3. Synchronization Primitives: Mutexes, Semaphores, and Condition Variables

Learning Objectives Define and explain the purpose of race conditions and critical sections in concurrent programming. Differentiate between a mutex, a semaphore, and a condition variable, identifying the ideal use case for each. Analyze a concurrent programming problem and select the appropriate synchronization primitive to prevent data corruption. Implement the standard lock/unlock pattern for a mutex to protect a critical section in pseudocode. Trace the execution of threads in a producer-consumer scenario using semaphores and a mutex. Explain how a condition variable prevents inefficient busy-waiting. Identify the causes of common synchronization issues like deadlock and starvation. Imagine two people trying to edit the same sentence in a shared document at the exact s...

TermDefinitionExample Race ConditionA situation where the outcome of a program depends on the unpredictable sequence or timing of operations from multiple threads accessing a shared resource.Two threads try to increment a shared counter (initially 0) at the same time. Both read the value 0, both calculate 0+1=1, and both write 1 back. The final value is 1, when it should be 2. Critical SectionA segment of code that accesses a shared resource (like a variable or data structure) and must not be executed by more than one thread at a time to avoid race conditions.In the shared counter example, the lines of code that read the counter's value, increment it, and write it back form the critical section. Mutex (Mutual Exclusion)A locking mechanism that ensures only one thread can enter a crit...

Mutex Lock/Unlock Pattern mutex.lock() // Critical Section: Access shared data here mutex.unlock() This is the fundamental pattern for protecting a critical section. Always acquire the lock before touching shared data and, crucially, always release the lock afterward, even if an error occurs. Semaphore Wait/Signal Pattern semaphore.wait() // Decrements counter, may block if 0 // Access the limited resource semaphore.signal() // Increments counter, may unblock a waiting thread Used to control access to a pool of N resources. 'wait' (also called P or down) requests a resource, and 'signal' (also called V or up) releases it for others to use. Condition Variable Wait/Signal Pattern mutex.lock() while (condition_is_false) { condition_variable.wait(mut...