PVA: Search cleanup

.. and if TCP handler can't connect, quit so that client will then
re-start the search

Author: kasemir

core/pva/src/main/java/org/epics/pva/client/ChannelSearch.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2019-2023 Oak Ridge National Laboratory.
+ * Copyright (c) 2019-2025 Oak Ridge National Laboratory.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
@@ -13,10 +13,11 @@
 import java.nio.ByteBuffer;
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.LinkedList;
+import java.util.HashMap;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Random;
-import java.util.concurrent.ConcurrentHashMap;
+import java.util.Set;
 import java.util.concurrent.Executors;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.TimeUnit;
@@ -99,27 +100,47 @@ private class SearchedChannel
             // Otherwise run risk of getting reply without being able
             // to handle it
         }
+
+        // Hash by channel name
+        @Override
+        public int hashCode()
+        {
+            return channel.getName().hashCode();
+        }
+
+        // Compare by channel name
+        @Override
+        public boolean equals(Object obj)
+        {
+            if (obj instanceof SearchedChannel other)
+                return other.channel.getName().equals(channel.getName());
+            return false;
+        }
     }
 
     // SearchedChannels are tracked in two data structures
     //
-    // - searched_channels (concurrent)
+    // - searched_channels
     //   Fast lookup of channel by ID,
-    //   efficient `computeIfAbsent(cid, ..` mechanism for creating
-    //   at most one SearchedChannel per CID.
+    //   creating at most one SearchedChannel per CID.
     //   Allows checking if a channel is indeed searched,
     //   and locating the channel for a search reply.
     //
-    //  - search_buckets (need to SYNC)
+    //  - search_buckets
     //   Efficiently schedule the search messages for all channels
     //   up to MAX_SEARCH_PERIOD.
+    //
+    //  Access to either one needs to be synchronized
 
-    /**  Map of searched channels by channel ID */
-    private ConcurrentHashMap<Integer, SearchedChannel> searched_channels = new ConcurrentHashMap<>();
+    /**  Map of searched channels by channel ID
+     *
+     *   Access only from synchronized method
+     */
+    private HashMap<Integer, SearchedChannel> searched_channels = new HashMap<>();
 
     /** Search buckets
      *
-     *  <p>The {@link #current_search_bucket} selects the list
+     *  <p>The {@link #current_search_bucket} selects the set
      *  of channels to be searched by {@link #runSearches()},
      *  which runs roughly once per second, each time moving to
      *  the next search bucket in a ring buffer fashion.
@@ -136,13 +157,13 @@ private class SearchedChannel
      *  which would result in an endless loop.
      *
      *  <p>Access to either {@link #search_buckets} or {@link #current_search_bucket}
-     *  must SYNC on {@link #search_buckets}.
+     *  must only occur in a 'synchronized' method.
      */
-    private final ArrayList<LinkedList<SearchedChannel>> search_buckets = new ArrayList<>();
+    private final ArrayList<Set<SearchedChannel>> search_buckets = new ArrayList<>(MAX_SEARCH_PERIOD+2);
 
     /** Index of current search bucket, i.e. the one about to be searched.
      *
-     *  <p>Access must SYNC on {@link #search_buckets}.
+     *  <p>Access must only occur in a 'synchronized' method.
      */
     private final AtomicInteger current_search_bucket = new AtomicInteger();
 
@@ -185,11 +206,9 @@ public ChannelSearch(final ClientUDPHandler udp,
         this.udp = udp;
         this.tcp_provider = tcp_provider;
 
-        synchronized (search_buckets)
-        {
-            for (int i=0; i<MAX_SEARCH_PERIOD+2; ++i)
-                search_buckets.add(new LinkedList<>());
-        }
+        // Each bucket holds set of channels to search in that time slot
+        for (int i=0; i<MAX_SEARCH_PERIOD+2; ++i)
+            search_buckets.add(new HashSet<>());
 
         // Searches sent to multicast (IPv4, IPv6) or broadcast addresses (IPv4) reach every PVA server
         // on that multicast group or bcast subnet.
@@ -227,7 +246,7 @@ else if (addr.isBroadcast())
 
     public void start()
     {
-        // +-jitter to prevent multiple clients from sending concurrent search requests
+        // 1 second +-jitter to prevent multiple clients from sending concurrent search requests
         final long period = SEARCH_PERIOD_MS + (new Random().nextInt(2*SEARCH_JITTER_MS+1) - SEARCH_JITTER_MS);
 
         logger.log(Level.FINER,
@@ -246,19 +265,20 @@ public void register(final PVAChannel channel, final boolean now)
     {
         logger.log(Level.FINE, () -> "Register search for " + channel + (now ? " now" : " soon"));
 
