[gclist] Real-Time GC for high-level languages

Robert Virding rv@bluetail.com
Wed, 31 Jan 2001 13:35:44 +0100

Francois-Rene Rideau <fare@tunes.org> writes:
>Dear GC Listers,
>   I'm looking for real-time memory management solutions so as to develop
>embedded software using high-level languages. Is there a compendium listing
>whatever language implementations, GC libraries, etc, provide real-time
>behavior, preferrably hard real-time? My employer is mostly interested
>in free software, although we're also interested in knowing what
>proprietary is available. We're also possibly interested in real-time
>Notably, the Boehm GC, the RScheme GC (one of them), the Erlang GC (which?)
>are said to be "soft real-time". What does that mean? When do they fail?
>What if paging is disabled: will that make them "hard real-time"?
>What high-level language implementation can boast about real-time latency?

I have some references to real-time garbage collection papers:

Mats Bengtsson: Real-Time Compacting Garbage Collection Algorithms
Lund University, LUTEDX/(TECS-3028)/1-118(1990) & LU-CS-TR:90-61

Roger Henriksson: Scheduling Garbage Collection in Embedded Systems
Lund University, LUTEDX/(TECS-1008)/1-164/(1998)

As someone has already pointed out "hard real-time" is when you really
worry about worst-case and soft real-time is when you worry about
average-case.  As the second paper (PhD thesis) points out that a
collector is part of a complete hard-real time system so that it is not
enough for the collector to have hard bounds, the system as a whole must
meet its bounds.

This means that the memory system must not only be able to supply enough
memory when needed, but also be able to delay collecting to when it is
suitable for the system.  Typically there will be bursts of high
priority real-time activity when no latency is allowed and sufficient
memory must exist interspersed with low-priority activity which can be 
interrupted for collection.  The collector must fit in.


Robert Virding                          Tel: +46 (0)8 545 55 017
Alteon Web Systems                      Email: rv@bluetail.com
S:t Eriksgatan 44                       WWW: http://www.bluetail.com/~rv
SE-112 34 Stockholm, SWEDEN
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