Author: Armin Rigo <ar...@tunes.org>
Branch:
Changeset: r2209:08e9e358f971
Date: 2015-07-05 09:33 +0200
http://bitbucket.org/cffi/cffi/changeset/08e9e358f971/
Log: Document 'onerror'.
diff --git a/doc/source/using.rst b/doc/source/using.rst
--- a/doc/source/using.rst
+++ b/doc/source/using.rst
@@ -506,7 +506,7 @@
@ffi.callback("int(int, int)", error=-1)
-In all cases the exception is printed to stderr, so this should be
+The exception is still printed to stderr, so this should be
used only as a last-resort solution.
Deprecated: you can also use ``ffi.callback()`` not as a decorator but
@@ -514,6 +514,30 @@
discouraged: using this a style, we are more likely to forget the
callback object too early, when it is still in use.
+.. versionadded:: 1.2
+
+ If you want to be sure to catch all exceptions, use
+ ``ffi.callback(..., onerror=func)``. If an exception occurs and
+ ``onerror`` is specified, then ``onerror(exception, exc_value,
+ traceback)`` is called. This is useful in some situations where
+ you cannot simply write ``try: except:`` in the main callback
+ function, because it might not catch exceptions raised by signal
+ handlers: if a signal occurs while in C, it will be called after
+ entering the main callback function but before executing the
+ ``try:``.
+
+ If ``onerror`` returns normally, then it is assumed that it handled
+ the exception on its own and nothing is printed to stderr. If
+ ``onerror`` raises, then both tracebacks are printed. Finally,
+ ``onerror`` can itself provide the result value of the callback in
+ C, but doesn't have to: if it simply returns None---or if
+ ``onerror`` itself fails---then the value of ``error`` will be
+ used, if any.
+
+ Note the following hack: in ``onerror``, you can access some of the
+ original callback arguments by attempting to read
+ ``traceback.tb_frame.f_locals['argname']``.
+
FFI Interface
-------------
diff --git a/doc/source/whatsnew.rst b/doc/source/whatsnew.rst
--- a/doc/source/whatsnew.rst
+++ b/doc/source/whatsnew.rst
@@ -41,6 +41,14 @@
only for NULL: if you dereference random or dead pointers you might
still get segfaults.
+* Issue #152: callbacks: added an argument ``ffi.callback(...,
+ onerror=...)``. If the main callback function raises an exception
+ and ``onerror`` is provided, then ``onerror(exception, exc_value,
+ traceback)`` is called. This is similar to writing a ``try:
+ except:`` in the main callback function, but in some cases (e.g. a
+ signal) an exception can occur at the very start of the callback
+ function---before it had time to enter the ``try: except:`` block.
+
1.1.2
=====
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