RFR: 8138916: Logging write function does not allow for long enough messages

[Dmitry Samersoff]

Mikael,

> If your libc only provides a ::malloc which takes a
> lock on every allocation then you should switch OS (or use libumem on
> Solaris).

Thank you for advice.

Default glibc malloc (ptmalloc) maintain multiple arenas. Each arena has
it's own lock and it allows multiple threads do allocation at the same
time, but in heavy multi-threaded environment like hotspot number of
arenas is less than number of threads (see MALLOC_ARENA_MAX) so
extensive use of malloc still could be an issue.

-Dmitry


On 2015-10-27 15:57, Mikael Gerdin wrote:
> On 2015-10-27 12:52, Dmitry Samersoff wrote:
>> Rachel,
>>
>> In worst case (windows, overflow) the code would parse format string
>> four times. Also NEW_C_HEAP_ARRAY takes a lock and might become a
>> performance bottleneck.
> 
> NEW_C_HEAP_ARRAY does not take any VM lock but is dependent on the libc
> ::malloc function. If your libc only provides a ::malloc which takes a
> lock on every allocation then you should switch OS (or use libumem on
> Solaris).
> /Mikael
> 
> 
>>
>> POSIX equivalent of _vscprintf(fmt, args) is vsnprintf(NULL, 0, fmt,
>> args)
>>
>> So it might be better to create os::log_vcprintf(fmt, args), then write
>> code at log.hpp as:
>>
>> int buf_len = os::log_vcprintf(fmt, args);
>> assert(buf_len < 2*page_size, "Stack overflow in logging");
>> char buf[buf_len];
>> vsprintf(buf, fmt, args);
>>
>> -Dmitry
>>
>>
>>
>> On 2015-10-26 23:58, Rachel Protacio wrote:
>>> Hello, all,
>>>
>>> Please review this fix to the faulty write function from the Unified
>>> Logging framework.
>>>
>>> Summary: In logging/log.hpp, the logging vwrite function previously
>>> asserted that the buffer remains within 512 characters, which is too
>>> short for logging message of non-pre-determined length, e.g. for vtable
>>> and itable function names. Now, the function resizes the buffer to the
>>> appropriate length, asserting only that the resulting buffer is valid.
>>> Includes tag "logtest" to test that logging can print an output of 518
>>> characters.
>>>
>>> Open webrev: http://cr.openjdk.java.net/~rprotacio/8138916/
>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8138916
>>>
>>> Includes own acceptance test, and passes JPRT and remote hotspot/test
>>> tests.
>>>
>>> Thank you,
>>> Rachel
>>
>>
> 


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