sample/ch12/goodcnt.c: 使用信号量来实现互斥

sample/ch12/Makefile

@@ -14,11 +14,13 @@ OBJS += echoservert.o
 OBJS += echo.o
 OBJS += sharing.o
 OBJS += badcnt.o
+OBJS += goodcnt.o
 
 PROGRAMS += hello
 PROGRAMS += echoservert
 PROGRAMS += sharing
 PROGRAMS += badcnt
+PROGRAMS += goodcnt
 
 PHONY += all
 PHONY += clean
@@ -60,5 +62,11 @@ badcnt: badcnt.o csapp.o
 badcnt.o: badcnt.c $(csapp_h)
 	$(CC) $(CFLAGS) $(INCLUDES) -c $< -o $@
 
+goodcnt: goodcnt.o csapp.o
+	$(CC) $(CFLAGS) $^ $(LIBS) -o $@
+
+goodcnt.o: goodcnt.c $(csapp_h)
+	$(CC) $(CFLAGS) $(INCLUDES) -c $< -o $@
+
 clean:
 	rm -f $(OBJS) $(PROGRAMS)

sample/ch12/goodcnt.c

@@ -0,0 +1,58 @@
+/*
+ * p669
+ *
+ * 使用信号量来实现互斥
+ *
+ * 在类 UNIX 系统中编译和运行：
+ *
+ * unix> make goodcnt
+ * unix> ./goodcnt
+ */
+
+#include "csapp.h"
+
+void *thread(void *vargp);      /* Thread routine prototype */
+
+/* Global shared variable */
+volatile int cnt = 0;           /* Counter */
+sem_t mutex;                    /* Semaphore that protects counter */
+
+int main(int argc, char **argv)
+{
+        int niters;
+        pthread_t tid1, tid2;
+
+        /* Check input argument */
+        if (argc != 2) {
+                printf("usage: %s <niters>\n", argv[0]);
+                exit(0);
+        }
+        niters = atoi(argv[1]);
+
+        Sem_init(&mutex, 0, 1); /* mutex = 1 */
+
+        /* Created threads and wait for them to finish */
+        Pthread_create(&tid1, NULL, thread, &niters);
+        Pthread_create(&tid2, NULL, thread, &niters);
+        Pthread_join(tid1, NULL);
+        Pthread_join(tid2, NULL);
+
+        /* Check result */
+        if (cnt != (2 * niters))
+                printf("BOOM! cnt=%d\n", cnt);
+        else
+                printf("OK cnt=%d\n", cnt);
+        exit(0);
+}
+
+/* Thread routine */
+void *thread(void *vargp)
+{
+        int i, niters = *((int *)vargp);
+        for (i = 0; i < niters; i++) {
+                P(&mutex);
+                cnt++;
+                V(&mutex);
+        }
+        return NULL;
+}