Backend program logic

Work generator

for each wu created
    wu.transition_time = now

Scheduler

when send a result
    result.report_deadline = now + wu.delay_bound
    wu.transition_time = min(wu.transition_time, result.report_deadline)
when receive a result
    if client error
        result.outcome = client_error
        result.validate_state = INVALID
    else
        result.outcome = success
    result.server_state = OVER
    wu.transition_time = now
when a result falls off the bottom of infeasible queue
    result.server_state = OVER
    result.outcome = COULDNT_SEND
    wu.transition_time = now

Transitioner

// gets run when either
// - a result becomes done (via timeout or client reply)
// - the WU error mask is set (e.g. by validator)
// - assimilation is finished
for each WU with now > transition_time:

    // check for timed-out results
    for each result of WU
        if result.server_state = in_progress and now > result.report_deadline
            result.server_state = OVER
            result.outcome = NO_REPLY

    // trigger validation if needed
    K = # of SUCCESS results
    if K >= M
        if any result is server_state OVER, outcome SUCCESS, validate_state INIT
            wu.need_validate = true

    // check for WU error conditions
    if any result has outcome couldnt_send
        error_mask |= couldnt_send
    K = # results with outcome = client_error
    if K > A
        error_mask |= too_many_error_results

    // Note: check on # of success results is done in validator

    K = total # results
    if K > B
        error_mask |= too_many_total_results

    // if no WU errors, generate new results if needed
    if error_mask == 0
        K = # results w/ server_state = unsent or in_progress
        L = N - K
        generate L new results

    // if WU errors, clean up unsent results
    // and trigger assimilation if needed
    if error_mask
        for all results server_state = unsent
            server_state = over
            outcome = didnt_need
        if wu.assimilate_state == init
            wu.assimilate_state = ready

    // if WU is assimilated, trigger deletion of files
    if wu.assimilated_state = DONE
        // trigger input file deletion if needed
        if (all results are OVER and those that are outcome SUCCESS
            have validate_state != INIT)
            wu.file_delete_state = ready

        // outputs of error results can be deleted immediately;
        // outputs of successful results can be deleted when validated
        for results of WU
            if canonical result and not all results OVER
                continue
            if outcome = CLIENT_ERROR or (SUCCESS and (VALID or INVALID))
                if file_delete_state = INIT
                    result.file_delete_state = READY

    // get next result timeout if any
    transition_time = MAX_INT
    for all results IN_PROGRESS
        transition_time = min(transition_time, result.report_deadline)

    // if transitioner is way behind schedule,
    // don't repeatedly handle this WU
    transition_time = max(transition_time, now+delay_bound)

Validator

for each WU w/ need_validate true
    if have canonical result
        for each result w/ validate_state INIT and outcome SUCCESS
            // possible that we've already deleted canonical output files
            if canonical_result.file_delete_state = DONE
                validate_state = INVALID
            else
                if matches canonical, grant credit
                validate_state = VALID or INVALID
            need_to_handle_over_results = true
    else
        S = set of results w/ outcome SUCCESS
        if consensus(S)
            set canonical_result
            set success results as VALID or INVALID
            grant credit
            need_to_handle_over_results = true
            wu.assimilate_state = READY
            for all results server_state UNSENT
                server_state = OVER
                outcome = DIDNT_NEED
        else
            if # of successful results > C
                wu.error_mask |= too_many_success_result
                need_to_handle_over_results = true

    if need_to_handle_over_results:
        wu.transition_time = now

Assimilator

for each WU with assimilate_state = READY
    call project-specific handler function
    wu.assimilate_state = done
    wu.transition_time = now

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