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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{| width='100%'|-| width='120' | '''Signatures'''|{{Func|jobs:current||xs:string}}|-side process, which will start | '''Summary'''|Returns the time-consuming process, and fetch id of the result later on as soon as it is availablecurrent job.|}
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This [[Module Library|XQuery Module]] provides functions for organizing scheduled, queued, running and cached jobs. Jobs can be commands and , queries (…more to come), client or HTTP requests.
=Conventions=
All functions in this module are assigned to the <code><nowiki>http://basex.org/modules/jobs</nowiki></code> namespace, which is statically bound to the {{Code|jobs}} prefix. Errors will be bound to the same prefix.
=FunctionsServices=
A job can be registered as ''service'' by supplying the {{Code|service}} option to {{Function|Jobs|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services will be scheduled for evaluation when the BaseX server or BaseX HTTP server is started.* If a job service is outdated (e.g. because a supplied end time has been exceeded), it will be removed from the jobs file at startup time.* The job definitions are stored in a {{Code|jobs.xml}} file in the database directory. It can also be edited manually. =Executing Jobs= 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 [[Transaction Management#Concurrency Control|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:currenteval==
{| width='100%'
|-
| width='120' | '''Signatures'''
|{{Func|jobs:currenteval|$query as xs:anyAtomicItem|xs:string}}<br />{{Func|jobs:eval|$query as xs:anyAtomicItem, $bindings as map(*)?|xs:string}}<br />{{Func|jobs:eval|$query as xs:anyAtomicItem, $bindings as map(*)?, $options as map(*)?|xs:string}}<br />
|-
| '''Summary'''
|Returns Schedules the evaluation of the supplied {{Code|$query}} ({{Code|xs:string}}, or of type {{Code|xs:anyURI}}, pointing to a resource), and returns a query id . The query will be queued, and the result will optionally be cached. Queries can be updating. Variables and the context value can be declared via {{Code|$bindings}} (see [[XQuery Module#xquery:eval|xquery:eval]] for more details). The following {{Code|$options}} can be supplied:* {{Code|cache}}: indicates if the query result will be cached or ignored (default: <code>false</code>):** The result will be cached in main-memory until it is fetched via [[#jobs:result|jobs:result]], or until {{Option|CACHETIMEOUT}} is exceeded.** If the query raises an error, it will be cached and returned instead.* {{Code|start}}: a dayTimeDuration, time, dateTime or integer 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: <code>P1D</code> (1 day), <code>PT5M</code> (5 minutes), <code>PT0.1S</code> (100 ms). An error will be raised if a negative value is specified.** If a dateTime is specified, the query will be executed at this date. Examples for valid values are: <code>2018-12-31T23:59:59</code> (New Year's Eve 2018, close to midnight). An error will be raised if the specified time lies in the past.** If a time is specified, the query will be executed at this time of the day. Examples for valid times are: <code>02:00:00</code> (2am local time), <code>12:00:00Z</code> (noon, UTC). If the time lies in the past, the query will be executed the next day.** An integer will be interpreted as minutes. If the specified number is greater than the elapsed minutes of the current hour, the query will be executed one hour later.* {{Code|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 (<code>PT1S</code>). If the next scheduled call is due, and if a query with the same id is still running, it will be skipped.* {{Code|end}}: scheduling can be stopped after a given time or duration. The string format is the same as for {{Code|start}}. An error is raised if the resulting end time is smaller than the start time.* {{Code|base-uri}}: sets the [https://www.w3.org/TR/xquery-31/#dt-static-base-uri base-uri property] for the query . This URI will be used when resolving relative URIs, such as with {{Code|fn:doc}}.* {{Code|id}}: sets a custom job id. The id must not start with the standard <code>job</code> prefix, and it can only be assigned if no job with the same name exists.* {{Code|service}}: additionally registers the job as [[#Services|service]]. Registered services must have no variable bindings.* {{Code|log}}: writes the specified string to the [[Logging|database logs]]. Two log entries are stored, one at the beginning and another one after the execution of the job.|-| '''Errors'''|{{Error|overflow|#Errors}} Query execution is rejected, because too many jobs are queued or being executed. {{Option|CACHETIMEOUT}} can be decreased if the default setting is too restrictive.<br/>{{Error|range|#Errors}} A specified time or duration is out of range.<br/>{{Error|id|#Errors}} The specified id is invalid or has already been assigned.<br/>{{Error|options|#Errors}} The specified options are conflicting.|-| '''Examples'''|* Cache query result. The returned id can be used to pick up the result with [[#jobs:result|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:listresult== {{Mark|Updated with Version 9.7:}} Return empty sequence if no result is cached.
