hotspot.log overlapping log statements (JITWatch)

[Dmitry Samersoff]

David,

> That's why I said per-thread buffering (not that I see a way to
> implement it). No-one blocks but *no thread starts to write
> a line until it has a full line to write*.

if the single line is result of different events it can take a while to
get something printed.  It's not always acceptable.

-Dmitry


On 2014-02-27 07:03, David Holmes wrote:
> On 27/02/2014 3:21 AM, John Rose wrote:
>> On Feb 26, 2014, at 4:35 AM, David Holmes <david.holmes at oracle.com
>> <mailto:david.holmes at oracle.com>> wrote:
>>
>>> I really didn't follow how you could untangle arbitrary non-delimited
>>> text, but I think it will still require changes to the use of the
>>> print functions to fix it - right? Logically what we want is
>>> per-thread buffering so that we only do a write() of a full line of
>>> text.
>>
>> The log is line-oriented, so switching threads in the middle of a line
>> requires that extra info.
> 
> Line-oriented in that we always start a new line when we switch threads
>  - ok. Hadn't realized that.
> 
>> You could queue up threads until the writer has finished his line but
>> I'd rather not, given that lines might require internal computation.
> 
> That's why I said per-thread buffering (not that I see a way to
> implement it). No-one blocks but no thread starts to write a line until
> it has a full line to write.
> 
>> It's better (IMO) to push the work to decode/reassemble after the JVM
>> exits.
>>
>> Here's approximately what I had in mind:
>>
>> diff --git a/src/share/vm/utilities/ostream.cpp
>> b/src/share/vm/utilities/ostream.cpp
>> --- a/src/share/vm/utilities/ostream.cpp
>> +++ b/src/share/vm/utilities/ostream.cpp
>> @@ -961,7 +961,11 @@
>>     // got the lock
>>     if (writer_id != _last_writer) {
>>       if (has_log) {
>> -      _log_file->bol();
>> +      int pos = _log_file->position();
>> +      if (pos > 0) {
>> +        _log_file->bol();
>> +        _log_file->print_cr("<partial_line pos='%d'/>", pos);
>> +      }
>>         // output a hint where this output is coming from:
>>         _log_file->print_cr("<writer thread='" UINTX_FORMAT "'/>",
>> writer_id);
>>       }
> 
> I see.
> 
> David
> -----
> 
> 
>> The "pos" bit is redundant, an extra clue about trailing spaces.
>>
>> — John


-- 
Dmitry Samersoff
Oracle Java development team, Saint Petersburg, Russia
* I would love to change the world, but they won't give me the sources.