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Posted to dev@tomcat.apache.org by ma...@apache.org on 2017/06/19 12:24:56 UTC
svn commit: r1799190 - in /tomcat/trunk:
java/org/apache/tomcat/websocket/WsSession.java webapps/docs/changelog.xml
Author: markt
Date: Mon Jun 19 12:24:56 2017
New Revision: 1799190
URL: http://svn.apache.org/viewvc?rev=1799190&view=rev
Log:
Fix https://bz.apache.org/bugzilla/show_bug.cgi?id=61183
Correct a regression in the previous fix for BZ 58624 that could trigger a deadlock depending on the locking strategy employed by the client code.
Modified:
tomcat/trunk/java/org/apache/tomcat/websocket/WsSession.java
tomcat/trunk/webapps/docs/changelog.xml
Modified: tomcat/trunk/java/org/apache/tomcat/websocket/WsSession.java
URL: http://svn.apache.org/viewvc/tomcat/trunk/java/org/apache/tomcat/websocket/WsSession.java?rev=1799190&r1=1799189&r2=1799190&view=diff
==============================================================================
--- tomcat/trunk/java/org/apache/tomcat/websocket/WsSession.java (original)
+++ tomcat/trunk/java/org/apache/tomcat/websocket/WsSession.java Mon Jun 19 12:24:56 2017
@@ -648,28 +648,48 @@ public class WsSession implements Sessio
* @param f2sh The handler
*/
protected void registerFuture(FutureToSendHandler f2sh) {
- boolean fail = false;
- synchronized (stateLock) {
- // If the session has already been closed the any registered futures
- // will have been processed so the failure result for this future
- // needs to be set here.
- if (state == State.OPEN) {
- futures.put(f2sh, f2sh);
- } else if (f2sh.isDone()) {
- // NO-OP. The future completed before the session closed so no
- // need to register in case the session closes before it
- // completes.
- } else {
- // Construct the exception outside of the sync block
- fail = true;
- }
+ // Ideally, this code should sync on stateLock so that the correct
+ // action is taken based on the current state of the connection.
+ // However, a sync on stateLock can't be used here as it will create the
+ // possibility of a dead-lock. See BZ 61183.
+ // Therefore, a slightly less efficient approach is used.
+
+ // Always register the future.
+ futures.put(f2sh, f2sh);
+
+ if (state == State.OPEN) {
+ // The session is open. The future has been registered with the open
+ // session. Normal processing continues.
+ return;
}
- if (fail) {
- IOException ioe = new IOException(sm.getString("wsSession.messageFailed"));
- SendResult sr = new SendResult(ioe);
- f2sh.onResult(sr);
+ // The session is closed. The future may or may not have been registered
+ // in time for it to be processed during session closure.
+
+ if (f2sh.isDone()) {
+ // The future has completed. It is not known if the future was
+ // completed normally by the I/O layer or in error by doClose(). It
+ // doesn't matter which. There is nothing more to do here.
+ return;
}
+
+ // The session is closed. The Future had not completed when last checked.
+ // There is a small timing window that means the Future may have been
+ // completed since the last check. There is also the possibility that
+ // the Future was not registered in time to be cleaned up during session
+ // close.
+ // Attempt to complete the Future with an error result as this ensures
+ // that the Future completes and any client code waiting on it does not
+ // hang. It is slightly inefficient since the Future may have been
+ // completed in another thread or another thread may be about to
+ // complete the Future but knowing if this is the case requires the sync
+ // on stateLock (see above).
+ // Note: If multiple attempts are made to complete the Future, the
+ // second and subsequent attempts are ignored.
+
+ IOException ioe = new IOException(sm.getString("wsSession.messageFailed"));
+ SendResult sr = new SendResult(ioe);
+ f2sh.onResult(sr);
}
Modified: tomcat/trunk/webapps/docs/changelog.xml
URL: http://svn.apache.org/viewvc/tomcat/trunk/webapps/docs/changelog.xml?rev=1799190&r1=1799189&r2=1799190&view=diff
==============================================================================
--- tomcat/trunk/webapps/docs/changelog.xml (original)
+++ tomcat/trunk/webapps/docs/changelog.xml Mon Jun 19 12:24:56 2017
@@ -201,6 +201,11 @@
and/or stack traces on web application stop and/or start when running
under a security manager. (markt)
</fix>
+ <fix>
+ <bug>61183</bug>: Correct a regression in the previous fix for
+ <bug>58624</bug> that could trigger a deadlock depending on the locking
+ strategy employed by the client code. (markt)
+ </fix>
</changelog>
</subsection>
<subsection name="Other">
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