The simplifications focus on avoiding tests that can be done
elsewhere and on avoiding excessive use of local variable aliases for
attributes.

Move tests for too-long transaction metadata to _begin(), where the
variables are set instead of here where they are read.

fixed ZClass-related type-checking breakage introduced in reformatting in rev 1.45. I guess there are no unit tests for ZClasses?

I think it's safe to run this code without extra checking.

Also, reformat a test in testTransaction.

constructor, since it is ignored and there is no current plan to
support two caches with almost-but-not-quite-the-same arguments.

This change has effects in many files.  The Connection and DB don't
pass this argument and don't bother setting it explicitly when it is
reset via DB APIs like setCacheDeactivateAfter().  XXX These APIs
remain, since existing code may depend on them, but they have no
effect.

New policy in cPersistence.c: A Persistent object can't have its
_p_jar set or deleted once it is in a cache.  Persistent already
implemented this policy for _p_oid; it seems safer to do the same for
the jar.

Add ringlen() method to cache objects (implemented as cc_ringlen).
This returns the length of the doubly linked list of non-ghost
objects.  Same as len(cache.lru_items()), but more efficient.  Only
used for testing at the moment.

In ring_corrupt(), don't raise a new exception if one has already been
set.  The old behavior masked useful information about the original
error / traceback.

Implement behavior for minimize() and full_sweep() as discussed on
zodb-dev.  minimize() ghostifies all unmodified objects.  full_sweep()
with age==0 is the same as minimize(), otherwise it's the same as
incrgc().

Reformat and/or reindent lots of code.

Use PyObject_Compare() instead of PyObject_Cmp() because it has a
simpler return value.

Fix a few more PyDict_SetItem() and PyDict_DelItem() calls to make
correct check for error return.

Break up the logic into a bunch of helper methods:
 _commit_objects()
 _commit_subtrans()
 _finish_one()
 _finish_rest()
and possibly
 _commit_error()

As a result of the changes, the high-level logic of a commit fits into
28 lines inside a try/finally.  There are lots of details hidden in
the methods, but the names capture the high-level behavior of the
helpers.

This fixes the transient failure in testExceptionInSubAbortSub() and
is presumed to be correct, too.  The old code had the comment:
    # This should never fail
but did not to guarantee that it never failed.  I'm assuming that the
write fix is to log the error and ignore it, because that's what the
call to tpc_abort() immediately above does.

XXX commit() is a really long method.  It would be nice to break it up
into easier-to-understand chunks.

including some use of assert/fail methods instead of assert stmt.

    The rationale is that this is an internal detail of the cache
    implementation called by Per_dealloc().  It's nice to make it
    fast, and it's good to prevent it from being called with anything
    other than an about-to-be-freed object.

    As a result of it being in the C API, omit tests of refcounts.  We
    would have been in Per_dealloc() otherwise.

    Initialize the percachdel slot of cPersistenceAPIstruct to NULL in
    cPersistence.  In cPickleCache, import the CObject and fill in the
    struct.

Also, reformat many of the comments so that all the text starts to the
right of the /*.

Fiddle the text of the placeholder comment.  I think I understand it
now :-).

Add an XXX comment about the "old" cache API e.g. fullsweep and
reallyfullsweep.

Fix cc_get().  object_from_oid() doesn't ever set an exception.

Remove a Py_FatalError() check from the end of a module init
function.  We don't do that anymore.

I expect this code will become ZEO 1.1.

description fields, which are assigned to attributes on the
Transaction object.

takes an exception object as its first argument, and the return value
should be a -1 instead of NULL (this function's signature has an int
return).

I'm surprised no one else's build caught this compiler warning.

Merged shane-better-tracebacks-branch.  The changes are explained in http://dev.zope.org/Wikis/DevSite/Proposals/BetterTracebacks

(Thanks for the comments, Toby!)

Add check that argument to cc_ass_sub() is a string.  The cache maps
oids to objects, and oids must be strings for now.

Re-indent a bunch of code.

Replace an XXX comment about v->oid with a comment explaining why
getattr is necessary.

on ->cache and references to its members.

Quite a bit of reformatting and unless-undoing.  Add whitespace
between 'if' and '('.

ring_home and use it explicitly.

Remove now unused KEEP_THIS_ONE_AROUND_FOR_A_WHILE() macro.

check_ring() rename to ring_corrupt() since that matches the return
semantics a bit better.

scan_gc_items(): Get rid of the placeholder, which just seemed like a
confusing way to stash here->next until after the PyObject_SetAttr()
call.

UPDATE_STATE_IF_NECESSARY: Un-macroize this.  Renamed to function
unghostify() and changed (slightly) the return semantics.

ghostify(): Don't use the NON_GHOST_COUNT macro.  Add some comments.

Per_setstate(), Per__getstate__(), Per_getattr(), _setattro(): Use
unghostify() instead of UPDATE_STATE_IF_NECESSARY.

did you use?

A few substantive changes:

Split internals of cc_ass_sub() into two smaller function
cc_add_item() and cc_del_item(), removing several levels of
indentation in the process.

Fix incorrect check for return value from PyDict_SetItem().

Remove use of staticforward.

Avoid forward reference to Cctype by defining newccobject after type
struct.

Define the contents of ccobject_head_struct via CACHE_HEAD macro.
Don't rely on two different files to define a struct with the same
layout by convention.

Remove many levels of parentheses from the HOME and NON_GHOST_COUNT
macros.

Replace KEEP_THIS_ONE_AROUND_FOR_A_WHILE() macro with a call to the
accessed() function.  (Who comes up with these names :-).

Remove include of string.h in cPersistence.c.

Expand cPersistent_HEAD macro so that it has one line for each
attribute!

Use typedef to define PerCache as "struct ccobject_head_struct" and
use this for the entry cache slot in cPersistent_HEAD instead of
PyObject *.

In cPickleCache.c, reflow a bunch of long lines, add some whitespace,
and an XXX comment explaining that I don't understand a different
comment.

These tests verify that transactional undo works with abortVersion and
commitVersion, even in the face of a pack that invalidates the file
position contained in the transaction record.

Use the file position stored in the transaction_id whenever possible.
It is possible when _check_txn_pos() returns true; i.e. when the file
position does point to the transaction record header.

Remove ostloc and here arguments to _txn_undo_write(), as they can be
computed after the call.

Omit redundant tests in _txn_undo_write().  All the paths that lead
here verify that the file position is valid.

Remove some attribute lookup optimizations.

transactionalUndo() does argument checking and locking.  It calls
_transactional_undo(), which finds the right transaction record.  It calls
_txn_undo_write(), which writes the data records.

Add a summary comment above undoLog() that explains how the
transaction_id is created and used.

It makes more sense in this order, because the comments in undoLog()
help to explain what transactionalUndo() is doing.