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Docs: Update information on thread safety.

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Fixes #387
This commit is contained in:
Corey Farrell 2018-01-22 19:37:36 -05:00
parent 37e0ee4d48
commit 3aee856d7b
2 changed files with 12 additions and 17 deletions
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5
doc/apiref.rst
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@ -58,6 +58,11 @@ the library:
/* Code specific to version 1.3 and above */ /* Code specific to version 1.3 and above */
#endif #endif
``JANSSON_THREAD_SAFE``
If this value is defined all read-only operations and reference counting in
Jansson are thread safe. This value is not defined for versions older than
``2.11`` or when the compiler does not provide built-in atomic functions.
Value Representation Value Representation
==================== ====================

24
doc/portability.rst
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@ -13,23 +13,13 @@ see below.
There's no locking performed inside Jansson's code, so a multithreaded There's no locking performed inside Jansson's code, so a multithreaded
program must perform its own locking if JSON values are shared by program must perform its own locking if JSON values are shared by
multiple threads. Jansson's reference counting semantics may make this multiple threads. Jansson uses built-in compiler atomic functions to
a bit harder than it seems, as it's possible to have a reference to a manage reference counts. If compiler support is not available it may
value that's also stored inside a list or object. Modifying the be very difficult to ensure thread safety of reference counting.
container (adding or removing values) may trigger concurrent access to It's possible to have a reference to a value that's also stored inside
such values, as containers manage the reference count of their a list or object. Modifying the container (adding or removing values)
contained values. Bugs involving concurrent incrementing or may trigger concurrent access to such values, as containers manage the
decrementing of deference counts may be hard to track. reference count of their contained values.
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.
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