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From "Oleg Kalnichevski (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HTTPCORE-172) SharedInputBuffer stops returing data to reading thread once shutdown is called
Date Wed, 10 Sep 2008 21:32:44 GMT

    [ https://issues.apache.org/jira/browse/HTTPCORE-172?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12629982#action_12629982
] 

Oleg Kalnichevski commented on HTTPCORE-172:
--------------------------------------------

Hi Jason

I see the problem but I am not sure the proposed fix is the right thing to do, as the endOfStream
flag should retain its original semantics, that is, indicating that the buffer should close
in orderly fashion by flushing buffered content first. I think the right thing to do is to
call #shutdown() on the SharedOutputBuffer, not #close(), in case the underlying connection
is no longer writable / open.

Does this make sense to you?

Oleg  

> SharedInputBuffer stops returing data to reading thread once shutdown is called
> -------------------------------------------------------------------------------
>
>                 Key: HTTPCORE-172
>                 URL: https://issues.apache.org/jira/browse/HTTPCORE-172
>             Project: HttpComponents HttpCore
>          Issue Type: Bug
>          Components: HttpCore NIO
>    Affects Versions: 4.0-beta2
>         Environment: Synapse 1.2
>            Reporter: Jason Walton
>             Fix For: 4.0-beta3
>
>         Attachments: sharedbuf.patch
>
>
> This problem won't happen in Synapse 1.2 without the fix I proposed for https://issues.apache.org/jira/browse/SYNAPSE-415
in ClientHandler.java.
> To briefly recap:  If a ClientWorker attempts to read from a SharedInputBuffer, but no
data is availabled, SharedInputBuffer.read() will call into waitForData().  If the next event
to the ClientHandler is a "closed()" event, then the ClientHandler will remove its references
to the SharedInputBuffer.  At this point in time, the ClientWorker is left waiting for data
forever.  The fix I proposed for SYNAPSE-415 was to call into SharedInputBuffer.shutdown()
from ClientHandler.closed(), as this will send a notify to the SharedInputBuffer and wake
up the ClientWorker.
> This seemed like a good fix at the time, but now I'm running into this from the "other
side", so to speak.  Suppose the ClientWorker is a bit late in reading the stream.  
> 1) I/O Dispatcher thread receives data from the socket, and calls ClientHandler.inputReady(),
which in turn calls SharedInputBuffer.consumeContent().  This puts some data into the SharedInputBuffer's
buffer.
> 2) I/O Dispathcer thread sees the socket close, and so calls ClientHandler.closed().
 This calls into SharedInputBuffer.shutdown().
> 3) The ClientWorker thread calls into SharedInputBuffer.read(), which starts out with:
>         if (this.shutdown) {
>             return -1;
>         }
> The result is that the ClientWorker will erroneously think we never got a reply.
> A similar issue exists in SharedOutputBuffer, except here you would have to call "shutdown()"
followed by "produceContent()".  Since both of these methods are called from the I/O dispatcher
side, this wouldn't make a lot of sense (how can we produce content for a socket which is
closed?).  I suppose someone might call "shutdown()" instead of "writeCompleted()" in some
sort of error scenario on the worker side?  Probably not really worth worrying about.
> Here's my proposed fix (comments welcome, since I don't know this code as well as I could):
> Index: module-nio/src/main/java/org/apache/http/nio/util/SharedInputBuffer.java
> ===================================================================
> --- module-nio/src/main/java/org/apache/http/nio/util/SharedInputBuffer.java   (revision
689999)
> +++ module-nio/src/main/java/org/apache/http/nio/util/SharedInputBuffer.java   (working
copy)
> @@ -125,11 +125,11 @@
>      }
>      protected boolean isEndOfStream() {
> -        return this.shutdown || (!hasData() && this.endOfStream);
> +        return !hasData() && (this.shutdown || this.endOfStream);
>      }
>      public int read() throws IOException {
> -        if (this.shutdown) {
> +        if (this.isEndOfStream()) {
>              return -1;
>          }
>          synchronized (this.mutex) {
> @@ -144,7 +144,7 @@
>      }
>      public int read(final byte[] b, int off, int len) throws IOException {
> -        if (this.shutdown) {
> +        if (this.isEndOfStream()) {
>              return -1;
>          }
>          if (b == null) {
> @@ -168,7 +168,7 @@
>      }
>      public int read(final byte[] b) throws IOException {
> -        if (this.shutdown) {
> +        if (this.isEndOfStream()) {
>              return -1;
>          }
>          if (b == null) {

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