Test2::Harness::Runner::Resource - Base class for resource management classes


Sometimes you have limited resources that must be shared/divided between tests that run concurrently. Resource classes give you a way to leverage the IPC system used by Test2::Harness to manage resource assignment and recovery.


Here is a resource class that simply assigns an integer to each test. It would be possible to re-use integers, but since there are infinite integers this example is kept simple and just always grabs the next one.

    package Test2::Harness::Runner::Resource::Foo;
    use strict;
    use warnings;

    use parent 'Test2::Harness::Runner::Resource';

    sub available {
        my $self = shift;
        my ($task) = @_;

        # There are an infinite amount of integers, so we always return true
        return 1;

    sub assign {
        my $self = shift;
        my ($task, $state) = @_;

        # Next ID, do not record the state change yet!
        my $id = 1 + ($self->{ID} //= 0);

        print "ASSIGN: $id = $task->{job_id}\n";

        # 'record' should get whatever we need to record the resource, whatever you
        # pass in will become the argument to the record() sub below. This may be a
        # scalar, a hash, an array, etc. It will be serialized to JSON before
        # record() sees it.
        $state->{record} = $id;

        # Pass the resource into the test, this can be done as envronment variables
        # and/or arguments to the test (@ARGV).
        $state->{env_vars}->{FOO_ID} = $id;
        push @{$state->{args}} => $id;

        # The return is ignored.

    sub record {
        my $self = shift;
        my ($job_id, $record_arg_from_assign) = @_;

        # The ID from $state->{record}->{$pkg} in assign.
        my $id = $record_arg_from_assign;

        # Update our internal state to reflect the new ID.
        $self->{ID} = $id;

        # Add a mapping of what job ID gets what integer ID.
        $self->{ID_TO_JOB_ID}->{$id}     = $job_id;
        $self->{JOB_ID_TO_ID}->{$job_id} = $id;

        print "RECORD: $id = $job_id\n";

        # The return is ignored

    sub release {
        my $self = shift;
        my ($job_id) = @_;

        # Clear the internal mapping, the integer ID is now free. Theoretically it
        # can be reused, but this example is not that complex.
        my $id = delete $self->{JOB_ID_TO_ID}->{$job_id};

        # This is called for all tests that complete, even if they did not use
        # this resource, so we return if the job_id is not applicable.
        return unless defined $id;

        delete $self->{ID_TO_JOB_ID}->{$id};

        print "  FREE: $id = $job_id\n";

        # The return is ignored

    sub cleanup {
        my $self = shift;

        print "CLEANUP!\n";


The print statements generated will look like this when running 2 tests concurrently:

    yath test -R Foo -j2 t/testA.t t/testB.t
    (INTERNAL)     ASSIGN: 1 = 4F7CF5F6-E43F-11EA-9199-24FCBF610F44
    (INTERNAL)     RECORD: 1 = 4F7CF5F6-E43F-11EA-9199-24FCBF610F44
    (INTERNAL)     ASSIGN: 2 = E19CD98C-E436-11EA-8469-8DF0BF610F44
    (INTERNAL)     RECORD: 2 = E19CD98C-E436-11EA-8469-8DF0BF610F44
    (INTERNAL)       FREE: 1 = 4F7CF5F6-E43F-11EA-9199-24FCBF610F44
    (INTERNAL)       FREE: 2 = E19CD98C-E436-11EA-8469-8DF0BF610F44

Depending on the tests run the 'FREE' prints may be out of order.



Depending on your preload configuration, yath may have several runners launching tests. If a runner has nothing to do it will lock the queue and try to find the next test that should be run. Only 1 of the runners will be in control of the queue at any given time, but the control of the queue may pass between runners. To manage this there is a mechanism to record messages that allow each runner to maintain a copy of the current state.


Each runner will have an instance of your resource class. When the runner is in control of the queue, and wants to designate the next test to run, it will check with the resource classes to make sure the correct resources are available. To do that it will call available($task) on each resource instance.

The $task will contain the specification for the test, it is a hashref, and you SHOULD NOT modify it. The only key most people care about is the 'file' key, which has the test file that will be run if resources are available.

If resources are available, or if the specific file does not need the resource, the available() method should return true. If the file does need your resource(s), and none are available, this should return false. If any resource class returns false it means the test cannot be run yet and the runner will look for another test to run.


