boinc/doc/backend_programs.php

<?php
require_once("docutil.php");
page_head("Work-handling daemons");
echo "

<p>
A BOINC project includes of a set of daemons
for generating and handling work.
Each program should be listed as a
<a href=project_daemons.php>daemon</a> in the
<a href=configuration.php>config.xml</a> file.
Most daemons have the command-line options:
";
list_start();
list_item("-d N",
	"Sets the verbosity level.
	1 = critical messages only,
	2 = normal messages,
	3 = detailed debugging info."
);
list_item("-one_pass",
	"Process all available items, then quit."
);
list_item("-mod n i",
	"Handle only workunits for which mod(id, n) = i.
	This lets you run the daemon on arbitrarily many machines.
	(available for feeder, transitioner, validator)."
);
list_item("-sleep_interval N",
    "How long to sleep when there's nothing to do."
);
list_end();

echo "
<h3>Work generator</h3>
<p>
There is one work generator per application.
It creates workunits and the corresponding input files.
It is application-specific, and uses
<a href=tools_work.php>BOINC library functions</a>
for registering the workunits in the database.
<p>
During testing, you can create a single workunit using
<a href=tools_work.php>create_work</a>,
then use the daemon program
<a href=busy_work.php>make_work</a>
to copy this workunit as needed to maintain a given supply of work.

<h3>Feeder</h3>
<p>
This program is supplied by BOINC and is application independent.
It creates a shared-memory segment used to pass database records
to CGI scheduler processes.
This data includes applications, application versions,
and 'work items' (an unsent result and its corresponding workunit).
It has the following command-line options:
";
list_start();
list_item("-random_order",
    "Enumerate work items in order of increasing result.random"
);
list_item("-priority_order",
    "Enumerate work items in order of decreasing result.priority"
);
list_item("-priority_order_create_time",
    "Enumerate work items in order of decreasing result.priority,
    then increasing workunit.create_time"
);
list_item("-sleep_interval N",
    "Sleep N seconds if nothing to do"
);
list_item("-allapps",
    "Interleave work items from all applications.
    Weight applications according to the value of their 'weight' field;
    if all weights are zero, results are interleaved uniformly.
    Without this option, runnable results are enumerated 
    in an indeterminate order,
    and there may be periods when only results from
    one application are available for sending.
    "
);
list_item("-purge_stale X",
    " remove work items from the shared memory segment
    that have been there for longer then x minutes
    but haven't been assigned"
);
list_end();
echo "
<p>
If a user's project preferences include elements of the form
&lt;app_id&gt;N&lt;/app_id&gt;
then the scheduler will send the user work only from those applications.

<h3>Transitioner</h3>
<p>
This program is supplied by BOINC and is application independent.
It handles state transitions of workunits and results.
It generates initial results for workunits,
and generates more results when timeouts or errors occur.

<h3>Validator</h3>
<p>
There is one validator per application.
It compares redundant results and selects a <b>canonical result</b>
representing the correct output,
and a <b>canonical credit</b> granted to users and hosts
that return the correct output.
Depending on your application,
you may be able to use a BOINC-supplied validator,
or you may have to develop a customized validator;
<a href=validate.php>details are here</a>.

<h3>Assimilator</h3>
There is one assimilator per application.
It handles workunits that are 'completed':
that is, that have a canonical result or for which
an error condition has occurred.
Handling a successfully completed result might involve
record results in a database and perhaps generating more work.

<h3>File deletion</h3>
The application-independent program
<a href=file_deleter.php>file_deleter</a>
deletes input and output files when they are no longer needed.

<h3>Database purging</h3>
The application-independent program
<a href=db_purge.php>db_purge</a>
removes work-related database entries when they are no longer needed.
This keeps your database at a constant size even
when your project runs for a long time.
";
page_tail();
?>