From 0dbdb862b1ace77546c3d58a9dd799bb1779756c Mon Sep 17 00:00:00 2001
From: Anthony DeRobertis <asd@suespammers.org>
Date: Tue, 24 Nov 2009 11:00:46 +1100
Subject: [PATCH] watch: add precision wait time option -p
A patch from Debian.
Bug-Debian: http://bugs.debian.org/183486
Reviewed-by: Craig Small <csmall@debian.org>
Backported-by: Sami Kerola <kerolasa@iki.fi>
---
watch.1 | 54 +++++++++++++++++++++++++++++++++++++++++++++++++++---
watch.c | 31 +++++++++++++++++++++++++++++--
2 files changed, 80 insertions(+), 5 deletions(-)
diff --git a/watch.1 b/watch.1
index cbfa3b32..99ffa6b3 100644
--- a/watch.1
+++ b/watch.1
@@ -4,7 +4,7 @@ watch \- execute a program periodically, showing output fullscreen
.SH SYNOPSIS
.na
.B watch
-.RB [ \-bdehvtx ]
+.RB [ \-bdehpvtx ]
.RB [ \-n
.IR seconds ]
.RB [ \-\-beep ]
@@ -15,6 +15,7 @@ watch \- execute a program periodically, showing output fullscreen
.RB [ \-\-help ]
.RB [ \-\-interval=\fIseconds\fP]
.RB [ \-\-no\-title ]
+.RB [ \-\-precise ]
.RB [ \-\-version ]
.I command
.SH DESCRIPTION
@@ -28,7 +29,24 @@ every 2 seconds; use
.B \-n
or
.B \-\-interval
-to specify a different interval.
+to specify a different interval. Normally, this interval is interpreted
+as the amout of time between the completion of one run of
+.I command
+and the beginning of the next run. However, with the
+.I \-p
+or
+.I \-\-precise
+option, you can make
+.BR watch
+attempt to run
+.I command
+every
+.I interval
+seconds. Try it with
+.B ntptime
+and notice how the fractional seconds stays
+(nearly) the same, as opposed to normal mode where they continuously
+increase.
.PP
The
.B \-d
@@ -102,11 +120,21 @@ watch echo '$$'
.br
watch echo "'"'$$'"'"
.PP
+To see the effect of precision time keeping, try adding
+.I \-p
+to
+.IP
+watch \-n 10 sleep 1
+.PP
You can watch for your administrator to install the latest kernel with
.IP
watch uname \-r
.PP
-(Just kidding.)
+(Note that
+.I \-p
+isn't guaranteed to work across reboots, especially in the face of
+.B ntpdate
+or other bootup time-changing mechanisms)
.SH BUGS
Upon terminal resize, the screen will not be correctly repainted until the
next scheduled update. All
@@ -115,6 +143,22 @@ highlighting is lost on that update as well.
.PP
Non-printing characters are stripped from program output. Use "cat -v" as
part of the command pipeline if you want to see them.
+.PP
+.I \-\-precise
+mode doesn't yet have advanced temporal distortion technology to
+compensate for a
+.I command
+that takes more than
+.I interval
+seconds to execute.
+.B watch
+also can get into a state where it rapid-fires as many executions of
+.I command
+as it can to catch up from a previous executions running longer than
+.I interval
+(for example,
+.B netstat
+taking ages on a DNS lookup).
.SH AUTHORS
The original
.B watch
@@ -122,3 +166,7 @@ was written by Tony Rems <rembo@unisoft.com> in 1991, with mods and
corrections by Francois Pinard. It was reworked and new features added by
Mike Coleman <mkc@acm.org> in 1999. The beep, exec, and error handling
features were added by Morty Abzug <morty@frakir.org> in 2008.
