Author: Armin Rigo <[email protected]>
Branch: use-gc-del-3
Changeset: r84323:837ed78ee722
Date: 2016-05-09 10:28 +0200
http://bitbucket.org/pypy/pypy/changeset/837ed78ee722/
Log: Documentation (thanks cfbolz)
diff --git a/pypy/doc/discussion/finalizer-order.rst
b/pypy/doc/discussion/finalizer-order.rst
--- a/pypy/doc/discussion/finalizer-order.rst
+++ b/pypy/doc/discussion/finalizer-order.rst
@@ -33,26 +33,25 @@
it from a finalizer. A finalizer runs earlier, and in topological
order; care must be taken that the object might still be reachable at
this point if we're clever enough. A destructor on the other hand runs
-last; nothing can be done with the object any more.
+last; nothing can be done with the object any more, and the GC frees it
+immediately.
Destructors
-----------
A destructor is an RPython ``__del__()`` method that is called directly
-by the GC when there is no more reference to an object. Intended for
-objects that just need to free a block of raw memory or close a file.
+by the GC when it is about to free the memory. Intended for objects
+that just need to free an extra block of raw memory.
There are restrictions on the kind of code you can put in ``__del__()``,
including all other functions called by it. These restrictions are
-checked. In particular you cannot access fields containing GC objects;
-and if you call an external C function, it must be a "safe" function
-(e.g. not releasing the GIL; use ``releasegil=False`` in
-``rffi.llexternal()``).
+checked. In particular you cannot access fields containing GC objects.
+Right now you can't call any external C function either.
-If there are several objects with destructors that die during the same
-GC cycle, they are called in a completely random order --- but that
-should not matter because destructors cannot do much anyway.
+Destructors are called precisely when the GC frees the memory of the
+object. As long as the object exists (even in some finalizer queue or
+anywhere), its destructor is not called.
Register_finalizer
diff --git a/pypy/interpreter/executioncontext.py
b/pypy/interpreter/executioncontext.py
--- a/pypy/interpreter/executioncontext.py
+++ b/pypy/interpreter/executioncontext.py
@@ -548,11 +548,15 @@
def gc_disabled(self, w_obj):
# If we're running in 'gc.disable()' mode, record w_obj in the
- # "call me later" list and return True. Use this function
- # from _finalize_() methods that would call app-level some
- # things that we consider shouldn't be called in gc.disable().
- # (The exact definition is of course a bit vague, but most
- # importantly this includes all user-level __del__().)
+ # "call me later" list and return True. In normal mode, return
+ # False. Use this function from some _finalize_() methods:
+ # if a _finalize_() method would call some user-defined
+ # app-level function, like a weakref callback, then first do
+ # 'if gc.disabled(self): return'. Another attempt at
+ # calling _finalize_() will be made after 'gc.enable()'.
+ # (The exact rule for when to use gc_disabled() or not is a bit
+ # vague, but most importantly this includes all user-level
+ # __del__().)
pdd = self.pending_with_disabled_del
if pdd is None:
return False
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