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
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Summary
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Returns the id of the current query job.
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jobs:list
Signatures
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jobs:list() as xs:string*
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Summary
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Returns the ids of all jobs that are currently queued or executed.
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Examples
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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.
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jobs:finished
Signatures
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jobs:finished($id as xs:string) as xs:boolean
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Summary
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Indicates if the evaluation of a job with the specified job $id has finished:
true indicates that the job has either finished, or that the job id is unknown.
false indicates that a job with this id is queued or currently running.
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jobs:stop
Signatures
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jobs:stop($id as xs:string) as empty-sequence()
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Summary
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Cancels the execution of a job with the specified $id , or drops the cached result of a query. Unknown ids are ignored.
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Asynchronous Execution
Asynchronous query execution is recommendable if a client does not, or cannot, wait until a request is fully processed. This is e. g. the case with web browsers, which will usually cancel a request after a specific timeout. In such cases, you can use asynchronous execution to trigger another server-side process, which will start the time-consuming process, and fetch the result later on as soon as it is available.
jobs:eval
Signatures
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jobs:eval($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
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Summary
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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 $options parameter contains evaluation options:
cache : indicates if the query result will be cached or ignored (default: true ). If the query result will not be cached, the query id will immediately be discarded after query execution, too.
base-uri : set base-uri property for the query. This URI will be used when resolving relative URIs by functions such as fn:doc (default: empty string).
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Errors
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overflow : Too many queries or query results are queued. CACHETIMEOUT can be decreased if the default setting is too restrictive.
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Examples
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jobs:eval("1+3", map{}, map{ 'cache': true() }) returns a query id, e.g. CachedXQuery-1 . The result can be retrieved via a second query in the same BaseX context: jobs:result("CachedXQuery-1")
- The following RESTXQ function will return the id of the query thread, which evaluates the query that has been specified in the body of a POST request:
declare %rest:POST("{$query}") %rest:path('/eval') function local:eval($query) {
jobs:eval($query)
};
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jobs:result
Signatures
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jobs:result($id as xs:string) as item()*
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Summary
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Returns the cached result of a query with the specified job $id :
- Results can only be retrieved once. After retrieval, the cached result will be dropped.
- If the query raised an error, the cached error will be raised instead.
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Errors
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running : the query is still running.
unknown : the supplied query id is unknown: The query result may already have been retrieved, or query execution may have been stopped.
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Examples
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- The following RESTXQ function will either return the result of a previously started query or an error:
declare %rest:path('/result/{$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)
)
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jobs:results
Signatures
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jobs:results() as xs:string*
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Summary
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Returns the ids of all jobs for which results have been cached.
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Errors
Code
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Description
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unknown
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The supplied query id is unknown or not available anymore.
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running
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A query is still running.
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overflow
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Too many queries or query results are queued.
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Changelog
The module was introduced with Version 8.5.