From 74f54da67eb9ff44bf92165a7389a0f2728473e5 Mon Sep 17 00:00:00 2001
From: Joakim Erdfelt <joakim.erdfelt@gmail.com>
Date: Thu, 4 Aug 2022 07:38:29 -0500
Subject: [PATCH] Adding FileSystemPool.Listener support

---
 .../jetty/util/resource/FileSystemPool.java   | 95 ++++++++++++++++++-
 1 file changed, 93 insertions(+), 2 deletions(-)

diff --git a/jetty-core/jetty-util/src/main/java/org/eclipse/jetty/util/resource/FileSystemPool.java b/jetty-core/jetty-util/src/main/java/org/eclipse/jetty/util/resource/FileSystemPool.java
index 83fa2b8b4da..0701a1a2336 100644
--- a/jetty-core/jetty-util/src/main/java/org/eclipse/jetty/util/resource/FileSystemPool.java
+++ b/jetty-core/jetty-util/src/main/java/org/eclipse/jetty/util/resource/FileSystemPool.java
@@ -51,6 +51,36 @@ public class FileSystemPool implements Dumpable
     private static final Logger LOG = LoggerFactory.getLogger(FileSystemPool.class);
     public static final FileSystemPool INSTANCE = new FileSystemPool();
 
+    /**
+     * Listener for pool events
+     */
+    public interface Listener
+    {
+        /**
+         * FileSystem URI is retained for the first time
+         * @param fsUri the filesystem URI
+         */
+        void onRetain(URI fsUri);
+
+        /**
+         * FileSystem URI exists in the pool and its reference count is incremented
+         * @param fsUri the filesystem URI
+         */
+        void onIncrement(URI fsUri);
+
+        /**
+         * FileSystem URI exists in the pool and its reference count is decremented
+         * @param fsUri the filesystem URI
+         */
+        void onDecrement(URI fsUri);
+
+        /**
+         * FileSystem URI exists in the pool and reached no references and has been closed
+         * @param fsUri the filesystem URI
+         */
+        void onClose(URI fsUri);
+    }
+
     private static final Map<String, String> ENV_MULTIRELEASE_RUNTIME;
 
     static
@@ -64,6 +94,8 @@ public class FileSystemPool implements Dumpable
     private final Map<URI, Bucket> pool = new HashMap<>();
     private final AutoLock poolLock = new AutoLock();
 
+    private Listener listener;
+
     private FileSystemPool()
     {
     }
@@ -126,11 +158,15 @@ public class FileSystemPool implements Dumpable
                     LOG.debug("Ref counter reached 0, closing pooled FS {}", bucket);
                 IO.close(bucket.fileSystem);
                 pool.remove(fsUri);
+                if (listener != null)
+                    listener.onClose(fsUri);
             }
             else
             {
                 if (LOG.isDebugEnabled())
                     LOG.debug("Decremented ref counter to {} for FS {}", count, bucket);
+                if (listener != null)
+                    listener.onDecrement(fsUri);
             }
         }
         catch (FileSystemNotFoundException fsnfe)
@@ -204,14 +240,69 @@ public class FileSystemPool implements Dumpable
         Bucket bucket = pool.get(fsUri);
         if (bucket == null)
         {
-            LOG.debug("Pooling new FS {}", fileSystem);
+            if (LOG.isDebugEnabled())
+                LOG.debug("Pooling new FS {}", fileSystem);
             bucket = new Bucket(fsUri, fileSystem, mount);
             pool.put(fsUri, bucket);
+            if (listener != null)
+                listener.onRetain(fsUri);
         }
         else
         {
             int count = bucket.counter.incrementAndGet();
-            LOG.debug("Incremented ref counter to {} for FS {}", count, fileSystem);
+            if (LOG.isDebugEnabled())
+                LOG.debug("Incremented ref counter to {} for FS {}", count, fileSystem);
+            if (listener != null)
+                listener.onIncrement(fsUri);
+        }
+    }
+
+    /**
+     * Set a listener on the FileSystemPool to monitor for pool events.
+     *
+     * @param listener the listener for pool events
+     */
+    public void setListener(Listener listener)
+    {
+        try (AutoLock ignore = poolLock.lock())
+        {
+            this.listener = listener;
+        }
+    }
+
+    /**
+     * Show a StackTrace
+     */
+    public static class StackLoggingListener implements Listener
+    {
+        private static final Logger LOG = LoggerFactory.getLogger(StackLoggingListener.class);
+
+        @Override
+        public void onRetain(URI uri)
+        {
+            if (LOG.isDebugEnabled())
+                LOG.debug("Retain {}", uri, new Throwable("Retain"));
+        }
+
+        @Override
+        public void onIncrement(URI uri)
+        {
+            if (LOG.isDebugEnabled())
+                LOG.debug("Increment {}", uri, new Throwable("Increment"));
+        }
+
+        @Override
+        public void onDecrement(URI uri)
+        {
+            if (LOG.isDebugEnabled())
+                LOG.debug("Decrement {}", uri, new Throwable("Decrement"));
+        }
+
+        @Override
+        public void onClose(URI uri)
+        {
+            if (LOG.isDebugEnabled())
+                LOG.debug("Close {}", uri, new Throwable("Close"));
         }
     }