task::arena::execute is not compatible with move-only functors

[anton-potapov]

both task::arena::execute and task::arena::enqueue require it argument to be copyable. So following code simply wont compile:

task_arena{}.execute( 
       [p = std::unique_ptr<int>(new int)] () {
		*p = 1;
	}
); 

[alexey-katranov]

Hi Anton!

Thank you for the reported problem. I could not reproduce the problem with tbb::task_arena::execute (because it uses references inside the implementation); however, tbb::task_arena::enqueue has this issue. We will investigate if we are able to fix it

If using move-only objects is critical, you may want to use the following work-around:

tbb::task_arena{}.enqueue( 
+        [l = new auto(
        [p = std::unique_ptr<int>(new int)]() {
            *p = 1;
        }
+        )] { l->operator()(); delete l; }
);

Regards,
Alex

[anton-potapov]

IMHO, the work-around is not functional when cancellation appears, and in this particular case leads to memory leak, as delete l; will not be called (as it called from lambda body only, and not from lambda object destructor). Thus the only work-around i see is "move via copy" wrappers, which IMHO is ugly :)

[alexey-katranov]

Let me improve it a bit:

tbb::task_arena{}.enqueue(
+   [l = [](auto&& p) { typedef typename std::decay<decltype(p)>::type T; return std::make_shared<T>(std::forward<T>(p)); } (
    [p = std::unique_ptr<int>(new int)]() {
        *p = 1;
    }
+   )] { (*l)(); }
);

[PovelikinRostislav]

Hi Anton,

We released fix for your issue and would like you to confirm that it works as you wished.
Could you please check the status?

Thanks!