-        final ClientChannelState old = channel.setState(ClientChannelState.SEARCHING);
-        if (old == ClientChannelState.SEARCHING)
-            logger.log(Level.WARNING, "Registering channel " + channel + " to be searched more than once ");
+        synchronized (this)
+        {
+            final ClientChannelState old = channel.setState(ClientChannelState.SEARCHING);
+            if (old == ClientChannelState.SEARCHING)
+                logger.log(Level.WARNING, "Registering channel " + channel + " to be searched more than once ");
 
-        final SearchedChannel sc = searched_channels.computeIfAbsent(channel.getCID(), id -> new SearchedChannel(channel));
+            final SearchedChannel sc = searched_channels.computeIfAbsent(channel.getCID(), id -> new SearchedChannel(channel));
 
-        synchronized (search_buckets)
-        {
             int bucket = current_search_bucket.get();
             if (!now)
-                bucket = (bucket + SEARCH_SOON_DELAY)  % search_buckets.size();
-            search_buckets.get(bucket).add(sc);
+                bucket = (bucket + SEARCH_SOON_DELAY) % search_buckets.size();
+            search_buckets.get(bucket).add(sc);            
         }
+
         // Jumpstart search instead of waiting up to ~1 second for current bucket to be handled
         if (now)
             timer.execute(this::runSearches);
@@ -268,17 +288,15 @@ public void register(final PVAChannel channel, final boolean now)
      *  @param channel_id
      *  @return {@link PVAChannel}, <code>null</code> when channel wasn't searched any more
      */
-    public PVAChannel unregister(final int channel_id)
+    public synchronized PVAChannel unregister(final int channel_id)
     {
         final SearchedChannel searched = searched_channels.remove(channel_id);
         if (searched != null)
         {
             logger.log(Level.FINE, () -> "Unregister search for " + searched.channel.getName() + " " + channel_id);
-            // NOT removing `searched` from all `search_buckets`.
-            // Removal would be a slow, linear operation.
-            // `runSearches()` will drop the channel from `search_buckets`
-            // because it's no longer listed in `searched_channels`
-
+            // Remove `searched` from all `search_buckets`.
+            for (Set<SearchedChannel> bucket : search_buckets)
+                bucket.remove(searched);
             return searched.channel;
         }
         return null;
@@ -288,7 +306,7 @@ public PVAChannel unregister(final int channel_id)
      *
      *  <p>Resets their search counter so they're searched "real soon".
      */
-    public void boost()
+    public synchronized void boost()
     {
         for (SearchedChannel searched : searched_channels.values())
         {
@@ -299,12 +317,9 @@ public void boost()
             if (period == MIN_SEARCH_PERIOD)
             {
                 logger.log(Level.FINE, () -> "Restart search for '" + searched.channel.getName() + "'");
-                synchronized (search_buckets)
-                {
-                    final LinkedList<SearchedChannel> bucket = search_buckets.get(current_search_bucket.get());
-                    if (! bucket.contains(searched))
-                        bucket.add(searched);
-                }
+
+                final Set<SearchedChannel> bucket = search_buckets.get(current_search_bucket.get());
+                bucket.add(searched);
             }
             // Not sending search right now:
             //   search(channel);
@@ -322,17 +337,17 @@ public void boost()
     @SuppressWarnings("unchecked")
     private void runSearches()
     {
+        // Determine current search bucket
+        final int current = current_search_bucket.getAndUpdate(i -> (i + 1) % search_buckets.size());
+        // Collect channels to be searched while sync'ed
         to_search.clear();
-        synchronized (search_buckets)
+        synchronized (this)
         {
-            // Determine current search bucket
-            final int current = current_search_bucket.getAndUpdate(i -> (i + 1) % search_buckets.size());
-            final LinkedList<SearchedChannel> bucket = search_buckets.get(current);
+            final Set<SearchedChannel> bucket = search_buckets.get(current);
             logger.log(Level.FINEST, () -> "Search bucket " + current);
 
             // Remove searched channels from the current bucket
-            SearchedChannel sc;
-            while ((sc = bucket.poll()) != null)
+            for (SearchedChannel sc : bucket)
             {
                 if (sc.channel.getState() == ClientChannelState.SEARCHING  &&
                     searched_channels.containsKey(sc.channel.getCID()))
@@ -349,8 +364,8 @@ private void runSearches()
                     // in case that search bucket is quite full
                     final int i_n   = (current + period) % search_buckets.size();
                     final int i_n_n = (i_n + 1)          % search_buckets.size();
-                    final LinkedList<SearchedChannel> next = search_buckets.get(i_n);
-                    final LinkedList<SearchedChannel> next_next = search_buckets.get(i_n_n);
+                    final Set<SearchedChannel> next      = search_buckets.get(i_n);
+                    final Set<SearchedChannel> next_next = search_buckets.get(i_n_n);
                     if (i_n == current  ||  i_n_n == current)
                         throw new IllegalStateException("Current, next and nextnext search indices for " + sc.channel + " are " +
                                                         current + ", " + i_n + ", " + i_n_n);
@@ -362,9 +377,9 @@ private void runSearches()
                 else
                     logger.log(Level.FINE, "Dropping channel from search: " + sc.channel);
             }
+            bucket.clear();
         }
 
