Ensure closing a Socket / FileDescriptor multiple times will not throw exception

Motivation:

If an user will close a Socket / FileDescriptor multiple times we should handle the extra close operations as NOOP.

Modifications:

Only do the actual closing one time

Result:

No exception if close is called multiple times.

transport-native-epoll/src/main/java/io/netty/channel/unix/FileDescriptor.java

@@ -15,9 +15,12 @@
  */
 package io.netty.channel.unix;
 
+import io.netty.util.internal.PlatformDependent;
+
 import java.io.File;
 import java.io.IOException;
 import java.nio.ByteBuffer;
+import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
 
 import static io.netty.channel.unix.Errors.CONNECTION_RESET_EXCEPTION_READ;
 import static io.netty.channel.unix.Errors.CONNECTION_RESET_EXCEPTION_WRITE;
@@ -31,8 +34,18 @@ import static io.netty.util.internal.ObjectUtil.checkNotNull;
  * {@link FileDescriptor} for it.
  */
 public class FileDescriptor {
+    private static final AtomicIntegerFieldUpdater<FileDescriptor> openUpdater;
+    static {
+        AtomicIntegerFieldUpdater<FileDescriptor> updater
+                = PlatformDependent.newAtomicIntegerFieldUpdater(FileDescriptor.class, "open");
+        if (updater == null) {
+            updater = AtomicIntegerFieldUpdater.newUpdater(FileDescriptor.class, "open");
+        }
+        openUpdater = updater;
+    }
+
     private final int fd;
-    private volatile boolean open = true;
+    private volatile int open = 1;
 
     public FileDescriptor(int fd) {
         if (fd < 0) {
@@ -52,18 +65,19 @@ public class FileDescriptor {
      * Close the file descriptor.
      */
     public void close() throws IOException {
-        open = false;
+        if (openUpdater.compareAndSet(this, 1, 0)) {
             int res = close(fd);
             if (res < 0) {
                 throw newIOException("close", res);
             }
         }
+    }
 
     /**
      * Returns {@code true} if the file descriptor is open.
      */
     public boolean isOpen() {
-        return open;
+        return open == 1;
     }
 
     public final int write(ByteBuffer buf, int pos, int limit) throws IOException {

transport-native-epoll/src/test/java/io/netty/channel/unix/SocketTest.java

@@ -44,80 +44,56 @@ public class SocketTest {
 
     @Test
     public void testKeepAlive() throws Exception {
-        Socket socket = Socket.newSocketStream();
-        try {
         assertFalse(socket.isKeepAlive());
         socket.setKeepAlive(true);
         assertTrue(socket.isKeepAlive());
-        } finally {
-            socket.close();
-        }
     }
 
     @Test
     public void testTcpCork() throws Exception {
-        Socket socket = Socket.newSocketStream();
-        try {
         assertFalse(socket.isTcpCork());
         socket.setTcpCork(true);
         assertTrue(socket.isTcpCork());
-        } finally {
-            socket.close();
-        }
     }
 
     @Test
     public void testTcpNoDelay() throws Exception {
-        Socket socket = Socket.newSocketStream();
-        try {
         assertFalse(socket.isTcpNoDelay());
         socket.setTcpNoDelay(true);
         assertTrue(socket.isTcpNoDelay());
-        } finally {
-            socket.close();
-        }
     }
 
     @Test
     public void testReceivedBufferSize() throws Exception {
-        Socket socket = Socket.newSocketStream();
-        try {
         int size = socket.getReceiveBufferSize();
         int newSize = 65535;
         assertTrue(size > 0);
         socket.setReceiveBufferSize(newSize);
         // Linux usually set it to double what is specified
         assertTrue(newSize <= socket.getReceiveBufferSize());
-        } finally {
-            socket.close();
-        }
     }
 
     @Test
     public void testSendBufferSize() throws Exception {
-        Socket socket = Socket.newSocketStream();
-        try {
         int size = socket.getSendBufferSize();
         int newSize = 65535;
         assertTrue(size > 0);
         socket.setSendBufferSize(newSize);
         // Linux usually set it to double what is specified
         assertTrue(newSize <= socket.getSendBufferSize());
-        } finally {
-            socket.close();
-        }
     }
 
     @Test
     public void testSoLinger() throws Exception {
-        Socket socket = Socket.newSocketStream();
-        try {
         assertEquals(-1, socket.getSoLinger());
         socket.setSoLinger(10);
         assertEquals(10, socket.getSoLinger());
-        } finally {
+    }
+
+    @Test
+    public void testDoubleCloseDoesNotThrow() throws IOException {
+        Socket socket = Socket.newSocketStream();
+        socket.close();
         socket.close();
     }
-    }
 }
-