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Posted to dev@tomcat.apache.org by bu...@apache.org on 2012/10/17 20:18:23 UTC
[Bug 54022] New: CometEvent.END event is not sent on a suspended
socket disconnect when running with Tomcat Native (tcnative-1.dll) on Windows
Vista / Windows Server 2008 or newer.
https://issues.apache.org/bugzilla/show_bug.cgi?id=54022
Priority: P2
Bug ID: 54022
Assignee: dev@tomcat.apache.org
Summary: CometEvent.END event is not sent on a suspended socket
disconnect when running with Tomcat Native
(tcnative-1.dll) on Windows Vista / Windows Server
2008 or newer.
Severity: blocker
Classification: Unclassified
Reporter: doug.beachy@verizon.net
Hardware: PC
Status: NEW
Version: 7.0.32
Component: Connectors
Product: Tomcat 7
Created attachment 29492
--> https://issues.apache.org/bugzilla/attachment.cgi?id=29492&action=edit
Tomcat 7.0.32 source file with the bugfix
Our Web application uses an asynchronous 3.0 servlet (via Atmosphere 1.0,
actually) to send notification messages to clients connected via long-running
sockets (e.g., HTTP streaming, long polling, etc.) I found a bug where Tomcat
was not sending the CometEvent.END event on x64 platforms that used Tomcat
Native when a socket would disconnect (e.g., by pressing CTRL-C from an HTTP
GET curl command).
After narrowing it down and debugging the Tomcat 7.0.32 source, I tracked the
problem down to org.apache.coyote.AbstractProtocol.java. Due to the way that
APR handles socket polling in Tomcat Native, the bug only occurs on Windows
platforms that 1) use tcnative-1.dll, and 2) are Vista/Server 2008 or newer.
Here is what is happening:
1) On startup, APR in tcnative-1.dll looks for a method named "WSAPoll" method
in Ws2_32.dll. If it finds it, it assigns that function as the function to use
to poll sockets. Otherwise, it falls back to the legacy method of polling
sockets. WSAPoll is only present on Windows Vista/Server 2008 or newer.
2) In org.apache.tomcat.util.net.AprEndpoint, the doPoll(long pollset) method
invokes Poll.poll(pollset, pollTime, desc, true), which delegates the call to
tcnative-1.dll if present.
3) If doPoll returns > 0, it means that at least one socket requires
processing, so it falls through to this block in the doPoll method
AprEndpoint.java (comments added below marked with "{DB}"):
for (int n = 0; n < rv; n++) {
// Check for failed sockets and hand this socket off to a worker
if (((desc[n*2] & Poll.APR_POLLHUP) == Poll.APR_POLLHUP) //
{DB} only the WSAPoll method sets the APR_POLLHUP flag when a socket
disconnects; neither the legacy tcnative polling method nor the pure Java
Coyote polling method sets this flag (which is fine)
|| ((desc[n*2] & Poll.APR_POLLERR) == Poll.APR_POLLERR)
|| (comet && (!processSocket(desc[n*2+1],
SocketStatus.OPEN))) // {DB} this line is executed for comet sockets if
WSAPoll is not available on this platform (e.g., pre-Vista/Server 2008) or if
tcnative-1.dll is not present. (This is also fine.)
|| (!comet && (!processSocket(desc[n*2+1])))) {
// Close socket and clear pool
if (comet) {
processSocket(desc[n*2+1], SocketStatus.DISCONNECT); //
{DB} this is only reached if tcnative-1.dll is present and we are running on
Vista/Server 2008 or newer. This is OK, but there is a bug with
SocketStatus.DISCONNECT handling for comet sockets in processSocket (described
in the next step)
} else {
destroySocket(desc[n*2+1]);
}
}
}
4) The processSocket(long socket, SocketStatus status) method fires up a
SocketEventProcessor and runs it, which excutes this:
Handler.SocketState state = handler.process(socket, status); // {DB}
this does not send CometEvent.END for comet if status ==
SocketStatus.DISCONNECT (details in next steps)
if (state == Handler.SocketState.CLOSED) {
// Close socket and pool
destroySocket(socket.getSocket().longValue()); // {DB} this closes
the socket and frees it for reuse, but since the Comet application was not
notified that the socket went away, the next time it tries to send data down
the socket it either crashes the JVM or writes the data to the response which
is now owned by somebody else. Chaos ensues.
