??這應該是最后一次，還是認認真真滴完成。
??本次內容圍繞一個問題，線程并發時對于全局變量會錯位控制。所以必須加以限制，限制的手段有兩種：條件變量、互斥信號量。

?? 一、條件變量

??條件變量的操作就三個：初始化、等待、喚醒線程。具體的用法如下：

??有了條件變量，就可以在全局變量前面加上。線程并發時就會在執行前獲取條件變量的情況了。

?? 二、互斥信號量

??信號量的使用是通過鎖來實現的，所以信號量的操作包括初始化、上鎖、解鎖。具體如下：

?? 其實我覺得二者沒有什么區別，完成的功能都一樣。而且在理論課上只講了信號量，沒有提及條件變量。所以可能各有所好吧，我就不知道啦～

??老規矩，還是有作業。是解決一個經典的生產者-消費者問題，做了一點兒拓展，加了一個計算者。題目如下：

??代碼如下：

#include <stdio.h> #include <unistd.h> #include <pthread.h>#define CAPACITY 4 int buffer1[CAPACITY]; int buffer2[CAPACITY]; int in1; int out1; int in2; int out2;int buffer1_is_empty() {return in1 == out1; }int buffer1_is_full() {return (in1 + 1) % CAPACITY == out1; }int buffer2_is_empty() {return in2 == out2; }int buffer2_is_full() {return (in2 + 1) % CAPACITY == out2; }// buffer1操作,操作變量是out1,in1 int get_item1() {int item;item = buffer1[out1];out1 = (out1 + 1) % CAPACITY;return item; }void put_item1(int item) {buffer1[in1] = item;in1 = (in1 + 1) % CAPACITY; }// buffer2操作,操作變量是out2,in2 int get_item2() {int item;item = buffer2[out2];out2 = (out2 + 1) % CAPACITY;return item; }void put_item2(int item) {buffer2[in2] = item;in2 = (in2 + 1) % CAPACITY; }pthread_mutex_t mutex; pthread_cond_t wait_empty_buffer1; pthread_cond_t wait_full_buffer1;pthread_cond_t wait_empty_buffer2; pthread_cond_t wait_full_buffer2;#define ITEM_COUNT (CAPACITY * 2)// consume對于buffer2是消費者 void *consume(void *arg) {int i;int item;for (i = 0; i < ITEM_COUNT; i++) { pthread_mutex_lock(&mutex);while (buffer2_is_empty())pthread_cond_wait(&wait_full_buffer2, &mutex);item = get_item2(); printf(" consume item: %c\n", item); pthread_cond_signal(&wait_empty_buffer2);pthread_mutex_unlock(&mutex);}return NULL; }// produce對于buffer1是生產者 void *produce(void *arg) {int i;int item;for (i = 0; i < ITEM_COUNT; i++) { pthread_mutex_lock(&mutex);while (buffer1_is_full()) pthread_cond_wait(&wait_empty_buffer1, &mutex);item = 'a' + i;put_item1(item);printf("produce item: %c\n", item); pthread_cond_signal(&wait_full_buffer1);pthread_mutex_unlock(&mutex);}return NULL; } /*calculate對于buffer1是消費者，對于buffer2是生產者*/ void *calculate(void *arg) {int i;int item;for (i = 0; i < ITEM_COUNT; i++) {// buffer1操作pthread_mutex_lock(&mutex);while (buffer1_is_empty())pthread_cond_wait(&wait_full_buffer1, &mutex);item = get_item1();item = item-32; // 完成計算者功能pthread_cond_signal(&wait_empty_buffer1);pthread_mutex_unlock(&mutex);// buffer2操作pthread_mutex_lock(&mutex);while(buffer2_is_full())pthread_cond_wait(&wait_empty_buffer2, &mutex);put_item2(item);pthread_cond_signal(&wait_full_buffer2);pthread_mutex_unlock(&mutex);}return NULL;} int main() { pthread_t consumer_tid;pthread_t calculator_tid;pthread_mutex_init(&mutex, NULL);pthread_cond_init(&wait_empty_buffer1, NULL);pthread_cond_init(&wait_full_buffer1, NULL);pthread_cond_init(&wait_empty_buffer2, NULL);pthread_cond_init(&wait_full_buffer2, NULL);pthread_create(&calculator_tid, NULL, calculate, NULL);pthread_create(&consumer_tid, NULL, consume, NULL);produce(NULL); // 此處一定要寫線程等待，因為生產者最先結束，不寫主進程會隨之結束pthread_join(calculator_tid, NULL);pthread_join(consumer_tid, NULL);return 0;}

