Synchronization

1. Synchronization and Mutual Exclusion

1.1. Synchronization

Multiple processes execute in a certain order.

1.2. Mutual Exclusion

Among multiple processes, only one process can enter the critical section at the same time.

1.2.1. Critical Section

Code that accesses the same resource is called a critical section.

2. Synchronization Methods

2.1. Semaphore

An integer variable on which down and up operations can be performed.

• down: if the semaphore is greater than 0, perform a -1 operation; if the semaphore equals 0, the process sleeps and waits for the semaphore to become greater than 0.
• up: perform a +1 operation on the semaphore and wake a sleeping process so that it can complete the down operation.

2.1.1. Mutex

If the semaphore can only take the value 0 or 1, it becomes a mutex. 0 means the critical section is locked, and 1 means the critical section is unlocked.

2.2. Monitor

Semaphores require handling many details, so monitors were introduced. A monitor introduces Condition operations: wait() and signal.

3. Classic Synchronization Problems

3.1. Producer/Consumer Problem

• Semaphore
  • Mutex
• Monitor

3.2. Readers/Writers Problem

3.3. Dining Philosophers Problem

4. References

• Master Operating System Interviews with This Article (1) - Juejin