On 16/09/2010 9:53 PM, Steven Schveighoffer wrote:
On Thu, 16 Sep 2010 06:41:14 -0400, Rounin
<[email protected]> wrote:
Thank you for that advice. I'm using GDC because it's available from
Ubuntu
Linux's package system, whereas DMD currently is not. (And the .deb
posted on
digitalmars.com is only for i386.) Hopefully, D will gain more
popularity and more
up-to-date tools will be made available.
I've heard that dmd is a bit tricky to set up on a 64-bit system (mine
is 32-bit), but it will give more credence to your position to use the
latest available tools.
By the way, today I re-compiled the program with a "std.gc.enable;"
right before
the final "return 0" statement, and it still runs in 0.68 seconds. So
either those
objects aren't marked as needing garbage collection, or it's really
just an issue
of keeping the garbage collector from activating too quickly.
The GC runs are not scheduled. Essentially, you are probably
encountering a syndrome where the GC runs more than it should. This
usually occurs when incrementally allocating large amounts of memory
without dropping any of it.
The GC colleciton runs when allocating memory cannot find any free
memory. Most likely this is what's happening:
allocate -> No free memory available -> run GC collection, get nothing
back -> allocate more memory from OS -> allocate...
Of course, the allocations will succeed for a bit after getting OS
memory, but the GC collection is run way too often (as your profiling
suggests).
Disabling it at the beginning, then enabling it at the end means it's
going to run at most once. Essentially, you take out the "run GC
collection" step, everything else is the same. Given that 87% of the run
time is spent in the collection cycle, it's pretty obvious why this
reduced your runtime ;)
-Steve
The redux of this discussion is surely that no matter how "good" the
semantics of a PL are, the proof of the pudding is in the GC. Given
the more-or-less well-founded value vs reference semantics in D, it
might be useful to condider region-based memory management idioms and
integrate these idioms into the language. Perhaps we might see this
in D99 as a measure to circumvent traditional GC issues.
