Pro tip: if you really do know that contention is unlikely, and uncontended acquisition is super important, then it's theoretically impossible to do better than a spinlock.
Reason: locks that have the ability to put the thread to sleep on a queue must do compare-and-swap (or at least an atomic RMW) on `unlock`. But spinlocks can get away with just doing a store-release (or just a store with a compiler fence on X86) to `unlock`.
Spinlocks also have excellent throughput under most contention scenarios, though at the cost of power and being unkind to other apps on the system. If you want your spinlock to be hella fast on contention just make sure you `sched_yield` before each retry (or `SwitchToThread` on Windows, and on Darwin you can do a bit better with `thread_switch(MACH_PORT_NULL, SWITCH_OPTION_DEPRESS, 1)`).
Pro tip: if you really do know that contention is unlikely, and uncontended acquisition is super important, then it's theoretically impossible to do better than a spinlock.
Reason: locks that have the ability to put the thread to sleep on a queue must do compare-and-swap (or at least an atomic RMW) on `unlock`. But spinlocks can get away with just doing a store-release (or just a store with a compiler fence on X86) to `unlock`.
Spinlocks also have excellent throughput under most contention scenarios, though at the cost of power and being unkind to other apps on the system. If you want your spinlock to be hella fast on contention just make sure you `sched_yield` before each retry (or `SwitchToThread` on Windows, and on Darwin you can do a bit better with `thread_switch(MACH_PORT_NULL, SWITCH_OPTION_DEPRESS, 1)`).