Jobs Module

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This XQuery Module provides functions for organizing scheduled, queued, running and cached jobs. Jobs can be commands, queries, client or HTTP requests.

Contents

[edit] 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.

[edit] Functions

[edit] jobs:current

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

[edit] jobs:list

Signatures jobs:list() as xs:string*
Summary Returns the ids of all jobs that are currently registered. The list includes scheduled, queued, running jobs, and cached jobs.
Examples
  • jobs:list() returns the same job id as jobs:current if no other job is registered.
  • jobs:list()[. != jobs:current()] ! jobs:stop(.) stops and invalidates all asynchronous queries and results except for the current one.

[edit] jobs:list-details

Signatures jobs:list-details() as element(job)*
jobs:list-details($id as xs:string) as element(job)*
Summary Returns information on all jobs that are currently registered, or on a job with the specified $id (or an empty sequence if this job is not found). The list includes scheduled, queued, running jobs, and cached jobs. A string representation of the job, or its URI, will be returned as value. The returned elements have additional attributes:
  • id: job id
  • type: type of the job (command, query, REST, RESTXQ, etc.)
  • state: current state of the job (scheduled, queued, running, or cached)
  • user: the user who started the job
  • duration: evaluation time (for running and cached jobs)
  • start: dateTime string with next start (for jobs that will be executed repeatedly)
Examples
  • jobs:list-details() returns information on the currently running job and possibly others:
<job id="job1" type="XQuery" state="running" user="admin" duration="PT0.001S">
  XQUERY jobs:list-details()
</job>

[edit] jobs:finished

Signatures jobs:finished($id as xs:string) as xs:boolean
Summary Indicates if the evaluation of an already running job with the specified $id has finished. As the ids of finished jobs will usually be discarded, unless caching is enabled, the function will also return true for unknown jobs.
  • false indicates that the job id is scheduled, queued, or currently running.
  • true will be returned if the job has either finished, or if the id is unknown (because the ids of all finished jobs will not be cached).

[edit] jobs:stop

Signatures jobs:stop($id as xs:string) as empty-sequence()
Summary Triggeres the cancelation of a job with the specified $id, drops the cached result of a query, or cancels a scheduled job. Unknown ids are ignored. All jobs are gracefully stopped; it is up to the process to decide when it is safe to shut down.

[edit] jobs:wait

Signatures jobs:wait($id as xs:string) as empty-sequence()
Summary Waits for the completion of a job with the specified $id:
  • The function will terminate immediately if the job id is unknown. This is the case if a future job has not been queued yet, or if the id has already been discarded after job evaluation.
  • If the function is called with the id of a queued job, or repeatedly executed job, it may stall and never terminate.
Errors self: if the current job is addressed.

[edit] 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.

[edit] jobs:eval

Updated with Version 8.6: id option added.