socket = null;
}
5) When running Tomcat Native, the handler.process(socket, status) method is
implemented by
org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler, which
extends AbstractConnectionHandler defined as an inner class in
org.apache.coyote.AbstractProtocol. The method and the fix that I made on my
test instance are shown below [the fix was to add '&& (!processor.isComet())'
to the beginning condition of the 'if' block]:
======
public SocketState process(SocketWrapper<S> socket, SocketStatus status)
{
...<snip>...
do {
// {DB} NOTE: status only == SocketStatus.DISCONNECT here if we
are running tcnative on Windows Vista / Server 2008 or newer
// {DB} For all other cases status == SocketStatus.OPEN
here even if a disconnect has occurred, so it falls through to the '} else if
(processor.isComet()) {' line all is well.
// {DB} Original line: if (status == SocketStatus.DISCONNECT) {
if ( (status == SocketStatus.DISCONNECT) &&
(!processor.isComet()) ) { // <<<<<< {DB} BUGFIX: if comet, must allow
processor.event(SocketStatus.DISCONNECT) later in the 'if' block to send the
Comet.END event and return SocketState.CLOSED
//do nothing here, just wait for it to get recycled
} else if (processor.isAsync() || state == SocketState.ASYNC_END)
{
state = processor.asyncDispatch(status);
} else if (processor.isComet()) {
state = processor.event(status); // {DB} this sends
CometEvent.END and returns SocketState.CLOSED if status ==
SocketStatus.DISCONNECT, which is what we want
} else if (processor.isUpgrade()) {
state = processor.upgradeDispatch();
} else {
state = processor.process(socket);
}
...<snip>...
======
After I made the fix above and deployed the updated tomcat-coyote.jar I am now
getting the CometEvent.END events as expected when using Tomcat Native on
Windows 7. We are using Atmosphere (which uses Comet) for our next release,
but we will need this Tomcat bugfix before we can deploy. We could ship a
custom patched tomcat-coyote.jar but obviously we would prefer to have an
official fix in the next Tomcat patch release so we could just deploy that.
The fix I made above works for me, but if you need to reproduce the problem,
all you need to do is:
1) Install Tomcat 7.0.32 along with Tomcat Native on a Windows 7 or Windows
Server 2008 PC (I was using a 64-bit Windows 7 PC).
2) Run a servlet that:
a) implements org.apache.catalina.comet.CometProcessor, and
b) logs the CometEvents received, and
c) suspends the HttpRequest when it receives one.
3) Connect to that servlet by doing an HTTP GET via Curl.
4) Press CTRL-C to abort the socket connection. The CometEvent.END event is
never fired.
I attached the source file containing the bugfix (AbstractProtocol.java). The
fix is marked with "{DB}" comments. Thanks.
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[Bug 54022] CometEvent.END event is not sent on a suspended socket
disconnect when running with Tomcat Native (tcnative-1.dll) on Windows Vista
/ Windows Server 2008 or newer.
Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=54022
Mark Thomas <ma...@apache.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |FIXED
OS| |All
--- Comment #1 from Mark Thomas <ma...@apache.org> ---
Many thanks for the detailed analysis. One day, all bug reports will be this
easy to work with. The Tomcat developers really appreciate it when folks put
this sort of effort into their bug report as it saves us a lot of time.
Fixed in trunk and 7.0.x and will be included in 7.0.33 onwards.
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[Bug 54022] CometEvent.END event is not sent on a suspended socket
disconnect when running with Tomcat Native (tcnative-1.dll) on Windows Vista
/ Windows Server 2008 or newer.
Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=54022
--- Comment #2 from Douglas Beachy <do...@verizon.net> ---
No problem. Thanks for incorporating the fix so quickly!
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[Bug 54022] CometEvent.END event is not sent on a suspended socket
disconnect when running with Tomcat Native (tcnative-1.dll) on Windows Vista
/ Windows Server 2008 or newer.
Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=54022
chenzero <ch...@netease.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |chenzero@netease.com
--- Comment #3 from chenzero <ch...@netease.com> ---
Created attachment 30580
--> https://issues.apache.org/bugzilla/attachment.cgi?id=30580&action=edit
a test comet servlet
a basic CometProcessor servlet(Test1.java), I found that the CometEvent END is
not fired.only BEGIN event is fired. (tested on the lastest tomcat 7.0.42)
please use a browser to access the servlet, and the code attached.
I am confused on when will the END event will be fired ?
Thanks and sorry if post in the wrong place.(my email is in black list of
apache maillist)
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