Test::MultiFork - Test suite support for multi-process programs

            use Test::MultiFork;

            ($name, $letter, $number) = procname([new name])
            @oldvalues = getcommon()

            use Test::MultiFork qw(groupwait setgroup dofork stderr bail_on_bad_plan)

            $oldgroup = setgroup([$newgroup])

    This test module is to support creating test suites for programs and
    modules that run as multiple processes and do mostly blocking I/O.

    Test::MultiFork handles the forking so that it can set up each child to
    coordinate the output. The output from each child fork is redirected to
    the parent. Each fork produces normal test output -- possibly using
    normal test modules like Test::Simple. The output is collected and
    rewritten by the parent process.

    Each child fork has a letter and number designation. The forks are
    created by "dofork()". Dofork takes a specifiction on the form:
    ([a-z](\d*))+. That is to say, one or more lower-case letters, each
    optionally followd by a number. The number says how many children to
    fork for that letter (default one). The specifier "ab2c3" means have one
    "a" child (numbered 1); two "b" children (numbered 1, 2); and three "c"
    children (numbered 1, 2, 3).

    To aid in writing tests, Test::MultiFork will pass data between the
    child processes. The data is test-writer defined.

    Test::MultiFork acts as a source filter on your code. It does this so
    that it can do lock-step execution control.

    The source filtering is controlled with pseudo labels. The labels must
    be the only thing on the line. The main source control is a label like
    "FORK_abc:". This label tells Test::MultiFork how many times to fork
    (see above). Whatever comes after the "FORK_" and before the ":" is a
    fork specifier.

    With a "FORK_abc:" label, varient execution labels are enabled. Varient
    execution labels must be all lowercase. This is to allow you to use
    something different for you loop control labels. This module can be used
    without putting in any special labels.

    Outside of a function, a varient execution label will synchronize all
    the program forks to that line of code. As each fork reaches that line,
    it will stop and wait until all forks get there. At that point, all of
    the forks will start up and run again.

    Inside or outside of a function, once a varient execution labels is
    seen, source code is turned on or off (commented out) depending on if
    the process fork letter is in the label.

    For example:

            # let's fork 5 times

            print "I'm an 'a' or 'b' process\n";

            print "I'm an 'c' or 'd' process\n";

            print "we are all running in lockstep\n";

            sub xyz {
                    print "only a does something in this function\n";

    Since the processes run in lockstep (synchronized at the labels), loop
    controls must cover all processes.

    In addition to fork() and the varient execution labels, you can override
    a default signal selection for debugging. By default the "USR1" signal
    is used to aid debugging: if the parent process bails out, it will send
    "USR1" signals to all the children to ask them to print out some
    diagnostics. The special label "SIGNAL_xyz:" changes which signal to
    use. Substitute "xyz" with your choice of signal or "none" to disable
    this feature.

    Import 'stderr' to send the STDERR output from each fork through the
    parent for tagging. The default is to leave STDERR alone.

    Bail out if a test plan isn't followed. This is most useful as a way to
    exit early if one of the fork()ed children exits early.

    If "$ENV{TERM} =~ /xterm/", then escape codes will be printed to change
    the background and foreground text colors so that each fork()ed child
    has a different color scheme.

    Sets a lock on the shared common data.

    Returns the current value of the common data. The common data is an
    array. In scalar context, the first element is returned. getcommon does
    not care if the common data is locked.

    Sets the value of the common data to the new values. Dies if common data
    lock isn't held.

    Releases a lock on the shared common data. Dies if the lock isn't
    already held.

    Wait for all process forks in the process group to get reach this same
    synchronization point as designated by the $tag. The default tag is the
    current source file name and line number. All processes start in the
    "default" group. This is the function used to implement the varient
    execution lockstep synchronization.

    With a $newgroup, changes the process' group identity. All processes
    start in group "default". Returns the old group name.

    Fork off children processes. The parent process becomes the
    special-purpose test coordinator. The specification is as detailed in
    the DESCRIPTION above.

    Change the fork's name. The return value is a list: the current name,
    process' letter, the process' number.

    Test::Simple and Test::More encourage you to specify a test plan at
    compile time. Make sure that dofork() is called before the test plan is

    When using Test::MultiFork's source filter in conjunction with
    Test::Builder anything built on top of it (eg: Test::Simple or
    Test::More) put Test::MultiFork first in the "use" list.

    Test::Harness Test::Builder Test::Simple Test::More Test

    This is new and bearly tested. Please provide feedback!

    Copyright (C) 2003-2006 David Muir Sharnoff <>. This
    module may be used/copied/etc on the same terms as Perl itself.