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.
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.
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, and the result will be cached in main-memory until it is fetched via async:result, or until ASYNCTIMEOUT is exceeded. Queries may be updating. Variables and context items can be declared via $bindings (see xquery:eval for more details). The $options parameter contains evaluation options:
cache : indicates if the query result will be cached or ignored (default: true ). If the query result will not be cached, the query id will immediately be discarded after query execution, too.
base-uri : set base-uri property for the query. This URI will be used when resolving relative URIs by functions such as fn:doc (default: empty string).
|
Errors
|
overflow : Too many queries or query results are queued. To fix this, the query results should be retrieved.
|
Examples
|
async:eval("1+3") returns a query id, e.g. Query-abc . The result can be retrieved via a second query in the same BaseX context: async:result("Query-abc")
- The following RESTXQ function will return the id of the query thread, which evaluates the query that has been specified in the body of a POST request:
declare %rest:POST("{$query}") %rest:path('/eval') function local:eval($query) {
async:eval($query)
};
|
async:result
Signatures
|
async:result($id as xs:string) as item()*
|
Summary
|
Returns the result of an asynchronously executed query with the specified query $id :
- Results can only be retrieved once. After retrieval, the cached result will be discarded.
- If the query raised an error, the error will be raised instead.
|
Errors
|
is-running : the query is still running.
unknown : the supplied query id is unknown: The query result may already have been retrieved, or query execution may have been stopped.
|
Examples
|
- The following RESTXQ function will either return the result of a previously started query or an error:
declare %rest:path('/result/{$id}') function local:result($id) {
async:result($id)
};
- 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:
let $query := async:eval('(1 to 10000000)[. = 1]')
return (
hof:until(
function($result) { async:finished($query) },
function($curr) { prof:sleep(10) },
()
),
async:result($query)
)
|
async:finished
Signatures
|
async:finished($id as xs:string) as xs:boolean
|
Summary
|
Indicates if the evaluation of a query with the specified query $id has finished. If false is returned, the query is still running. An error will be raised if the query result was not cached or has already been retrieved.
|
Errors
|
unknown : the supplied query id is unknown: The query result may already have been retrieved, or query execution may have been stopped.
|
async:stop
Signatures
|
async:stop($id as xs:string) as empty-sequence()
|
Summary
|
Cancels the execution of a query with the specified query $id , or drops the query result if it has already been executed.
|
Errors
|
unknown : the supplied query id is unknown: The query result may already have been retrieved, or query execution may have been stopped.
|
async:ids
Signatures
|
async:ids() as xs:string*
|
Summary
|
Returns the ids of all queries that are either being executed asynchronously, or that have been executed and the results of which have been cached.
|
Examples
|
async:ids() ! async:stop(.) stops and invalidates all asynchronous queries and results.
|
Errors
Code
|
Description
|
unexpected
|
An unexpected error occurred while running a query or function in a separate thread.
|
unknown
|
The supplied query id is unknown or not available anymore.
|
is-running
|
A query is still running.
|
overflow
|
Too many queries or query results are queued.
|
Changelog
The module was introduced with Version 8.5.