alt Hacker NewsReference counting in multithreaded systems is much more expensive than it sounds because of the synchronization overhead. I don't see it coming back. I don't think it saves massive amounts of memory, either, especially given my observation with vmmap upthread that in many cases the code itself is a dominant part of the (virtual) memory usage.
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If you use an ownership/lifetime system under the hood you only pay that synchronization overhead when ownership truly changes, i.e. when a reference is added or removed that might actually impact the object's lifecycle. That's a rare case with most uses of reference counting; most of the time you're creating a "sub"-reference and its lifetime is strictly bounded by some existing owning reference.
That's why Rust has Rc<> for single-threaded structs, and Arc<> for thread-safe structs.
Incrementing or decrementing a shared counter is done with an atomic instruction, not with a locked critical section.
This has negligible overhead in most cases. For instance, if the shared counter is already in some cache memory the overhead is smaller than a normal non-atomic access to the main memory. The intrinsic overhead of an atomic instruction is typically about the same as that of a simple memory access to data that is stored in the L3 cache memory, e.g. of the order of 10 nanoseconds at most.
Moreover, many memory allocators use separate per-core memory heaps, so they avoid any accesses to shared memory that need atomic instructions or locking, except in the rare occasions when they interact with the operating system.