[9] RFR(S): JDK-8040798: compiler/startup/SmallCodeCacheStartup.java timed out in RT_Baseline

Thu Apr 24 20:07:09 UTC 2014

This looks good to me.

igor

On Apr 24, 2014, at 3:50 AM, Albert <albert.noll at oracle.com> wrote:

> Hi Igor,
> 
> you are right. I implemented a new version based on your suggestions.
> Here is the new webrev:
> http://cr.openjdk.java.net/~anoll/8040798/webrev.02/
> Best,
> Albert
> 
> 
> On 04/23/2014 09:49 PM, Igor Veresov wrote:
>> Albert,
>> 
>> You’re doing notify_all() on the *compile queue* lock, but the waiting happens on one of *task* locks (there is a separate lock for each task). I think you have to call notify() for each individual task lock as you are removing the tasks for the queue.
>> 
>> Also, you definitely don’t want to do an actual delete of the task (like in delete_all()). You can’t delete the task, because later in wait_for_completion() you check things like is_complete() and do free_task(), and you’re actually using the memory that has already been freed. So, perhaps you should implement something like free_all() instead that would remove the elements from queue and call free_task for each of them to put them back on the free list (and call notify() for each of them to wake the waiters). I think it’s ok if you just leave the tasks on the free list after that.
>> 
>> You should however take care not to call free_task() multiple times (one time in free(former delete)_all() the other time in wait_for_completion()). Perhaps you need another flag to check for that, or you can just assume that if it’s a part of the compile shutdown the free_task() in wait_for_completion() can be skipped.
>> You would need to check for this flag in the loop in wait_for_completion() as well. So in addition to check for is_completed() you would check for is_freed() (which you’ll have to add) or is_compilation_disabled_forever() like you did before.
>> 
>> igor
>> 
>> On Apr 23, 2014, at 1:22 AM, Albert <albert.noll at oracle.com> wrote:
>> 
>>> Igor, Vladimir, thanks for looking at this.
>>> 
>>> @Igor: You are right. If we do the notify in delete_all(), all threads that wait on the lock of a compilation task
>>> will wake up. I removed the timed wait in CompileBroker::wait_for_completion() since I think it is not needed
>>> anymore.
>>> 
>>> @Vladimir: Please see comments inline:
>>> 
>>> Here is the new webrev:
>>> http://cr.openjdk.java.net/~anoll/8040798/webrev.01/
>>> 
>>> 
>>> On 04/22/2014 07:36 PM, Vladimir Kozlov wrote:
>>>> Hi Albert,
>>>> 
>>>> compileBroker.hpp I think you want:
>>>> 
>>>>  NOT_PRODUCT( void print(); )
>>>> 
>>> Done.
>>>> and you need to use #ifndef PRODUCT in compileBroker.cpp.
>>>> 
>>> Done.
>>>> Next comment is not finished:
>>>> +     // Delete all queued compilation tasks to make
>>>> 
>>> Done.
>>>> We have 2 queues (c1 and C2). Does it means that C1 compilation may block C2 compilation too?:
>>>> 
>>> Yes, I think we have a single bit per Method*.
>>>> + /**
>>>> +  * See if this compilation is already requested.
>>>> +  *
>>>> +  * Implementation note: there is only a single "is in queue" bit
>>>> +  * for each method.  This means that the check below is overly
>>>> +  * conservative in the sense that an osr compilation in the queue
>>>> +  * will block a normal compilation from entering the queue (and vice
>>>> +  * versa).  This can be remedied by a full queue search to disambiguate
>>>> +  * cases.  If it is deemed profitable, this may be done.
>>>> +  */
>>>> + bool CompileBroker::compilation_is_in_queue(methodHandle method) {
>>>> 
>>>> 
>>>> Why next code in CompileBroker::compile_method() is not working?:
>>>> 
