三種關系：互斥，同步，互斥和同步
兩類角色:生產者，消費者（線程）
一個交易場所：生產者消費者共享的區域

賣蘋果的模型

• dish上面只有一個蘋果
• 買家必須要等賣家把蘋果放到dish上才可以去買蘋果。
• 賣家必須等待買家把蘋果買走才可以生產蘋果
• pthread_mutex_lock(&mutex); 和pthread_mutex_unlock(&mutex); 成對出現，里面的操作為一個原子操作
• pthread_cond_wait(&empty,&mutex);內部有一個加鎖解鎖操作
• 過程詳解
  
  • 蘋果為0
  • 初始化時蘋果為0，買家在pthread_cond_wait(&empty,&mutex); 開始等待，賣家不進入while循環，生產蘋果后發出pthread_cond_signal(&empty);讓正在因dish上蘋果為0的買家停止等待pthread_cond_wait(&empty,&mutex);
  • 蘋果為1
  • 當一個賣家進入pthread_mutex_lock(&mutex); 但是發現蘋果為1時，就在while循環處等待pthread_cond_wait(&empty,&mutex);，直到買家發出信號 pthread_cond_signal(&full);賣家停止等待，此時蘋果為0，跳出while循環，開始生產蘋果。生產蘋果后發出pthread_cond_signal(&empty);讓正在因dish上蘋果為0的買家停止等待pthread_cond_wait(&empty,&mutex); 這樣這個過程就結束了
    *

#include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <pthread.h>int dish = 0; pthread_cond_t full; pthread_cond_t empty; pthread_mutex_t mutex;void * consumer(void * arg) {int id = (int)arg;while(1){pthread_mutex_lock(&mutex);//上鎖while(dish == 0){//買家發現沒有蘋果開始等待pthread_cond_wait(&empty,&mutex);}usleep(100000);dish = 0;printf("consumer %d get an apple!!\n", id);//給賣家發送信號pthread_cond_signal(&full);pthread_mutex_unlock(&mutex);//解鎖}return NULL; }void * product(void *arg) {int id = (int)arg;while(1){pthread_mutex_lock(&mutex); while(dish == 1){pthread_cond_wait(&full,&mutex);}dish =1;printf("producer %d put an apple!!\n", id); pthread_cond_signal(&empty);pthread_mutex_unlock(&mutex);}return NULL; }int main() {pthread_t tid;int set ;//初始化pthread_cond_init(&full,NULL);pthread_cond_init(&empty,NULL);pthread_mutex_init(&mutex,NULL);//四個賣家生產蘋果for(int i = 0;i<4;i++){pthread_create(&tid,NULL,product,(void *)i);}//四個買家買蘋果for(int i = 0;i<4;i++){pthread_create(&tid,NULL,consumer,(void *)i);}//等待thread標識的線程終止，防止僵尸進程產生pthread_join(tid,NULL);//銷毀所有資源pthread_cond_destroy(&full);pthread_cond_destroy(&empty);pthread_mutex_destroy(&mutex); }

如果對于互斥量含義尚不清楚，建議閱讀Linux/UNIX系統編程手冊

pthread_mutex_t pthread_mutex_init pthread_mutex_lock pthread_mutex_unlock pthread_mutex_destroy

模型采取Linux/UNIX系統編程手冊
這個模型很好，也把概念講清楚了，加了中文注釋

生產者

s = pthread_mutex_lock(&mtx); if (s != 0)errExitEN(s, "pthread_mutex_lock");avail++; /*這是一個原子操作 */s = pthread_mutex_unlock(&mtx); if (s != 0)errExitEN(s, "pthread_mutex_unlock");s = pthread_cond_signal(&cond); /* 喚醒消費者 */ if (s != 0)errExitEN(s, "pthread_cond_signal");

消費者

s = pthread_mutex_lock(&mtx); if (s != 0)errExitEN(s, "pthread_mutex_lock");while (avail == 0){ s = pthread_cond_wait(&cond, &mtx);if (s != 0)errExitEN(s, "pthread_cond_wait"); }

完整代碼

#include <time.h> #include <pthread.h> #include "tlpi_hdr.h"static pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER; static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;static int avail = 0;static void * threadFunc(void *arg) {int cnt = atoi((char *) arg);int s, j;for (j = 0; j < cnt; j++) {sleep(1);/* Code to produce a unit omitted */s = pthread_mutex_lock(&mtx);if (s != 0)errExitEN(s, "pthread_mutex_lock");avail++; /* Let consumer know another unit is available */s = pthread_mutex_unlock(&mtx);if (s != 0)errExitEN(s, "pthread_mutex_unlock");s = pthread_cond_signal(&cond); /* Wake sleeping consumer */if (s != 0)errExitEN(s, "pthread_cond_signal");}return NULL; }int main(int argc, char *argv[]) {pthread_t tid;int s, j;int totRequired; /* Total number of units that all threadswill produce */int numConsumed; /* Total units so far consumed */Boolean done;time_t t;t = time(NULL);/* Create all threads */totRequired = 0;for (j = 1; j < argc; j++) {totRequired += atoi(argv[j]);s = pthread_create(&tid, NULL, threadFunc, argv[j]);if (s != 0)errExitEN(s, "pthread_create");}/* Loop to consume available units */numConsumed = 0;done = FALSE;for (;;) {s = pthread_mutex_lock(&mtx);if (s != 0)errExitEN(s, "pthread_mutex_lock");while (avail == 0) { /* Wait for something to consume */s = pthread_cond_wait(&cond, &mtx);if (s != 0)errExitEN(s, "pthread_cond_wait");}/* At this point, 'mtx' is locked... */while (avail > 0) { /* Consume all available units *//* Do something with produced unit */numConsumed ++;avail--;printf("T=%ld: numConsumed=%d\n", (long) (time(NULL) - t),numConsumed);done = numConsumed >= totRequired;}s = pthread_mutex_unlock(&mtx);if (s != 0)errExitEN(s, "pthread_mutex_unlock");if (done)break;/* Perhaps do other work here that does not require mutex lock */}exit(EXIT_SUCCESS); }

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