This program uses POSIX advisory locking to prevent more than a specifed
number of instances of a program from running at one time.

A typical invocation looks like this:
exectimes /var/run/mylockfile 10 command-to-run command-arguments
which is usually placed in a shell script.

exectimes will then execute the program only if the number of currently
running instances, determined by the lock file, is less than the maxmimum
allowed, specified as the second program argument.

See the included pdf documentation or the blog post at 
http://www.robertgamble.net/2011/04/cooperative-limiting-of-concurrent.html for details.