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# Latch implementations

\#1 Blocking OS Mutex

* Simple to use
* Non-scalable (about 25ns per lick/unlock invocation)
* Example std::mutex

\#2 Test-and-Set Spin Latch (TAS)

* Very efficient (single instruction to latch/unlatch)
* Non-scalable, not cache friendly
* Example: std::atomic\<T>

\#3 Reader-Writer Latch

* Allows for concurrent readers
* Must manage read/write queues to avoid starvation
* Can be implemented on top of spinlocks