RFR(S/M): 8150646: Add support for blocking compiles through whitebox API

Nils Eliasson nils.eliasson at oracle.com
Tue Mar 1 14:24:10 UTC 2016

Hi Volker,

An excellent proposition. This is how it should be used.

I polished a few rough edges:
* CompilerBroker.cpp - The directives was already access in 
compile_method - but hidden incompilation_is_prohibited. I moved it out 
so we only have a single directive access. Wrapped compile_method to 
make sure the release of the directive doesn't get lost.
* Let WB_AddCompilerDirective return a bool for success. Also fixed the 
state - need to be in native to get string, but then need to be in VM 
when parsing directive.

And some comments:
* I am against adding new compile option commands (At least until the 
stringly typeness is fixed). Lets add good ways too use compiler 
directives instead.

I need to look at the stale task removal code tomorrow - hopefully we 
could save the blocking info in the task so we don't need to access the 
directive in the policy.

All in here:
Webrev: http://cr.openjdk.java.net/~neliasso/8150646/webrev.03/

The code runs fine with the test I fixed for JDK-8073793:

Best regards,
Nils Eliasson

On 2016-02-26 19:47, Volker Simonis wrote:
> Hi,
> so I want to propose the following solution for this problem:
> http://cr.openjdk.java.net/~simonis/webrevs/2016/8150646_toplevel
> http://cr.openjdk.java.net/~simonis/webrevs/2016/8150646_hotspot/
> I've started from the opposite site and made the BackgroundCompilation
> manageable through the compiler directives framework. Once this works
> (and it's actually trivial due to the nice design of the
> CompilerDirectives framework :), we get the possibility to set the
> BackgroundCompilation option on a per method base on the command line
> via the CompileCommand option for free:
> -XX:CompileCommand="option,java.lang.String::charAt,bool,BackgroundCompilation,false"
> And of course we can also use it directly as a compiler directive:
> [{ match: "java.lang.String::charAt", BackgroundCompilation: false }]
> It also becomes possible to use this directly from the Whitebox API
> through the DiagnosticCommand.compilerDirectivesAdd command.
> Unfortunately, this command takes a file with compiler directives as
> argument. I think this would be overkill in this context. So because
> it was so easy and convenient, I added the following two new Whitebox
> methods:
>    public native void addCompilerDirective(String compDirect);
>    public native void removeCompilerDirective();
> which can now be used to set arbitrary CompilerDirective command
> directly from within the WhiteBox API. (The implementation of these
> two methods is trivial as you can see in whitebox.cpp).
> v
> The blocking versions of enqueueMethodForCompilation() now become
> simple wrappers around the existing methods without the need of any
> code changes in their native implementation. This is good, because it
> keeps the WhiteBox API stable!
> Finally some words about the implementation of the per-method
> BackgroundCompilation functionality. It actually only requires two
> small changes:
> 1. extending CompileBroker::is_compile_blocking() to take the method
> and compilation level as arguments and use them to query the
> DirectivesStack for the corresponding BackgroundCompilation value.
> 2. changing AdvancedThresholdPolicy::select_task() such that it
> prefers blocking compilations. This is not only necessary, because it
> decreases the time we have to wait for a blocking compilation, but
> also because it prevents blocking compiles from getting stale. This
> could otherwise easily happen in AdvancedThresholdPolicy::is_stale()
> for methods which only get artificially compiled during a test because
> their invocations counters are usually too small.
> There's still a small probability that a blocking compilation will be
> not blocking. This can happen if a method for which we request the
> blocking compilation is already in the compilation queue (see the
> check 'compilation_is_in_queue(method)' in
> CompileBroker::compile_method_base()). In testing scenarios this will
> rarely happen because methods which are manually compiled shouldn't
> get called that many times to implicitly place them into the compile
> queue. But we can even completely avoid this problem by using
> WB.isMethodQueuedForCompilation() to make sure that a method is not in
> the queue before we request a blocking compilation.
> I've also added a small regression test to demonstrate and verify the
> new functionality.
> Regards,
> Volker
On Fri, Feb 26, 2016 at 9:36 AM, Nils Eliasson 
<nils.eliasson at oracle.com> wrote:
>> Hi Vladimir,
>> WhiteBox::compilation_locked is a global state that temporarily stops all
>> compilations. I this case I just want to achieve blocking compilation for a
>> single compile without affecting the rest of the system. The tests using it
>> will continue executing as soon as that compile is finished, saving time
>> where wait-loops is used today. It adds nice determinism to tests.
>> Best regards,
>> Nils Eliasson
>> On 2016-02-25 22:14, Vladimir Kozlov wrote:
>>> You are adding parameter which is used only for testing.
>>> Can we have callback(or check field) into WB instead? Similar to
>>> WhiteBox::compilation_locked.
>>> Thanks,
>>> Vladimir
>>> On 2/25/16 7:01 AM, Nils Eliasson wrote:
>>>> Hi,
>>>> Please review this change that adds support for blocking compiles in the
>>>> whitebox API. This enables simpler less time consuming tests.
>>>> Motivation:
>>>> * -XX:-BackgroundCompilation is a global flag and can be time consuming
>>>> * Blocking compiles removes the need for waiting on the compile queue to
>>>> complete
>>>> * Compiles put in the queue may be evicted if the queue grows to big -
>>>> causing indeterminism in the test
>>>> * Less VM-flags allows for more tests in the same VM
>>>> Testing:
>>>> Posting a separate RFR for test fix that uses this change. They will be
>>>> pushed at the same time.
>>>> RFE: https://bugs.openjdk.java.net/browse/JDK-8150646
>>>> JDK rev: http://cr.openjdk.java.net/~neliasso/8150646/webrev_jdk.01/
>>>> Hotspot rev: http://cr.openjdk.java.net/~neliasso/8150646/webrev.02/
>>>> Best regards,
>>>> Nils Eliasson

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