std::async from C++11 does not work

std::async from C++11 does not work

[Ilya Razenshteyn]

Hi all,

I'm trying to compile and run the below code. As a result, only one copy 
of "f" is being executed at a time, that is, no new threads are spawned. 
Does anyone know what's going on?

cygwin 2.4.1, gcc 5.3.0, compilation options are "g++ test.cpp -o test 
-O3 -Wall -std=c++11 -lpthread".


Ilya

#include <future>
#include <iostream>

using namespace std;

void f(int id) {
   for (int i = 0; i < 100000; ++i) {
     cout << id << endl;
   }
}

int main() {
   std::async(std::launch::async, &f, 1);
   std::async(std::launch::async, &f, 2);
   return 0;
}

--
Problem reports:       http://cygwin.com/problems.html
FAQ:                   http://cygwin.com/faq/
Documentation:         http://cygwin.com/docs.html
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple

Re: std::async from C++11 does not work

[Yaakov Selkowitz]

On 2016-03-15 19:00, Ilya Razenshteyn wrote:
> I'm trying to compile and run the below code. As a result, only one copy
> of "f" is being executed at a time, that is, no new threads are spawned.
> Does anyone know what's going on?

Could be your code.  I tried other code[1] using std::async, and 
multiple cores are definitely used when std::launch::async is specified.

[1] https://github.com/sol-prog/async_tutorial

-- 
Yaakov

--
Problem reports:       http://cygwin.com/problems.html
FAQ:                   http://cygwin.com/faq/
Documentation:         http://cygwin.com/docs.html
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple