https://issues.apache.org/bugzilla/show_bug.cgi?id=53173
Priority: P2
Bug ID: 53173
Assignee: dev@tomcat.apache.org
Summary: maxConnections feature hangs the system
Severity: normal
Classification: Unclassified
Reporter: fha...@apache.org
Hardware: PC
Status: NEW
Version: 7.0.27
Component: Connectors
Product: Tomcat 7
Created attachment 28704
--> https://issues.apache.org/bugzilla/attachment.cgi?id=28704&action=edit
fix missing count down for maxConnections latch
We've run into a scenario where the JIO Acceptor thread hangs as connections
are not counted down properly.
<Executor name="tomcatThreadPool"
namePrefix="tomcat-8080-"
minSpareThreads="50"
maxThreads="300"/>
<Connector port="8080"
redirectPort="${bio.https.port}"
protocol="org.apache.coyote.http11.Http11Protocol"
maxKeepAliveRequests="15"
executor="tomcatThreadPool"
connectionTimeout="20000"
acceptCount="100"/>
Thread dump yields
"http-bio-8080-Acceptor-0" daemon prio=3 tid=0xXXXXXXXX nid=0xXX waiting on
condition [0xXXXXXXXX..0xXXXXXXXX]
java.lang.Thread.State: WAITING (parking)
at sun.misc.Unsafe.park(Native Method)
- parking to wait for <0xXXXXXXXX> (a
org.apache.tomcat.util.threads.LimitLatch$Sync)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:158)
at
java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:747)
at
java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireSharedInterruptibly(AbstractQueuedSynchronizer.java:905)
at
java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(AbstractQueuedSynchronizer.java:1217)
at
org.apache.tomcat.util.threads.LimitLatch.countUpOrAwait(LimitLatch.java:99)
at
org.apache.tomcat.util.net.AbstractEndpoint.countUpOrAwaitConnection(AbstractEndpoint.java:660)
at
org.apache.tomcat.util.net.JIoEndpoint$Acceptor.run(JIoEndpoint.java:210)
at java.lang.Thread.run(Thread.java:619)
This, as you may imagine, is a fairly hard use case to reproduce into a simple
test case. The easiest way to reproduce it is to create the following
configuration
<Executor name="tomcatThreadPool"
namePrefix="catalina-exec-"
maxThreads="5"
minSpareThreads="0"
maxQueueSize="15"/>
<Connector port="8080"
protocol="HTTP/1.1" executor="tomcatThreadPool"
connectionTimeout="10000"
redirectPort="8443"
maxConnections="30"/>
This reproduces one test case, where the state machine is not taking into
account that connections may be rejected by the queue, but it doesn't count
down the latch.
I'm attaching a patch to fix this specific use case, but it may not be a
complete fix. As a workaround, the patch also introduces the
maxConnections="-1" configuration that disables the usage of maxConnections.
The -1 setting is important to give administrator a workaround while the other
edge cases are tracked down.
I have not been able to reproduce this error with NIO connector.
There is one more place in the JioEndpoint that requires handling of
RejectedExecutionException in the
public boolean processSocketAsync(SocketWrapper<Socket> socket,SocketStatus
status)
This is currently unhandled.
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