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Shared Memory Synchronization

Problem: need mutual exclusion on shared data structures

int stack[];
int sptr = 0;
P: loop                
     v = produce()          
     stack[sptr] = v  | C1
     sptr++           |     
C: loop
     sptr--           | C2
     v = stack[sptr]  |
     consume(v)

• C₁ and C₂ are critical regions.
• Execution must not overlap.
• Must be executed atomically.