located over network domain

As well as local on the same machine


• Bidirectional



• Can be located over network domain

• Limited message length

MS say 424 byte! Unicode string of size 212 character

Mailslots - CreateMailSlot

• When creating a mailslot: \\.\mailslot\[mailslotname]

• When accessing a mailslot: \\[.|*|Domain|Computer]\mailslot\[mailslotname]

Mailslots - Example

References

• MSDN article: Interprocess Communication

• RPC overview blog post

• Windows via C/C++ book 5th edition

• Windows System Programming book 4th edition

http://msdn.microsoft.com/en-us/library/windows/desktop/aa365574(v=vs.85).aspx

http://mhesham.wordpress.com/2011/08/03/remote-procedure-call-rpc/

Thanks…

Questions?Muhamad HeshamQFS [email protected]

Documents

NTP Software Jan 2012 Monthly Meeting IPC Presentation