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...

Did you know?Explore Trending and Topic pages for more stories like this.
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

Add code to enable passing of checkbox variable on login
Ok, I have a login page, but want to add a checkbox that when checked and successful login is made i

Problem with DB connection
Hello there! I'm new to this forum and I'm new to PHP coding also. I wrote something that doesn't ma

Most basic form question ever?
Hello,

I want to use this snippet to make sure the fields in a form are ok before processing

Significance of BPM
Hi Experts,
I am a novice in BPM , I just want to know how BPM as permenant department is

Get content from table into a list, without repeating.
Alright this is kinda an odd thing, so I need some help.

I have a table "quote" wit

Is there a more efficient way to code this than what I have?
I have three associative arrays.

$combinedSettings
$userSettings
$defaultSettings

Breaking results into week blocks
I have a set of dates (and times), which are returned from a mySQL query.

These usually span

Confusing Functions
So, I've been reading up on Functions and I like them! However, I need some help using variables in

HTML form problem
Ive made a form to that i want to send to my email via PHP. but when it send only the name's etc sen

Custom array sort? asc then desc
Any ideas how I could sort this array? I've been trying for a while. Maybe with usort, but I have no

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



Play Free Quiz and Win Cash