On 8/4/2015 3:13 PM, Semyon Sadetsky wrote:
On 8/4/2015 2:03 PM, Alexander Scherbatiy wrote:
On 8/4/2015 12:32 PM, Semyon Sadetsky wrote:
On 8/4/2015 11:47 AM, Alexander Scherbatiy wrote:
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.
Is not it the same as the previous attempt to fix this issue (see
8030118 )?
8030118 fix does a strange thing like firing InsertUpdate
document event out of the lock. Do not do that.
Document change event need to be fired under write lock because the
change to the document should be atomic. Queue of changes is undo
manager's responsibility not the document.
And such queue in the AbstractDocument would require complex
coordination with all its undo managers queues. What if undo called
on undo manager during the doc's queue processing? The right
undo/redo requests and edit events order need to be preserved in
this case and it would be too complex or we would have to change the
concept and make AbstractDocument to maintain its undo/redo history
internally instead of external undo managers.
It only needs to pass undoable edits in the right order from
abstract document to the UndoManager.
Consider the scenario: UndoManager executes undo/redo before it
receives the undoable edits. As result it will undo not the last edit
but intermediate and it will crash because the document state is
changed and intermediate the undoable edit cannot be applied to the
final document state.
This is a good point. But this does not work neither with the
current behavior nor with your proposed fix.
Consider the following scenario:
-----------------------
document.insertString("AAA") // "AAA" UndoableEdit is added to
the UndoManager
document.insertString("BBB")
writeLock();
handleInsertString();
// a user press undo, the "AAA" UndoableEdit is selected in
UndoManager but not executed, because of the write lock
fireUndoableEditUpdate("BBB") // UndoManager is waiting for
the "AAA" UndoableEdit execution
writeUnlock() // "AAA" UndoableEdit is executed instead of "BBB"
// "BBB" UndoableEdit is added to
the UndoManager
-----------------------
Yet another argument do not do this from the user experience: if
user starts a long edit operation and press undo after that he
expects when the long edit is finished it will be rolled back
immediately.
It is not true. The first process adds his undo edit to the
UndoManager. While a user trying to press undo the second long
process can be started.
That is what led to this issue because when undo is in progress
document writing should be allowed.
Sorry but I didn't see why is "It not true"? Then what is your
expectation when you press undo button while edit is not finished yet
and there is no way to abort it?
It would be good if it works as you described. But it does not work
in this way with or without your fix.
undo() action has writeLock in AbstractDocument and because of it
is always executed after insert string action.
If a user sees that undo is available, he can call it but the
second long insertString process can start earlier and acquire the
writeLock.
So undo should be executed after the edit is fully performed because
the corresponding UndoableEdit which undos this edit can be produced
only after the edit is done.
I think at first we need to look on the situation externally rather
than concentrate on implementation questions like in which class do
references go.
Yes, please look on this situation from a user point of view which
wants to implement simple Java Painter.
But could you describe this scenario? Just steps when this simple
Painter fails under the proposed fix?I
Note, if this Painter's content is not an AbstarctDocument it will
work as before the fix.
Any application that uses UndoManager and wants to have the same
synchronization (have the same lock both for UndoableEdit adding and
undo() method execution) will have the same deadlock problems.
As I have already written:
---------------
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.
Thanks,
Alexandr.
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
