Job Module

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

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.

Services

A job can be registered as service by supplying the service option to jobs:eval:

<syntaxhighlight lang="xquery"> (: register job as service; will be run every day at 1 am :) jobs:eval('db:drop("tmp")', (), map { 'id':'cleanup', 'start':'01:00:00', 'interval':'P1D', 'service': true() }),

(: list registered services :) jobs:services(), (: result: <job base-uri="..." id="cleanup" interval="P1D" start="01:00:00">db:drop("tmp")</job> :)

(: unregister job :) jobs:stop('cleanup', map { 'service': true() }) </syntaxhighlight>

Some more notes:

• All job services will be scheduled for evaluation when the BaseX server or BaseX HTTP server is started.
• If a job service is outdated (e.g. because a supplied end time has been exceeded), it will be removed from the jobs file at startup time.
• Job services can be updated: If a new job is registered, and if there is already a job with the same id, the old entry will be replaced.
• The job definitions are stored in a jobs.xml file in the database directory. It can also be edited manually.

Basic Functions

jobs:current

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

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, stopped, and finished jobs with cached results.
Examples	jobs:list() returns the same job id as jobs:current if no other job is registered.

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, cached user: user who started the job duration: evaluation time (included if a job is running or if the result was cached) start: next start of job (included if a job will be executed repeatedly) time: time when job was registered
Examples	jobs:list-details() returns information on the currently running job and possibly others: <syntaxhighlight lang="xml"> <job id="job1" type="XQuery" state="running" user="admin" duration="PT0.001S"> XQUERY jobs:list-details() </job> </syntaxhighlight>

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).

jobs:services

Signatures	jobs:services() as element(job)*
Summary	Returns a list of all jobs that have been persistently registered as Services.
Errors	services: Registered services cannot be parsed.

Execution

There are cases in which a client does not, or cannot, wait until a request is fully processed. The client may be a browser, which sends an HTTP request to the server in order to start another time-consuming query job. The functions in this section allow you to register a new query job from a running query. Jobs can be executed immediately (i.e., as soon as the Concurrency Control allows it) or scheduled for repeated execution. Each registered job gets a job id, and the id can be used to retrieve a query result, stop a job, or wait for its termination.

jobs:eval

Signatures	jobs:eval($query as xs:anyAtomicItem) as xs:string jobs:eval($query as xs:anyAtomicItem, $bindings as map(*)?) as xs:string jobs:eval($query as xs:anyAtomicItem, $bindings as map(*)?, $options as map(*)?) 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. The query can be a URI or a string, and variables and context items can be declared via $bindings (see xquery:eval for more details). The following $options can be supplied: 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. service: additionally registers the job as service. Registered services must have no variable bindings.
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. options: The specified options are conflicting.
Examples	Cache query result. The returned id can be used to pick up the result with jobs:result: <syntaxhighlight lang="xquery"> jobs:eval("1+3", (), map { 'cache': true() }) </syntaxhighlight> A happy birthday mail will be sent at the given date: <syntaxhighlight lang="xquery"> jobs:eval("import module namespace mail='mail'; mail:send('Happy birthday!')", (), map { 'start': '2018-09-01T06:00:00' })}} </syntaxhighlight> 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: <syntaxhighlight lang="xquery"> 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) }; </syntaxhighlight> 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: <syntaxhighlight lang="xquery"> jobs:eval("prof:sleep(1500)", (), map { 'interval': 'PT1S', 'end': 'PT10S' }) </syntaxhighlight> The query in the specified file will be evaluated once: <syntaxhighlight lang="xquery"> jobs:eval(xs:anyURI('cleanup.xq')) </syntaxhighlight> The following expression, if stored in a file, will be evaluated every 5 seconds: <syntaxhighlight lang="xquery"> jobs:eval( static-base-uri(), map { }, map { 'start': 'PT5S' } ) </syntaxhighlight>

jobs:result

Signatures	jobs:result($id as xs:string) as item()*
Summary	Returns the cached result of a job with the specified job $id: Results can only be retrieved once. After retrieval, the cached result will be dropped. If the original job has raised an error, the cached error will be raised instead.
Errors	running: the job is still running. unknown: the supplied id is unknown: The id is unknown, or the result has already been retrieved.
Examples	The following RESTXQ function will either return the result of a previously started job or raise an error: <syntaxhighlight lang="xquery"> declare %rest:path('/result/{$id}') function local:result($id) { jobs:result($id) }; </syntaxhighlight> The following query demonstrates how the results of an executed query can be returned within the same query (see below why you should avoid this pattern in practice): <syntaxhighlight lang="xquery"> let $query := jobs:eval('(1 to 10000000)[. = 1]', map { }, map { 'cache': true() }) return ( jobs:wait($query), jobs:result($query) ) </syntaxhighlight> Queries of this kind can cause deadlocks! If the original query and the new query perform updates on the same database, the second query will only be run after the first one has been executed, and the first query will wait for the second query forever. You should resort to xquery:fork-join if you want to have full control on parallel query execution.

jobs:stop

Signatures	jobs:stop($id as xs:string) as empty-sequence()
Summary	Triggers 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. The following $options can be supplied: service: additionally removes the job from the job services list.
Examples	jobs:list()[. != jobs:current()] ! jobs:stop(.) stops and discards all jobs except for the current one.

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: The current job is addressed.

Errors

Code	Description
options	The specified options are conflicting.
id	The specified id is invalid or has already been assigned.
overflow	Too many queries or query results are queued.
range	A specified time or duration is out of range.
running	A query is still running.
self	The current job cannot be addressed.
service	Registered services cannot be parsed, added or removed.
unknown	The supplied query id is unknown or not available anymore.

Changelog

Version 9.2

• Deleted: jobs:invoke (merged with jobs:eval)

Version 9.1

• Updated: jobs:list-details: registration time added.

Version 9.0

• Added: jobs:invoke, Services

Version 8.6

• Updated: jobs:eval: id option added.

The module was introduced with Version 8.5.