If the runner has determined the test can be run, and all necessary resources are available, it will then call assign($task, $state) on all resource class instances. At this time the resource class should decide what resource(s) to assign to the class.

CRITICAL NOTE: the assing() method MUST NOT alter any internal state on the resource class instance. State modification must wait for the record() method to be called. This is because the assign() method is only called in one runner process, the record() method call will happen in every runner process to insure they all have the same internal state.

The assign() sub should modify the $state hash, which has 3 keys:

env_vars => {}

Env vars to set for the test

args => []

Arguments to pass to the test

record => ...

Data needed to record the state change for resource classes. Can be a scalar, hashref, arrayref, etc. It will be serialized to JSON to be passed between processes.


Once a resource is assigned, a message will be sent to all runner processes INCLUDING THE ONE THAT DID THE ASSIGN that says it should call record($job_id, $record_val) on your resource class instance. Your resource class instance must use this to update the state so that once done ALL processes will have the proper internal state.

The $record_val is whatever you put into $state->{record} in the assign() method above.


Once the above has been done, queue management will be unlocked. You can be guarenteed that only one process will be run the available(), and assign() sequence at a time, and that they will be called in order, though assign() may not be called if another resource was not available. If assign() is called, you can be guarenteed that all processes, including the one that called assign() will have their record() called with the proper argument BEFORE they try to manage the queue (which is the only place resources are checked or assigned).


Whenever a process that is using a resource exits, the runner that waits on that process will eventually send an IPC message announcing that the job_id has completed. Every time a job_id completes the release($job_id) method will be called on your resource class in all runner processes. This allows the state to be updated to reflect the freed resource.

You can be guarenteed that any process that locks the queue to run a new test will eventually see the message. The message may come in during a loop that is checking for resources, in which case the state will not reflect the resource being available, however in such cases the loop will end and be called again later with the message having been receieved. There will be no deadlock due to a queue manager waiting for the message.

There are no guarentees about what order resources will be released in.


$res = $class->new(settings => $settings);

A default new method, returns a blessed hashref with the settings key set to the Test2::Harness::Settings instance.

$bool = $res->available(\%task)



Return true if the resource is available, or if the task does not require the resource.

Return false if the resource is not available, but is needed.

The only key in \%task hashref that most resources will care about is the 'file' key, which contains the test file to be run.

$res->assign(\%task, \%state)



If the task does not need any resources you may simply return.

If resources are needed you should deduce what resources to assign.

You should put any data needed to update the internal state of your resource instance in the $state->{record} hash key. It WILL be serialized to JSON before being used as an argument to record().

    $state->{record} = $id;

If you do not set the 'record' key, or set it to undef, then the record() method will not be called.

If your tests need to know what resources to use, you may set environment variables and/or command line arguments to pass into the test (@ARGV).

    $state->{env_vars}->{FOO_ID} = $id;
    push @{$state->{args}} => $id;

The \%state hashref is used only by your instance, you are free to fully replace the 'env_vars' and 'args' keys. They will eventually be merged into a master state along with those of other resources, but this ref is exclusive to you in this method.

$inst->record($job_id, $record_arg_from_assign)


This will be called in all processes so that your instance can update any internal state.

The $job_id variable contains the id for the job to which the resource was assigned. You should use this to record any internal state. The $job_id will be passed to release() when the job completes and no longer needs the resource.

This is intended only for modifying internal state, you should not do anything in this sub that will explode if it is also done in another process at the same time with the same arguments. For example creating a database should not be done here, multiple processes will fight to do the create. The creation, if necessary should be done in assign() which will be called in only one process.



This will be called for every test job that completes, even if it did not use this resource. If the job_id did not use the resource you may simply return, otherwise update the internal state to reflect that the resource is no longer in use.

This is intended only for modifying internal state, you should not do anything in this sub that will explode if it is also done in another process at the same time with the same arguments. For example deleting a database should not be done here, multiple processes will fight to do the delete. assign() is the only method that will be run in a single process, so if a database needs to be cleaned before it can be used you should clean it there. Any final cleanup should be done in cleanup() which will only be called by one process at the very end.


This will be called once by the parent runner process just before it exits. This is your chance to do any final cleanup tasks such as deleting databases that are no longer going to be used by tests as no more will be run.


The source code repository for Test2-Harness can be found at


Chad Granum <>


Chad Granum <>


Copyright 2020 Chad Granum <>.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.