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1. BACKGROUND

   • Processes can execute concurrently
   • Concurrent access to shared data may result in data inconsistency
   • Maintaining data consistency requires mechanisms to ensure the orderly execution of cooperating processes

2. The Critical-Section Problem

   • Each process has critical section segment of code
   • Each process must ask permission to enter critical section in entry section, may follow critical section with exit section, then remainder section

3. Synchronization Hardware

   • Many systems provide hardware support for implementing the critical section code.
   • All solutions below based on idea of locking
     • Protecting critical regions via locks
   • Uniprocessors – could disable interrupts
     • Currently running code would execute without preemption
     • Generally too inefficient on multiprocessor systems

4. Semaphores

   • Synchronization tool that provides more sophisticated ways (than Mutex locks) for process to synchronize their activities.
   • Semaphore S – integer variable

5. Classic Problems of Synchronization

   • Bounded-Buffer Problem
   • Readers and Writers Problem
   • Dining-Philosophers Problem

6. Monitors

   • A high-level abstraction that provides a convenient and effective mechanism for process synchronization
   • Abstract data type, internal variables only accessible by code within the procedure
   • Only one process may be active within the monitor at a time
   • Only one process may be active within the monitor at a time