Mutex Pattern

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# Example 0059: Mutex Pattern
# Simple mutual exclusion with lock/unlock
# Demonstrates: mutex pattern, critical section, deadlock-free locking

MAX_OPERATIONS = 3

action Init:
    lock_holder = None
    counter = 0
    operations = 0

atomic action AcquireLock:
    require operations < MAX_OPERATIONS
    # Only acquire if not held
    require lock_holder == None

    lock_holder = "thread_a"

atomic action CriticalSection:
    require lock_holder == "thread_a"

    # Protected operation
    counter = counter + 1
    operations = operations + 1

atomic action ReleaseLock:
    require lock_holder == "thread_a"

    lock_holder = None

# Safety: counter only increments when lock is held
always assertion MutualExclusion:
    return lock_holder == None or lock_holder == "thread_a"

atomic action NoOp:
    if operations >= MAX_OPERATIONS:
        pass

StateSpaceOptions: options:{max_actions:100 max_concurrent_actions:2}
Nodes: 199, queued: 0
Valid Nodes: 199 Unique states: 199
IsLive: true
PASSED: Model checker completed successfully

gdoc_arrow_left_alt Distributed Systems Patterns Read-Write Lock Pattern gdoc_arrow_right_alt