RFR: 8187667: Disable deprecation warning for readdir_r

[David Holmes]

FYI background reading:

https://www.gnu.org/software/libc/manual/html_node/Reading_002fClosing-Directory.html#Reading_002fClosing-Directory

Seems the deprecation has merit.

David

On 20/09/2017 7:05 AM, David Holmes wrote:
> Hi Erik,
> 
> Reviewed!
> 
> On 19/09/2017 10:42 PM, Erik Helin wrote:
>> Hi all,
>>
>> I'm continuing to run into some small problems when compiling HotSpot 
>> with a more recent toolchain. It seems like readdir_r [0] has been 
>> deprecated beginning with glibc 2.24 [1]. In HotSpot, we use readdir_r 
>> for os::readdir on Linux (defined in os_linux.inline.hpp). Since 
>> readdir_r most likely will stay around for a long time in glibc (even 
>> though in deprecated form), I figured it was best to just silence the 
>> deprecation warning from gcc. If readdir_r finally is removed one day, 
>> then we might have to look up the appropriate readdir function using 
>> dlopen, dlsym etc.
> 
> I find it very odd that they have deprecated the thread-safe variant of 
> this function, and recommend use of the basic readdir. I can only assume 
> they have made readdir itself thread-safe, but given the POSIX spec does 
> not require that, noone can take advantage without locking into knowing 
> which glibc version they are running on! That seems an awful mess for 
> programmers.
> 
> It is a good idea to just keep using it.
> 
>> Patch:
>> http://cr.openjdk.java.net/~ehelin/8187667/00/
>>
>> Bug:
>> https://bugs.openjdk.java.net/browse/JDK-8187667
>>
>> Testing:
>> - Compiles with:
>>    - gcc 7.1.1 and glibc 2.25 on Fedora 26
>>    - gcc 4.9.2 and glibc 2.12 on OEL 6.4
>> - JPRT
> 
> The change will cause warnings on gcc < 4.6, so this reinforces the need 
> to switch to our minimim gcc version ... which I forget :)
> 
> Thanks,
> David
> 
> 
>> Thanks,
>> Erik
>>
>> [0]: 
>> http://pubs.opengroup.org/onlinepubs/009695399/functions/readdir.html
>> [1]: https://sourceware.org/bugzilla/show_bug.cgi?id=19056