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Thread safety

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Starting with 2.4.7, libxml2 makes provisions to ensure that concurrent threads can safely work in parallel parsing different documents. There is however a couple of things to do to ensure it:

  • configure the library accordingly using the --with-threads options
  • call xmlInitParser() in the "main" thread before using any of the libxml2 API (except possibly selecting a different memory allocator)

Note that the thread safety cannot be ensured for multiple threads sharing the same document, the locking must be done at the application level, libxml exports a basic mutex and reentrant mutexes API in <libxml/threads.h>. The parts of the library checked for thread safety are:

  • concurrent loading
  • file access resolution
  • catalog access
  • catalog building
  • entities lookup/accesses
  • validation
  • global variables per-thread override
  • memory handling

XPath has been tested for threaded usage on non-modified document for example when using libxslt, but make 100% sure the documents are accessed read-only !

Daniel Veillard