RFR[9u-dev]: 8151442: jstack doesn't close quotation marks properly with threads' name greater than 1996 characters

[Dmitry Samersoff]

David,

> Ignoring Dmitry's issue it still seems simpler/cleaner to just add the
> desired precision value to the %s than to split into two print
> statements. Or bite the bullet now and make the length immaterial by
> breaking the name into chunks. It's as easy to fix as to write the
> RFE :)

For this particular case the simplest solution is to use print_raw:

print_raw("\""\"); print_raw(get_thread_name()); print_raw("\""\");


But as soon as print() finally ends up with:

const int written = vsnprintf(buffer, buflen, format, ap);
...
DEBUG_ONLY(warning("increase O_BUFLEN in ostream.hpp -- output truncated");)

Complete fix should be something like:

int desired_size = vsnprintf(NULL, 0, format, ap);
if (desired_size > O_BUFLEN) {
    malloc
    ....
}

but it has performance penalty, so we should use some tricks to cover
most common %s/%d/%p cases.

-Dmitry




On 2016-03-18 15:51, David Holmes wrote:
> On 18/03/2016 10:03 PM, Cheleswer Sahu wrote:
>> Hi David,
>>
>> -----Original Message-----
>> From: David Holmes
>> Sent: Friday, March 18, 2016 2:42 PM
>> To: Cheleswer Sahu; hotspot-runtime-dev at openjdk.java.net;
>> serviceability-dev at openjdk.java.net
>> Subject: Re: RFR[9u-dev]: 8151442: jstack doesn't close quotation
>> marks properly with threads' name greater than 1996 characters
>>
>> On 18/03/2016 5:54 PM, Cheleswer Sahu wrote:
>>> Hi,
>>>
>>> Please review the code changes for
>>> https://bugs.openjdk.java.net/browse/JDK-8151442.
>>>
>>> Webrev Link: http://cr.openjdk.java.net/~csahu/8151442/
>>>
>>> Bug Brief:
>>>
>>> In jstack thread dumps , thread name greater than 1996 characters
>>> doesn't close quotation marks properly.
>>
>> Anyone giving a thread a name that long deserves to get a core dump! ;-)
>>
>>> Problem Identified:
>>>
>>> Jstack is using below code to print thread name
>>>
>>> src/share/vm/runtime/thread.cpp
>>>
>>> void JavaThread::print_on(outputStream *st) const {
>>>
>>>     st->print("\"%s\" ", get_thread_name());
>>>
>>> Here "st->print()"  internally uses max buffer length as O_BUFLEN
>>> (2000).
>>>
>>> void outputStream::do_vsnprintf_and_write_with_automatic_buffer(const
>>> char* format, va_list ap, bool add_cr) {
>>>
>>>     char buffer[O_BUFLEN];
>>>
>>> do_vsnprintf_and_write_with_automatic_buffer() finally calls
>>>    "vsnprintf()"  which truncates the anything greater than the max
>>> size(2000). In this case thread's name(> 1996) along with quotation
>>> marks (2)
>>>
>>> plus one terminating character exceeds the  max buffer size (2000),
>>> therefore the closing quotation  marks gets truncated.
>>>
>>> Solution:
>>>
>>> Split the  "st->print("\"%s\" ", get_thread_name())" in two statements
>>>
>>> 1.st->print("\"%s", get_thread_name());
>>>
>>> 2.st->print("\" ");
>>>
>>> This will ensure presence of closing quotation mark always.
>>
>> Can't we just limit the number of characters read by %s?
>>
>> Yes we can do it, but just one thing which I think of is, if the
>> truncation of output inside  output stream issue get resolves as
>> Dmritry suggested or O_BUFFLEN size gets increased in any  future fix
>> then we have to again make changes in this code, as limiting the no.
>> of character read by %s will give truncated output . In such case
>> present fix will have no effect.
> 
> Ignoring Dmitry's issue it still seems simpler/cleaner to just add the
> desired precision value to the %s than to split into two print
> statements. Or bite the bullet now and make the length immaterial by
> breaking the name into chunks. It's as easy to fix as to write the RFE :)
> 
> David
> 
>> David
>>
>>> Regards,
>>>
>>> Cheleswer
>>>


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