RFR: 8146705: Improve JVMCI support for blocking compilation

[Christian Thalinger]

…or not:

/scratch/jprt/T/P1/192954.cthaling/s/hotspot/src/share/vm/runtime/advancedThresholdPolicy.cpp: In member function 'virtual CompileTask* AdvancedThresholdPolicy::select_task(CompileQueue*)':
/scratch/jprt/T/P1/192954.cthaling/s/hotspot/src/share/vm/runtime/advancedThresholdPolicy.cpp:201:9: error: 'UseJVMCICompiler' was not declared in this scope
     if (UseJVMCICompiler && task->is_blocking()) {
         ^
/scratch/jprt/T/P1/192954.cthaling/s/hotspot/src/share/vm/runtime/advancedThresholdPolicy.cpp:202:11: error: 'max_blocking_task' was not declared in this scope
       if (max_blocking_task == NULL || compare_methods(method, max_blocking_task->method())) {
           ^

> On Jan 11, 2016, at 8:35 AM, Christian Thalinger <christian.thalinger at oracle.com> wrote:
> 
>> 
>> On Jan 11, 2016, at 7:30 AM, Doug Simon <doug.simon at oracle.com <mailto:doug.simon at oracle.com>> wrote:
>> 
>>> 
>>> On 11 Jan 2016, at 18:23, Christian Thalinger <christian.thalinger at oracle.com <mailto:christian.thalinger at oracle.com>> wrote:
>>> 
>>> 
>>>> On Jan 11, 2016, at 3:18 AM, Doug Simon <doug.simon at oracle.com <mailto:doug.simon at oracle.com>> wrote:
>>>> 
>>>> The CompileBroker currently uses a simple timeout of 1 second when waiting for a blocking JVMCI compilation to complete. This approach is too simple. JVMCI compiler threads themselves flood the compilation queues with compilation requests; such compilations cannot be blocking (the JVMCI compiler can easily cause the system to deadlock). This flooding means that application submitted tasks often timeout before the tasks even start compiling. 
>>>> Once a JVMCI thread starts compiling a task, there is still the risk of it deadlocking. The current timeout mechanism needs to be augmented with a test of the compiler thread's state. As long as it's not blocked for too long, we know the compiler is making progress and will eventually complete.
>>>> 
>>>> This review is for changes that address the above issues as follows: 
>>>> 
>>>> 1. Non-blocking tasks are selected before blocking tasks from the compilation queue. 
>>> 
>>> Aren’t blocking tasks selected before non-blocking tasks?
>> 
>> Yes, exactly the opposite of what I said ;-) I’ve fixed the bug description and thankfully got the implementation the right way round.
> 
> Then it looks good :-)
> 
>> 
>> -Doug

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