Changes

This [[Module Library|XQuery Module]] provides functions for evaluating XQuery expressions in separate threadsorganizing scheduled, queued, running and cached jobs. Query execution Jobs can both be parallelized and postponed to be executed asynchronouslycommands, queries, client or HTTP requests.

All functions in this module are assigned to the <code><nowiki>http://basex.org/modules/asyncjobs</nowiki></code> namespace, which is statically bound to the {{Code|asyncjobs}} prefix. Errors will be bound to the same prefix.

=Parallelized ExecutionServices=

Parallel query execution is recommendable if you have various calls that require a lot of time, but cannot A job can be sped up registered as ''service'' by rewriting supplying the code. This is e. g. the case if external URLs are called. If you are parallelizing local data reads (such as accessing a database), your single-threaded query will usually be faster, because parallelized access {{Code|service}} option to disk data will often lead to randomized access patterns, which can hardly be optimized by your HD or SSD.{{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=async"01:00:00">db:drop("tmp")</job> :) (: unregister job :)jobs:stop('cleanup', map { 'service': true() })</syntaxhighlight> '''Some more notes:fork''' * 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services will be scheduled for evaluation when the BaseX server or BaseX HTTP server is started.* If a job service is outdated (e.g. because a supplied end time has been exceeded), it will be removed from the jobs file at startup time.* The job definitions are stored in a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-joinconsuming 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:eval==

|{{Func|asyncjobs:fork-joineval|$query as xs:anyAtomicItem|xs:string}}<br />{{Func|jobs:eval|$functions query as functionxs:anyAtomicItem, $bindings as map(*)*?|item()*xs:string}}<br/ >{{Func|asyncjobs:fork-joineval|$functions query as xs:anyAtomicItem, $bindings as functionmap(*)*?, $options as map(*)?|xs:string}}<br />|-| '''Summary'''|Schedules the evaluation of the supplied {{Code|$query}} ({{Code|xs:string}}, or of type {{Code|xs:stringanyURI}}, 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|iteminterval}}: 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<br/ 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.

|'''SummaryErrors'''|This function executes the supplied (non-updating) functions in parallel{{Error|overflow|#Errors}} Query execution is rejected, because too many jobs are queued or being executed. The following {{CodeOption|$optionsCACHETIMEOUT}} are available:* <code>threadscan be decreased if the default setting is too restrictive.<br/code>: maximum number {{Error|range|#Errors}} A specified time or duration is out of parallel threads (default: available number of cores)* <code>thread-sizerange.<br/code>: number of functions to be evaluated by each thread (default: <code>1{{Error|id|#Errors}} The specified id is invalid or has already been assigned.<br/code>){{Error|options|#Errors}} The specified options are conflicting.

* Cache query result. The following function sleeps in parallel; it 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 finished in 1 second if your system has sent at least 2 coresthe given date:<pre classsyntaxhighlight lang="xquery">jobs:eval("import module namespace mail='mail'; mail:send('Happy birthday!')", (), map { 'start'brush:'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'">asyncdeclare %rest:forkPOST("{$query}") %rest:path('/start-joinscheduling') function local:start($query) { for jobs:eval($i in 1 to 2query, (), map { 'start': '02:00:00', 'interval': 'P1D' })}; return declare %rest:path('/stop-scheduling/{$id}') functionlocal: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(10001500)", (), 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' }

</pre>* In the following query, up to two URLs will be requested in parallel:<pre class='brush:xquery'>let $funcs := for $segment in 1 to 4 let $url := 'http://url.com/path' || $segment return function() { http:send-request((), $url) }return async:fork-join($funcs, map { 'threads': 2 })</pre>|-|'''Errors'''|{{Error|unexpected|#Errors}} an unexpected error occurred while running a query or function in a separate thread.<br/>{{Error|out-of-range|#Errors}} a supplied option is out of range.<br/syntaxhighlight>

