[JENKINS-40491] - Improve diagnostincs of the preliminary FifoBuffer termination

src/main/java/org/jenkinsci/remoting/nio/FifoBuffer.java

@@ -9,8 +9,11 @@
 import java.nio.channels.ClosedChannelException;
 import java.nio.channels.ReadableByteChannel;
 import java.nio.channels.WritableByteChannel;
+import javax.annotation.CheckForNull;
 import javax.annotation.Nonnegative;
 import javax.annotation.concurrent.GuardedBy;
+import org.kohsuke.accmod.Restricted;
+import org.kohsuke.accmod.restrictions.NoExternalUse;
 
 /**
  * FIFO buffer for a reader thread and a writer thread to collaborate.
@@ -167,6 +170,14 @@ public int receive(ReadableByteChannel ch, int max) throws IOException {
      */
     @GuardedBy("lock")
     private boolean closed;
+
+    /**
+     * Contains the reason why the buffer has been closed.
+     * The cause also stores the stacktrace of the close command.
+     */
+    @CheckForNull
+    private CloseCause closeCause;
+
     private boolean closeRequested = false;
 
     public FifoBuffer(int pageSize, int limit) {
@@ -243,6 +254,16 @@ public boolean isClosed() {
         return closed;
     }
 
+    /**
+     * Returns Exception with stacktrace of the command, which invoked the buffer close.
+     * @return Close cause or {@code null}
+     * @since TODO
+     */
+    @CheckForNull
+    public CloseCause getCloseCause() {
+        return closeCause;
+    }
+
     /**
      * Read from this buffer write as much as possible to the channel until
      * the channel gets filled up.
@@ -402,6 +423,7 @@ public void write(byte[] buf, int start, int len) throws InterruptedException, I
     public void close() {
         // Async modification of the field in order to notify other threads that we are about closing this buffer
         closeRequested = true;
+        closeCause = new CloseCause("Buffer close has been requested");
 
         // Now perform close operation
         handleCloseRequest();
@@ -593,4 +615,21 @@ public int read(byte[] b, int off, int len) throws IOException {
             }
         };
     }
+
+    /**
+     * Explains the reason of the buffer close.
+     * @since TODO
+     */
+    public static class CloseCause extends Exception {
+
+        private static final long serialVersionUID = 1L;
+
+        /*package*/ CloseCause(String message) {
+            super(message);
+        }
+
+        /*package*/ CloseCause(String message, Throwable cause) {
+            super(message, cause);
+        }  
+    }
 }

src/main/java/org/jenkinsci/remoting/nio/NioChannelHub.java

@@ -613,8 +613,10 @@ public void run() {
                                     t.swimLane.submit(new Runnable() {
                                         public void run() {
                                             // if this EOF is unexpected, report an error.
-                                            if (!t.getChannel().isInClosed())
-                                                t.getChannel().terminate(new EOFException());
+                                            if (!t.getChannel().isInClosed()) {
+                                                t.getChannel().terminate(new IOException("Unexpected EOF while receiving the data from the channel. "
+                                                        + "FIFO buffer has been already closed", t.rb.getCloseCause()));
+                                            }
                                         }
                                     });
                                 }
@@ -628,13 +630,14 @@ public void run() {
                             }
                             t.reregister();
                         } catch (IOException e) {
-                            LOGGER.log(WARNING, "Communication problem", e);
+                            // It causes the channel failure, hence it is severe
+                            LOGGER.log(SEVERE, "Communication problem in " + t + ". NIO Transport will be aborted.", e);
                             t.abort(e);
                         } catch (CancelledKeyException e) {
                             // see JENKINS-24050. I don't understand how this can happen, given that the selector
                             // thread is the only thread that cancels keys. So to better understand what's going on,
                             // report the problem.
-                            LOGGER.log(SEVERE, "Unexpected key cancellation for "+t, e);
+                            LOGGER.log(SEVERE, "Unexpected key cancellation for " + t + ". NIO Transport will be aborted.", e);
                             // to be on the safe side, abort the communication. if we don't do this, it's possible
                             // that the key never gets re-registered to the selector, and the traffic will hang
                             // on this channel.