Hang in PreClose method during dup2 system call

[shruacha1234]

During fcntl, dup2 system calls if read/write happens then PreClose method gets hang. This issue is not seen if we Signal/Kill the thread first and then call the preClose method.

Signed-off-by: Shruthi.Shruthi1 Shruthi.Shruthi1@ibm.com

[shruacha1234]

@pshipton @keithc-ca Can you please review this PR

[pshipton]

Pls update the original source rather than copying it to the closed directory and modifying it.

[keithc-ca]

I think we need a much more detailed description of why the original order is wrong and why it should apply to all "unix" platforms. Further, the same order (preClose then signal) also exists in each of these files

src/java.base/share/classes/sun/nio/ch/DatagramChannelImpl.java
src/java.base/share/classes/sun/nio/ch/ServerSocketChannelImpl.java
src/java.base/share/classes/sun/nio/ch/SocketChannelImpl.java
src/java.base/unix/classes/sun/nio/ch/SinkChannelImpl.java
src/jdk.sctp/unix/classes/sun/nio/ch/sctp/SctpChannelImpl.java
src/jdk.sctp/unix/classes/sun/nio/ch/sctp/SctpMultiChannelImpl.java
src/jdk.sctp/unix/classes/sun/nio/ch/sctp/SctpServerChannelImpl.java

Please either correct each of those instances or explain why they don't need similar treatment.

[keithc-ca]

Ok, I think you've convinced me that reordering those calls makes sense. Other threads that might retry their read or write operation will fail because the channel has been closed (notice assert !isOpen(); on line 823.

However, you haven't explained why the same pattern that exists in the classes I listed above doesn't need correcting.

[shruacha1234]

@keithc-ca
The changes are applicable to the files you have listed. I have made the changes to those files

[shruacha1234]

@keithc-ca
The preClose() method internally calls the dup2() system call. If there is a dup2() call on a file descriptor on a thread while another thread is blocked in a read/write operation on the same file descriptor, then the dup2() call is known to hang. Currently, preClose() experiences a hang because we call dup2() before killing the reader/writer thread(s). The solution/workaround is to first kill the reader/writer thread(s) and then do the preClose() sequence. This reordering in the different channel implementations resolves the problem.

This is a known issue on AIX (and z/OS) since Java 6 and the solution mentioned above has been adopted in IBM Java since then.

We wanted to take this solution to OpenJDK, but there we require a Java reproducer test. Unfortunately, we haven't been able to reproduce the issue using a simple Java test case. This has been reported by an IBM customer who is able to reproduce the issue consistently on an AIX machine, but only with the IBM Integration Server running with the Terracotta server. Without a simple Java reproducer, OpenJDK is unlikely to accept a bug report and hence a PR. So, we want to propose this solution to the extensions repo.

[shruacha1234]

@keithc-ca Can you please review the changes made to the files you have listed

[keithc-ca]

I think we need to tread carefully here. I think we need to consider whether the change here will make the problem reported in eclipse-openj9/openj9#12582 more likely. @pshipton, do you have any thoughts or opinions on that?

[pshipton]

I think we need to consider whether the change here will make the problem reported in eclipse-openj9/openj9#12582 more likely.

We can run grinders on the test with this change.

Rather than assuming we won't get anything from OpenJDK, we should take this to OpenJDK even without a testcase. Even if we can't get the change made at OpenJDK, we should try, and we may get some useful information.

I'm also thinking that if the problem only affects AIX and z/OS, the changes should be restricted to those platforms rather than modify other platforms and potentially cause a regression or change in behavior there.