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

Petr Pchelko petr.pchelko at oracle.com
Wed Jul 2 07:44:03 UTC 2014

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?

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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