{| width='100%'
|-
| width='120' | '''Signatures'''
|{{Func|jobs:list|result|$id as xs:string|item()*}}
|-
| '''Summary'''
|Returns the ids cached result of all jobs that are either being executed asynchronouslya job with the specified job {{Code|$id}}:* If the original job has raised an error, the cached error will be raised instead.* Results can only be retrieved once. After retrieval, the cached result will be dropped.* If the result has already been retrieved, or that are still registered because their results have if it has not been cached, an empty sequence is returned.
|-
| '''Examples'''
|
* The following [[RESTXQ]] function will either return the result of a previously started job or raise an error:<codesyntaxhighlight lang="xquery">declare %rest:path('/result/{$id}') function local:result($id) { jobs:listresult($id)};</codesyntaxhighlight> returns * The following query demonstrates how the results of an executed query can be returned within the same job id as [[#jobsquery (see below why you should avoid this pattern in practice):<syntaxhighlight lang="xquery">let $query :current|= jobs:currenteval('(1 to 10000000)[. = 1]] if no other job is running.', map { }, map { 'cache': true() })return (* <code> jobs:listwait($query) ! , jobs:stopresult(.$query))</codesyntaxhighlight> stops Queries of this kind can cause deadlocks! If the original query and invalidates all asynchronous queries the new query perform updates on the same database, the second query will only be run after the first one has been executed, and resultsthe first query will wait for the second query forever. You should resort to [[XQuery Module#xquery:fork-join|xquery:fork-join]] if you want to have full control on parallel query execution.
|}
==jobs:finishedstop==
{| width='100%'
|-
| width='120' | '''Signatures'''
|{{Func|jobs:finishedstop|$id as xs:string|xs:booleanempty-sequence()}}
|-
| '''Summary'''
|Indicates if Triggers the evaluation cancelation of a job with the specified {{Code|$id}}, drops the cached result of a query, or cancels a scheduled job . Unknown ids are ignored. All jobs are gracefully stopped; it is up to the process to decide when it is safe to shut down. The following {{Code|$idoptions}} has finishedcan be supplied:* <code>false</code> indicates that a {{Code|service}}: additionally removes the job from the [[#Services|job with this id is currently runningservices]] list.* |-| '''Examples'''| <code>truejobs:list()[. != jobs:current()] ! jobs:stop(.)</code> indicates that stops and discards all jobs except for the job has either finished, or that the job id is unknowncurrent one.
|}
==jobs:stopwait==
{| width='100%'
|-
| width='120' | '''Signatures'''
|{{Func|jobs:stopwait|$id as xs:string|empty-sequence()}}
|-
| '''Summary'''
|Cancels Waits for the execution completion of a job with the specified {{Code|$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 drops if the cached result id has already been discarded after job evaluation.* If the function is called with the id of a queryqueued job, or repeatedly executed job, it may stall and never terminate. Unknown query ids are ignored|-| '''Errors'''|{{Error|self|#Errors}} The current job is addressed.<br/>
|}
=Asynchronous ExecutionListing Jobs= ==jobs:current==
==jobs:evallist==
{| width='100%'
|-
| width='120' | '''Signatures'''
|{{Func|jobs:evallist|$query as xs:string|xs:string}}<br />{{Func|jobs:eval|$query as xs:string, $bindings as map(*)|xs:string}}<br />{{Func|jobs:eval|$query as xs:string, $bindings as map(*), $options as map(xs:string, xs:string)|xs:string}}<br />
|-
| '''Summary'''
|Prepares Returns the supplied {{Code|$query}} string for asynchronous execution and returns a query idids of all jobs that are currently registered. The query will be list includes scheduled, queued as described in the article on [[Transaction Management]], running, stopped, and the result will be finished jobs with cached in mainresults.|-memory until it is fetched via [[#jobs:result| '''Examples'''|<code>jobs:result]], or until {{Option|ASYNCTIMEOUT}} is exceeded. Queries may be updating.list()<br/code>Variables and context items can be declared via returns the same job id as {{CodeFunction|$bindings}} (see [[XQuery Module#xquery:evalJobs|xquery:eval]] for more details). The {{Code|$options}} parameter contains evaluation optionsjobs:* {{Code|cachecurrent}}: indicates if the query result will be cached or ignored (default: <code>true</code>). If the query result will not be cached, the query id will immediately be discarded after query execution, toono other job is registered.* {{Code|base-uri}}: set [https ==jobs://www.w3.org/TR/xquerylist-31/#dt-static-base-uri base-uri property] for the query. This URI will be used when resolving relative URIs by functions such as {details== {Code|fn:doc}} (default: width='100%'empty string'').
