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

start new row of pictures
on my site www.budstreasureauctions.com there is a featured auctions box that users will pay to get

ECC6 - Single sign-on
We are in the process of upgrading to ECC 6 which will support single sign on with user passwords al

BIG file upload!
Hey guys!

I'm trying to upload a file, it works well with smaller files but with 60mb+, I get

Inserting into MySQL Newbie
Hi ive got a slight problem where ive made a simple web form where the customer inserts the ammount

Why will this program not run if the variables are not global?
Hey guys I have a kind of perplexing situation that is probably simple, but I can't seem to understa

IP Logger for Voting Script
Can anybody help me place an IP logger into my voting script?
I know that maybe it is not as secu

how to transport the Query and insfoset
Hi

I have created the query using SQ01........
How to created T-code for query..

Javascript using window.location seems to lose state
Not sure what forum so let me know if I'm in the wrong place. I have a main window with a ajax grid

data type in column definition
Hi,
I create a table with column called "Direction of Travel code ".
The travel codes in t

Getting number of affected rows in SQLPLUS..
Hi everyone,
I have a shell script where i am invoking sqlplus, running a query and saving t

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