Hi David, -----Original Message----- From: David Holmes Sent: Friday, March 18, 2016 2:42 PM To: Cheleswer Sahu; hotspot-runtime-...@openjdk.java.net; serviceability-dev@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. David > Regards, > > Cheleswer >
