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https://issues.apache.org/jira/browse/HADOOP-11957?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14551088#comment-14551088
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Anu Engineer commented on HADOOP-11957:
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bq. This is very dangerous because it means that we may call close on a file
descriptor while another thread is still using it. If this happens, a third
thread may open another file, which will get the same file descriptor number as
the one which was just closed. And then the second thread is doing some
arbitrary operation on the wrong file descriptor
Sorry I did not specifically answer this concern. In our current code path, we
have already called shutdown -- so from our point of view we are ready to lose
that file handle. It is *not* the java code, it is OS code path - Linux , BSD
or Mac OS as the case may be. So we are more than willing to close the file
handle, and OS says sorry this is not a valid socket or there is no connection.
In that scenario, I don't see the danger of second thread doing something
arbitrary on a wrong handle since we decided to call shutdown and throw away
the handle anyway. if what you are saying is possible , then we have some other
locking bugs higher up in the stack which really cannot be solved at this layer.
> if an IOException error is thrown in DomainSocket.close we go into infinite
> loop.
> ---------------------------------------------------------------------------------
>
> Key: HADOOP-11957
> URL: https://issues.apache.org/jira/browse/HADOOP-11957
> Project: Hadoop Common
> Issue Type: Bug
> Components: net
> Affects Versions: 2.7.1
> Reporter: Anu Engineer
> Assignee: Anu Engineer
> Attachments: HADOOP-11957.001.patch
>
>
> if an IOException error is thrown in DomainSocket.close we go into infinite
> loop.
> Issue : If the shutdown0(fd) call throws an IOException we break out of the
> if shutdown call but will continue to loop in the while loop infinitely since
> we have no way of decrementing the counter. Please scroll down and see the
> comment marked with Bug Bug to see where the issue is.
> {code:title=DomainSocket.java}
> @Override
> public void close() throws IOException {
> // Set the closed bit on this DomainSocket
> int count = 0;
> try {
> count = refCount.setClosed();
> } catch (ClosedChannelException e) {
> // Someone else already closed the DomainSocket.
> return;
> }
> // Wait for all references to go away
> boolean didShutdown = false;
> boolean interrupted = false;
> while (count > 0) {
> if (!didShutdown) {
> try {
> // Calling shutdown on the socket will interrupt blocking system
> // calls like accept, write, and read that are going on in a
> // different thread.
> shutdown0(fd);
> } catch (IOException e) {
> LOG.error("shutdown error: ", e);
> }
> didShutdown = true;
> // *BUG BUG* <-- Here the code will never exit the loop
> // if the count is greater then 0. we need to break out
> // of the while loop in case of IOException Error
> }
> try {
> Thread.sleep(10);
> } catch (InterruptedException e) {
> interrupted = true;
> }
> count = refCount.getReferenceCount();
> }
> // At this point, nobody has a reference to the file descriptor,
> // and nobody will be able to get one in the future either.
> // We now call close(2) on the file descriptor.
> // After this point, the file descriptor number will be reused by
> // something else. Although this DomainSocket object continues to hold
> // the old file descriptor number (it's a final field), we never use it
> // again because this DomainSocket is closed.
> close0(fd);
> if (interrupted) {
> Thread.currentThread().interrupt();
> }
> }
> {code}
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