RFR(L): 8056049: getProcessCpuLoad() stops working in one process when a different process exits

[Markus Grönlund]

Greetings,

 

Kindly asking for reviews for the following changeset.

 

Bug: https://bugs.openjdk.java.net/browse/JDK-8056049 

Webrev: http://cr.openjdk.java.net/~mgronlun/8056049/webrev01/ 

 

Description:

 

The issue is  Windows specific. And the problem relates to using the Performance Data Helper API (PDH), more specifically how to use the "Process" PDH object in PDH queries:

 

// code comment extract

 

/*

* Working against the Process object and it's related counters is inherently problematic

* when using the PDH API:

*

* For PDH, a process is not primarily identified by it's process id,

* but with a sequential number, for example \Process(java#0), \Process(java#1), ....

* The really bad part is that this list is reset as soon as one process exits:

* If \Process(java#1) exits, \Process(java#3) now becomes \Process(java#2) etc.

*

* The PDH query api requires a process identifier to be submitted when registering

* a query, but as soon as the list resets, the query is invalidated (since the name

* changed).

*

* Solution:

* The #number identifier for a Process query can only decrease after process creation.

*

* Therefore we create an array of counter queries for all process object instances

* up to and including ourselves:

*

* Ex. we come in as third process instance (java#2), we then create and register

* queries for the following Process object instances:

* java#0, java#1, java#2

*

* currentQueryIndexForProcess() keeps track of the current "correct" query

* (in order to keep this index valid when the list resets from underneath,

* ensure to call getCurrentQueryIndexForProcess() before every query involving

* Process object instance data).

*/

 

I have already fixed this in the VM as of https://bugs.openjdk.java.net/browse/JDK-8019921 

 

In the process of fixing this issue now in the JDK, I realized that the previous implementation of using PDH in the JDK was a bit convoluted - especially if you would like to reuse functionality / add new counters.

 

Therefore this change also includes an overall rewrite of the how the JDK will interface with the PDH library, a rewrite of which (hopefully) improves both readability and extensibility.

 

I can do a code walkthrough live if anyone is interested to know the exact details of this change.

 

Testing completed : Testset SVC (includes jdk_instrument, jdk_management, jdk_jmx, jdk_jdi)

 

Thanks in advance

Markus

 
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