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

[Staffan Larsen]

Hi Sharath,

Ah, I see: it is the call to System.exit() that is causing readLine to return. That makes sense, and I now understand the fix.

Reviewed.

Thanks,
/Staffan

> On 28 apr. 2016, at 10:25, Sharath Ballal <sharath.ballal at oracle.com> wrote:
> 
> 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 <sharath.ballal at oracle.com <mailto:sharath.ballal at oracle.com>> wrote:
>  
> Hi,
>  
> Pls review the change for bug 
>  
> JDK-8154144 <https://bugs.openjdk.java.net/browse/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/ <http://cr.openjdk.java.net/~sballal/8154144/webrev.00/>
>  
> -Sharath Ballal

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.openjdk.java.net/pipermail/serviceability-dev/attachments/20160428/9bbfa6be/attachment-0001.html>