<?php
require_once("docutil.php");
page_head("Workunit and result state transitions");
echo "

<p>
The processing of workunits and results
can be described in terms of transitions of their state variables.

<h3>Workunit state variables</h3>
<p>
Workunits parameters are described <a href=work.php>here</a>.

<p>
Workunit state variables are as follows:
";
list_start();
list_item(
    "canonical_resultid",
    "The ID of the canonical result for this workunit, or zero.
    <ul>
    <li> Initially zero
    <li> Set by the validator (by check_set())
    </ul>
    "
);

list_item("transition_time",
    "The next time to check for state transitions for this WU.
    <ul>
    <li>Initially now.
    <li>Set to now by scheduler when get a result for this WU.
    <li>Set to min(current value, now + delay_bound) by scheduler
    when send a result for this WU
    <li>Set to min(x.sent_time + wu.delay_bound) over IN_PROGRESS results x
    by transitioner when done handling this WU
    <li>Set to now by validator if it finds canonical result,
    or if there is already a canonical result
    and some other results have validate_state = INIT,
    or if there is no consensus and the number of successful results
    is > wu.max_success_results
    </ul>
    "
);
list_item("file_delete_state",
    "Indicates whether input files should be deleted.
    <ul>
    <li>Initially INIT
    <li>Set to READY by transitioner when all results have server_state=OVER
        and wu.assimilate_state=DONE
        Note: db_purge purges a WU and all its results when
        file_delete_state=DONE;
        therefore it is critical that it only be set to DONE
        if all results have server_state=OVER.
    <li>Set to DONE by file_deleter when it has attempted to delete files.
    </ul>
    "
);

list_item("assimilate_state",
    "Indicates whether the workunit should be assimilated.
    <ul>
    <li> Initially INIT
    <li> Set to READY by transitioner if wu.assimilate_state=INIT
        and WU has error condition
    <li> Set to READY by validator when find canonical result
        and wu.assimilate_state=INIT
    <li> Set to DONE by assimilator when done
    </ul>
    "
);

list_item("need_validate",
    "Indicates that the workunit has a result that needs validation.
    <ul>
    <li> Initially FALSE
    <li> Set to TRUE by transitioner if the number of success results
        is at least wu.min_quorum and there is a success result
        not validated yet
    <li> Set to FALSE by validator
    </ul>
    "
);

list_item("error_mask",
    "A bit mask for error conditions.
    <ul>
    <li> Initially zero
    <li> Transitioner sets COULDNT_SEND_RESULT if some result couldn't be sent.
    <li> Transitioner sets TOO_MANY_RESULTS if too many error results
    <li> Transitioner sets TOO_MANY_TOTAL_RESULTS if too many total results
    <li> Validater sets TOO_MANY_SUCCESS_RESULTS if no consensus
        and too many success results
    </ul>
    "
);
list_end();
echo "

Workunit invariants:
<ul>
<li> eventually either canonical_resultid or error_mask is set
<li> eventually transition_time = infinity
<li> Each WU is assimilated exactly once
</ul>

<p>
Notes on deletion of input files:
<ul>
<li> Input files are eventually deleted,
but only when all results have state=OVER
(so that clients don't get download failures)
and the WU has been assimilated
(in case the project wants to examine input files in error cases).
</ul>

<h3>Result state variable</h3>
Result state variables are listed in the following table:
";


list_start();
list_item("report_deadline",
    "Give up on result (and possibly delete input files)
    if don't get reply by this time.
    <ul>
    <li> Set by scheduler to now + wu.delay_bound when send result
    </ul>
    "
);
list_item("server_state",
    "Values: UNSENT, IN_PROGRESS, OVER
    <ul>
    <li> Initially UNSENT
    <li> Set by scheduler to IN_PROGRESS when send result
    <li> Set by scheduler to OVER when get reply from client
    <li> Set by transitioner to OVER if now > result.report_deadline
    <li> Set by transitioner to OVER if WU has error condition
        and result.server_state=UNSENT
    <li> Set by validator to OVER if WU has canonical result
        and result.server_state=UNSENT
    </ul>
    "
);
list_item("outcome",
    "Values: SUCCESS, COULDNT_SEND, CLIENT_ERROR, NO_REPLY, DIDNT_NEED.
    <br>Defined iff result.server_state=OVER
    <ul>
    <li> Set by scheduler to SUCCESS if get reply and no client error
    <li> Set by scheduler to CLIENT_ERROR if get reply and client error
    <li> Set by transitioner to NO_REPLY if server_state=IN_PROGRESS
        and now<report_deadline
    <li> Set by transitioner to DIDNT_NEED if WU has error condition
        and result.server_state=UNSENT
    <li> Set by validator to DIDNT_NEED if WU has canonical result
        and result.server_state=UNSENT
    </ul>
    "
);
list_item("client_state",
    "Records the client state (upload, process, or download)
    where an error occurred.
    Defined if outcome is CLIENT_ERROR.
    "
);

list_item("file_delete_state",
    "
    <ul>
    <li> Initially INIT
    <li> Set by transitioner to READY if this is the canonical result,
        and file_delete_state=INIT,
        and wu.assimilate_state=DONE,
        and all the results have server_state=OVER,
        and all all the results with outcome=SUCCESS have validate_state<>INIT 
    <li> Set by transitioner to READY if wu.assimilate_state=DONE
        and result.outcome=CLIENT_ERROR
        or result.validate_state!=INIT
    </ul>
    "
);

list_item("validate_state",
    "
    Defined iff result.outcome=SUCCESS
    <ul>
    <li> Initially INIT
    <li> Set by validator to VALID if outcome=SUCCESS and matches canonical result
    <li> Set by validator to INVALID if outcome=SUCCESS and doesn't match canonical result
    <li> Set by validator to ERROR if outcome=SUCCESS and
        had a permanent error trying to read an output file,
        or an output file had a syntax error.
    <li> Set by validator to INCONCLUSIVE if check_set()
        didn't find a consensus in a set of results containing this one.
    </ul>
    "
);
list_end();

echo "

<p>
Result invariants:
<ul>
<li> Eventually server_state = OVER.
<li> Output files are eventually deleted.
</ul>
Notes on deletion of output files:
<ul>
<li> Non-canonical results can be deleted as soon as the WU is assimilated.
<li> Canonical results can be deleted only when all results have server_state=OVER and all success results are validated.
<li> If a result reply arrives after its timeout,
the output files can be immediately deleted.

</ul>
How do we delete output files that arrive REALLY late?
(e.g. uploaded after all results have timed out, and never reported)?
Possible answer:
let X = create time of oldest unassimilated WU.
Any output files created before X can be deleted.
";
page_tail();
?>