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Correction on Heap API available from ISR (#8708)

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* Correction on Heap API available from ISR

* Expand reason for avoid realloc/free
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M Hightower 2022-11-04 06:07:31 -07:00 committed by GitHub
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doc/reference.rst
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@ -27,15 +27,22 @@ and have several limitations:
or use a scheduled function (which will be called outside of the interrupt
context when it is safe) to do long-running work.
* Memory operations can be dangerous and should be avoided in interrupts.
Calls to ``new`` or ``malloc`` should be minimized because they may require
a long running time if memory is fragmented. Calls to ``realloc`` and
``free`` must NEVER be called. Using any routines or objects which call
``free`` or ``realloc`` themselves is also forbidden for the same reason.
This means that ``String``, ``std::string``, ``std::vector`` and other
classes which use contiguous memory that may be resized must be used with
extreme care (ensuring strings aren't changed, vector elements aren't
added, etc.).
* Heap API operations can be dangerous and should be avoided in interrupts.
Calls to ``malloc`` should be minimized because they may require a long
running time if memory is fragmented. Calls to ``realloc`` and ``free``
must NEVER be called. Using any routines or objects which call ``free`` or
``realloc`` themselves is also forbidden for the same reason. This means
that ``String``, ``std::string``, ``std::vector`` and other classes which
use contiguous memory that may be resized must be used with extreme care
(ensuring strings aren't changed, vector elements aren't added, etc.).
The underlying problem, an allocation address could be actively in use at
the instant of an interrupt. Upon return, the address actively in use may
be invalid after an ISR uses ``realloc`` or ``free`` against the same
allocation.
* The C++ ``new`` and ``delete`` operators must NEVER be used in an ISR. Their
call path is not in IRAM. Using any routines or objects that use the ``new``
or ``delete`` operator is also forbidden.
Digital IO
----------