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

[Dmitry Samersoff]

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.

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 source code.