.TH MDM.SCREEN 1 "2009-03-06" Linux "User Commands"

.SH NAME
mdm.screen \- run a command under mdm-master

.SH SYNOPSIS
.B mdm.screen
.RI [ "-c iospec" ]
.RI [ "-n slaves" ]
.I command

.SH DESCRIPTION
.B mdm.screen
runs
.I command
under
.B mdm-master
so that
.B mdm-run
commands in
.I command
can run in parallel.

This program is a part of the Middleman System (mdm).

.SH OPTIONS
The
.B mdm.screen
command has two optional options.

.IP "-c iospec"
The iospec file (see below).

.IP "-n slaves"
The number of
.B mdm-slave
process to start (default 6).

.SH THE IOSPEC FILE
.B mdm-master
uses the
.I iospec
file to decide whether two commands interfere with each other, and it
only runs two commands at the same time if they do not interfere.

Each line of the
.I iospec
file specifies the I/O behavior of a program, unless the line starts
with a '#' character, in which case the line is treated as comments and
ignored.
The format is as follows:

.RS
.I program spec spec ...
.RE

.P
.I program
names the program whose behavior you are specifying.
For each
.I spec
element, the first character indicates
.IR usage ,
and the remaining characters indicate
.IR resource .

A
.I resource
that starts with a '-' character represents the argument of the
corresponding program option.
A
.I resource
that is an empty string represents a program argument.
A
.I resource
that is not empty and does not start with a '-' character represents the
.I resource
string itself.

A
.I usage
is typically an upper-case character.
If two commands access the same resource with different
.IR usage ,
.B mdm-master
will not run these two commands at the same time.
Furthermore, if a command access a resource with \'W\'
.IR usage ,
.B mdm-master
will not run it with any command that access the same resource in any
way (including 'W').
There is a special case: if
.I usage
is '0' and
.I resource
starts with a '-' character,
it means that the
.I resource
program option does not take any arguments.

All programs has an implicit
.IR spec " 'Rglobal',"
so if you mark a program as 'Wglobal', it will not run while any other
command is running.

Here is an example to help clarify matters.
Suppose we have the following iospec file:

.RS
cc W-o 0-c R
.br
rm W
.RE

.P
Then these two commands
.B can
run at the same time:

.RS
cc -o pa pa.o lib.o
.br
cc -o pb pb.o lib.o
.RE

.P
These two commands
.B cannot
run at the same time:

.RS
cc -o pa.o -c pa.c
.br
cc -o pa pa.o lib.o
.RE

.P
And these two commands also
.B cannot
run at the same time:

.RS
cc -o pa pa.o lib.o
.br
rm pa
.RE

.SH EXIT STATUS
The exit status of
.B mdm.screen
is 0.

.SH EXAMPLE
Here is what you do to decompress all files with .gz extension in the
current directory tree.

.RS
mdm.screen find . -iname '*.gz' -exec mdm-run gunzip {} \\;
.RE

.P
Since we run
.B find
under
.B mdm.screen
and invoking
.B gunzip
under
.BR mdm-run ,
we specify that we wish to run the
.B gunzip
commands in parallel.

.SH SEE ALSO
.BR mdm-run "(1), " mdm-sync "(1), " ncpus (1)