c++ - Why garbage collection when RAII is available?

Question

I hear talks of C++14 introducing a garbage collector in the C++ standard library itself. What is the rationale behind this feature? Isn't this the reason that RAII exists in C++?

• How will the presence of standard library garbage collector affect the RAII semantic?
• How does it matter to me(the programmer) or the way in which I write C++ programs?

question from:https://stackoverflow.com/questions/17261912/why-garbage-collection-when-raii-is-available

Answer 1

Garbage collection and RAII are useful in different contexts. The presence of GC should not affect your use of RAII. Since RAII is well-known, I give two examples where GC is handy.

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Garbage collection would be a great help in implementing lock-free data structures.

[...] it turns out that deterministic memory freeing is quite a fundamental problem in lock-free data structures. (from Lock-Free Data Structures By Andrei Alexandrescu)

Basically the problem is that you have to make sure you are not deallocating the memory while a thread is reading it. That's where GC becomes handy: It can look at the threads and only do the deallocation when it is safe. Please read the article for details.

Just to be clear here: it doesn't mean that the WHOLE WORLD should be garbage collected as in Java; only the relevant data should be garbage collected accurately.

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In one of his presentations, Bjarne Stroustrup also gave a good, valid example where GC becomes handy. Imagine an application written in C/C++, 10M SLOC in size. The application works reasonably well (fairly bug free) but it leaks. You neither have the resources (man hours) nor the functional knowledge to fix this. The source code is a somewhat messy legacy code. What do you do? I agree that it is perhaps the easiest and cheapest way to sweep the problem under the rug with GC.

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As it has been pointed out by sasha.sochka, the garbage collector will be optional.

My personal concern is that people would start using GC like it is used in Java and would write sloppy code and garbage collect everything. (I have the impression that shared_ptr has already become the default 'go to' even in cases where unique_ptr or, hell, stack allocation would do it.)