Added example chapter 7 on Threads

chp7/thread.c

@@ -0,0 +1,30 @@
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+void *start_thread(void *message)
+{
+	printf("%s\n", (const char *)message);
+	return message;
+}
+
+int main(void)
+{
+	pthread_t thing1, thing2;
+	const char *message1 = "Thing 1";
+	const char *message2 = "Thing 2";
+
+	/* Create two threads, each with a different message. */
+	pthread_create(&thing1, NULL, start_thread, (void *)message1);
+	pthread_create(&thing2, NULL, start_thread, (void *)message2);
+
+	/*
+	 * Wait for the threads to exit. If we didn't join here,
+	 * we'd risk terminating this main thread before the
+	 * other two threads finished.
+	 */
+	pthread_join(thing1, NULL);
+	pthread_join(thing2, NULL);
+
+	return EXIT_SUCCESS;
+}