2025/4/22 生产者&消费者并发模型

Producer 和 Consumer 共享一个缓冲区

• Producer (生产数据)：如果缓冲区有空位，放入；否则等待
• Consumer (消费数据)：如果缓冲区有数据，取走；否则等待

example(from jyy)

void T_produce() {

while (1) {

retry:

mutex_lock(&lk);

int ready = (depth < n);

mutex_unlock(&lk);

if (!ready)

goto retry;

  

// assert(depth < n);

  

mutex_lock(&lk);

printf("(");

depth++;

mutex_unlock(&lk);

}

}

  

void T_consume() {

while (1) {

retry:

mutex_lock(&lk);

int ready = (depth > 0);

mutex_unlock(&lk);

if (!ready)

goto retry;

  

// assert(depth > 0);

  

mutex_lock(&lk);

printf(")");

depth--;

mutex_unlock(&lk);

}

}

使用条件变量

void T_produce() {

while (1) {

mutex_lock(&lk);

  

if (!CAN_PRODUCE) {

cond_wait(&cv, &lk);

// This is subtle. Seemingly "more efficient"

// implementation is dangerous for newbies.

// Also not correct changing "if" to "while".

}

  

printf("(");

depth++;

  

cond_signal(&cv);

mutex_unlock(&lk);

}

}

  

void T_consume() {

while (1) {

mutex_lock(&lk);

  

if (!CAN_CONSUME) {

cond_wait(&cv, &lk);

}

  

printf(")");

depth--;

  

cond_signal(&cv);

mutex_unlock(&lk);

}

}

广播

void T_produce() {

while (1) {

mutex_lock(&lk);

  

while (!CAN_PRODUCE) {

cond_wait(&cv, &lk);

// We are here if the thread is being waked up, with

// the mutex being acquired. Then we check once again,

// and move out of the loop if CAN_PRODUCE holds.

}

  

// We still hold the mutex--and we check again.

assert(CAN_PRODUCE);

  

printf("(");

depth++;

  

cond_broadcast(&cv);

mutex_unlock(&lk);

}

}

  

void T_consume() {

while (1) {

mutex_lock(&lk);

  

while (!CAN_CONSUME) {

cond_wait(&cv, &lk);

}

  

printf(")");

depth--;

  

cond_broadcast(&cv);

mutex_unlock(&lk);

}

}