Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!news.mixmin.net!news.albasani.net!.POSTED!not-for-mail
From: Melzzzzz <mel@zzzzz.com>
Newsgroups: comp.lang.c++,comp.programming.threads
Subject: Re: Why is java consumer/producer so much faster than C++
Date: Mon, 23 Jul 2012 01:28:01 +0200
Organization: albasani.net
Lines: 67
Message-ID: <jui2a3$a3a$2@news.albasani.net>
References: <juht3o$a3a$1@news.albasani.net> <ba6e5833-f9a2-428e-815b-aad0ebdf3c55@s6g2000pbi.googlegroups.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
X-Trace: news.albasani.net ag1OGn3xnRX1La+NJDwmda5jlHrFgWfVvWuH792l4Juhi8u6H0ogv0sI2IC4QdEBC5+V1YJ71n8QQohV7rTsmZVG7hzsPbpFYhjY1UyeKPOu2qzefoW4LgFDckH70CNZ
NNTP-Posting-Date: Sun, 22 Jul 2012 23:28:03 +0000 (UTC)
Injection-Info: news.albasani.net; logging-data="YcijAujngn4EbKC/x3XktWnT/vloiNhOBKSWxoIWkdqG6qrezMDGz/tlgmgXXPEImmGcmEtN2P+A6JVFP8XsvG9dVTPHQoca3FMAm2KdKeupX24HzjmeF55xUGRlkb32"; mail-complaints-to="abuse@albasani.net"
X-Newsreader: Claws Mail 3.8.0 (GTK+ 2.24.10; x86_64-pc-linux-gnu)
Cancel-Lock: sha1:fxd7J/ZcDR1t3CHm/WfSteWgau0=
Xref: csiph.com comp.lang.c++:17186 comp.programming.threads:962

On Sun, 22 Jul 2012 15:42:55 -0700 (PDT)
Joshua Maurice <joshuamaurice@gmail.com> wrote:

>=20
>=20
> What g++ optimization options did you use? If you didn't compile with
> proper optimization flags (e.g. at least -O2), then the numbers you
> have are meaningless.

I have used -O2.

>=20
> Also, you might be testing the difference between std::rand() and
> Java's Random.

Possibly.

>=20
> Also, why did you use dynamic allocation in the C++ code for an int?

Actually with non dynamical allocation seems to be slower ;)

> If your original goal was to compare the Java way to the C++ way, you
> are not doing it right. This is especially troubling after you
> apparently went through the effort to make the queue support move-only
> types. (Not sure. I'm still new to move-semantics.)

That was necessary in order to put unique_ptr in queue.

>=20
> Also,
> >         std::unique_ptr<int> arr[size];
> ...
> >             arr[std::rand()%size] =3D produced.take();
> I wonder if it's possible to optimize that into a simple assignment,
> or whether there will be a call to delete() - or at least a branch to
> test if the internal member pointer is null.

I have removed that statement , removed called to rand, left=20
only take, made int's non dynamic
and I got following time:

bmaxa@maxa:~/examples$ g++ -Wall -O2 -pthread -std=3Dc++0x consprod1.cpp -o=
 consprod1
consprod1.cpp: In lambda function:
consprod1.cpp:58:19: warning: unused variable =E2=80=98size=E2=80=99 [-Wunu=
sed-variable]
bmaxa@maxa:~/examples$ time ./consprod1

real	0m23.335s
user	0m22.177s
sys	0m16.417s

with java, I have removed rand too...
bmaxa@maxa:~/examples$ javac consprod.java
bmaxa@maxa:~/examples$ time java consprod

real	0m12.491s
user	0m21.001s
sys	0m0.524s

Still twice as fast as c++.
What it looks like, is that c++ spends much more time in syscalls
(futex) than java and that explains big difference.