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From: reeder@stanley.hf.intel.com.ogc.edu
Newsgroups: comp.realtime
Subject: Re: Lightweight Tasks
Message-ID: <634@gandalf.littlei.UUCP>
Date: 31 Jul 89 20:06:42 GMT
References: <2153@gmu90x.UUCP> <70900004@m.cs.uiuc.edu>
Sender: news@littlei.UUCP
Reply-To: reeder@stanley.hf.intel.com (Ed Reeder)
Organization: Intel Corp., OMSO UNIX Development, Hillsboro, OR
Lines: 37

In article <70900004@m.cs.uiuc.edu> gillies@m.cs.uiuc.edu writes:
>
>Zalman Stern, Let me see if I can summarize your definition.
>Lightweight tasks --
>  (1) have stack & register set.
>  (2) have no address space, signal masks, uid, file descriptor tables, etc.
>  (3) are also called threads, LWPs.
>  (4) predate UNIX [Ed -- then why the new name?]
>  (5) solve different problems than UNIX tasks.
>  (6) Most LWP systems have Heavy Weight Processes too
>      [Not true in Xerox DLion/Pilot/Cedar, with VM + lightweight tasks]
>  (7) Some implementations of LWPs exist within UNIX processes.
>
>I have no qualms with (1), (2), (3).  About (4) -- I think it is
>historically correct to say that network protocols were a major
>impetus for developing lightweight tasks (in the three systems I
>worked with -- PDP11 MIT V7 TCP/IP/Telnet & C-gateway, IBM PC/IP, and
>Xerox Pilot OS, this was precisely the reason for them).  Certainly

Another "lightweight/threads" impetus was simply that it was the only
sensible implementation available.  In 1973 I was involved with the
production of a commercial multi-user DBMS on IBM mainframes running the
predominant OSs of the time (MFT, MVT, VS/1, SVS, etc.  etc).  To
efficiently control multi-user access to a single resource (the database)
you created a "monitor" (i.e., simple OS) that "multi-threaded" user's
database requests within the single address space (process) controlled by
the monitor.  The OSs of the time were batch oriented and developers had
to fabricate all of the necessary environment (such as compilers that supported
stacks) to have a decent implementation.  This was a common practice in the
database community and many of the "multi-threaded" DBMSs would now be
said to support "lightweight processes."

> ... etc. ...

Ed Reeder
Intel Corp
Hillsboro, OR