=Asynchronous Execution=jobs:result==

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 {{Mark|Updated with web browsers, which will usually cancel a request after a specific timeoutVersion 9. In such cases, you can use asynchronous execution to trigger another server-side process, which will start the time-consuming process, and fetch the 7:}} Return empty sequence if no result later on as soon as it is availablecached. ==async:eval==

|{{Func|asyncjobs:evalresult|$query id as xs:string|xs:string}}<br />{{Func|async:eval|$query as xs:string, $bindings as mapitem(*)|xs:string}}<br />{{Func|async:eval|$query as xs:string, $bindings as map(*), $options as map(xs:string, xs:string)|xs:string}}<br />

|Prepares Returns the supplied cached result of a job with the specified job {{Code|$queryid}} string for asynchronous execution and returns a query id. The query will be queued as described in :* If the article on [[Transaction Management]]original job has raised an error, and the result cached error will be cached in main-memory until it is fetched via [[#async:result|async:result]], or until {{Option|ASYNCTIMEOUT}} is exceededraised instead.<br/>Variables and context items * Results can only be declared via {{Code|$bindings}} (see [[XQuery Module#xquery:eval|xquery:eval]] for more details)retrieved once. The {{Code|$options}} parameter contains evaluation options:* {{Code|cache}}: indicates if After retrieval, the query cached result will be cached or ignored (default: <code>true</code>)dropped. * If the query result will has already been retrieved, or if it has not be been cached, the query id will immediately be discarded after query execution, too.* {{Code|base-uri}}: set [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 by functions such as {{Code|fn:doc}} (default: ''an empty string'').|-| '''Errors'''|{{Error|updating|#Errors}} the query contains update operationssequence is returned.

* {{Code|async:eval("1+3")}} returns a query id, e.g. {{Code|Query-abc}}. The result can be retrieved via a second query in the same BaseX context: {{Code|async:result("Query-abc")}}<br />* The following [[RESTXQ]] function will either return the id of the query thread, which evaluates the query that has been specified in the body result of a POST requestpreviously started job or raise an error:<pre classsyntaxhighlight lang='brush:"xquery'">declare %rest:POSTpath("'/result/{$queryid}") %rest:path('/eval') function local:evalresult($queryid) { asyncjobs:evalresult($queryid)

</presyntaxhighlight>* 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 Module#xquery:fork-join|xquery:fork-join]] if you want to have full control on parallel query execution.

==asyncjobs:updatestop==

|{{Func|asyncjobs:updatestop|$query id as xs:string|xs:string}}<br />{{Func|async:update|$query as xs:string, $bindings as mapempty-sequence(*)|xs:string}}<br />{{Func|async:update|$query as xs:string, $bindings as map(*), $options as map(xs:string, xs:string)|xs:string}}<br />

|Prepares Triggers the supplied cancelation of a job with the specified {{Code|$queryid}} string for asynchronous execution and returns , drops the cached result of a query id, or cancels a scheduled job. Unknown ids are ignored. The query will be queued as described in All jobs are gracefully stopped; it is up to the article on [[Transaction Management]]process to decide when it is safe to shut down.<br/>See [[#async:evalThe following {{Code|async:eval]] for information on the <code>$bindings</code> and <code>$options</code> arguments.|-| '''Errors'''}} can be supplied:|* {{Error|non-updatingCode|#Errorsservice}} : additionally removes the query does not contain any update operationsjob from the [[#Services|job services]] list.<br/>

|* <code>asyncjobs:updatelist("delete node db)[. != jobs:open('db')//textcurrent()", map {}, map { 'cache'] ! jobs: falsestop() }.)</code> returns a query id. The text nodes of stops and discards all jobs except for the database <code>db</code> will be deleted once the database is available for write accesscurrent one.

==asyncjobs:resultwait==

|{{Func|asyncjobs:resultwait|$id as xs:string|itemempty-sequence()*}}

|Returns Waits for the result completion of an asynchronously executed query a job with the specified query {{Code|$id}}:* Results can only be retrieved onceThe function will terminate immediately if the job id is unknown. After retrievalThis is the case if a future job has not been queued yet, or if the cached result will be id has already been discardedafter job evaluation.* If the query raised an errorfunction is called with the id of a queued job, the error will be raised insteador repeatedly executed job, it may stall and never terminate.

