Start a program N-M times in parallel by running it it each A-B seconds
# $Header: /CVSROOT/timestart/DESCRIPTION,v 1.2 2011-10-13 00:14:13 tino Exp $
#
# $Log: DESCRIPTION,v $
# Revision 1.2  2011-10-13 00:14:13  tino
# Bugfix and minor improvements.  Statistics with SIGWINCH added
#

<b>timestart N M A B program</b> tries to keep N running programs in parallel.
The interval between program execution is adjusted accordingly.

timestart keeps some bounds, it never executes more than M programs in parallel
and the interval is kept between A and B seconds.

If the program not returns 0 (or true), the next invocation is delayed B seconds,
but this has no influence on the calculated interval.

Also following signals are honored:
SIGHUP makes the program terminate after all childs are finished;
SIGUSR1 halts the spawning of new programs;
SIGUSR2 continues and immediately spawns a new program;
SIGWINCH print statistics to stderr

Note that timestart will run more than M programs if SIGUSR2 is sent more often,
as these signals are meant to help in debugging.  Signals to parent processes
can be sent easily using $PPID, so the child tasks can control timestart a bit.

The debug output of timestart is written to FD3 if this FD is redirected somewhere.