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 Schedules the evaluation of the supplied $query and returns a query id. The query will be queued, and the result will optionally be cached. Queries can be updating. Variables and context items can be declared via $bindings (see xquery:eval for more details). The $options parameter contains scheduling options:
  • cache: indicates if the query result will be cached or ignored (default: false):
    • The result will be cached in main-memory until it is fetched via jobs:result, or until CACHETIMEOUT is exceeded.
    • If the query raises an error, it will be cached and returned instead.
  • start: a dayTimeDuration, time or dateTime can be specified to delay the execution of the query:
    • If a dayTimeDuration is specified, the query will be queued after the specified duration has passed. Examples for valid values are: P1D (1 day), PT5M (5 minutes), PT0.1S (100 ms). An error will be raised if a negative value is specified.
    • If a time is specified, the query will be executed at this time of the day. Examples for valid times are: 02:00:00 (2am local time), 12:00:00Z (noon, UTC). If the time lies in the past, the query will be executed the next day.
    • If a dateTime is specified, the query will be executed at this date. Examples for valid values are: 2018-12-31T23:59:59 (New Year's Eve 2018, close to midnight). An error will be raised if the specified time lies in the past.
  • interval: a dayTimeDuration string can be specified to execute the query periodically. An error is raised if the specified interval is less than one second (PT1S). If the next scheduled call is due, and if a query with the same id is still running, it will be skipped.
  • end: scheduling can be stopped after a given time or duration. The string format is the same as for start. An error is raised if the resulting end time is smaller than the start time.
  • base-uri: sets the base-uri property for the query. This URI will be used when resolving relative URIs, such as with fn:doc.
  • id: sets a custom job id. The id must not start with the standard job prefix, and it can only be assigned if no job with the same name exists.
Errors overflow: Query execution is rejected, because too many jobs are queued or being executed. CACHETIMEOUT can be decreased if the default setting is too restrictive.
range: A specified time or duration is out of range.
id: The specified id is invalid or has already been assigned.
Examples
  • Cache query result. The returned id can be used to pick up the result with jobs:result:
jobs:eval("1+3", (), map { 'cache': true() })
  • A happy birthday mail will be sent at the given date:
jobs:eval("import module namespace mail='mail'; mail:send('Happy birthday!')",
  (), map { 'start': '2018-09-01T06:00:00' })}}
  • The following RESTXQ functions can be called to execute a query at 2 am every day. An id will be returned by the first function, which can be used to stop the scheduler via the second function:
declare %rest:POST("{$query}") %rest:path('/start-scheduling') function local:start($query) {
  jobs:eval($query, (), map { 'start': '02:00:00', 'interval': 'P1D' })
};
declare %rest:path('/stop-scheduling/{$id}') function local:stop($id) {
  jobs:stop($id)
};
  • Query execution is scheduled for every second, and for 10 seconds in total. As the query itself will take 1.5 seconds, it will only be executed every second time:
jobs:eval("prof:sleep(1500)", (), map { 'interval': 'PT1S', 'end': 'PT10S' })
  • The following expression, if stored as a file, calls and evaluates itself every 5 seconds:
jobs:eval(
  file:read-text(static-base-uri()),
  map { },
  map { 'start': 'PT5S' }
)

[edit] jobs:invoke

Introduced with Version 9.0

Signatures jobs:invoke($uri as xs:string) as xs:string
jobs:invoke($uri as xs:string, $bindings as map(*)?) as xs:string
jobs:invoke($uri as xs:string, $bindings as map(*)?, $options as map(xs:string, xs:string)) as xs:string
Summary Schedules the evaluation of the XQuery expression located at $uri and returns a query id. The semantics and remaining arguments are identical to jobs:eval.
Errors overflow: Query execution is rejected, because too many jobs are queued or being executed. CACHETIMEOUT can be decreased if the default setting is too restrictive.
range: A specified time or duration is out of range.
id: The specified id is invalid or has already been assigned.
Examples
  • Runs an XQuery expression that may perform some cleanups:
jobs:invoke("cleanup.xq", (), ())

[edit] jobs:result

Signatures jobs:result($id as xs:string) as item()*
Summary Returns the cached result of a job with the specified job $id:
  • Results can only be retrieved once. After retrieval, the cached result will be dropped.
  • If the original job has raised an error, the cached error will be raised instead.
Errors running: the job is still running.
unknown: the supplied id is unknown: The id is unknown, or the result has already been retrieved.
Examples
  • The following RESTXQ function will either return the result of a previously started job or raise an error:
declare %rest:path('/result/{$id}') function local:result($id) {
  jobs:result($id)
};
  • The following query demonstrates how the results of an asynchronously executed query can be returned within the same query:
let $query := jobs:eval('(1 to 10000000)[. = 1]', map{}, map{ 'cache': true() })
return (
  jobs:wait($query),
  jobs:result($query)
)

Please note that queries of this kind can cause deadlocks. For example, if both the original query and the query to be executed asynchronously perform updates on the same database, the second query would only be run after the first one has been executed, and the first query will wait forever. This is why you should avoid this pattern in practice and resort to xquery:fork-join if you want to do things in parallel.

[edit] 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.
range A specified time or duration is out of range.
id The specified is invalid or has already been assigned.
self The current job cannot be addressed.

[edit] Changelog

Version 9.0
Version 8.6

The module was introduced with Version 8.5.

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