<AWT Dev> [9] Review request for 8046495: KeyEvent can not be accepted in quick mouse clicking

[Petr Pchelko]

Hello, Anton.

Thanks for clarifications and additional testing.
The fix looks good to me too.

With best regards. Petr.

On 02 июля 2014 г., at 19:34, Anton V. Tarasov <anton.tarasov at oracle.com> wrote:

> On 02.07.2014 19:28, anton nashatyrev wrote:
>> Hello, Anton
>> 
>> On 02.07.2014 18:13, Anton V. Tarasov wrote:
>>> On 02.07.2014 11:44, Petr Pchelko wrote:
>>>> Hello, Anton.
>>>> 
>>>> I'm not sure I have a detailed understanding of what's happening. 
>>>> 
>>>> Before your fix the timestamp of the event represented the time when the event was created, and now it's the time when it's sent to java.
>>>> This might be important if some events cause other events to be issued on the java side. 
>>>> 
>>>> So suppose the following:
>>>> Toolkit thread: InputEvent#1 created      - timestamp 0
>>>> Toolkit thread: InputEvent#2 created      - timestamp 1
>>>> Toolkit thread: InputEvent#1 sent           - timestamp 2
>>>> EDT:
>>>>                            InputEvent#1 dispatched - timestamp 3
>>>> EDT:               FocusEvent  created        - timestamp 4
>>>> Toolkit thread: InputEvent#2 sent           - timestamp 5
>>>> 
>>>> Before you fix we had the following event order: InputEvent#1(ts=0), InputEvent#2(ts=1), FocusEvent(ts=4).
>>>> But after your fix we will have a different order: InputEvent#1(ts=2), FocusEvent(ts=4), InputEvent#2(ts=5).
>>>> So now we would have troubles, because the Input Event will go to the new focused component instead of the old one. 
>>>> Do you think that my arguments are correct? I understand that the likelihood of such a situation is very low, but for me it looks possible? Am I missing something?
>>> 
>>> A timestamp for a FocusEvent is taken from the_most_recent_KeyEvent_time which is set on EDT when the event is dispatched. So the fix shouldn't affect it.
>>> 
>>> Also, in awt_Window.cpp, when a TimedWindowEvent is created it is passed a timestamp got with TimeHelper::getMessageTimeUTC(). It appears, that the fix makes key events times even more consistent with it. So, from the kbd focus perspective, it shouldn't make any harm.
>>> 
>>> Anton, could you just please run the following tests, at least:
>>> 
>>> test/java/awt/Focus/6981400/*
>>> test/java/awt/KeyboardFocusManager/TypeAhead/*
>> 
>> I've tested with the following set: 
>> [closed]/java/awt/event/* 
>> [closed]/java/awt/Focus/* 
>> [closed]java/awt/KeyboardFocusManager/*
>> 
>> : no unexpected failures here.
>> 
>> I've also verified that my regression test which comes with the fix works fine on Linux and Mac (despite the fix is Win specific). 
> 
> Great, thanks!
> 
> Anton.
> 
>> 
>> Thanks for review!
>> Anton.
>> 
>>> 
>>> Thanks,
>>> Anton.
>>> 
>>>> 
>>>> Another thing I do not understand is why we were used to use the complicated formula instead of initializing the msg.time field with the JVM current time and using it when sending the event?
>>>> Wouldn't that resolve both your issue and the issue the original fix was made for?
>>>> 
>>>> I have a couple of comments about the code, but let's postpone that until we decide on the approach.
>>>> 
>>>> Thank you.
>>>> With best regards. Petr.
>>>> 
>>>> On 01 июля 2014 г., at 21:20, anton nashatyrev <anton.nashatyrev at oracle.com> wrote:
>>>> 
>>>>> Hello, 
>>>>>     could you please review the following fix:
>>>>> 
>>>>> fix: http://cr.openjdk.java.net/~anashaty/8046495/9/webrev.00/
>>>>> bug: https://bugs.openjdk.java.net/browse/JDK-8046495
>>>>> 
>>>>>     Problem: 
>>>>> On Windows the later InputEvent may have earlier timestamp (getWhen()), which results in incorrect processing of enqueued input events and may also potentially be the reason of other artifacts 
>>>>> 
>>>>>     Evaluation: 
>>>>> On Windows we have some algorithm for calculating input event timestamp: jdk/src/windows/native/sun/windows/awt_Component.cpp:2100
>>>>> Shortly the timestamp is calculated by the following formula: 
>>>>>     when = JVM_CurrentTimeMillis() - (GetTickCount() - GetMessageTime())
>>>>> 
>>>>> Where: 
>>>>>   JVM_CurrentTimeMillis() - the same as System.currentTimeMillis()
>>>>>   GetTickCount() - Win32 function, current millis from boot time
>>>>>   GetMessageTime() - Win32 function, millis from boot time of the latest native Message
>>>>> 
>>>>> In theory the formula looks good: we are trying our best to calculate the actual time of the OS message by taking the current JVM time (JVM_CurrentTimeMillis) and adjusting it with the offset (GetTickCount - GetMessageTime) which should indicate how many milliseconds ago from the current moment (GetTickCount) the message has been actually issued (GetMessageTime).
>>>>> In practice due to usage of different system timers by the JVM_CurrentTimeMillis and GetTickCount their values are not updated synchronously and we may get an earlier timestamp for the later event. 
>>>>> 
>>>>>     Fix: 
>>>>> Just to use JVM_CurrentTimeMillis only as events timestamp. On Mac this is done in exactly the same way: CPlatformResponder.handleMouse/KeyEvent()
>>>>> 
>>>>> The message time offset calculation has been introduced with the fix for JDK-4434193 and it seems that the issue has addressed very similar problem (At times getWhen()in ActionEvent returns higher value than the CurrentSystemTime) which has not been completely resolved in fact.
>>>>> I also didn't find any benefits in using the existing approach: 
>>>>> - all the usages of the TimerHelper are in fact reduced to the mentioned formula: when = JVM_CurrentTimeMillis() - (GetTickCount() - GetMessageTime())
>>>>> - GetMessageTime() always increases (except of the int overflow moments), thus we couldn't get earlier OS messages after later ones
>>>>> - TimerHelper::windowsToUTC(DWORD windowsTime) doesn't guarantee returning the same timestamp across different calls for the same message time 
>>>>> 
>>>>> Thanks! 
>>>>> Anton. 
>>>> 
>>> 
>> 
> 

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