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

[David Holmes]

On 18/03/2016 11:28 PM, Dmitry Samersoff wrote:
> 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("\""\");

I still see %.Ns as the simplest solution - but whatever.

>
> 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.

So you want to remove the internal limitation instead of have the 
clients deal with it? Not sure it is worth the effort - IIRC that code 
can be used at sensitive times hence the simple approach to buffer 
management.

David

> -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
>>>>
>
>