53 lines
2.2 KiB
ReStructuredText
53 lines
2.2 KiB
ReStructuredText
***********
|
|
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.
|