[libxml2.wiki] Create Thread safety

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 7076305e6a25e9a0f9f10b9328a3764b4c029b0e
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Sat Feb 12 18:15:28 2022 +0000

    Create Thread safety

 Thread-safety.md | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)
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diff --git a/Thread-safety.md b/Thread-safety.md
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index 0000000..ee2ece7
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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
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