LAB 4 IS DONE.

lab/user/yield.c

@@ -0,0 +1,17 @@
+// yield the processor to other environments
+
+#include <inc/lib.h>
+
+void
+umain(int argc, char **argv)
+{
+	int i;
+
+	cprintf("Hello, I am environment %08x.\n", thisenv->env_id);
+	for (i = 0; i < 5; i++) {
+		sys_yield();
+		cprintf("Back in environment %08x, iteration %d.\n",
+			thisenv->env_id, i);
+	}
+	cprintf("All done in environment %08x.\n", thisenv->env_id);
+}