Lab4: add examples

lab4/demos/parallel_count.c

@@ -0,0 +1,42 @@
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+int max;
+// WOW, new word: it means the compiler is not allowed to optimize this varible
+volatile int counter = 0;
+
+void* mythread(void* arg) {
+    char* letter = arg;
+    int i;
+
+    printf("%s: begin [addr of i: %p]\n", letter, (void*) &i);
+
+    for (i = 0; i < max; i++) {
+        counter = counter + 1;
+    }
+
+    printf("%s: done with counter at %d\n", letter, counter);
+    return NULL;
+}
+
+int main(int argc, char* argv[]) {
+    if (argc != 2) {
+        fprintf(stderr, "usage: main-first <loopcount>\n");
+        exit(1);
+    }
+    max = atoi(argv[1]);
+
+    pthread_t p1, p2;
+    printf("main: begin [counter = %d] [%x]\n", counter,
+           *(unsigned int*)&counter);
+
+    pthread_create(&p1, NULL, mythread, "A");
+    pthread_create(&p2, NULL, mythread, "B");
+
+    pthread_join(p1, NULL);
+    pthread_join(p2, NULL);
+
+    printf("main: done\n [counter: %d]\n [should: %d]\n", counter, max * 2);
+    return 0;
+}

lab4/demos/pthread_exit_status.c

@@ -0,0 +1,32 @@
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+void* integer_return(void* arg) {
+    return (void*) 1;
+}
+
+void* string_return(void* arg) {
+    char* string = calloc(4, sizeof(char));
+
+    string[0] = 'c';
+    string[1] = 'a';
+    string[2] = 't';
+
+    pthread_exit((void*) string);
+}
+
+int main(void) {
+    pthread_t thread_id_1;
+    pthread_t thread_id_2;
+
+    pthread_create(&thread_id_1, NULL, integer_return, NULL);
+    pthread_create(&thread_id_2, NULL, string_return, NULL);
+
+    void* thread_return_value;
+    pthread_join(thread_id_1, &thread_return_value);
+    printf("The first thread returned: %d\n", *(int*) thread_return_value);
+
+    pthread_join(thread_id_2, &thread_return_value);
+    printf("The second thread returned: %s\n", (char*) thread_return_value);
+}