On Monday, 15 December 2014 at 11:54:44 UTC, Daniel Murphy wrote:
"Stephan Schiffels" wrote in message
news:[email protected]...
I see several ways how to improve my code:
1.) Is there a way to tell the GC the maximum heap size
allowed before it initiates a collection cycle? Cranking that
up would cause fewer collection cycles and hence spend more
time in my multithreaded code?
Yes, sort of. You can use
http://dlang.org/phobos/core_memory.html#.GC.reserve to have
the GC grab a big chunk of memory, and collections won't run
until that is exhausted. As it is only allocating virtual
memory, it should be more or less equivalent to setting the max
heap size.
2.) Is there a way to "pause" the GC collection for the
parallel part of my program, deliberately accepting higher
memory usage?
Yes, with GC.enable and GC.diable
3.) Most of the memory is used in one huge array, perhaps I
should simply use malloc and free for that particular array to
avoid the GC from running so often.
Yes, this may work if it's a reasonable design for your
application. Other options like re-using one GC buffer per
thread might work too.
I am a bit surprised that there is no command line option for
dmd to control GC maximum heap size. Who determines how often
the GC is run? For example, in Haskell I can simply set the
maximum heap size to 10Mb in GHC using -A10m, which I used in
the past to help exactly the same problem and dramatically
reduce the frequency of GC collection cycles.
Being able to configure the GC at run-time is something that's
currently being worked on. I assume this will be possible
rather soon, probably in the next release.
Excellent, thanks everyone, problem solved. I use GC.disable and
GC.enable for now, works like a charm. I new about these
functions, but I thought they prevent GC-allocation, not just
collection.
Using ThreadLocal storage with std.parallelism is also
interesting, I won't need it now, as the memory is still within
manageable bounds, but certainly an option to reduce the memory
footprint... nice!
And yes, I saw GC.reserve just after I wrote this thread, it
seems to do what I wanted.
Stephan
