On Wednesday, 10 April 2013 at 06:14:24 UTC, Rainer Schuetze
wrote:
I'm not sure if these have been proposed already in this long
thread, but 2 very small patches could help a lot for realtime
applications:
1. a thread local flag to disallow and detect GC allocations
2. a flag per thread to specify that the thread should not be
paused by the GC during collections.
The latter would then put the responsibility on the programmer
to ensure that no references are mutated in the non-pausing
thread that don't exist anywhere else (to avoid the collection
of objects used in the realtime thread). As anything in a
realtime thread usually has to be pre-allocated anyway, that
doesn't put a lot more constraints on it but to ensure having
references to the pre-allocated data in other threads or global
state.
One concept is abused quite nicely in Erlang VM/GC - there is one
gc instance per process(fiber) and it gets own pre-allocated
memory pool for all its needs. That memory is prohibited to
escape to other processes. When process lifespan is short enough
(and it is Erlang Way, spawning hell lot of small processes),
true garbage collection is never called, whole memory block is
just sent back to pool on process termination.
I have tested it few times and such approach allowed to meet some
soft real-time requirements. Don't know if something like that
can be abused in D with its fibers and scope storage class.
