Job Module

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.

Functions

jobs:current

Signatures	jobs:current() as xs:string
Summary	Returns the id of the current query job.

jobs:list

Signatures	jobs:list() as xs:string*
Summary	Returns the ids of all jobs that are currently queued or executed.
Examples	jobs:list() returns the same job id as jobs:current if no other job is running. jobs:list() ! jobs:stop(.) stops and invalidates all asynchronous queries and results.

jobs:finished

Signatures	jobs:finished($id as xs:string) as xs:boolean
Summary	Indicates if the evaluation of a job with the specified job $id has finished: true indicates that the job has either finished, or that the job id is unknown. false indicates that a job with this id is queued or currently running.

jobs:stop

Signatures	jobs:stop($id as xs:string) as empty-sequence()
Summary	Cancels the execution of a job with the specified $id, or drops the cached result of a query. Unknown ids are ignored.

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 CACHETIMEOUT is exceeded. Queries may be updating. Variables and context items can be declared via $bindings (see xquery:eval for more details). The $options parameter contains evaluation options: cache: indicates if the query result will be cached or ignored (default: true). If the query result will not be cached, the query id will immediately be discarded after query execution, too. base-uri: set base-uri property for the query. This URI will be used when resolving relative URIs by functions such as fn:doc (default: empty string).
Errors	overflow: Too many queries or query results are queued. CACHETIMEOUT can be decreased if the default setting is too restrictive.
Examples	jobs:eval("1+3") returns a query id, e.g. Query-abc. The result can be retrieved via a second query in the same BaseX context: jobs:result("Query-abc") The following RESTXQ function will return the id of the query thread, which evaluates the query that has been specified in the body of a POST request: declare %rest:POST("{$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 cached result of a query with the specified job $id: Results can only be retrieved once. After retrieval, the cached result will be dropped. If the query raised an error, the cached error will be raised instead.
Errors	running: the query is still running. unknown: the supplied query id is unknown: The query result may already have been retrieved, or query execution may have been stopped.
Examples	The following RESTXQ function will either return the result of a previously started query or an error: declare %rest:path('/result/{$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) )

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.