Interprocess communication

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Interprocess Communication (IPC) is the mechanism that facilitates communications and data sharing between applications. It enables one application to control another and multiple applications to share the same data without interfering with one another. IPC utilizes a set of programming interfaces, called communication protocols, which allow programmers to coordinate activities among different applications.

Applications using IPC are categorized as either Client or Server, in which the Client requests data and the Server responds to Client requests. Many applications (including ExtendSim) can be either Client or Server, depending on the circumstances.
ExtendSim provides support for IPC through the industry standard technologies shown below. This allows external applications to control and communicate with ExtendSim and vice versa, in much the same way a user would. Note that, in addition to several interfaces for interactive data exchange, ExtendSim supports multiple methods for storing and managing data, such as global and dynamic arrays, embedded objects, linked lists, and (most importantly) an internal relational database.

IPC Protocols and methods - communicating between external applications and ExtendSim




COM (Component Object Model)

A set of object-oriented programming technologies and tools for IPC.

Communicate with, exchange data with, or control another application. Embed or link data that, when chosen, automatically starts another application for data editing.

ExtendSim COM Object Model

The objects and methods that ExtendSim exports for Automation, including Execute, Poke, and Request.

Primary method for ExtendSim to be controlled and communicated with as a COM Automation Server.

DLLs (Dynamic-Link Libraries)

Libraries of routines or functions written in an external language, such as C++. These are the standard methods for linking between the ExtendSim internal programming language (ModL) and other languages and applications.

Call an external code segment from a block's code and perform operations. A block can pass data to the DLL, cause the DLL to calculate using that data, and get the results back from the DLL. For example, in ExtendSim, the Rate library blocks communicate with the LPSolve DLL.


A library developed in an external language, such as C++, to create or define Active X objects.

ExtendSim can load up and communicate with a COM DLL or be controlled by a COM DLL. For example, see how ADO is implemented in ExtendSim.


A subset of COM (previously OLE Automation). Enables applications to expose their unique features (properties, methods, and events) to scripting tools and other applications. The exposed objects are called ActiveX objects.

Access and manipulate (i.e. set properties of or call methods on) shared automation objects that are exported by other applications.

ADO (ActiveX Data Objects)

An Automation protocol for exchanging information with ADO-compliant databases.

Send an entire table of information at one time; high-speed data interchange. In ExtendSim ADO is implemented as a COM DLL for communication with ADO-compliant databases such as Microsoft Access.

FTP (File Transfer Protocol)

Protocol for sending files or data to and from internet web pages.

Import from, or export to, files located on a server or on the web.

Mail Slots

Functions for inter-computer communication.

An easy way for ExtendSim to send and receive short (<400 byte) messages. Also provides the ability to broadcast messages across all computers in a network domain.

ODBC (Open Database Connectivity)

A standard programming language middleware API for accessing database management systems (DBMS).

This legacy technology has been superseded by ADO.

DDE (Dynamic Data Exchange)

A protocol that enables applications to exchange data in a variety of formats.

This legacy technology has been superseded by Automation.

Communicating between external applications and ExtendSim

The IPC technologies listed above have been developed as industry standards to allow applications to share and access data independent of programming language, operating system, and file type. You can incorporate IPC into ExtendSim models by:

  1. Using ExtendSim menu commands and blocks for import/export

  2. Embedding objects (Windows only)

  3. Using the ExtendSim I/O functions – ExtendSim as IPC Client

  4. Using an external language to access ExtendSim Automation protocols - ExtendSim as IPC Server

ExtendSim can act as a Client, connecting to and requesting data and services from a Server application. It can also act as a Server application that is controlled by any Windows application that can be configured as an Automation controller.

The table below shows how ExtendSim can communicate with other applications and with ExtendSim models running on other computers, even while the simulation is running. This allows ExtendSim to work on a wide variety of tasks jointly with external applications such as spreadsheets, external databases, word processors, statistics packages, and so forth.

ExtendSim uses and supports IPC technologies through:

Text File


ADO-Compliant Databases

Other Communication & Control


Read or Write blocks



Value and Item libraries. UG 755.

Data Import Export block




FTP site

Value library – UG 763; Import and Export commands – UG 766.

Command block


Excel Macro, DDE command

Value library. Select a command to send and choose when it is sent.

Internal Database



Integrated in ExtendSim. UG 728-742.

ExtendSim DB Add-In


External databases

Allows Excel to create, edit, and export an ExtendSim DB file. UG 742-747.

OLE Automation - ExtendSim as Server

External languages control ExtendSim

DR 111-118. See examples in folder ExtendSim9\Examples\Developer Tips\OLE Automation.

IPC functions


Other applications

DR 239-241; UG 765-771.

OLE/COM functions

Other applications, COM DLLs

DR 241-249; UG 767-769. Example in ModL library>OLE category.

DLL functions



Other applications

DR 254-256. Example in the folder ExtendSim9\Examples\Developer Tips\DLLs.

ADO (user-defined functions)


DR 380-383 & UG 769 for ADO; DR 79 for Include Files.

Mailslot functions

Other computers

DR 249

Internet Access

Web, internet

DR 236.

Serial I/O functions


DR 253-254.

ODBC functions


DR 250-253. Example in ModL Tips library > Input/Output category.

All references are to the ExtendSim 9 User Guide (UG) or Developer Reference (DR), released February 13, 2015.
Communicating with external devices and equipment

There are two methods you can use to communicate with external devices such as scientific equipment and other hardware:

  1. Dynamic Link Libraries (DLLs) on Windows or Shared Libraries for Mac OS. DLLs and Shared Libraries are segments of code written in a language other than the ExtendSim ModL language, such as Visual Basic or C++. A standardized interface provides a method for linking between other languages and ModL. DLLs can also be used to perform complex calculations utilizing specialized hardware.

  2. Serial port functions on Windows. To pass data through serial devices, use the serial port functions. (Note that this is a legacy technology.)

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