a

libc/nsec.c

@@ -0,0 +1,66 @@
+#include <u.h>
+#include <libc.h>
+
+
+static uvlong order = (uvlong) 0x0001020304050607;
+
+static void
+be2vlong(vlong *to, uchar *f)
+{
+	uchar *t, *o;
+	int i;
+
+	t = (uchar*)to;
+	o = (uchar*)&order;
+	for(i = 0; i < 8; i++)
+		t[o[i]] = f[i];
+}
+
+/*
+ *  After a fork with fd's copied, both fd's are pointing to
+ *  the same Chan structure.  Since the offset is kept in the Chan
+ *  structure, the seek's and read's in the two processes can
+ *  compete at moving the offset around.  Hence the retry loop.
+ *
+ *  Since the bintime version doesn't need a seek, it doesn't
+ *  have the loop.
+ */
+vlong
+nsec(void)
+{
+	char b[12+1];
+	static int f = -1;
+	static int usebintime;
+	int retries;
+	vlong t;
+
+	if(f < 0){
+		usebintime = 1;
+		f = open("/dev/bintime", OREAD|OCEXEC);
+		if(f < 0){
+			usebintime = 0;
+			f = open("/dev/nsec", OREAD|OCEXEC);
+			if(f < 0)
+				return 0;
+		}
+	}
+
+	if(usebintime){
+		if(read(f, b, sizeof(uvlong)) < 0)
+			goto error;
+		be2vlong(&t, (uchar*)b);
+		return t;
+	} else {
+		for(retries = 0; retries < 100; retries++){
+			if(seek(f, 0, 0) >= 0 && read(f, b, sizeof(b)-1) >= 0){
+				b[sizeof(b)-1] = 0;
+				return strtoll(b, 0, 0);
+			}
+		}
+	}
+
+error:
+	close(f);
+	f = -1;
+	return 0;
+}