Shared list between threads

[languid ravine]

Hey, I wonder how lists work between threads. For example I want to have a list like std::list<int> numbers
And then on one thread I would have a while loop

while(true)
{
  if(numbers.size() > 0)
  {
      std::cout << list[0];
      list.pop_front();
  }

and then from other threads I would like to add something to that list one in a while, in random moments.
Will that work? Or should I use something else than list?

[slender vessel]

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[tired flicker]

You would need to ensure only one thread is doing operation on the list at a time.

[karmic silo]

It's undefined behavior. You're not allowed to read or write a variable when another thread is writing it, unless the type of the variable explicitly says that it's fine (for example some std::mutex and std::atomic<T> operations).

Typically you write a wrapper that locks a mutex before accessing list to ensure that only 1 thread can access it at a time.

Though your while (true) makes a busy loop, using up a core for nothing. You should probably use a condition variable or semaphore to make the thread sleep until a number is available.

[languid ravine]

but then if i would lock that list cuz the while loop is using it, then if i would try to add something to that list from the other thread it would fail right?

[karmic silo]

Depends on how you implement it. Typically you don't fail, you just wait until whoever else is currently accessing it is done with it.

[languid ravine]

!solved