Inter-process communication

For other uses, see IPC.

An example showing a grid computing system connecting many personal computers over the Internet using inter-process network communication

In computer science, inter-process communication (IPC) refers specifically to the mechanisms an operating system provides to allow processes it manages to share data. Typically, applications can use IPC categorized as clients and servers, where the client requests data and the server responds to client requests. Many applications are both clients and servers, as commonly seen in distributed computing. Methods for achieving IPC are divided into categories which vary based on software requirements, such as performance and modularity requirements, and system circumstances, such as network bandwidth and latency.

Approaches

Method	Short Description	Provided by (operating systems or other environments)
File	A record stored on disk, or a record synthesized on demand by a file server, which can be accessed by multiple processes.	Most operating systems
Signal; also Asynchronous System Trap	A system message sent from one process to another, not usually used to transfer data but instead used to remotely command the partnered process.	Most operating systems
Socket	A data stream sent over a network interface, either to a different process on the same computer or to another computer on the network. Typically byte-oriented, sockets rarely preserve message boundaries. Data written through a socket requires formatting to preserve message boundaries.	Most operating systems
Message queue	A data stream similar to a socket, but which usually preserves message boundaries. Typically implemented by the operating system, they allow multiple processes to read and write to the message queue without being directly connected to each other.	Most operating systems
Pipe	A two-way data stream between two processes interfaced through standard input and output and read in one character at a time.	All POSIX systems, Windows
Named pipe	A pipe implemented through a file on the file system instead of standard input and output. Multiple processes can read and write to the file as a buffer for IPC data.	All POSIX systems, Windows, AmigaOS 2.0+
Semaphore	A simple structure that synchronizes multiple processes acting on shared resources.	All POSIX systems, Windows, AmigaOS
Shared memory	Multiple processes are given access to the same block of memory which creates a shared buffer for the processes to communicate with each other.	All POSIX systems, Windows
Message passing	Allows multiple programs to communicate using message queues and/or non-OS managed channels, commonly used in concurrency models.	Used in MPI paradigm, Java RMI, CORBA, DDS, MSMQ, MailSlots, QNX, others
Memory-mapped file	A file mapped to RAM and can be modified by changing memory addresses directly instead of outputting to a stream. This shares the same benefits as a standard file.	All POSIX systems, Windows

Implementations

There are several mechanisms which may be used for IPC, including the following:

• Anonymous pipes and named pipes
• Unix domain sockets
• TIPC

The following are platform or programming language-specific APIs:

• Apple Computer's Apple events (previously known as Interapplication Communications (IAC)).
• Enea's LINX for Linux (open source) and various DSP and general purpose processors under OSE
• The Mach kernel's Mach Ports
• Microsoft's ActiveX, Component Object Model (COM), Microsoft Transaction Server (COM+), Distributed Component Object Model (DCOM), Dynamic Data Exchange (DDE), Object Linking and Embedding (OLE), anonymous pipes, named pipes, Local Procedure Call, MailSlots, Message loop, MSRPC, .NET Remoting, and Windows Communication Foundation (WCF)
• Novell's SPX
• POSIX mmap, message queues, semaphores, and shared memory
• RISC OS's messages
• Solaris Doors
• System V's message queues, semaphores, and shared memory
• OpenBinder Open binder
• QNX's PPS (Persistent Publish/Subscribe) service

Uses

The following are platform or programming language specific-APIs that use IPC, but do not themselves implement it:

• Java's Remote Method Invocation (RMI)
• KDE's Desktop Communications Protocol (DCOP) – deprecated by D-Bus
• Libt2n for C++ under Linux only, handles complex objects and exceptions
• PHP's sessions
• Distributed Ruby

The following are messaging and information systems that utilize IPC mechanisms, but don't implement IPC themselves:

• 9P (Plan 9 Filesystem Protocol)
• Common Object Request Broker Architecture (CORBA)
• D-Bus
• Distributed Computing Environment (DCE)
• Message Bus (Mbus) (specified in RFC 3259)
• MCAPI Multicore Communications API
• ONC RPC
• XML XML-RPC or SOAP
• JSON JSON-RPC
• SIMPL The Synchronous Interprocess Messaging Project for Linux (SIMPL)
• Thrift
• ZeroC's Internet Communications Engine (ICE)
• ØMQ

See also

• Computer network programming
• Communicating Sequential Processes (CSP paradigm)
• Data Distribution Service
• .NET Remoting
• Microkernel
• Nanokernel
• Protected procedure call

References

• Stevens, Richard. UNIX Network Programming, Volume 2, Second Edition: Interprocess Communications. Prentice Hall, 1999. ISBN 0-13-081081-9
• U. Ramachandran, M. Solomon, M. Vernon Hardware support for interprocess communication Proceedings of the 14th annual international symposium on Computer architecture. Pittsburgh, Pennsylvania, United States. Pages: 178 - 188. Year of Publication: 1987 ISBN 0-8186-0776-9
• Crovella, M. Bianchini, R. LeBlanc, T. Markatos, E. Wisniewski, R. Using communication-to-computation ratio in parallel program designand performance prediction 1–4 December 1992. pp. 238–245 ISBN 0-8186-3200-3

External links

• Linux ipc(5) man page describing System V IPC
• Windows IPC
• Beej's Guide to Unix IPC
• Unix Network Programming (Vol 2: Interprocess Communications) by W. Richard Stevens
• Interprocess Communication and Pipes in C

Inter-process communication at the International Paralympic Committee

• Inter-process communication at IPC.InfostradaSports.com (archived)