RFR: 8146705: Improve JVMCI support for blocking compilation

[Christian Thalinger]

> On Jan 11, 2016, at 7:30 AM, Doug Simon <doug.simon at oracle.com> wrote:
> 
>> 
>> On 11 Jan 2016, at 18:23, Christian Thalinger <christian.thalinger at oracle.com> wrote:
>> 
>> 
>>> On Jan 11, 2016, at 3:18 AM, Doug Simon <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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