IPC mechanisms in windows

IPC mechanisms in Windows
A brief description of different IPC
mechanisms in Windows OS
Compiled By:
B. Vinoth Raj
Senior Software Engineer
Mindfire Solutions

IPC mechanisms in Windows
 Clipboard
 Data Copy
 Dynamic Data Exchange (DDE)
 Component Object Model (COM)
 File Mapping
 Mailslots
 Pipes
 Remote Procedure Call (RPC)
 Sockets

IPC using Clipboard
 Loosely coupled exchange medium
 Applications agree on data format
 Following Windows API functions used
OpenClipboard()
EmptyClipboard()
SetClipboardData()
CloseClipboard()
GetClipboardData()
 Applications can reside on the same computer or on
different computers on a network

IPC using Data Copy
 Use WM_COPYDATA windows message to share data
 SendMessage() API function used to send data
 COPYDATASTRUCT structure used to send data
SendMessage(hwnd, // Handle to destination window
WM_COPYDATA, // Message to send to destination window
(WPARAM)wparam, // Handle to window passing the data
(LPARAM)lparam); // Data (pointer to COPYDATASTRUCT)
 The data sent is read-only for the receiving application
 Works only for processes running on same computer

IPC using DDE
 DDE is a message-based protocol
 Uses shared memory to exchange data
 Share data between applications running on the same
computer or on different computers on a network
 Nine DDE message are defined. All DDE transactions are
conducted by passing these messages b/w client and
server
 An application calls SendMessage to issue the
WM_DDE_INITIATE message or a WM_DDE_ACK
message sent in response to WM_DDE_INITIATE

IPC using DDE (cont.)
 All other messages are sent by PostMessage
LRESULT WINAPI SendMessage( _In_ HWND hWnd,
_In_ UINT Msg,
_In_ WPARAM wParam,
_In_ LPARAM lParam);
 First parameter of these calls is a handle to the receiving
window
 Second parameter contains the message to be sent
 Third parameter identifies the sending window
 Fourth parameter contains the message-specific
arguments

IPC using File Mapping
 Allows one-way and bi-directional communication between
applications
 Windows API functions used: CreateFileMapping(),
MapViewOfFile(), UnMapViewOfFile(), CloseHandle()
 A synchronization object (e.g., semaphore) is required to
prevent data corruption in multi-tasking environment
 Uses shared memory for data sharing

IPC using File Mapping (cont.)
 Server process does the following:
– Create file mapping by invoking CreateFileMapping function
– Map the view of the file mapping into the address space of the current process
(MapViewOfFile)
– Use CopyMemory function to write message to the file view
– Unmap the file view and close the file mapping objects (UnmapViewOfFile,
CloseHandle)

IPC using File Mapping (cont.)
 Client process does the following:
– Open a named file mapping using OpenFileMapping
– Map the view of the file mapping into the address space of the current process
using MapViewOfFile
– Read message from the view of the shared memory
– Unmap the file view and close the file mapping objects (UnmapViewOfFile,
CloseHandle)

IPC using Mailslots
 Provides one-way communication
 Process that creates mailslot is a mailslot server
 Mailslot clients send data to mailslot server
 Mailslot IPC mechanism is a Windows only feature
 A process can be both mailslot server and mailslot client so
two-way communication is possible using multiple
mailslots
 Mailslot messages can be broadcasted

IPC using Mailslots (cont.)
 A mailslot server does the following:
- Create a mailslot using CreateMailslot() function
- Check messages in the mailslotusing ReadMailslot() function
- Check for the number of messages in the mailslotusing GetMailslotInfo() function
- Retrieve the messages one by one from the mailslot. While reading, update the number of
messages that are left in the mailslot. (ReadFile, GetMailslotInfo)
- Close the handle of the mailslot instance using CloseHandle() function

IPC using Mailslots (cont.)
 A mailslot client does the following:
- Open the mailslot using CreateFile() function
- Write messages to the mailslot. (WriteMailslot, WriteFile)
- Close the slotusing CloseHandle() function

IPC using Pipes
 Allows two-way communication
 Two types of pipes available: named and anonymous
 Named pipes are used to transfer data between unrelated
processes
 Anonymous pipe works between processes on same
computer
 To have two-way communication, two anonymous pipes
can be used

IPC using Pipes (cont.)
 Windows API functions used are:
CreateNamedPipe()
ConnectNamedPipe()
WaitNamedPipe()
DisconnectNamedPipe()
ReadFile()
WriteFile()
CloseHandle()
 A Named Pipe name needs to be in the following format:
For named pipe server – .pipePipeName
For named pipe client – ComputerNamepipePipeName

IPC using Windows sockets
 Socket is a communication endpoint
 Applications can send or receive packets of data across a
network
 Two types of sockets available
Stream Sockets – stream of bytes. No record boundaries
Datagram Sockets - record-oriented data flow that is not guaranteed to be delivered
Packets may not be sequenced and duplication can occur

IPC using Sockets (cont.)
 Sockets are highly useful in at least three communications
contexts:
– Client/Server models
– Peer-to-peer scenarios, such as chat applications
– Making remote procedure calls (RPC) by having the
receiving application interpret a message as a function call

IPC mechanisms in windows

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IPC mechanisms in windows