Example 1: Two CPUs doing their best encoding mp3
With parexec you can execute multiple commands in parallel and have their output clearly displayed in one shell, as well as terminating all with one keystroke.
Usage: parexec NUMTHREADS
where NUMTHREADS is the number of commands you want to execute in parallel
The commands are read from stdin. Empty lines are ignored. Lines containing a
single `-' instruct parexec to wait until all previous commands have finished
before starting to execute further commands.
When sending a SIGINT to parexec (usually done when you hit CTRL-C) it will wait
for currently running processes, but if they are done parexec will exit ignoring
all the following commands.
When sending a SIGQUIT to parexec (usually done when you hit CTRL-\) or by
sending SIGTERM to parexec (e.g. with kill parexec_pid) it will terminate the
running processes immediately and exit.
After the start of parexec your shell window will be split up horizontally into
NUMTHREADS sections. Each section containing the output of one command (which
will scroll away as your command writes too much) and a status bar. The status
bar may show:
> cdda2wav -B -Owav
> for f in *.wav; do echo "lame -q 0 -b 128 $f ${f%.wav}.mp3 && rm $f"; done | parexec 2
To efficiently compress all Postscript files in a given path on a 4 CPU machine do:
> find /path/to/ps -name '*.ps' -printf 'gzip --best --verbose "%p"\n' | parexec 4
Example 1: Two CPUs doing their best encoding mp3
You must not read nor understand this to use parexec :-)
The program parexec is written in C++ and utilizes the pthreads and ncurses lib.
For each NUMTHREADS a writer thread is started that execute their command via a
modified system() call. All output of the command is send through a pipe to the
reader thread. This reader thread waits for output of any command to arrive in
the pipes (via poll() call). The serialized output is then written on the screen
via ncurses. A signal handler is installed to catch the SIGINT, SIGQUIT and
SIGTERM signals. Of course synchronisation (with mutexes and semaphores) is used
for critical resources, such as the reading of commands or the output with
ncurses.