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

FROM_UNIXTIME($phpdate);
Hello,

I tried to use this :

$date = FROM_UNIXTIME($phpdate);

ANd I was t

Why Are These Functions Causing MASSIVE Memory Problems? Please Help!
Hi,

I have a script with some options.

I use regex to replace patterns in strings, but

blank page.... nothing is happening.
I'm new to a lot of this but in the last 24hrs have learned a lot.
Installed latest version of my

Help Import Animoto and Youtube
CAn someone help me urgently want to allow users on my website to import youtube/revver/dailymotion

Best way to check for end of a record and send it back to the first record
I'm hoping someone can help me out and explain the best way to accomplish this.

What I'm doin

help with contest script
I would like to code a contest script to my site but i don't know how. Could someone just give me pu

Please Help my PHP Dating Function.
Hi everyone!

Well here is my code that displays this:

It works wonderful.


Is it a good practice to store user info. in sessions?
I am making a user class for my script which stores all the user information in sessions. It takes u

php problem?
I don't think I'm stupid, but maybe I am.

I am working on a sit for a friend I am try to put

Please help understand this code
I noticed the index page on my site was modified this morning and found this code inserted at the bo

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