RFR 8203369 : Check for both EAGAIN and EWOULDBLOCK error codes

[David Holmes]

Hi Ivan,

On 25/05/2018 1:58 PM, Ivan Gerasimov wrote:
> Hi David!
> 
> Thank you for reviewing the fix!

I looked but did not review - it was just an observation :)

> 
> 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..."

Yes but that's the native code that calls the library methods. That 
doesn't necessarily mean we have to propagate the ambiguity through our 
own native wrappers and/or Java code.

> 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.

I'm more worried about a new compiler warning - especially if you 
happened to use them in a switch! - resulting in future build failures.

Cheers,
David

> 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!
>>>
>>
>