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DependentExtensions/jansson-2.4/doc/portability.rst

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+***********
+Portability
+***********
+
+Thread safety
+-------------
+
+Jansson is thread safe and has no mutable global state. The only
+exception are the memory allocation functions, that should be set at
+most once, and only on program startup. See
+:ref:`apiref-custom-memory-allocation`.
+
+There's no locking performed inside Jansson's code, so a multithreaded
+program must perform its own locking if JSON values are shared by
+multiple threads. Jansson's reference counting semantics may make this
+a bit harder than it seems, as it's possible to have a reference to a
+value that's also stored inside a list or object. Modifying the
+container (adding or removing values) may trigger concurrent access to
+such values, as containers manage the reference count of their
+contained values. Bugs involving concurrent incrementing or
+decrementing of deference counts may be hard to track.
+
+The encoding functions (:func:`json_dumps()` and friends) track
+reference loops by modifying the internal state of objects and arrays.
+For this reason, encoding functions must not be run on the same JSON
+values in two separate threads at the same time. As already noted
+above, be especially careful if two arrays or objects share their
+contained values with another array or object.
+
+If you want to make sure that two JSON value hierarchies do not
+contain shared values, use :func:`json_deep_copy()` to make copies.
+
+Locale
+------
+
+Jansson works fine under any locale.
+
+However, if the host program is multithreaded and uses ``setlocale()``
+to switch the locale in one thread while Jansson is currently encoding
+or decoding JSON data in another thread, the result may be wrong or
+the program may even crash.
+
+Jansson uses locale specific functions for certain string conversions
+in the encoder and decoder, and then converts the locale specific
+values to/from the JSON representation. This fails if the locale
+changes between the string conversion and the locale-to-JSON
+conversion. This can only happen in multithreaded programs that use
+``setlocale()``, because ``setlocale()`` switches the locale for all
+running threads, not only the thread that calls ``setlocale()``.
+
+If your program uses ``setlocale()`` as described above, consider
+using the thread-safe ``uselocale()`` instead.