spurious reportings of System.gc()???

[Kirk Pepperdine]

Hi Per,

Thanks for the response. The confusion here is that the System.gc() isn’t being reported as a Full GC. In fact this all looks like a young gen collection.

Regards,
Kirk

On Apr 4, 2014, at 12:28 PM, Per Liden <per.liden at oracle.com> wrote:

> Hi,
> 
> On 04/04/2014 09:56 AM, Kirk Pepperdine wrote:
>> Hi all,
>> 
>> I’ve been puzzling over this….
>> 
>> 0.925: [GC (System.gc())
>> Desired Survivor size 11010048 bytes, new threshold 7 (max 15)
>>  [PSYoungGen: 19838->4025K(76800K)] 19838K->4097K(251392K), 0.0047450 secs] [Times: user=0.02 sys=0.00, real=0.00 secs]
>> 
>> Aside from 3 cases of Allocation Failure, System.gc() is the only cause that is ever printed for every other GC record. Am I to assume this is a bug as my understanding is that this cause is only suppose to be printed when the application or RMI triggers a collection.
> 
> There are at least two uses of System.gc() inside the JDK itself. The first case is heavy use of ByteBuffer.allocateDirect(), which could cause a System.gc() if reference processing isn't keeping up and you're bumping into the MaxDirectMemorySize limit. I think the other case is heavy use of FileChannel.transferFrom/To(). Maybe that's what you're seeing?
> 
> cheer,
> /Per
> 
>> 
>> Regards,
>> Kirk
>> 
>> PS apologies for not providing JVM version, I’m not sure what it is at the moment but I’m assuming 7 but it might be from a preview version of 8.
>> 
>