+On a not so dark and stormy morning
+in March of 2003, Anthony DeRobertis <asd@suespammers.org> got sick of
+his watches that should update every minute eventually updating many
+seconds after the minute started, and added microsecond precision.
diff --git a/watch.c b/watch.c
index bfd15e68..cf407925 100644
--- a/watch.c
+++ b/watch.c
@@ -19,6 +19,7 @@
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
+#include <sys/time.h>
#include <time.h>
#include <unistd.h>
#include <termios.h>
@@ -39,13 +40,14 @@ static struct option longopts[] = {
{"beep", no_argument, 0, 'b'},
{"errexit", no_argument, 0, 'e'},
{"exec", no_argument, 0, 'x'},
+ {"precise", no_argument, 0, 'p'},
{"no-title", no_argument, 0, 't'},
{"version", no_argument, 0, 'v'},
{0, 0, 0, 0}
};
static char usage[] =
- "Usage: %s [-bdhntvx] [--beep] [--color] [--differences[=cumulative]] [--exec] [--help] [--interval=<n>] [--no-title] [--version] <command>\n";
+ "Usage: %s [-bdhnptvx] [--beep] [--color] [--differences[=cumulative]] [--exec] [--help] [--interval=<n>] [--no-title] [--version] <command>\n";
static char *progname;
@@ -54,6 +56,7 @@ static int height = 24, width = 80;
static int screen_size_changed = 0;
static int first_screen = 1;
static int show_title = 2; // number of lines used, 2 or 0
+static int precise_timekeeping = 0;
#define min(x,y) ((x) > (y) ? (y) : (x))
#define MAX_ANSIBUF 10
@@ -206,6 +209,15 @@ get_terminal_size(void)
}
}
+/* get current time in usec */
+typedef unsigned long long watch_usec_t;
+#define USECS_PER_SEC (1000000ull)
+watch_usec_t get_time_usec() {
+ struct timeval now;
+ gettimeofday(&now, NULL);
+ return USECS_PER_SEC*now.tv_sec + now.tv_usec;
+}
+
int
main(int argc, char *argv[])
{
@@ -221,6 +233,8 @@ main(int argc, char *argv[])
char *command;
char **command_argv;
int command_length = 0; /* not including final \0 */
+ watch_usec_t next_loop; /* next loop time in us, used for precise time
+ keeping only */
int pipefd[2];
int status;
pid_t child;
@@ -228,7 +242,7 @@ main(int argc, char *argv[])
setlocale(LC_ALL, "");
progname = argv[0];
- while ((optc = getopt_long(argc, argv, "+bced::hn:vtx", longopts, (int *) 0))
+ while ((optc = getopt_long(argc, argv, "+bced::hn:pvtx", longopts, (int *) 0))
!= EOF) {
switch (optc) {
case 'b':
@@ -266,6 +280,9 @@ main(int argc, char *argv[])
interval = ~0u/1000000;
}
break;
+ case 'p':
+ precise_timekeeping = 1;
+ break;
case 'v':
option_version = 1;
break;
@@ -289,6 +306,7 @@ main(int argc, char *argv[])
fputs(" -e, --errexit\t\t\t\texit watch if the command has a non-zero exit\n", stderr);
fputs(" -h, --help\t\t\t\tprint a summary of the options\n", stderr);
fputs(" -n, --interval=<seconds>\t\tseconds to wait between updates\n", stderr);
+ fputs(" -p, --precise\t\t\t\tprecise timing, ignore command run time\n", stderr);
fputs(" -v, --version\t\t\t\tprint the version number\n", stderr);
fputs(" -t, --no-title\t\t\tturns off showing the header\n", stderr);
fputs(" -x, --exec\t\t\t\tpass command to exec instead of sh\n", stderr);
@@ -336,6 +354,9 @@ main(int argc, char *argv[])
noecho();
cbreak();
+ if (precise_timekeeping)
+ next_loop = get_time_usec();
+
for (;;) {
time_t t = time(NULL);
char *ts = ctime(&t);
@@ -486,6 +507,12 @@ main(int argc, char *argv[])
first_screen = 0;
refresh();
+ if (precise_timekeeping) {
+ watch_usec_t cur_time = get_time_usec();
+ next_loop += USECS_PER_SEC*interval;
+ if (cur_time < next_loop)
+ usleep(next_loop - cur_time);
+ } else
usleep(interval * 1000000);
}
--
2.40.0