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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.
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