I’ve heard it mentioned in very general terms that such things exist, but the details are rarely discussed. What are your favourites? What makes it difficult?
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I’ve heard it mentioned in very general terms that such things exist, but the details are rarely discussed. What are your favourites? What makes it difficult?
The standard implementation of many lock-free structures like a concurrent hash table often are nearly impossible to write without a garbage collector. These structures work by storing long linked lists of elements, then changing the heads of the lists whenever a new value is added or removed. That way, one thread can make a change to the structure so that new threads see the change (they traverse a new linked list) while older threads continue reading older linked lists. It’s crucial that the memory be reclaimed by a garbage collector, since otherwise the thread that changed the linked list would have to somehow clean up the list it just replaced, but that list is in use by other threads, this either leads to data races or requires the use of locks, both of which are bad.
A similar argument can be made for multithreaded lock free binary search trees, which use a related trick.