CPP std::thread attempt to use a deleted function

Question

First of all, I want to say that i already made researches on the subject, but nothing relevant...

(Error creating std::thread on Mac OS X with clang: "attempt to use a deleted function")

(Xcode 7: C++ threads ERROR: Attempting to use a deleted function)

(xcode - "attempt to use a deleted function" - what does that mean?)

And here's my issue...:

clang error:

/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/thread:347:5: error: attempt to use a deleted function
__invoke(_VSTD::move(_VSTD::get<0>(__t)), _VSTD::move(_VSTD::get<_Indices>(__t))...);

And that's my code:

bool GenAI::loadAIs()
{
    bool ret = true;

    if (_nbThread > 1)
    {
        std::vector<std::thread> threads;

        for (unsigned int i = 0; i < _nbThread; ++i)
            threads.push_back(std::thread(static_cast<void (GenAI::*)(bool &, unsigned int)>(&GenAI::loadAIs), this, ret, i));
        for (unsigned int i = 0; i < _nbThread; ++i)
            threads[i].join();
    }
    else
        loadAIs(ret, 0);
    return ret;
}

// And the prototype of the function that i try to call
void GenAI::loadAIs(bool & ret, unsigned int iThread);

If some one could help me that'd be really helpful ! :)

Regards ;)

It should be something like std::ref(ret), and you should have one bool by thread or use std::atomic<bool>... — Jarod42
– Jarod42, Commented May 9, 2017 at 9:43
Thanks you very much, it was the std::ref(ret) that didnt compile... If you write it as an answer i'll be able to close this ticket :) — Rodolphe Chartier
– Rodolphe Chartier, Commented May 9, 2017 at 11:21

Jarod42 · Accepted Answer · 2017-05-09 11:35:22Z

3

To pass reference to thread, you have to use std::reference_wrapper, that you can obtain with std::ref. So your code becomes:

threads.emplace_back(static_cast<void (GenAI::*)(bool &, unsigned int)>(&GenAI::loadAIs),
                     this,
                     std::ref(ret),
                     i));

Note: bool ret should probably be std::atomic<bool> ret, or should should have one bool by thread. Else you may have concurrent access on ret.

answered May 9, 2017 at 11:35

Jarod42

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2 Comments

Rodolphe Chartier Over a year ago

Thank you a lot ! :) But it still works with vector::push_back();

Jarod42 Over a year ago

I used emplace_back as it makes shorter line (and avoid one (elided?) move).

didiz · Accepted Answer · 2017-05-09 10:36:28Z

0

The deleted function that it is complaining about is a deleted copy constructor for const thread.

For the deleted function problem, you can use:

threads.emplace_back(

Instead of:

threads.push_back(

What the commenter also referred to is that the function is creating more than one thread and passing to them a reference to the same boolean return variable.

It will crash if you don't use atomic_bool and even if you do, they will all report back to the same memory location, making the function miss the notification if one of them returns false.

edited May 9, 2017 at 10:36

answered May 9, 2017 at 9:20

didiz

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7 Comments

Rodolphe Chartier Over a year ago

that's why i write this as first argument. And i sent the function address to std::thread. And I know it can works with non-static function member

Rodolphe Chartier Over a year ago

I have an other part of my code that I compiled some weeks ago and I did call non-static member function with std::thread... I really dont know why it doesnt work... plus it is in the same file...

Rodolphe Chartier Over a year ago

I tried to rename the overload with an underscore ahead its name, but nothing changed... I start to think to reboot lol

Rodolphe Chartier Over a year ago

I'm only working within one class. Theres no other class. But still strange... I'll reboot (can try it ^^)

Jarod42 Over a year ago

push_back should handle rvalue too. With emplace, you may remove std::thread constructor call.

|

Vladimir Mikov · Accepted Answer · 2024-01-07 07:59:48Z

-1

I would get back to reading. Just use another language - Python!

Or use emplace_back

Vladimir Mikov 4044087744

answered Jan 7, 2024 at 7:59

Vladimir Mikov

1

1 Comment

Community Over a year ago

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