>>> Do you mean why that code does not prevent the deadlock?
>>> 
>>> I think that code does not cover the following scenario:
>>> 1) All compiler threads wait for new tasks
>>> 2) We put a blocking task in the compilation queue and wake up the compiler thread
>>> 3) The Java thread that issued the blocking compilation calls wait() on the compilation task
>>> 4) We run out of code cache and shut down compilation
>>> 5) All compiler threads exit the while loop in CompileQueue::get()
>>> 6) The Java thread blocks forever.
>>> 
>>> Best,
>>> Albert
>>>> // If the compiler is shut off due to code cache getting full
>>>>    // fail out now so blocking compiles dont hang the java thread
>>>>    if (!should_compile_new_jobs()) {
>>>>      CompilationPolicy::policy()->delay_compilation(method());
>>>>      return NULL;
>>>>    }
>>>>    compile_method_base(method, osr_bci, comp_level, hot_method, hot_count, comment, THREAD);
>>>> 
>>>> Thanks,
>>>> Vladimir
>>>> 
>>>> On 4/22/14 6:42 AM, Albert wrote:
>>>>> Hi,
>>>>> 
>>>>> could I get reviews for this small change?
>>>>> 
>>>>> Bug:
>>>>> https://bugs.openjdk.java.net/browse/JDK-8040798
>>>>> 
>>>>> Problem:
>>>>> The test starts the JVM with 3m code cache and 64 compiler threads. As a
>>>>> result, it is very likely
>>>>> that not all compiler threads can be started due to insufficient space
>>>>> in the code cache. It is also
>>>>> possible that the compiler runtime initialization of C1 and/or C2 fails.
>>>>> There is a race between a
>>>>> the blocking compilations (the test is started with -Xcomp) and the
>>>>> process of shutting down the
>>>>> compilers. More specifically, it can happen that (1) a blocking
>>>>> compilation task is put into a compilation
>>>>> queue, (2) the compilers are shut down, and (3) the application thread
>>>>> waits forever until the compilation
>>>>> completes (The compilation will never complete, since all compiler
>>>>> threads are exited).
>>>>> 
>>>>> Solution:
>>>>> Add a timeout to the wait() that waits for a compilation to complete and
>>>>> check if compilation is shut down
>>>>> forever. Furthermore, if we shut down the compiler runtimes, make sure
>>>>> that we use the interpreter to
>>>>> continue execution. The changes that fix the bug are in the following
>>>>> functions:
>>>>> 
>>>>> CompileBroker::wait_for_completion(CompileTask* task)
>>>>> shutdown_compiler_runtime(AbstractCompiler* comp, CompilerThread* thread)
>>>>> 
>>>>> 
>>>>> The patch also removes the destruction of the compile queue objects in
>>>>> shutdown_compiler_runtime().
>>>>> The destruction is removed, since it does not reclaim significant
>>>>> portions of memory, but possible introduces
>>>>> problems, since pointers to the compile queues can be used at other
>>>>> locations in the code. An assert ensures
>>>>> that no more tasks are put into a compilation queue once the compilers
>>>>> have been shut down.
>>>>> 
>>>>> In addition, the patch adds two locks in:
>>>>> 
>>>>> void CompileBroker::mark_on_stack()
>>>>> 
>>>>> 
>>>>> The two locks ensure that compilation tasks are not removed from the
>>>>> compilation queue or freed by a
>>>>> different (compiler) thread while the method mark_on_stack is executed.
>>>>> I am not really sure if that lock
>>>>> is needed. However, the lock seems to prevent concurrent read/writes of
>>>>> the compilation queue.
>>>>> 
>>>>> The rest of the changes are simple optional refactorings.
>>>>> 
>>>>> Testing:
>>>>> The timeout does not occur with the proposed changes. JPRT.
>>>>> 
>>>>> Webrev:
>>>>> http://cr.openjdk.java.net/~anoll/8040798/webrev.00/
>>>>> 
>>>>> Many thanks in advance,
>>>>> Albert
>>>>> 
> 