mdm.screen(1) run a command under mdm-master


mdm.screen [-c iospec] [-n slaves] command


mdm.screen runs command under mdm-master so that mdm-run commands in command can run in parallel.

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


The mdm.screen command has two optional options.

-c iospec
The iospec file (see below).

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


mdm-master uses the 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 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:

program spec spec ...

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

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

A usage is typically an upper-case character. If two commands access the same resource with different usage, mdm-master will not run these two commands at the same time. Furthermore, if a command access a resource with 'W' usage, 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 usage is '0' and resource starts with a '-' character, it means that the resource program option does not take any arguments.

All programs has an implicit 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:

cc W-o 0-c R
rm W

Then these two commands can run at the same time:

cc -o pa pa.o lib.o
cc -o pb pb.o lib.o

These two commands cannot run at the same time:

cc -o pa.o -c pa.c
cc -o pa pa.o lib.o

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

cc -o pa pa.o lib.o
rm pa


The exit status of mdm.screen is 0.


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

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

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