RFR 8203369 : Check for both EAGAIN and EWOULDBLOCK error codes

[Ivan Gerasimov]

Hi David!

>> If gcc, then we already have the same test for both constants in code 
>> with no issues.
>> For example, java.base/unix/native/libnet/SocketInputStream.c, in 
>> NET_ReadWithTimeout():
>>          result = NET_NonBlockingRead(fd, bufP, len);
>>          if (result == -1 && ((errno == EAGAIN) || (errno == 
>> EWOULDBLOCK))) {
>>
>>
>> If javac, then, I was thinking about it too, but I don't have a good 
>> a universal solution to propose right now.
>
> javac should treat these symbolically rather than based on actual 
> value, so I don't see any issue there. It's the C compiler that sees 
> the raw value after preprocessing and so sees "duplicate" clauses.
>
If fact, as UnixContant.java is built from the template file 
UnixConstants.java.template, which is processed with cpp preprocessor, 
javac also sees the raw values.

So if someone decides to write something like
switch (exc.errno()) {
     case UnixConstants.EAGAIN:
     case UnixConstants.EWOULDBLOCK:
}
then there will be compile time trouble on some platforms and no issues 
on the others.

Fortunately, UnixContant class is package private, so it is quite 
unlikely to happen.

I was even thinking about proposing a language-level enhancement: If a 
switch statement contains duplicate cases *and* these are combined, then 
treat them as just one case.
Though the use case it too limited to justify the need :)

With kind regards,
Ivan