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

Extending Exception to contain method name
I was wondering, if there's a way to extend Exception in such a way, that it would contain name of a

Problem with "dynamic" index page
Hi. I have one question. In my index.php page I have this kind of code:
Code: // listaa sivut

BAPI BBP_INB_DELIVERY_CREATE - material number missing in delivery
Hi Experts,

I was able to successfully create an Inbound delivery with reference to a PO

Adding Different Numbers From MySQL
Basically I have a mysql database with a couple prices as the following:

9.99
9.99
9.99

Combining Two Queries
I have two scripts that each work fine by themselves. One is a search script with a variable that de

fopen() security
As i understood the usage of fopen() for it to function correctly the Dir you write to has to be rw

Stumped by Third Day of Month problem
I am trying to build an algorithm that will essentially do this:
Code: [Select]$this_month = Oct

my login script page is not working on remote computers
hi my login is working on my computer, but when i tried 2 computers from 2 different locations, they

Not connecting to DB using ruby, error:env.c:257:in oci8lib.so: ORA-12154:
Hi All,

I am trying to connect to the database server from the client server using ruby and f

how to get values from $_Post with onchange="form.submit();"?
Hi, I have a form that submit to itself with a file upload field and two other hidden field values.<

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