Mutual%20Exclusion

1
Mutual Exclusion

• A History

2
Agenda

• Model
• Registers
• History

3
Model

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

4
Registers

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

5
Waiting Requirements

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

6
Fault Tolerance Requirements

• Shutdown safe
• Abortion safe
• Unannounced death
• Malfunctioning (Byzantine behavior)
• Fail safe
• Self Stabilizing

7
Upper Bounds

• 1 bit
• 3 bit
• N bit
• N! bit

8
Fast Path Algorithms

• Lamports Fast Mutual Exclusion
• 7 memory accesses with no contention
• Splitter method
• Take quick route if possible

9
Local Spin Algorithms

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

10
Adaptive Algorithms

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