== Aynchronous Communications (Pjotr) ==

AC has many possible implementations and the main danger is to overcomplicate a solution (trying to facilitate all wishes and real user requirements).

=== Typical use case ===

Typically, now, a user creates a webservice (HTTP) and needs a way of executing a job that may take longer than the time a browser times out (think of BLAST). Potentially the job can take a month to run and both the client, server and network may be occasionaly down. Finally the user gets the output from the job - with output on success, error on failure.

The webservice author will want a clean API which allows job submission and passing the feedback mechanism.

=== Minimal Specification ===

A only job of the AC is to provide the messaging service between client and job. 

What it should do:

  * Receive info from web-service (jobreceiver)
  * Start remote job on cluster (jobmonitor)
  * Pipe input data to job (jobmonitor)
  * Monitor job status (on failure perhaps restart) 
  * Get output (jobmonitor)
  * Push output to client (jobsender)

What it should *not* do:

  * Authentication/authorisation (is responsibility of the webservice)
  * Filtering of data (modifying the stream) is responsibility of webservice)
  * Job control (handled by cluster tools)

In its minimalistic fashion it does not even handle status reports (i.e. percentage of job executed).

=== API ===

  * jobreceiver may be able to receive jobs through SOAP, a pipe, or mail
  * jobmonitor may be able to give updates on percentage executed (SOAP, RPC)
  * jobsender may be able to return results through SOAP, pipe or mail

=== Notes ===

  * The jobmonitor has to be stateful as the server or node running the job may go down
  * Piping is an incredibly useful mechanism. The complication with webservices is the asynchronous nature (while the web protocol tends to by synchronous) - inspiration could be [http://www.aei.mpg.de/~peekas/modglue/ modglue] (a Plan9-inspired extension of the Unix pipe concept). What I would like to do is:

  acjob -t pipe "dbfetch URI:gb -t fasta|clustalw"|phyloanalyse > tree.ph

where dbfetch and clustalw run on the cluster and phyloanalyse locally - just as an example. Obviously with pipes you expect the client to keep running uninterrupted. The AC version could be (simplistically):

  acjob -t email me@waste.com "dbfetch URI:gb -t fasta|clustalw"
  cat email|phyloanalyse > tree.ph

or:

  acjob -t poll "dbfetch URI:gb -t fasta|clustalw"|acpoll -i 180|phyloanalyse > tree.ph

where acpoll polls the jobmonitor every 3 minutes for results.