The Logic of Backend Programs

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Contents 1 General 2 Work Generator 3 Scheduler 4 Transitioner 5 Validator 6 Assimilator 7 UCB Source 8 Copyright ©

[edit] General

The "pseudo"-code for the Back-End Server Daemons is listed in this page.

[edit] Work Generator

   for each wu created
       wu.transition_time = now

[edit] 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

[edit] 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)

[edit] 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

[edit] Assimilator

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

[edit] UCB Source

• Backend program logic

[edit] Copyright ©

• 2005 University of California
• 2005 Paul D. Buck

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation.