RFR: JDK-8154144 Tests in com/sun/jdi fails intermittently with "jdb input stream closed prematurely

[Sharath Ballal]

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 at 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.ballal at oracle.com"sharath.ballal at 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

 
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