Comment by usrnm
7 hours ago
Atomic operations, especially RMW operations are very expensive, though. Not as expensive as a syscall, of course, but still a lot more expensive than non-atomic ones. Exactly because they break things like caches
7 hours ago
Atomic operations, especially RMW operations are very expensive, though. Not as expensive as a syscall, of course, but still a lot more expensive than non-atomic ones. Exactly because they break things like caches
Not only that, they write back to main memory. There's limited bandwidth between the CPU and main memory and with multithreading you are looking at pretty significantly increasing the amount of data transferred between the CPU and memory.
This is such a problem that the JVM gives threads their own allocation pools to write to before flushing back to the main heap. All to reduce the number of atomic writes to the pointer tracking memory in the heap.