HACKER Q&A
📣 fctorial

Is there a difference between malloc/free and a gc


It looks like when you're using malloc/free, you're relying on the gc provided by the operating system. How do we know that this gc is better than the ones provided by runtimes(lower level?) that does gc only when the programmer asks it to?

Although that might expose the programs to some exploits (give input that delays gc until OOM) .

  👤 greenyoda Accepted Answer ✓
When you're using malloc, it's up to you to call free() when you want to release memory that you know is no longer needed by your program. The only time the operating system will free memory without being asked is when your process exits (which, in the case of a long-running program like a web server, could be never).

In contrast, a garbage collector periodically detects that memory is no longer being used (e.g., an object that no existing object has pointers to), and automatically frees it. The programmer is not required to do anything to make this happen.

👤 jki275
If you're using malloc/free, you're in a world with no gc. You are responsible for memory management.

If you're talking about runtimes, and lower level work -- in the malloc/free world of C/C++ there isn't anything. If you allocate memory, that memory is allocated until you free it or your code exits. The OS isn't going to free your memory while your process is running, at least not that I'm aware of. You have to do it manually.

Then again, in some code it simply doesn't matter.

https://devblogs.microsoft.com/oldnewthing/20180228-00/?p=98...