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

[David Holmes]

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?

David

Regards,

Cheleswer