|{{Error|is-runningself|#Errors}} the query The current job is still runningaddressed.<br/>|} =Listing Jobs= ==jobs:current== {| width='100%'|-| width='120' | '''Signatures'''|{{ErrorFunc|jobs:current|unknown|#Errorsxs:string}} |-| '''Summary'''|Returns the supplied query id is unknownof the current job.|} ==jobs:list== {| width='100%'|-| width='120' | '''Signatures'''|{{Func|jobs:list||xs: string*}}|-| '''Summary'''|Returns the ids of all jobs that are currently registered. The query result may already have been retrievedlist includes scheduled, queued, running, or query execution may have been stopped, and finished jobs with cached results.<br/>

|* The following [[RESTXQ]] function will either return the result of a previously started query or an error:<pre class='brush:xquery'code>declare %restjobs:pathlist('/result/{$id}') function local:result($id) { async:result($id)};</precode>* The following query demonstrates how returns the results of an asynchronously executed query can be returned in a single query. Please note that this is not the common way how these functions are used in practice (better use [[#async:fork-joinsame job id as {{Function|Jobs|async:fork-join]]):<pre class='brush:xquery'>let $query := asyncjobs:eval('(1 to 10000000)[. = 1]')return ( hof:until( function($result) { async:finished($query) current}, function($curr) { prof:sleep(10) }, () ), async:result($query))</pre>if no other job is registered.

==asyncjobs:finishedlist-details==

|{{Func|asyncjobs:finishedlist-details||element(job)*}}<br/>{{Func|jobs:list-details|$id as xs:string|xs:booleanelement(job)*}}

|Indicates if the evaluation of Returns information on all jobs that are currently registered, or on a query job with the specified query {{Code|$id}} has finished(or an empty sequence if this job is not found). The list includes scheduled, queued, running jobs, and cached jobs. If A 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, REST, RESTXQ, etc.)* <code>state</code>: current state of the job: <code>scheduled</code>, <code>falsequeued</code>, <code>running</code> is returned, <code>cached</code>* <code>user</code>: user who started the query job* <code>duration</code>: evaluation time (included if a job is still running. An error will be raised or if the query result was not cached or has already been retrieved.)* <code>start</code>: next start of job (included if a job will be executed repeatedly)* <code>time</code>: time when job was registered

| '''ErrorsExamples'''|{{Error|unknown|#Errors}} <code>jobs:list-details()</code> returns information on the supplied query currently running job and possibly others:<syntaxhighlight lang="xml"><job id is unknown="job1" type="XQuery" state="running" user="admin" duration="PT0.001S"> XQUERY jobs: The query result may already have been retrieved, or query execution may have been stopped.list-details()</job><br/syntaxhighlight>

==asyncjobs:stopbindings== {{Mark|Introduced with Version 10.0}}

|{{Func|asyncjobs:stopbindings|$id as xs:string|empty-sequencemap(*)}}

|Cancels Returns the execution variable bindings of a query an existing job with the specified query {{Code|$id}}. If no variables have been bound to this job, or drops the query result if it has already been executedan empty map is returned.|} ==jobs:finished== {| width='100%'|-| width='120' | '''Signatures'''|{{Func|jobs:finished|$id as xs:string|xs:boolean}}

| '''ErrorsSummary'''|Indicates if the evaluation of an already running job with the specified {{ErrorCode|unknown|#Errors$id}} has finished. As the ids of finished jobs will usually be discarded, unless caching is enabled, the function will also return <code>true</code> for unknown jobs.* <code>false</code> indicates that the supplied query job id is unknown: The query result may already have been retrievedscheduled, queued, or query execution may have been stoppedcurrently running.* <code>true<br/code>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).

==asyncjobs:idsservices==

|{{Func|asyncjobs:idsservices||xs:stringelement(job)*}}

|Returns the ids a list of all queries jobs that are either being executed asynchronously, or that have been executed and the results of which have been cachedpersistently registered as [[#Services|Services]].

| '''ExamplesErrors'''|* <code>async:ids() ! async:stop({{Error|services|#Errors}} Registered services cannot be parsed.)<br/code> stops and invalidates all asynchronous queries and results.

|{{Code|unexpectedoptions}}| An unexpected error occurred while running a query The specified options are conflicting.|-|{{Code|id}}| The specified id is invalid or function in a separate threadhas already been assigned.

|{{Code|out-of-rangeoverflow}}| The supplied option is out of rangeToo many queries or query results are queued.

|{{Code|updatingrange}}| A query specified time or duration is expected to be non-updating, but it performs updatesout of range.

|{{Code|non-updatingrunning}}| A query is expected to be updating, but it does not perform updatesstill running.

|{{Code|unknownself}}| The supplied query id is unknown or not available anymorecurrent job cannot be addressed.

|{{Code|is-runningservice}}| A query is still runningRegistered services cannot be parsed, added or removed.