Do not lock the handler calls in AsyncFile - see #3140

src/main/java/io/vertx/core/file/impl/AsyncFileImpl.java

@@ -400,22 +400,30 @@ public class AsyncFileImpl implements AsyncFile {
     });
   }
 
-  private synchronized void handleBuffer(Buffer buff) {
+
+  private void handleBuffer(Buffer buff) {
+    Handler<Buffer> handler;
+    synchronized (this) {
+      handler = this.handler;
+    }
     if (handler != null) {
       checkContext();
       handler.handle(buff);
     }
   }
 
-  private synchronized void handleEnd() {
-    handler = null;
+  private void handleEnd() {
+    Handler<Void> endHandler;
+    synchronized (this) {
+      handler = null;
+      endHandler = this.endHandler;
+    }
     if (endHandler != null) {
       checkContext();
       endHandler.handle(null);
     }
   }
 
-
   private synchronized void doFlush(Handler<AsyncResult<Void>> handler) {
     checkClosed();
     context.executeBlockingInternal((Promise<Void> fut) -> {

src/test/java/io/vertx/core/file/FileSystemTest.java

@@ -1564,6 +1564,25 @@ public class FileSystemTest extends VertxTestBase {
     await();
   }
 
+  @Test
+  public void testReadStreamNoLock() throws Exception {
+    String fileName = "some-file.dat";
+    int chunkSize = 16384;
+    int chunks = 1;
+    byte[] content = TestUtils.randomByteArray(chunkSize * chunks);
+    createFile(fileName, content);
+    vertx.fileSystem().open(testDir + pathSep + fileName, new OpenOptions(), onSuccess(rs -> {
+      rs.handler(buff -> {
+        assertFalse(Thread.holdsLock(rs));
+      });
+      rs.endHandler(v -> {
+        assertFalse(Thread.holdsLock(rs));
+        testComplete();
+      });
+    }));
+    await();
+  }
+
   @Test
   @SuppressWarnings("unchecked")
   public void testPumpFileStreams() throws Exception {