Hi Staffan,
The root cause of this problem is that BufferedReader.readLine() is
intermittently returning 'null' during System.exit(0).
In TTY.java:751 we are always blocking on readLine(). Whenever a user enters a
command in JDB, the readLine() returns the command, which gets executed. This
is running in the 'main' thread.
When JDB is done, as part of the shutdown it calls System.exit() at Env.java:92
in a different thread 'event-handler'.
Usually (in the passing cases) calling System.exit() is the end of the process
and readLine() doesn't return 'null', but in the failing case readLine() at
TTY.java:751 returns 'null'. This causes the string "Input stream closed." to
be printed. The jtreg testcase looks for this string to decide that the
testcase failed.
The fix I have done is avoiding the print because we know that we are shutting
down and hence can discard the ‘null’ returned by readLine().
Regarding the testing, I have run few of the failing jtreg testcases about 200
times and not seen the problem (earlier I was able to recreate without the
fix). I have to do other tests, but sent for review to do it in parallel.
jdk/src/jdk.jdi/share/classes/com/sun/tools/example/debug/tty/TTY.java
708 BufferedReader in =
709 new BufferedReader(new InputStreamReader(System.in));
.......
.......
748 // Process interactive commands.
749 MessageOutput.printPrompt();
750 while (true) {
751 String ln = in.readLine();
752 if (ln == null) {
753 MessageOutput.println("Input stream closed.");
754 ln = "quit";
755 }
jdk/src/jdk.jdi/share/classes/com/sun/tools/example/debug/tty/Env.java
79 static void shutdown(String message) {
80 if (connection != null) {
81 try {
82 connection.disposeVM();
83 } catch (VMDisconnectedException e) {
84 // Shutting down after the VM has gone away. This is
85 // not an error, and we just ignore it.
86 }
87 }
88 if (message != null) {
89 MessageOutput.lnprint(message);
90 MessageOutput.println();
91 }
92 System.exit(0);
93 }
-Sharath Ballal
From: Staffan Larsen
Sent: Thursday, April 28, 2016 1:17 PM
To: Sharath Ballal
Cc: serviceability-dev@openjdk.java.net
Subject: Re: RFR: JDK-8154144 Tests in com/sun/jdi fails intermittently with
"jdb input stream closed prematurely
Hi Sharath,
Can you explain more how this help with the problem in the bug?
It looks like you are trying to avoid a race by not printing the "Input stream
closed.” message while shutting down. You added this:
136 ((TTY)notifier).setShuttingDown(true);
137 Env.shutdown(shutdownMessageKey);
The call on line 137 will result in a System.exit(0) call if I am reading the
code right. So adding the shutdown flag to line 136 will maybe make the race
smaller, but isn’t really solving it?
What kind of testing have you run this fix through?
Thanks,
/Staffan
On 28 apr. 2016, at 09:22, Sharath Ballal <HYPERLINK
"mailto:sharath.bal...@oracle.com"sharath.bal...@oracle.com> wrote:
Hi,
Pls review the change for bug
HYPERLINK "https://bugs.openjdk.java.net/browse/JDK-8154144"JDK-8154144 - Tests
in com/sun/jdi fails intermittently with "jdb input stream closed prematurely
Webrev:
http://cr.openjdk.java.net/~sballal/8154144/webrev.00/
-Sharath Ballal
