Difference between revisions of "Job Module"

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==jobs:ids==
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==jobs:list==
  
 
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| width='120' | '''Signatures'''
 
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|{{Func|jobs:ids||xs:string*}}
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|{{Func|jobs:list||xs:string*}}
 
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| '''Summary'''
 
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* <code>jobs:ids() ! jobs:stop(.)</code> stops and invalidates all asynchronous queries and results.
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* <code>jobs:list() ! jobs:stop(.)</code> stops and invalidates all asynchronous queries and results.
 
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Revision as of 10:53, 26 June 2016

This XQuery Module provides functions for organizing running commands and queries (…more to come).

Conventions

All functions in this module are assigned to the http://basex.org/modules/jobs namespace, which is statically bound to the jobs prefix. Errors will be bound to the same prefix.

Asynchronous Execution

Asynchronous query execution is recommendable if a client does not, or cannot, wait until a request is fully processed. This is e. g. the case with web browsers, which will usually cancel a request after a specific timeout. In such cases, you can use asynchronous execution to trigger another server-side process, which will start the time-consuming process, and fetch the result later on as soon as it is available.

jobs:eval

Signatures jobs:eval($query as xs:string) as xs:string
jobs:eval($query as xs:string, $bindings as map(*)) as xs:string
jobs:eval($query as xs:string, $bindings as map(*), $options as map(xs:string, xs:string)) as xs:string
Summary Prepares the supplied $query string for asynchronous execution and returns a query id. The query will be queued as described in the article on Transaction Management, and the result will be cached in main-memory until it is fetched via jobs:result, or until ASYNCTIMEOUT is exceeded. Queries may be updating.
Variables and context items can be declared via $bindings (see xquery:eval for more details). The $options parameter contains evaluation options:
  • cache: indicates if the query result will be cached or ignored (default: true). If the query result will not be cached, the query id will immediately be discarded after query execution, too.
  • base-uri: set base-uri property for the query. This URI will be used when resolving relative URIs by functions such as fn:doc (default: empty string).
Errors overflow: Too many queries or query results are queued. To fix this, the query results should be retrieved.
Examples
  • jobs:eval("1+3") returns a query id, e.g. Query-abc. The result can be retrieved via a second query in the same BaseX context: jobs:result("Query-abc")
  • The following RESTXQ function will return the id of the query thread, which evaluates the query that has been specified in the body of a POST request:
declare %rest:POST("{$query}") %rest:path('/eval') function local:eval($query) {
  jobs:eval($query)
};

jobs:result

Signatures jobs:result($id as xs:string) as item()*
Summary Returns the result of an asynchronously executed query with the specified query $id:
  • Results can only be retrieved once. After retrieval, the cached result will be discarded.
  • If the query raised an error, the error will be raised instead.
Errors running: the query is still running.
unknown: the supplied query id is unknown: The query result may already have been retrieved, or query execution may have been stopped.
Examples
  • The following RESTXQ function will either return the result of a previously started query or an error:
declare %rest:path('/result/{$id}') function local:result($id) {
  jobs:result($id)
};
  • The following query demonstrates how the results of an asynchronously executed query can be returned in a single query. Please remember that this is not the common way how these functions are used in practice:
let $query := jobs:eval('(1 to 10000000)[. = 1]')
return (
  hof:until(
    function($result) { jobs:finished($query) },
    function($curr) { prof:sleep(10) },
    ()
  ),
  jobs:result($query)
)

jobs:finished

Signatures jobs:finished($id as xs:string) as xs:boolean
Summary Indicates if the evaluation of a query with the specified query $id has finished. If false is returned, the query is still running. An error will be raised if the query result was not cached or has already been retrieved.
Errors unknown: the supplied query id is unknown: The query result may already have been retrieved, or query execution may have been stopped.

jobs:stop

Signatures jobs:stop($id as xs:string) as empty-sequence()
Summary Cancels the execution of a query with the specified query $id, or drops the query result if it has already been executed.
Errors unknown: the supplied query id is unknown: The query result may already have been retrieved, or query execution may have been stopped.

jobs:list

Signatures jobs:list() as xs:string*
Summary Returns the ids of all queries that are either being executed asynchronously, or that have been executed and the results of which have been cached.
Examples
  • jobs:list() ! jobs:stop(.) stops and invalidates all asynchronous queries and results.

Errors

Code Description
unknown The supplied query id is unknown or not available anymore.
running A query is still running.
overflow Too many queries or query results are queued.

Changelog

The module was introduced with Version 8.5.