RFR 8203369 : Check for both EAGAIN and EWOULDBLOCK error codes

[Ivan Gerasimov]

Hi David!

Thank you for reviewing the fix!


On 5/24/18 7:44 PM, David Holmes wrote:
> Hi Ivan,
>
> Just a thought, but just because the actual native function may return 
> either code, that doesn't mean our native wrapper can't treat them the 
> same and present them to the Java code as one error?
>
Currently in some places we check for only one of the values (on the 
supported platforms we could have being checking for the other with 
exactly same effect).  In other places we already check for both values, 
so it is proposed to do it consistently with accordance to the 
documentation.

> It seems pointless to double up these condition checks everywhere just 
> in case there is some platform (do we know of one?) where this may be 
> necessary.
>
That's exactly what man pages suggest: "...a portable application should 
check for both..."
And yes, there exist such platforms.

> I also wonder whether a smart compiler might not flag code where the 
> errors do infact have the same value:
>
> if (errno == 11 || errno == 11) ...
>
At least gcc -O completely removes the second redundant test, so no 
observable changes is expected on supported platforms.

With kind regards,
Ivan

> Cheers,
> David
>
> On 25/05/2018 6:57 AM, Ivan Gerasimov wrote:
>> Hello!
>>
>> On Unix systems several system calls (including pread, read, readv, 
>> recvfrom, recvmsg, send, sendfile, sendmsg, sendto) may set errno to 
>> either EAGAIN or EWOULDBLOCK on the same condition.
>>
>> On Linux these two constants are the same, but they are not required 
>> to be the same.
>>
>> For example, here's an extract from the Linux man page of send():
>> EAGAIN or EWOULDBLOCK
>> The  socket  is marked nonblocking and the requested operation would 
>> block.  POSIX.1-2001 allows either error to be returned for this 
>> case, and does not require these constants to have the same value, so 
>> a portable application should check for both possibilities.
>>
>> We should check for both error codes when appropriate.
>>
>> Would you please help review the fix?
>>
>> BUGURL: https://bugs.openjdk.java.net/browse/JDK-8203369
>> WEBREV: http://cr.openjdk.java.net/~igerasim/8203369/00/webrev/
>>
>> Thanks!
>>
>

-- 
With kind regards,
Ivan Gerasimov