Saxon

Thank-you for your prompt response. For my part, I do a lot of pxslt rocessing in multithreading mode by putting a class that translates the xsl: message into log4j and it works very well. Maybe you are referring to multithreading within the same xslt (saxon:treads, allowMultiThreading ...) ?

Correct, Saxon can do multithreading within a single transformation (e.g. if you do xsl:result-document in Saxon-EE). The MessageEmitter interface involved making multiple calls to the same MessageEmitter for a single xsl:message instruction, and if two xsl:message instructions were executed in different threads there was no way the MessageEmitter could disentangle them.

We replaced the MessageEmitter quite a while ago with the MessageListener interface which made a single call to the supplied callback. But we've since revised that to capture all information about a message in a Message object, because we found it was difficult to extend the interface to supply additional information such as the location of the xsl:message instruction.