LAB 4 IS DONE.

lab/user/primes.c

@@ -0,0 +1,53 @@
+// Concurrent version of prime sieve of Eratosthenes.
+// Invented by Doug McIlroy, inventor of Unix pipes.
+// See http://swtch.com/~rsc/thread/.
+// The picture halfway down the page and the text surrounding it
+// explain what's going on here.
+//
+// Since NENV is 1024, we can print 1022 primes before running out.
+// The remaining two environments are the integer generator at the bottom
+// of main and user/idle.
+
+#include <inc/lib.h>
+
+unsigned
+primeproc(void)
+{
+	int i, id, p;
+	envid_t envid;
+
+	// fetch a prime from our left neighbor
+top:
+	p = ipc_recv(&envid, 0, 0);
+	cprintf("CPU %d: %d ", thisenv->env_cpunum, p);
+
+	// fork a right neighbor to continue the chain
+	if ((id = fork()) < 0)
+		panic("fork: %e", id);
+	if (id == 0)
+		goto top;
+
+	// filter out multiples of our prime
+	while (1) {
+		i = ipc_recv(&envid, 0, 0);
+		if (i % p)
+			ipc_send(id, i, 0, 0);
+	}
+}
+
+void
+umain(int argc, char **argv)
+{
+	int i, id;
+
+	// fork the first prime process in the chain
+	if ((id = fork()) < 0)
+		panic("fork: %e", id);
+	if (id == 0)
+		primeproc();
+
+	// feed all the integers through
+	for (i = 2; ; i++)
+		ipc_send(id, i, 0, 0);
+}
+