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watch: add precision wait time option -p

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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>
This commit is contained in:
Anthony DeRobertis 2009-11-24 11:00:46 +11:00 committed by Craig Small
parent 39a2f5d717
commit 0dbdb862b1
2 changed files with 80 additions and 5 deletions
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54
watch.1
View File

@ -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.

31
watch.c
View File

@ -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);
}