cstdatomic (c++0x std::atomic) / g++ 4.4


Posted on 16th Feb 2014 07:03 pm by admin

Hello,

I'm trying to use cstdatomic (std::atomic in the upcoming c++0x standard) in g++ 4.4, but it doesn't seems to work as expected and I would like to known if I missed something...

My goal in the code below is just to test differents ways of concurrency (mutex vs atomic) : 4 threads increments counters in 3 ways.

1 - with std::mutex : works perfectly but slightly slow (lock / unlock)
2 - with g++ atomics "builtins" : works perfectly
3 - with std::atomic : doesn't works.


here is the code :

#include
#include
#include

int cnt_mutex = 0;
int cnt_builtins = 0;
std::atomic cnt_stdatomic = {0};
std::mutex smutex;

/* thread code */
void thrcode(int thrid)
{
/* counter local to thread */
int cnt_local;
for (cnt_local = 0; cnt_local < 10000000; cnt_local++)
{
/* c++0x fetchadd -> FAIL */
cnt_stdatomic.fetch_add(1);

/* g++ builtin fetchadd -> OK */
__sync_fetch_and_add(&cnt_builtins,1);

/* scoped std::mutex : OK */
{
std::unique_lock lockit(smutex);
cnt_mutex++;
};
};
printf("thread(%d) : cnt_local %dn",thrid,cnt_local);
};


int main() {
/* thread init */
std::thread m1(thrcode,1),m2(thrcode,2),m3(thrcode,3),m4(thrcode,4);

/* wait all thread */
m1.join(); m2.join(); m3.join(); m4.join();

/* display counters */
printf("end : cnt_mutex %d, cnt_builtins %d, cnt_stdatomic %dn",
cnt_mutex,cnt_builtins,(int)cnt_stdatomic);

};


compile with : g++ -std=c++0x mt.cpp -O3 -pthread && date && ./a.out && date

it give :
dimanche 4 octobre 2009, 19:10:28 (UTC+0200) (french time...)
thread(1) : cnt_local 10000000
thread(3) : cnt_local 10000000
thread(4) : cnt_local 10000000
thread(2) : cnt_local 10000000
end : cnt_mutex 40000000, cnt_builtins 40000000, cnt_stdatomic 39990400
dimanche 4 octobre 2009, 19:10:46 (UTC+0200)

cnt_stdatomic counter is incorrect... Someone could tell me where i'm wrong, did i miss something in code ?

(I'm using g++ version 4.4.1 Ubuntu 4.4.1-4ubuntu6)

Thanks !

No comments posted yet

Your Answer:

Login to answer
268 Like 14 Dislike
Previous forums Next forums
Other forums

PHP submit form script causing blank page
Im trying to submit a form using this script, however nothing shows up on the page, does anyone know

need help with php get
i have a option box that gets filled with dates, but how do i get once the option value has been cli

Problem with passing variables
I'm not really a php programmer so I'm really struggling with this issue.

I have a banner s

mails going in spam??
The mails I sent to folks in my database using mail(function) are going in spam??

Any idea ho

Form always sends to error page...
Hello,
Any help will be greatly appreciated. I am having trouble getting multiple fields to be re

Greek characters in php
Hi,

I'm making a script and I m using for first time greek characters.
I started to write

Security Exception on pages using AJAX
I am getting the exception: attempted to perform an operation not allowed by the security policy on

Alternate messaging
I have 4 strings in MySQL db1

$string1 : Hello
$string2 : Hi
$string3 : Great
$strin

When file included, REMOTE_ADDR is server's?
I have an index file that handles my site, basically index.php?page=ip will activate "require('

'210010106140040100' == '210010106140040101'
Debugging this simple line of a PHP script

Code: if($a == $b){ }
I've found that with val

Sign up to write
Sign up now if you have flare of writing..
Login   |   Register
Follow Us
Indyaspeak @ Facebook Indyaspeak @ Twitter Indyaspeak @ Pinterest RSS



 
© indyaspeak.com. All Rights Reserved.
Play Free Quiz and Win Cash