Mutual Exclusion A History

Agenda Model Registers History

Model Shared Memory Registers Try, Critical, Exit, Non-Critical

Registers Assuming atomic registers is not satisfactory. Register Heirarchy Safe Regular Atomic

Waiting Requirements Mutual Exclusion DeadLock Freedom Lockout Freedom First-Come-First-Serve R-bounded Waiting

Fault Tolerance Requirements Shutdown safe Abortion safe Unannounced death Malfunctioning (Byzantine behavior) Fail safe Self Stabilizing

Upper Bounds 1 bit 3 bit N bit N! bit

Fast Path Algorithms Lamport’s Fast Mutual Exclusion 7 memory accesses with no contention “Splitter” method Take quick route if possible

Local Spin Algorithms Busy waiting looking at local variables only Remote variables more costly Time complexity based on remote accesses

Adaptive Algorithms Time complexity is a function of # of contenders Pinnacle of our project Local Spinning Adaptive Algorithms