|-
| width='120' | '''ErrorsSignatures'''|{{ErrorFunc|jobs:list-details||element(job)*}}<br/>{{Func|jobs:list-details|overflow$id as xs:string|element(job)*}}|-| '''Summary'''|Returns information on all jobs that are currently registered, or on a job with the specified {{Code|#Errors$id}} Too many queries (or query results are an empty sequence if this job is not found). The list includes scheduled, queued, running jobs, and cached jobs. To fix thisA string representation of the job, or its URI, will be returned as value. The returned elements have additional attributes:* <code>id</code>: job id* <code>type</code>: type of the job (command, query results should , REST, RESTXQ, etc.)* <code>state</code>: current state of the job: <code>scheduled</code>, <code>queued</code>, <code>running</code>, <code>cached</code>* <code>user</code>: user who started the job* <code>duration</code>: evaluation time (included if a job is running or if the result was cached)* <code>start</code>: next start of job (included if a job will be retrieved.executed repeatedly)* <code>time<br/code>: time when job was registered
|-
| '''Examples'''
|* {{Code|<code>jobs:evallist-details()</code> returns information on the currently running job and possibly others:<syntaxhighlight lang="1+3xml"><job id="job1" type="XQuery" state="running" user="admin" duration="PT0.001S"> XQUERY jobs:list-details()</job></syntaxhighlight>|}} returns a query id, e.g. ==jobs:bindings== {{CodeMark|Query-abcIntroduced with Version 10.0}}. The result can be retrieved via a second query in the same BaseX context: {| width='100%'|-| width='120' | '''Signatures'''|{{CodeFunc|jobs:resultbindings|$id as xs:string|map("Query-abc"*)}}<br />* The following [[RESTXQ]] function will return |-| '''Summary'''|Returns the id variable bindings of an existing job with the query threadspecified {{Code|$id}}. If no variables have been bound to this job, which evaluates the query that has been specified in the body of a POST requestan empty map is returned.|} ==jobs:finished==<pre class{| width='100%'|-| width='brush:xquery120' | '''Signatures'''>declare %rest|{{Func|jobs:POST("{finished|$queryid as xs:string|xs:boolean}}") %rest:path(|-| '''Summary''/eval') |Indicates if the evaluation of an already running job with the specified {{Code|$id}} has finished. As the ids of finished jobs will usually be discarded, unless caching is enabled, the function local:eval($query) { will also return <code>true</code> for unknown jobs:eval($query).};* <code>false</code> indicates that the job id is scheduled, queued, or currently running.* <code>true</precode>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:resultservices==
{| width='100%'
|-
| width='120' | '''Signatures'''
|{{Func|jobs:resultservices|$id as xs:string|itemelement(job)*}}
|-
| '''Summary'''
|Returns the cached result a list of a query with the specified job {{Codeall jobs that have been persistently registered as [[#Services|$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 insteadServices]].
|-
| '''Errors'''
|{{Error|runningservices|#Errors}} the query is still runningRegistered services cannot be parsed.<br/>{{Error|unknown|#Errors}} the supplied query id is unknown: The query result may already have been retrieved, or query execution may have been stopped.<br/>|-| '''Examples'''|* The following [[RESTXQ]] function will either return the result of a previously started query or an error:<pre class='brush:xquery'>declare %rest:path('/result/{$id}') function local:result($id) { jobs:result($id)};</pre>* 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:<pre class='brush:xquery'>let $query := jobs:eval('(1 to 10000000)[. = 1]')return ( hof:until( function($result) { jobs:finished($query) }, function($curr) { prof:sleep(10) }, () ), jobs:result($query))</pre>
|}
|Description
|-
|{{Code|unknownoptions}}| The supplied query specified options are conflicting.|-|{{Code|id}}| The specified id is unknown invalid or has already been assigned.|-|{{Code|overflow}}| Too many queries or not available anymorequery results are queued.|-|{{Code|range}}| A specified time or duration is out of range.
|-
|{{Code|running}}
| A query is still running.
|-
|{{Code|overflowself}}| Too many queries The current job cannot be addressed.|-|{{Code|service}}| Registered services cannot be parsed, added or query results are queuedremoved.
|}
=Changelog=
;Version 10.0
* Added: {{Function|Jobs|jobs:bindings}}
;Version 9.7
* Updated: {{Function|Jobs|jobs:result}}: return empty sequence if no result is cached.
;Version 9.5
* Updated: {{Function|Jobs|jobs:eval}}: integers added as valid start and end times.
;Version 9.4
* Updated: {{Function|Jobs|jobs:eval}}: option added for writing log entries.
* Updated: {{Function|Jobs|jobs:list-details}}: interval added.
;Version 9.2
* Deleted: jobs:invoke (merged with {{Function|Jobs|jobs:eval}})
;Version 9.1
* Updated: {{Function|Jobs|jobs:list-details}}: registration time added.
;Version 9.0
* Added: {{Function|Jobs|jobs:invoke}}, [[#Services|Services]]
;Version 8.6
* Updated: {{Function|Jobs|jobs:eval}}: <code>id</code> option added.
The module was introduced with Version 8.5.
