Condition Variable (条件变量)

Abstract

---

• Coordinate & synchronise Thread
• It allows a thread to wait for a particular condition to be met before it can continue execution
• Typically used in conjunction with Mutex (互斥体) to protect shared data

Benefis

---

Handles Producer Consumer Problem

• The condition variables are used to ensure that the Producer does not produce more data than the Consumer can consume, and that the consumer does not try to consume data from an empty Buffer

C Example

---

Wait for a particular condition

• condFuel is the condition variable
• mutexFuel is the Mutex (互斥体) to protect shared data
• pthread_cond_wait(&condFuel, &mutexFuel); equivalent to:

// 1. pthread_mutex_unlock(&mutexFuel); 
// 2. wait for signal on condFuel 
// 3. pthread_mutex_lock(&mutexFuel);`

Particular Condition fulfilled & execution is passed back

• pthread_cond_signal(&condFuel);
• The waiting thread mutex lock & continue with the execution