Changes

* Locks ''cannot be synchronized'' between across BaseX instances that run in different JVMs. If concurrent write operations are to be performed, we generally recommend working with the client/server or the HTTP architecture .

===* You can declare custom locks via the {{Code|query:read-lock}} and {{Code|query:write-lock}} options in the query prolog.* The value of the option contains the lock string, or multiple ones (separated with commas).* Similar to the internal database locks, write locks block all other operations while read locks allow parallel access.* The internal locks and XQuery Locking Options===locks can co-exist (there will be no conflicts, even if your lock string equals the name of a database that will be locked by the transaction manager).

Custom locks can be acquired by setting In the BaseX-specific XQuery options {{Code|query:read-lock}} and {{Code|query:write-lock}}. Multiple option declarations may occur in the prolog of a queryfollowing two example modules, but multiple values can also be separated with commas in a single declaration. These locks are in another namespace than have been added to prevent concurrent write operations on the database namessame file: the lock value {{Code|factbook}} will not lock a database named factbook.

These option declarations will put <pre class="brush:xquery">module namespace read locks on = 'read'foo'', ''bar'' and ''batz'' and a write ; (:~ Read lock on CONFIG key. :)declare option query:read-lock 'CONFIG'quix; declare function read:config() { file:read-text('config.txt':)};</pre>

declare option querymodule namespace write = 'write'; (:read-~ Write lock "foo,bar";on CONFIG key. :)declare option query:readwrite-lock "batz"'CONFIG'; declare option queryfunction write:file($data) { file:write-lock "quix"text('config.txt', $data)};

During the term of a database update, a locking file {{Code|upd.basex}} will reside in that database directory. If the update fails for some unexpected reason, or if the process is killed ungracefully, this file may will not be deleted. In this case, the database cannot be opened anymore using the default commands, and the message "Database ... is being updated, or update was not completed" will be shown instead.  If the locking file is manually removed, you may be able to reopen the database, but you should be aware that database may have got corrupt due to the interrupted update process, and you should revert to the most recent database backup.

To avoid database corruptions that are caused by accidental write operations running in from different JVMs, a shared lock is requested on the database table file ({{Code|tbl.basex}}) whenever a database is opened. If an update operation is triggered, and if no exclusive lock can be acquired, it will be rejected with the message "Database ... is currently opened by another process." if no exclusive lock can be acquired.

As the standalone versions of BaseX (command-linePlease note that you cannot 100% rely on this mechanism, GUI) cannot as it is not possible to synchronize operations across different JVMs. You will be synchronized with other BaseX instances, we generally recommend working with safe when using the client/server or HTTP architecture if concurrent write operations are to be performed.