Added common include for simple C programs, and threads-intro code

threads-intro/t1.c

@@ -0,0 +1,40 @@
+#include "common.h"
+#include "common_threads.h"
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+int max;
+volatile int counter = 0; // shared global variable
+
+void *mythread(void *arg) {
+    char *letter = arg;
+    int i; // stack (private per thread) 
+    printf("%s: begin [addr of i: %p]\n", letter, &i);
+    for (i = 0; i < max; i++) {
+	counter = counter + 1; // shared: only one
+    }
+    printf("%s: done\n", letter);
+    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");
+    // join waits for the threads to finish
+    Pthread_join(p1, NULL); 
+    Pthread_join(p2, NULL); 
+    printf("main: done\n [counter: %d]\n [should: %d]\n", 
+	   counter, max*2);
+    return 0;
+}
+