notes

Abstractions

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Client files
two main files:

prefs.xml
    user preferences.
    includes list of projects; for each:
        master URL
        authenticator
        project-specific prefs
        resource share
    prefs mod time

client_state.xml
    hostid
    per-project info
        list of sched servers for project
        project name
        hostid
        next_request_time
        rpc_seqno (specific to this host)
        work info
    files, WUs, results etc.

NOTES
- On startup, if there's no prefs.xml, the client prompts
  for a master URL and authenticator,
  and creates an initial prefs.xml with a zero mod time
  (so that any web-created prefs file will override)
- We need to safeguard against a buggy scheduling server
  sending back an incomplete or empty prefs file.
  Suggestions:
    1) verify that at least the responding project is present in the prefs;
       (or contain at least 1 project)
    2) back up the old prefs file (prefs.xml.date)
- prefs.xml has priority over client_state.xml
  If there's a project in prefs with no counterpart in client_state,
  a new entry in client_state is created.
  Entries in client_state absent from prefs are deleted.

- to "clone" an installation on a new computer,
  just need to copy the core client (or run the installer)
  then copy the account.xml file.

- a scheduler request can specify that no client_state.xml
  was found, so a new host record should be created.

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When does client contact scheduling server?
Each result has a max notification delay,
so when a client completes it there's a deadline for notification.

Contact a scheduling server if:
- you're below the low-water mark in work for that project,
  or you have a result past its deadline
- AND there's no delay in effect for that project.
    A delay may be explicitly returned by the scheduling server,
    or may be because of exponential backoff after failed attempts.
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Given that we can estimate the time it will take to get back
a result from a given host, it might be possible to assign
deadlines to results, and only send them to hosts that are fast enough
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Client logging
write events to log file:
    start/stop client
    start/finish file xfer
    start/finish application execution