my solution to lab5

lab/user/primespipe.c

@@ -0,0 +1,76 @@
+// 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(int fd)
+{
+	int i, id, p, pfd[2], wfd, r;
+
+	// fetch a prime from our left neighbor
+top:
+	if ((r = readn(fd, &p, 4)) != 4)
+		panic("primeproc could not read initial prime: %d, %e", r, r >= 0 ? 0 : r);
+
+	cprintf("%d\n", p);
+
+	// fork a right neighbor to continue the chain
+	if ((i=pipe(pfd)) < 0)
+		panic("pipe: %e", i);
+	if ((id = fork()) < 0)
+		panic("fork: %e", id);
+	if (id == 0) {
+		close(fd);
+		close(pfd[1]);
+		fd = pfd[0];
+		goto top;
+	}
+
+	close(pfd[0]);
+	wfd = pfd[1];
+
+	// filter out multiples of our prime
+	for (;;) {
+		if ((r=readn(fd, &i, 4)) != 4)
+			panic("primeproc %d readn %d %d %e", p, fd, r, r >= 0 ? 0 : r);
+		if (i%p)
+			if ((r=write(wfd, &i, 4)) != 4)
+				panic("primeproc %d write: %d %e", p, r, r >= 0 ? 0 : r);
+	}
+}
+
+void
+umain(int argc, char **argv)
+{
+	int i, id, p[2], r;
+
+	binaryname = "primespipe";
+
+	if ((i=pipe(p)) < 0)
+		panic("pipe: %e", i);
+
+	// fork the first prime process in the chain
+	if ((id=fork()) < 0)
+		panic("fork: %e", id);
+
+	if (id == 0) {
+		close(p[1]);
+		primeproc(p[0]);
+	}
+
+	close(p[0]);
+
+	// feed all the integers through
+	for (i=2;; i++)
+		if ((r=write(p[1], &i, 4)) != 4)
+			panic("generator write: %d, %e", r, r >= 0 ? 0 : r);
+}
+