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
>