Jobs Module

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This XQuery Module provides functions for evaluating XQuery expressions in separate threads. Query execution can both be parallelized and postponed to be executed asynchronously.

Conventions

All functions in this module are assigned to the http://basex.org/modules/async namespace, which is statically bound to the async prefix. Errors will be bound to the same prefix.

Parallelized Execution

async:fork-join

Signatures async:fork-join($functions as function(*)*) as item()*
async:fork-join($functions as function(*)*, $options as map(xs:string, xs:string)) as item()*
Summary This function executes the supplied functions in parallel. The following $options are available:
  • threads: maximum number of parallel threads (default: available number of cores)
  • thread-size: number of functions to be evaluated by each thread (default: 1)
Examples
  • The following function sleeps in parallel; it will be finished in 1 second if your system has at least 2 cores:
async:fork-join(
  for $i in 1 to 2
  return function() { prof:sleep(1000) }
)
  • In the following query, up to two URLs will be requested in parallel:
let $urls := (1 to 4) ! ('http://url.com/path' || .)
let $funcs := $urls ! function() { http:send-request((), .) },
return async:fork-join($funcs, map { 'threads': 2 })
Errors unexpected: an unexpected error occurred while running a query or function in a separate thread.
out-of-range: a supplied option is out of range.

Asynchronous Execution

async:eval

Signatures async:eval($query as xs:string) as xs:string
async:eval($query as xs:string, $bindings as map(*)) as xs:string
async:eval($query as xs:string, $bindings as map(*), $options as map(xs:string, xs:string)) as xs:string
Summary 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.
Variables and context items can be declared via $bindings (see xquery:eval for more details). The $options parameter contains evaluation options:
  • check: indicates if the query result will be cached.
  • base-uri: set base-uri property for the query. This URI will be used when resolving relative URIs by functions such as fn:doc.
Errors updating: the query contains update operations.
Examples
  • async:eval("1+3") returns a query id, e.g. Query-abc. The result can be retrieved via a second query in the same BaseX context: async:result("Query-abc")

async:update

Signatures async:update($query as xs:string) as xs:string
async:update($query as xs:string, $bindings as map(*)) as xs:string
async:update($query as xs:string, $bindings as map(*), $options as map(xs:string, xs:string)) as xs:string
Summary 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.
See async:eval for information on the $bindings and $options arguments.
Errors non-updating: the query does not contain any update operations.
Examples
  • async:update("delete node db:open('db')//text()", map {}, map { 'cache': false() }) returns a query id. The text nodes of the database db will be deleted once the database is available for write access.

async:result

Signatures async:result($id as xs:string) as item()*
Summary Returns the result of an asynchronously executed query with the specified query $id:
  • Results can only be retrieved once. After retrieval, the cached result will be discarded.
  • If the query raised an error, the error will be raised instead.
Errors is-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.
Examples The following query returns the results of an asynchronously executed query. It will succeed, because both the main and the asynchronous query do not include write operations on concurrently used databases:
let $query := async:eval('(1 to 10000000)[. = 1]')
return (
  hof:until(
    function($result) { not(async:is-running($query)) },
    function($curr) { prof:sleep(10) },
    ()
  ),
  async:result($query)
)

async:is-running

Signatures async:is-running($id as xs:string) as xs:boolean
Summary Indicates if a query with the specified query $id is currently being evaluated.
Errors unknown: the supplied query id is unknown: The query result may already have been retrieved, or query execution may have been stopped.

async:stop

Signatures async:stop($id as xs:string) as xs:boolean
Summary Cancels the execution of a query with the specified query $id.
Errors unknown: the supplied query id is unknown: The query result may already have been retrieved, or query execution may have been stopped.

Errors

Code Description
unexpected An unexpected error occurred while running a query or function in a separate thread.
out-of-range The supplied option is out of range.
updating A query is expected to be non-updating, but it performs updates.
non-updating A query is expected to be updating, but it does not perform updates.
unknown The supplied query id is unknown or not available anymore.
is-running A query is still running.

Changelog

Version 8.0
  • Updated: Bound values may now contain no or more than one item in client:query.
Version 7.5

The module was introduced with Version 7.3.