From dfa18fe6b395171c821cde02f081e12dd1565ba5 Mon Sep 17 00:00:00 2001
From: Alan Bateman <alanb@openjdk.org>
Date: Thu, 21 Nov 2024 16:25:43 +0000
Subject: [PATCH] 8344328: (dc) DatagramChannelImpl.blockingReceive can now
 synchronize on packet

Reviewed-by: dfuchs, jpai
---
 .../sun/nio/ch/DatagramChannelImpl.java       | 73 ++++++++-----------
 .../sun/nio/ch/DatagramSocketAdaptor.java     |  8 +-
 2 files changed, 37 insertions(+), 44 deletions(-)

diff --git a/src/java.base/share/classes/sun/nio/ch/DatagramChannelImpl.java b/src/java.base/share/classes/sun/nio/ch/DatagramChannelImpl.java
index 74c54105201..33948afbcb0 100644
--- a/src/java.base/share/classes/sun/nio/ch/DatagramChannelImpl.java
+++ b/src/java.base/share/classes/sun/nio/ch/DatagramChannelImpl.java
@@ -599,8 +599,7 @@ class DatagramChannelImpl
      * @throws SocketTimeoutException if the timeout elapses
      */
     void blockingReceive(DatagramPacket p, long nanos) throws IOException {
-        Objects.requireNonNull(p);
-        assert nanos >= 0;
+        assert Thread.holdsLock(p) && nanos >= 0;
 
         readLock.lock();
         try {
@@ -615,37 +614,31 @@ class DatagramChannelImpl
                 configureSocketNonBlockingIfVirtualThread();
             }
 
-            // p.bufLength is the maximum size of the datagram that can be received
-            int bufLength;
-            synchronized (p) {
-                bufLength = DatagramPackets.getBufLength(p);
-            }
-
             boolean completed = false;
             try {
                 SocketAddress remote = beginRead(true, false);
                 boolean connected = (remote != null);
+
+                // p.bufLength is the maximum size of the datagram that can be received
+                int bufLength = DatagramPackets.getBufLength(p);
                 ByteBuffer dst = tryBlockingReceive(connected, bufLength, nanos);
                 if (dst != null) {
-                    // if datagram received then get sender and copy to DatagramPacket
+                    // copy to DatagramPacket, set length and sender
                     try {
-                        SocketAddress sender = sourceSocketAddress();
-                        synchronized (p) {
-                            // copy bytes to the DatagramPacket, and set length and sender.
-                            // Need to re-read p.bufLength in case DatagramPacket changed
-                            int len = Math.min(dst.limit(), DatagramPackets.getBufLength(p));
-                            dst.get(p.getData(), p.getOffset(), len);
-                            DatagramPackets.setLength(p, len);
-                            p.setSocketAddress(sender);
-                        }
+                        int len = dst.limit();
+                        dst.get(p.getData(), p.getOffset(), len);
+                        DatagramPackets.setLength(p, len);
+                        p.setSocketAddress(sourceSocketAddress());
                     } finally {
                         Util.offerFirstTemporaryDirectBuffer(dst);
                     }
                     completed = true;
                 }
+
             } finally {
                 endRead(true, completed);
             }
+
         } finally {
             readLock.unlock();
         }
@@ -835,7 +828,7 @@ class DatagramChannelImpl
      * @throws IllegalBlockingModeException if the channel is non-blocking
      */
     void blockingSend(DatagramPacket p) throws IOException {
-        Objects.requireNonNull(p);
+        assert Thread.holdsLock(p);
 
         writeLock.lock();
         try {
@@ -843,38 +836,34 @@ class DatagramChannelImpl
             if (!isBlocking())
                 throw new IllegalBlockingModeException();
 
-            ByteBuffer src = null;
+            int len = p.getLength();
+            ByteBuffer src = Util.getTemporaryDirectBuffer(len);
             try {
+                // copy bytes to temporary direct buffer
+                src.put(p.getData(), p.getOffset(), len);
+                src.flip();
+
+                // target address
                 InetSocketAddress target;
-                synchronized (p) {
-                    int len = p.getLength();
-                    src = Util.getTemporaryDirectBuffer(len);
-
-                    // copy bytes to temporary direct buffer
-                    src.put(p.getData(), p.getOffset(), len);
-                    src.flip();
-
-                    // target address
-                    if (p.getAddress() == null) {
-                        InetSocketAddress remote = remoteAddress();
-                        if (remote == null) {
-                            throw new IllegalArgumentException("Address not set");
-                        }
-                        // set address/port to be compatible with long standing behavior
-                        p.setAddress(remote.getAddress());
-                        p.setPort(remote.getPort());
-                        target = remote;
-                    } else {
-                        target = (InetSocketAddress) p.getSocketAddress();
+                if (p.getAddress() == null) {
+                    InetSocketAddress remote = remoteAddress();
+                    if (remote == null) {
+                        throw new IllegalArgumentException("Address not set");
                     }
+                    // set address/port to be compatible with long-standing behavior
+                    p.setAddress(remote.getAddress());
+                    p.setPort(remote.getPort());
+                    target = remote;
+                } else {
+                    target = (InetSocketAddress) p.getSocketAddress();
                 }
 
                 // send the datagram (does not block)
                 send(src, target);
-
             } finally {
-                if (src != null) Util.offerFirstTemporaryDirectBuffer(src);
+                Util.offerFirstTemporaryDirectBuffer(src);
             }
+
         } finally {
             writeLock.unlock();
         }
diff --git a/src/java.base/share/classes/sun/nio/ch/DatagramSocketAdaptor.java b/src/java.base/share/classes/sun/nio/ch/DatagramSocketAdaptor.java
index 6ea20ec6270..4930e1447a3 100644
--- a/src/java.base/share/classes/sun/nio/ch/DatagramSocketAdaptor.java
+++ b/src/java.base/share/classes/sun/nio/ch/DatagramSocketAdaptor.java
@@ -174,7 +174,9 @@ public class DatagramSocketAdaptor
     @Override
     public void send(DatagramPacket p) throws IOException {
         try {
-            dc.blockingSend(p);
+            synchronized (p) {
+                dc.blockingSend(p);
+            }
         } catch (AlreadyConnectedException e) {
             throw new IllegalArgumentException("Connected and packet address differ");
         } catch (ClosedChannelException e) {
@@ -185,7 +187,9 @@ public class DatagramSocketAdaptor
     @Override
     public void receive(DatagramPacket p) throws IOException {
         try {
-            dc.blockingReceive(p, MILLISECONDS.toNanos(timeout));
+            synchronized (p) {
+                dc.blockingReceive(p, MILLISECONDS.toNanos(timeout));
+            }
         } catch (SocketTimeoutException | ClosedByInterruptException e) {
             throw e;
         } catch (InterruptedIOException e) {