生产者消费者问题 伪代码和C语言多线程实现
生产者消费者问题是操作系统中的一个经典的问题。
他描述的是一个，多个生产者与多个消费者共享多个缓冲区的事情，具体的定义百度。
然后看了操作系统的书籍如何解决书上给的伪代码是这样的
item B[k];
semaphore empty; empty=k; //可以使用的空缓冲区数
semaphore full; full=0; //缓冲区内可以使用的产品数
semaphore mutex; mutex=1; //互斥信号量
int in=0; //放入缓冲区指针
int out=0; //取出缓冲区指针
cobegin
process producer_i ( ) { process consumer_j( ) {
while(true) { while(true) {
produce( ); P(full);
P(empty); P(mutex);
P(mutex); take( ) from B[out];
append to B[in]; V(empty);
in=(in+1)%k; out=(out+1)%k;
V(mutex); V(mutex);
V(full); consume( );
} }
} }
coend上面的注释，和过程已经比较到位了，只是我习惯用我的方法，即把生产和消费，放入临界区所以下面是我解决生产消费模型所用的伪代码
item B[k];
semaphore empty; empty=k; //可以使用的空缓冲区数
semaphore full; full=0; //缓冲区内可以使用的产品数
semaphore mutex; mutex=1; //互斥信号量
int in=0; //放入缓冲区指针
int out=0; //取出缓冲区指针
cobegin
process producer_i ( ) { process consumer_j( ) {
while(true) { while(true) {
P(empty); P(full);
P(mutex); P(mutex);
produce( ); take( ) from B[out];
append to B[in]; consume( );
in=(in+1)%k; out=(out+1)%k;
V(mutex); V(mutex);
V(full); V(empty);
} }
} }
coend好了说了这么多我该帖下我的代码了，此代码在Linux环境下的多线程操作，用到了信号量的。。。
#include <unistd.h>
#include <sys/types.h>
#include <pthread.h>
#include <semaphore.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#define ERR_EXIT(m) \
do \
{ \
perror(m); \
exit(EXIT_FAILURE); \
} while(0)
#define CONSUMERS_COUNT 2 //消费者人数
#define PRODUCERS_COUNT 2 //生产者人数
#define BUFFSIZE 5
int g_buffer[BUFFSIZE]; //缓冲区数目
unsigned short in = 0; //放入产品的指针（生产到哪个缓冲区）
unsigned short out = 0; //取出缓冲区指针 （在哪个缓冲区消费的）
unsigned short produce_id = 0;
unsigned short consume_id = 0;
sem_t g_sem_full; //可以使用的空缓冲区数（缓冲区中可以生产多少产品）
sem_t g_sem_empty; //缓冲区内可以使用的产品数（可以消费的产品数）
pthread_mutex_t g_mutex; //互斥信号量
pthread_t g_thread[CONSUMERS_COUNT + PRODUCERS_COUNT];
void *consume(void *arg)
{
int i;
int num = (int)arg;
while (1)
{
printf("%d wait buffer not empty\n", num);
sem_wait(&g_sem_empty);
pthread_mutex_lock(&g_mutex);
//遍历缓冲区，看有哪些缓冲区是可以生产产品的
for (i = 0; i < BUFFSIZE; i++)
{
printf("%02d ", i);
if (g_buffer[i] == -1)
printf("%s", "null");
else
printf("%d", g_buffer[i]);
if (i == out)
printf("\t<--consume");
printf("\n");
}
//produce()操作(生产产品)
consume_id = g_buffer[out];
printf("%d begin consume product %d\n", num, consume_id);
g_buffer[out] = -1;
//将取出缓冲区的指针偏移1（下个生产的位置）
out = (out + 1) % BUFFSIZE;
printf("%d end consume product %d\n", num, consume_id);
pthread_mutex_unlock(&g_mutex);
sem_post(&g_sem_full);
sleep(1);
}
return NULL;
}
void *produce(void *arg)
{
int num = (int)arg;
int i;
while (1)
{
printf("%d wait buffer not full\n", num);
sem_wait(&g_sem_full);
pthread_mutex_lock(&g_mutex);
for (i = 0; i < BUFFSIZE; i++)
{
printf("%02d ", i);
if (g_buffer[i] == -1)
printf("%s", "null");
else
printf("%d", g_buffer[i]);
if (i == in)
printf("\t<--produce");
printf("\n");
}
printf("%d begin produce product %d\n", num, produce_id);
g_buffer[in] = produce_id;
in = (in + 1) % BUFFSIZE;
printf("%d end produce product %d\n", num, produce_id++);
pthread_mutex_unlock(&g_mutex);
sem_post(&g_sem_empty);
sleep(5);
}
return NULL;
}
int main(void)
{
int i;
for (i = 0; i < BUFFSIZE; i++)
g_buffer[i] = -1;
sem_init(&g_sem_full, 0, BUFFSIZE);
sem_init(&g_sem_empty, 0, 0);
pthread_mutex_init(&g_mutex, NULL);
for (i = 0; i < CONSUMERS_COUNT; i++)
pthread_create(&g_thread[i], NULL, consume, (void *)i);
for (i = 0; i < PRODUCERS_COUNT; i++)
pthread_create(&g_thread[CONSUMERS_COUNT + i], NULL, produce, (void *)i);
for (i = 0; i < CONSUMERS_COUNT + PRODUCERS_COUNT; i++)
pthread_join(g_thread[i], NULL);
sem_destroy(&g_sem_full);
sem_destroy(&g_sem_empty);
pthread_mutex_destroy(&g_mutex);
return 0;
}将程序运行，可得到这个结果