-
         // Search batch..
         // Size of a search request is close to 50 bytes
         // plus { int cid, string name } for each channel.
@@ -441,6 +456,7 @@ private void search(final Collection<SearchRequest.Channel> channels)
 
             // In case of connection errors (TCP connection blocked by firewall),
             // tcp will be null
+            // TODO CHECK THAT with updated ClientTCPHandler that connects on receive thread
             if (tcp != null)
             {
                 final RequestEncoder search_request = (version, buffer) ->
@@ -526,8 +542,10 @@ private void sendSearch(final int seq, final Collection<SearchRequest.Channel> c
     /** Stop searching channels */
     public void close()
     {
-        searched_channels.clear();
-
+        synchronized (this)
+        {
+            searched_channels.clear();
+        }
         timer.shutdown();
     }
 }

core/pva/src/main/java/org/epics/pva/client/ClientTCPHandler.java

@@ -140,7 +140,7 @@ protected boolean initializeSocket()
             socket.setKeepAlive(true);
         }
         catch (Exception ex)
-        {   
+        {
             logger.log(Level.WARNING, "PVA client cannot connect to " + server_address, ex);
             return false;
         }
@@ -157,6 +157,13 @@ protected boolean initializeSocket()
         return true;
     }
 
+    @Override
+    public InetSocketAddress getRemoteAddress()
+    {
+        // socket may not be connected or null, return address to which we want to connect
+        return new InetSocketAddress(server_address.getAddress(), server_address.getPort());
+    }
+
     /** @return Client context */
     PVAClient getClient()
     {

core/pva/src/main/java/org/epics/pva/common/TCPHandler.java

@@ -144,6 +144,9 @@ public TCPHandler(final boolean client_mode)
      */
     abstract protected boolean initializeSocket();
 
+    /** @return Remote address of the TCP socket */
+    abstract public InetSocketAddress getRemoteAddress();
+
     /** Start receiving data
      *  To be called by Client/ServerTCPHandler when fully constructed
      */
@@ -167,12 +170,6 @@ protected void startSender() throws Exception
             throw new Exception("Send thread already running");
     }
 
-    /** @return Remote address of this end of the TCP socket */
-    public InetSocketAddress getRemoteAddress()
-    {
-        return new InetSocketAddress(socket.getInetAddress(), socket.getPort());
-    }
-
     /** @return Is the send queue idle/empty? */
     protected boolean isSendQueueIdle()
     {
@@ -269,20 +266,14 @@ protected void send(final ByteBuffer buffer) throws Exception
     /** Receiver */
     private Void receiver()
     {
-        // Establish connection
-        Thread.currentThread().setName("TCP receiver");
-        while (! initializeSocket())
-            try
-            {   // Delay for (another) connection timeout, at least 1 sec
-                Thread.sleep(Math.max(1, PVASettings.EPICS_PVA_TCP_SOCKET_TMO) * 1000);
-            }
-            catch (Exception ignore)
-            {
-                // NOP
-            }
-        // Listen on the connection
         try
         {
+            // Establish connection
+            Thread.currentThread().setName("TCP receiver");
+            if (! initializeSocket())
+                return null;
+
+            // Listen on the connection
             Thread.currentThread().setName("TCP receiver " + socket.getLocalSocketAddress());
             logger.log(Level.FINER, () -> Thread.currentThread().getName() + " started for " + socket.getRemoteSocketAddress());
             logger.log(Level.FINER, "Native byte order " + receive_buffer.order());
@@ -348,8 +339,8 @@ private Void receiver()
         }
         finally
         {
-            onReceiverExited(running);
             logger.log(Level.FINER, Thread.currentThread().getName() + " done.");
+            onReceiverExited(running);
         }
         return null;
     }

core/pva/src/main/java/org/epics/pva/server/ServerTCPHandler.java

@@ -122,6 +122,12 @@ protected boolean initializeSocket()
         return true;
     }
 
+    @Override
+    public InetSocketAddress getRemoteAddress()
+    {
+        return new InetSocketAddress(socket.getInetAddress(), socket.getPort());
+    }
+
     PVAServer getServer()
     {
         return server;