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Concurrent Pascal

See:

Pascal   

Language type:

P - Parallel or Multi-programming

Description:

Concurrent Pascal is a dialect of the structure Pascal language, extended to support abstract data types, multi-tasking, and monitors. It was intended for operating system programming and research.
The syntax of Concurrent Pascal was essentially the same as that of original Pascal, except for the added concurrency and ADT features, and a few features omitted. The language is strongly typed and safe: variant records and pointers as defined in original Pascal are not supported. Concurrent Pascal adds the following fundamentally new features to Pascal: process types, monitors, class types (no inheritance), init and cycle statements, and queues. Some fundamental features of Pascal were dropped: recursion, goto statements, packed arrays, pointers, and file types.
Original versions of Concurrent Pascal were implemented on various mini-computer and mainframe hardware in the 1970s. No versions seem to be available on the web.

Origin:

P. Brinch Hansen, 1974.

See Also:

CSP    Algol68    Simula    Ada    Java   

Remarks:

According to its creator, Concurrent Pascal was created to satisfy the following beliefs:
• Concurrent programms can be written exclusively in high-level language [Note: PL/I and C don't count as high-level -- too unsafe!]
• Time-dependent programming errors must be detected during compilation
• A concurrent programming language must support a programming discipline that combines data and procedures into modules.
• A programming language should be abstract and secure [safe].

The high-level and formally defined process and synchronization constructs of Concurrent Pascal had a profound influence on the programming world, especially the operating system and real-time programming. The fundamental idea of monitors that Hansen introduced with the language was adopted in some fashion by many later, major languages including Modula, Ada, and Java. and

Date:

Last updated 3/7/98

Sample code:

{ A small example monitor and process from Hansen's 1993 }
{ paper given at HOPL-II. }
type linebuffer =
   monitor
var contents	    : line;
   full		    : Boolean;
   sender, receiver : queue;
   
procedure entry receive(var text :  line);
begin
   if not full then delay(receiver);
   text := contents; full := false;
   continue(sender);
end;

procedure entry send(text :  line);
begin
   if full then delay(sender);
   contents := text; full := true;
   continue(receiver);
end;

begin full := false;
end; { linebuffer }


type printerprocess =
   process(buffer: linebuffer)
var param : ioparam;
   text	  :  line;
begin
   param.operation := output;
   cycle
     buffer.receive(text);
     repeat io(text,param,printdevice)
     until param.status = complete;
   end
end;

Descriptions in this dictionary are ©1997-99 Neal Ziring. Some examples copyright of their respective authors. Some technologies and languages are trademarked. Permission to copy descriptions is granted as long as authorship credit is preserved.

Comments on this dictionary, corrections and suggestions, are all welcome. Please use email, the address is ziring@home.com