RFR(XXS) 8230385 [cds] No message is logged when shared image cannot be used due to mismatched configuration

[Ioi Lam]

On 11/27/19 1:39 PM, David Holmes wrote:
> On 28/11/2019 4:32 am, Thomas Stüfe wrote:
>> Looks good Ioi. I'm surprised UL works this early.
>
> I'm also surprised. no_shared_spaces() is called from three different 
> paths - will they all work? It is hard to see by code inspection.
>
The three paths are all called after the VM arguments have been parsed, 
at which point UL has already been set up. So it should be safe to call 
UL. E.g., if you tell UL to save to a file:

$ java -XX:-UseCompressedOops -Xlog:cds:file=foo.txt -version
java version "14-internal" 2020-03-17
Java(TM) SE Runtime Environment (fastdebug build 
14-internal+0-adhoc.iklam.open)
Java HotSpot(TM) 64-Bit Server VM (fastdebug build 
14-internal+0-adhoc.iklam.open, mixed mode)
$ cat foo.txt
[0.001s][info][cds] Unable to use shared archive: UseCompressedOops and 
UseCompressedClassPointers must be on for UseSharedSpaces.

In fact, all three call sites are preceded by something like:

     if (SomeJVMOption) { ....

So if this were done before all the VM arguments are parsed, we would 
already be doing something wrong ...

There are a bunch of log_debug/log_info calls in arguments.cpp. I think 
they all have the same assumption. This is kind of iffy, but that's 
beyond the scope of this patch :-)

Thanks
- Ioi


> Cheers,
> David
>
>> Cheers, Thomas
>>
>> On Wed, Nov 27, 2019 at 7:29 PM Ioi Lam <ioi.lam at oracle.com> wrote:
>>
>>> https://bugs.openjdk.java.net/browse/JDK-8230385
>>>
>>> http://cr.openjdk.java.net/~iklam/jdk14/8230385-log-when-cds-is-disabled.v01/ 
>>>
>>>
>>> Please review this one-liner addition that prints a log message when 
>>> CDS
>>> cannot be used. Output:
>>>
>>> $ java -XX:-UseCompressedOops -Xlog:cds -version
>>> [0.001s][info][cds] Unable to use shared archive: UseCompressedOops and
>>> UseCompressedClassPointers must be on for UseSharedSpaces.
>>> java version "14-internal" 2020-03-17
>>> Java(TM) SE Runtime Environment (fastdebug build
>>> 14-internal+0-adhoc.iklam.open)
>>> Java HotSpot(TM) 64-Bit Server VM (fastdebug build
>>> 14-internal+0-adhoc.iklam.open, mixed mode)
>>>
>>> Thanks
>>> - Ioi
>>>