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Posted to notifications@ant.apache.org by bu...@apache.org on 2008/11/27 07:55:36 UTC
DO NOT REPLY [Bug 46305] New: Hung forked JVM when reading from
standard input
https://issues.apache.org/bugzilla/show_bug.cgi?id=46305
Summary: Hung forked JVM when reading from standard input
Product: Ant
Version: 1.7.1
Platform: PC
OS/Version: Windows XP
Status: NEW
Severity: normal
Priority: P2
Component: Core tasks
AssignedTo: notifications@ant.apache.org
ReportedBy: slackiz@fansbola.com
Hi,
When launching a Java program from ant with "fork=true", the launched program
seems to have *no* problem reading from the standard input (e.g. via
System.in.read()), however this seems to stuff up the thread management of the
launched program (i.e. the forked/child JVM) and possibly also crashes the
child JVM.
To reproduce this on a Windows XP (with Service Pack 3) using Sun JDK 6 update
10, I wrote a class with a main method that simply contains:
try {
System.out.println("X[Return] to quit");
while (System.in.read() != 'X')
;
System.exit(0);
// see shutdown hook for subsequent shutdown operations
} catch (IOException e) {
e.printStackTrace();
}
When the program runs and blocks/waits for input from the user, if attached via
JMX using JVisualVM (a tool that comes with Sun JDK 6 installation, for viewing
the memory and thread state of a VM), JVisualVM will freeze and could not
return any info about the JVM. The main thread of the JVM itself still works
since System.in.read() still responds to user input, but the other threads of
the program's JVM seem to have died and therefore the program/JVM cannot be
connected via RMI, remote debugging, using -QUIT signal to get JVM thread dump,
etc.
The above is just a straightforward way to demostrate the problem, but in
practice, without using JMX, the problem can also be reproduced using certain
combinations of operations involving "complex" thread management, such as AWT
event handling, RMI connection, etc. As such, it looks like that the problem is
caused by a combination of the following factors:
1. Launching a program from ant using "fork=true"
2. The program blocks to receive input from user, e.g. System.in.read()
3. The program performs "complex" threading operation, such as exporting RMI
remote objects, displaying a java.awt.Frame, connecting to the VM via JMX etc.
The JVM hang problem is noticeable/reproducable:
- On Windows XP (Service Pack 3, not sure about other service packs), but *no*
problem on Linux and Windows Vista.
- Using Sun JDK 1.4.2_14, 1.5.0_12, 1.6.0_10, and IBM J9 2.3
- Ant 1.7.0 and 1.7.1
I have no idea what could cause this problem, but I suspect that I/O
redirection is not properly implemented in Windows XP, and thus crashing the
JVM (e.g. interfering with the JVM's thread management).
Thanks,
Hendrik
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DO NOT REPLY [Bug 46305] Hung forked JVM when reading from standard
input
Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=46305
--- Comment #4 from slackiz@fansbola.com 2010-01-18 19:17:14 UTC ---
Hi,
Just an update on this issue from an article that I found recently, which may
be related since the described symptom is similar (though not the same).
According to item G.2 in
http://java.sun.com/j2se/1.4.2/docs/guide/rmi/faq.html#stdinput
* Question:
G.2 I have a single-threaded program that waits on standard input for a user
command which will initiate an RMI call. However, my remote object cannot
service this incoming remote call as the program appears to be blocked on
standard input. What's the problem?
* Answer:
This is a known problem, not with RMI, but with the thread that reads standard
input. The thread does not yield on the blocking read, but instead stays
running, hardly letting the listener get any cycles. We have tried two
workarounds that seem successful: set the main thread (the one reading standard
input) to a lower priority, or yield while bytes are not available in the
stream before actually reading it.
Regards,
Hendrik
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DO NOT REPLY [Bug 46305] Hung forked JVM when reading from standard
input
Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=46305
--- Comment #6 from Nicolas Lalevée <ni...@hibnet.org> 2010-09-25 07:16:42 EDT ---
@flushdia: this is a known and fixed bug you are reporting, see #49119
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DO NOT REPLY [Bug 46305] Hung forked JVM when reading from standard
input
Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=46305
--- Comment #3 from slackiz@fansbola.com 2009-06-05 01:24:54 PST ---
Hi,
Sorry for the late response.
The problem is still not fixed in the source code that I downloaded from:
svn co http://svn.apache.org/repos/asf/ant/core/trunk/ ant-core
In this test, jvisualvm still freezed, when trying to connect to the
application.
Regards,
Hendrik
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DO NOT REPLY [Bug 46305] Hung forked JVM when reading from standard
input
Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=46305
flushdia <fl...@gmail.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |flushdia@gmail.com
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DO NOT REPLY [Bug 46305] Hung forked JVM when reading from standard
input
Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=46305
--- Comment #5 from flushdia <fl...@gmail.com> 2010-09-24 14:14:56 EDT ---
I am experiencing similar issues when using forked <java> followed by <input>.
Let me explain the details.
Consider the following snippet of Ant XML code:
<target name="java-input">
<java classname="org.apache.tools.ant.launch.Launcher" fork="true">
<classpath>
<pathelement location="${ant.home}/lib/ant-launcher.jar" />
</classpath>
<arg value="-buildfile" />
<arg file="echo.xml" />
<arg value="echo" />
</java>
<input message="Do you want to proceed" validargs="y,n" defaultvalue="y"
addproperty="proceed" />
<echo>User selected [${proceed}]</echo>
</target>
When running this target, <input> asks for input two times (not one) and
accepts second entry as actual input.
Issue is not reproduced when running with fork="true" and spawn="true" OR with
fork="false".
Issue can be fixed by adding inputstring="" to <java>, but what if <java> has
to accept some input as well?
Shouldn't Ant workaround such situation?
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DO NOT REPLY [Bug 46305] Hung forked JVM when reading from standard
input
Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=46305
J.M. (Martijn) Kruithof <jk...@apache.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEEDINFO |NEW
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DO NOT REPLY [Bug 46305] Hung forked JVM when reading from standard
input
Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=46305
Stefan Bodewig <bo...@apache.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |NEEDINFO
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DO NOT REPLY [Bug 46305] Hung forked JVM when reading from standard
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Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=46305
--- Comment #7 from flushdia <fl...@gmail.com> 2010-09-25 12:13:01 EDT ---
(In reply to comment #6)
> @flushdia: this is a known and fixed bug you are reporting, see #49119
Thank you for pointing me to the right bug. Didn't find it during initial
lookup.
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DO NOT REPLY [Bug 46305] Hung forked JVM when reading from standard
input
Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=46305
--- Comment #1 from J.M. (Martijn) Kruithof <jk...@apache.org> 2009-02-07 10:49:02 PST ---
Could you please verify if this is solved in the currend "head" release?
This could have to do with pr 44544.
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DO NOT REPLY [Bug 46305] Hung forked JVM when reading from standard
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Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=46305
--- Comment #2 from Stefan Bodewig <bo...@apache.org> 2009-05-07 02:32:02 PST ---
ping?
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