RFR(trivial): 8231024: Improve the debug info when the output is truncated

[Jie Fu]

Hi Ioi and David,

Updated: http://cr.openjdk.java.net/~jiefu/8231024/webrev.01/
   -1) The printed value has been changed from written + 1 to written + 2;
   -2) The input buffer size has been printed;
   -3) Adjust the error message to avoid some misleading.

- Before the patch
------------------------------------
[2019-09-14 16:07:55,752] Agent[1]: stderr: OpenJDK 64-Bit Server VM 
warning: increase O_BUFLEN in ostream.hpp -- output truncated
[2019-09-14 16:07:55,758] Agent[1]: stderr: OpenJDK 64-Bit Server VM 
warning: increase O_BUFLEN in ostream.hpp -- output truncated
[2019-09-14 16:07:55,763] Agent[1]: stderr: OpenJDK 64-Bit Server VM 
warning: increase O_BUFLEN in ostream.hpp -- output truncated
...
------------------------------------

- After the patch
------------------------------------
[2019-09-16 13:35:59,351] Agent[1]: stderr: OpenJDK 64-Bit Server VM 
warning: The buffer size is 2000, which (e.g., O_BUFLEN or BUFLEN) 
should be increased to 2014 or above -- output truncated
[2019-09-16 13:35:59,361] Agent[1]: stderr: OpenJDK 64-Bit Server VM 
warning: The buffer size is 2000, which (e.g., O_BUFLEN or BUFLEN) 
should be increased to 2032 or above -- output truncated
[2019-09-16 13:35:59,371] Agent[1]: stderr: OpenJDK 64-Bit Server VM 
warning: The buffer size is 2000, which (e.g., O_BUFLEN or BUFLEN) 
should be increased to 2050 or above -- output truncated
...
------------------------------------

Could you please review it and give me some advice?

Thanks a lot.
Best regards,
Jie


On 2019/9/16 下午12:04, Jie Fu wrote:
> Hi David,
>
> Thank you for your review.
> Will update the patch soon.
> Please seem comments inline.
>
> Best regards,
> Jie
>
> On 2019/9/15 上午10:03, David Holmes wrote:
>> Looks good. But given this keeps reporting different values, the 
>> input buffer size must be different in each case, so printing that 
>> size as well could also be useful for tracing back to the callsite. 
>
> OK. Will do.
>
>
>> There seems to be as assumption that the buffer is always O_BUFLEN in 
>> size but as it is set to 2000 that can't be the case. In which case 
>> the error message itself seems somewhat misleading.
> I agree that the error message itself seems somewhat misleading since 
> apart from O_BUFLEN [1], BUFLEN [2] may also be used as the buffer size.
>
> [1] 
> http://hg.openjdk.java.net/jdk/jdk/file/24df796eef3d/src/hotspot/share/utilities/ostream.cpp#l124
> [2] 
> http://hg.openjdk.java.net/jdk/jdk/file/24df796eef3d/src/hotspot/share/utilities/xmlstream.cpp#l138
>