ts(1): parse user format string only once

Currently, ts(1) reparses the user format string every time it prints
a timestamp.  This is wasteful.

If we isolate the parsing loop in fmtfmt() and move the rest of the
work into a new function, fmtprint(), we can cut some overhead out
of the hot loop.

We still need to update any microsecond substrings in the parsed
format string every time we print a timestamp.  So during parsing in
fmtfmt() we build a list of pointers to locations in the parsed buffer
where the microsecond substring needs to be copied during fmtprint().

With input from deraadt@.

Link1: https://marc.info/?l=openbsd-tech&m=165769139318084&w=2
Link2: https://marc.info/?l=openbsd-tech&m=165910022501353&w=2

OK job@

diff --git a/usr.bin/ts/ts.c b/usr.bin/ts/ts.c
index 284d8cc..62987ca 100644 (file)
--- a/usr.bin/ts/ts.c
+++ b/usr.bin/ts/ts.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: ts.c,v 1.9 2022/08/03 16:54:30 job Exp $      */
+/*     $OpenBSD: ts.c,v 1.10 2022/09/01 00:14:36 cheloha Exp $ */
 /*
  * Copyright (c) 2022 Job Snijders <job@openbsd.org>
  * Copyright (c) 2022 Claudio Jeker <claudio@openbsd.org>
@@ -17,6 +17,7 @@
  */
 
 #include <sys/types.h>
+#include <sys/queue.h>
 #include <sys/time.h>
 
 #include <err.h>
@@ -27,13 +28,20 @@
 #include <unistd.h>
 #include <time.h>
 
+SIMPLEQ_HEAD(, usec) usec_queue = SIMPLEQ_HEAD_INITIALIZER(usec_queue);
+struct usec {
+       SIMPLEQ_ENTRY(usec) next;
+       char *pos;
+};
+
 static char            *format = "%b %d %H:%M:%S";
 static char            *buf;
 static char            *outbuf;
 static size_t           bufsize;
 static size_t           obsize;
 
-static void             fmtfmt(const struct timespec *);
+static void             fmtfmt(void);
+static void             fmtprint(const struct timespec *);
 static void __dead      usage(void);
 
 int
@@ -90,6 +98,8 @@ main(int argc, char *argv[])
        if ((outbuf = calloc(1, obsize)) == NULL)
                err(1, NULL);
 
+       fmtfmt();
+
        /* force UTC for interval calculations */
        if (iflag || sflag)
                if (setenv("TZ", "UTC", 1) == -1)
@@ -108,7 +118,7 @@ main(int argc, char *argv[])
                                timespecadd(&now, &utc_offset, &ts);
                        else
                                ts = now;
-                       fmtfmt(&ts);
+                       fmtprint(&ts);
                        if (iflag)
                                start = now;
                }
@@ -134,15 +144,11 @@ usage(void)
  * so you can format while you format
  */
 static void
-fmtfmt(const struct timespec *ts)
+fmtfmt(void)
 {
-       struct tm *tm;
-       char *f, us[7];
+       char *f;
+       struct usec *u;
 
-       if ((tm = localtime(&ts->tv_sec)) == NULL)
-               err(1, "localtime");
-
-       snprintf(us, sizeof(us), "%06ld", ts->tv_nsec / 1000);
        strlcpy(buf, format, bufsize);
        f = buf;
 
@@ -161,12 +167,34 @@ fmtfmt(const struct timespec *ts)
                        f[0] = f[1];
                        f[1] = '.';
                        f += 2;
+                       u = malloc(sizeof u);
+                       if (u == NULL)
+                               err(1, NULL);
+                       u->pos = f;
+                       SIMPLEQ_INSERT_TAIL(&usec_queue, u, next);
                        l = strlen(f);
                        memmove(f + 6, f, l + 1);
-                       memcpy(f, us, 6);
                        f += 6;
                }
        } while (*f != '\0');
+}
+
+static void
+fmtprint(const struct timespec *ts)
+{
+       char us[8];
+       struct tm *tm;
+       struct usec *u;
+
+       if ((tm = localtime(&ts->tv_sec)) == NULL)
+               err(1, "localtime");
+
+       /* Update any microsecond substrings in the format buffer. */
+       if (!SIMPLEQ_EMPTY(&usec_queue)) {
+               snprintf(us, sizeof(us), "%06ld", ts->tv_nsec / 1000);
+               SIMPLEQ_FOREACH(u, &usec_queue, next)
+                       memcpy(u->pos, us, 6);
+       }
 
        *outbuf = '\0';
        if (*buf != '\0') {