On 8/3/2015 4:19 PM, Semyon Sadetsky wrote:
On 8/3/2015 3:12 PM, Alexander Scherbatiy wrote:
On 7/31/2015 9:44 AM, Semyon Sadetsky wrote:
Good question. But I did not add a concrete class.
The problem is that UndoManager provided by JDK wants to be
serialized but undoable objects knows nothing about that. The
contract between UndoManager and undoable is UndoableEditListener
which only notifies UndoManager to add a new edit. AbstractDocument
does not care about the specific UndoManager implementation and it
can contain plenty different UndoableEditListener. That is the
current API approach.
If our specific UndoManager wants to be serialized it should also
take into account that the undoable it controls may require
serialization. For that it needs undoable's synchronization monitor
and AbstractDocument can provide it using writeLock()/writeUnlock()
methods. I assumed that in the first turn UndoManger should work
well with JDK undoables than to serve as a general implementation.
Also I tried to preserve the current API.
And your suggestion is to change the existing UndoableEditListener
API by introducing synchronization methods in it. Am I correctly
understand you?
What I said is that UndoManager can be used not only by
AbstractDocument but also in other classes which can have the same
synchronization problems.
There should be a way to solve these problems without storing
links of external classes inside the UndoManager.
As well as AbstractDocument can use another undo managers. It can be
addressed to both parties. They need each others locks to serialize
changes without deadlock.
AbstarctDocument is related to UndoableEditListener as one to many
that means a lock should be taken for each undo manager before the
document change.
Undo manager does not have any methods to get its lock because it is
an UndoableEditListener implementation. AbstarctDocument has API to
receive its lock.
Do you still propose to fix the issue on AbstractDocument side?
Yes.
Could you clarify how do you see such fix?
Put an UndoableEdit/UndoableEditEvent/necessary information to a
queue instead of firing the undoable edit event under the write lock. Do
not read the queue under the write lock. The queue allows to preserve
the order of UndoableEdit's adding to an UndoManager.
Thanks,
Alexandr.
--Semyon
Thanks,
Alexandr.
--Semyon
On 7/30/2015 5:27 PM, Alexander Scherbatiy wrote:
Consider someone writes Java Painter application where it is
possible to draw lines and images and uses UndoManager for
undo/redo actions.
He might want that it was possible to work with copied images.
He can get lock on ctrl+v action, process an image, prepare
UndoableEdit and notify the UndoManager.
He also can use lock/unlock in the undo action to have a
consistent state with the processed image. If someone calls undo
action during the image processing and gets a deadlock does it mean
that link from Java Painter need to be added to the UndoManager?
Thanks,
Alexandr.
It looks like AbstractDocument violates UndoManager
synchronization contract when it both use lock to work with
UndoManager and in the implemented undo() method.
Thanks,
Alexandr.
--Semyon
