[datenwolf]

Comment on my mentioning on move semantics, because I feel that this really ought to be pointed out:

In all the C++ standard library implementations of std::thread the only member variable of that class is the native handle to the system thread itself; there are no additional member variables! This means that the size of a std::thread object is equal to the size of a native handle, usually the size of a pointer, but sometimes smaller.

If you create std::thread by `new` you're essentially creating a pointer to a "possibly a pointer", which comes with all the inefficiencies associated with it: Double indirection, small size allocations tend to fragment memory. And at the end of the day to actually use it, you have to at least lob around that outside pointer around on the stack anyway.

So there is zero benefit at all of using dynamic allocation for std::thread. Don't do it! Just create the std::thread instances on the stack, they're just handled/pointers with "smarts" around them, and you can copy them around just efficiently as you can copy a pointer or an integer. Better yet, if you're not trying to "outsmart" the compiler you'll often get copy elision where applicable.

[gmueckl]

sts::thread has its copy constructor deleted. This means that creating it on the heap is often your only option if you have to mix it with other types that don't handle noving properly because move semantics are strictly opt in.

[datenwolf]

> std::thread has its copy constructor deleted

and for good reason

> your only option if you have to mix it with other types that don't handle moving properly

It's not the only option. The other option is to implement move semantics on the containing type. Properly implemented move semantics gives you assurance about ownership and that you don't use the tread interface inappropriately.

[gmueckl]

Deleting the copy constructor is a very arbitrary design devision without any good reason.

Move semantics are a can of worms in themselves. You assume in your comment that you can modify the other types that interact with the types that are only movable. This is only possible if you own all relevant types, which is actually the exception rather than the norm. And even if you own the relevant related types, move semantics transitively enforce themselves onto containing types which turns their introduction into sprawling mess of cascading changes with hidden surprises.

[datenwolf]

Here's something to ponder on: What are the proper semantics for copying a thread? What is it you want to express by doing that?

You'll find that usually the copy constructor has been deleted only for those classes where the semantics of a copy are not well defined.

So let's assume you work around that by encapsulating that thread in a std::shared_ptr or a std::weak_ptr. What are the constraints you must work within when using that thread reference?

Usually when you run into "problems" caused by an object not being "move aware" triggered by encapsulating a non-copyable type, this is a red flag that something in your codes architecture is off. Think of it as a weaker variant of the strong typing of functional languages. You probably don't want to have a shared_ptr on a thread inside your object (and the object being copyable), but wrap that object in a shared_ptr (or weak_ptr) and pass those around.

[gmueckl]

Yourncery first question is already leading you down the wrong path: std::thread is a thread handle, not the thread itself. Equating the handle with the thread (a complex construct of a separate stack, seperate processor state, separate scheduling state etc.) is folly.

There are more software architectures between heaven and earth than exist in your philosophy. C++ especially is an old language and most code was written before C++11 started to be adopted. So a pure C++11 style codebase that follows the associated design best practices may be able to deal with std::thread and similarly restricted classes with little friction. But this just isn't the norm. Most big important codebases are too far down different roads to adjust them to play nice with move semantics.

[datenwolf]

> std::thread is a thread handle, not the thread itself

While technically true, semantically there's not much of a difference. Yes, you can copy around a handle, but then you have the burden of tracking all of these copies, so that you don't end up with a dangling handle to a thread long dead… or even worse, a reused handle for an entirely new thread that happens to have gotten the same handle value.

This is why you should not think of std::thread being a handle, but the actual thread. Yes, from a system level point of view there's the handle, and all the associated jazz that comes with threads (their dedicated stacks, maybe TLS, affinity masks, etc.), all of which are non-portable and hence not exposed by std::thread, because essentially you're not supposed to see all of that stuff.

> C++ especially is an old language and most code was written before C++11 started to be adopted.

That is true. Heck, I've still got some C++ code around which I wrote almost 25 years ago. But if you use a feature that was introduced only later, then you should use it within the constraints supported by the language version that introduced it and not shoehorn workarounds "just to make it work".