https://bz.apache.org/bugzilla/show_bug.cgi?id=57779
Bug ID: 57779
Summary: Deadlock if using separate thread to write to
ServletOutputStream
Product: Tomcat 7
Version: 7.0.59
Hardware: All
OS: All
Status: NEW
Severity: major
Priority: P2
Component: Connectors
Assignee: [email protected]
Reporter: [email protected]
If using a separate (non-container) thread to write to a ServletOutputStream, a
deadlock can occur, if an io-error occurs during write. For example, if the
client drops the connection.
This is caused by a synchronized operation on the the underlying socket-object.
The servlet handling thread is blocked, while waiting for the end of output
from the separate thread, and holds a lock on the socket-object:
"http-bio-25030-exec-10" daemon prio=10 tid=0x0000000001804800 nid=0x3fd0
waiting on condition [0x00007f767aeeb000]
java.lang.Thread.State: WAITING (parking)
at sun.misc.Unsafe.park(Native Method)
- parking to wait for <0x00000000c3b273b8> (a
java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
...
at
org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:314)
- locked <0x00000000c38ef6d8> (a
org.apache.tomcat.util.net.SocketWrapper)
at
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at
org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
The separate thread trys to write, but an io-error occurs:
"Thread-13" daemon prio=10 tid=0x00007f767c5c8000 nid=0x3fda waiting for
monitor entry [0x00007f767a4e2000]
java.lang.Thread.State: BLOCKED (on object monitor)
at
org.apache.tomcat.util.net.JIoEndpoint.processSocketAsync(JIoEndpoint.java:560)
- waiting to lock <0x00000000c38ef6d8> (a
org.apache.tomcat.util.net.SocketWrapper)
at
org.apache.coyote.AbstractProcessor.setErrorState(AbstractProcessor.java:84)
at
org.apache.coyote.http11.AbstractHttp11Processor.action(AbstractHttp11Processor.java:802)
at org.apache.coyote.Response.action(Response.java:172)
at
org.apache.catalina.connector.OutputBuffer.doFlush(OutputBuffer.java:363)
at
org.apache.catalina.connector.OutputBuffer.flush(OutputBuffer.java:331)
at
org.apache.catalina.connector.CoyoteOutputStream.flush(CoyoteOutputStream.java:101)
Now it trys to get a lock on the socket-object and both threads are blocked
forever.
In the former tomcat version we used (7.0.53) this was not an issue. I had a
look in the source code and saw that the failing code was invented later.
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