??代碼如下：

#include <stdio.h> #include <pthread.h> #include <unistd.h>#define CAPACITY 4 int buffer1[CAPACITY]; int in1; int out1; int buffer2[CAPACITY]; int in2; int out2;// 定義buffer1操作，操作對象為in1,out1 int buffer1_is_empty() {return in1 == out1; }int buffer1_is_full1() {return (in1 + 1) % CAPACITY == out1; }// 定義buffer2操作，操作對象為in2,ou2 int buffer2_is_empty() {return in2 == out2; }int buffer2_is_full1() {return (in2 + 1) % CAPACITY == out2; }// buffer1數據相關 int get_item1() {int item;item = buffer1[out1];out1 = (out1 + 1) % CAPACITY;return item; }void put_item1(int item) {buffer1[in1] = item;in1 = (in1 + 1) % CAPACITY; }// buffer2數據相關 int get_item2() {int item;item = buffer2[out2];out2 = (out2 + 1) % CAPACITY;return item; }void put_item2(int item) {buffer2[in2] = item;in2 = (in2 + 1) % CAPACITY; }typedef struct {int value;pthread_mutex_t mutex;pthread_cond_t cond; } sema_t;// 信號量操作是統一的，不需要單獨設定 void sema_init(sema_t *sema, int value) {sema->value = value;pthread_mutex_init(&sema->mutex, NULL);pthread_cond_init(&sema->cond, NULL); }void sema_wait(sema_t *sema) {pthread_mutex_lock(&sema->mutex);while (sema->value <= 0)pthread_cond_wait(&sema->cond, &sema->mutex);sema->value--;pthread_mutex_unlock(&sema->mutex); }void sema_signal(sema_t *sema) {pthread_mutex_lock(&sema->mutex);++sema->value;pthread_cond_signal(&sema->cond);pthread_mutex_unlock(&sema->mutex); }sema_t mutex_sema; sema_t empty_buffer1_sema; sema_t full_buffer1_sema; sema_t empty_buffer2_sema; sema_t full_buffer2_sema;#define ITEM_COUNT (CAPACITY * 2)// consume是buffer2數組的消費者 void *consume(void *arg) {int i;int item;for (i = 0; i < ITEM_COUNT; i++) { sema_wait(&full_buffer2_sema);sema_wait(&mutex_sema);item = get_item2();printf(" consume item: %c\n", item); sema_signal(&mutex_sema);sema_signal(&empty_buffer2_sema);}return NULL; }// produce是buffer1數組的生產者 void *produce() {int i;int item;for (i = 0; i < ITEM_COUNT; i++) { sema_wait(&empty_buffer1_sema);sema_wait(&mutex_sema);item = i + 'a';put_item1(item);printf("produce item: %c\n", item); sema_signal(&mutex_sema);sema_signal(&full_buffer1_sema);}return NULL; }// calculate是buffer1數組的消費者，buffer2數組的生產者 void *calculate() {int i;int item;for (i = 0; i < ITEM_COUNT; i++) {// buffer1相關操作sema_wait(&full_buffer1_sema);sema_wait(&mutex_sema);item = get_item1();item = item - 32;sema_signal(&mutex_sema);sema_signal(&empty_buffer1_sema);// buffer2相關操作sema_wait(&empty_buffer2_sema);sema_wait(&mutex_sema);put_item2(item);sema_signal(&mutex_sema);sema_signal(&full_buffer2_sema);}return NULL; } int main() { pthread_t consumer_tid;pthread_t calculator_tid;sema_init(&mutex_sema, 1);sema_init(&empty_buffer1_sema, CAPACITY - 1);sema_init(&full_buffer1_sema, 0);sema_init(&empty_buffer2_sema, CAPACITY - 1);sema_init(&full_buffer2_sema, 0);pthread_create(&consumer_tid, NULL, consume, NULL);pthread_create(&calculator_tid, NULL, calculate, NULL);// 必須線程等待，生產者會先完成，不寫提前結束主函數produce();pthread_join(consumer_tid, NULL);pthread_join(calculator_tid, NULL);return 0; }

因作者水平有限，如有錯誤之處，請在下方評論區指出，謝謝！

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