RFR(s): 8143291: Remove redundant coding around os::exception_name

[David Holmes]

Hi Thomas,

I like the idea of this, but it will take me a little time to check all 
the details. More below ...

On 19/11/2015 8:23 PM, Thomas Stüfe wrote:
> Hi,
>
> please take a look at this change.
>
> bug: https://bugs.openjdk.java.net/browse/JDK-8143291
> webrev: http://cr.openjdk.java.net/~stuefe/webrevs/8143291/webrev.00/webrev/
>
> This fix does some cleanups around os::exception_name().
>
> - os::exception_name() is identical on all Posix platforms (it returns a
> signal name string for a signal number), so it can be merged into
> os_posix.cpp
>
> - There is no need for a platform-specific implementation, as we have
> already os::Posix::get_signal_name(). Use that instead of platform-specific
> solutions.
>
> - I added a function os::Posix::get_signal_number() which is the inverse of
> os::Posix::get_signal_name().
>
> - Before, a signal-to-number table was kept in jvm_<os>.cpp. That was used
> to implement os::exception_name() and also for JVM_FindSignal
> -> on AIX, I removed the coding altogether and used
> os::Posix::get_signal_number() as a base for JVM_FindSignal.
> -> on the other Unices, I did not feel so confident, because strictly
> spoken we may change the behaviour slightly to before:
> os::Posix::get_signal_name() knows more signal names than the platform
> specific tables knew before, so now Signal.findSignal("<name>") would
> return more matches than before.

How so? If the additional names are platform specific then they won't 
exist at build time on the other platforms and so will be elided from 
the table.

BTW the existing Solaris code is incorrect when we start building on 
Solaris 11, so it would be good to use something that uses the actual 
build time signal value rather than the current array based approach.

Thanks,
David

> I am not sure whether I am overcautious here - should I treat the other
> Unices the same way I treated AIX, i.e. implement
> Signal.findSignal("<name>") -> JVM_FindSignal via
> os::Posix::get_signal_number()? This would further simplify the coding.
>
> Oh, this fix also fixes an issue where os::exception_name() would return
> NULL for an unknown signal number, but no caller ever checks for NULL
> before printing the result. The new os::exception_name() always returns a
> string and also distinguishes between "unknown but valid signal" and
> "invalid signal".
>
> Kind Regards, Thomas
>