undefect. CWE-407 — 63 sites patched across 27 ecosystems

Authors: russell@unturf.com · brackishbert@gmail.com · foxhop.net · TimeHexOn.com

Patches, unit tests, benchmarks, whitepaper, and outreach briefs.
Public domain — no copyright claimed. Use freely.

test/jdk/java/nio/channels/Selector/SelectWithConsumer.java

@@ -0,0 +1,819 @@
+/*
+ * Copyright (c) 2018, 2026, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/* @test
+ * @summary Unit test for Selector.select/selectNow(Consumer)
+ * @bug 8199433 8208780
+ * @run junit SelectWithConsumer
+ */
+
+/* @test
+ * @requires (os.family == "windows")
+ * @run junit/othervm -Djava.nio.channels.spi.SelectorProvider=sun.nio.ch.WindowsSelectorProvider SelectWithConsumer
+ */
+
+import java.io.Closeable;
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.nio.ByteBuffer;
+import java.nio.channels.ClosedSelectorException;
+import java.nio.channels.Pipe;
+import java.nio.channels.SelectionKey;
+import java.nio.channels.Selector;
+import java.nio.channels.ServerSocketChannel;
+import java.nio.channels.SocketChannel;
+import java.nio.channels.WritableByteChannel;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+import static java.util.concurrent.TimeUnit.*;
+
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class SelectWithConsumer {
+
+    /**
+     * Invoke the select methods that take an action and check that the
+     * accumulated ready ops notified to the action matches the expected ops.
+     */
+    void testActionInvoked(SelectionKey key, int expectedOps) throws Exception {
+        var callerThread = Thread.currentThread();
+        var sel = key.selector();
+        var interestOps = key.interestOps();
+        var notifiedOps = new AtomicInteger();
+
+        if (expectedOps == 0) {
+            // ensure select(Consumer) does not block indefinitely
+            sel.wakeup();
+        } else {
+            // ensure that the channel is ready for all expected operations
+            sel.select();
+            while ((key.readyOps() & interestOps) != expectedOps) {
+                Thread.sleep(100);
+                sel.select();
+            }
+        }
+
+        // select(Consumer)
+        notifiedOps.set(0);
+        int n = sel.select(k -> {
+            assertSame(callerThread, Thread.currentThread());
+            assertSame(key, k);
+            int readyOps = key.readyOps();
+            assertNotEquals(0, readyOps & interestOps);
+            assertEquals(0, readyOps & notifiedOps.get());
+            notifiedOps.set(notifiedOps.get() | readyOps);
+        });
+        assertTrue((n == 1) ^ (expectedOps == 0));
+        assertEquals(expectedOps, notifiedOps.get());
+
+        // select(Consumer, timeout)
+        notifiedOps.set(0);
+        n = sel.select(k -> {
+            assertSame(callerThread, Thread.currentThread());
+            assertSame(key, k);
+            int readyOps = key.readyOps();
+            assertNotEquals(0, readyOps & interestOps);
+            assertEquals(0, readyOps & notifiedOps.get());
+            notifiedOps.set(notifiedOps.get() | readyOps);
+        }, 1000);
+        assertTrue((n == 1) ^ (expectedOps == 0));
+        assertEquals(expectedOps, notifiedOps.get());
+
+        // selectNow(Consumer)
+        notifiedOps.set(0);
+        n = sel.selectNow(k -> {
+            assertSame(callerThread, Thread.currentThread());
+            assertSame(key, k);
+            int readyOps = key.readyOps();
+            assertNotEquals(0, readyOps & interestOps);
+            assertEquals(0, readyOps & notifiedOps.get());
+            notifiedOps.set(notifiedOps.get() | readyOps);
+        });
+        assertTrue((n == 1) ^ (expectedOps == 0));
+        assertEquals(expectedOps, notifiedOps.get());
+    }
+
+    /**
+     * Test that an action is performed when a channel is ready for reading.
+     */
+    @Test
+    public void testReadable() throws Exception {
+        Pipe p = Pipe.open();
+        try (Selector sel = Selector.open()) {
+            Pipe.SinkChannel sink = p.sink();
+            Pipe.SourceChannel source = p.source();
+            source.configureBlocking(false);
+            SelectionKey key = source.register(sel, SelectionKey.OP_READ);
+
+            // write to sink to ensure source is readable
+            scheduleWrite(sink, messageBuffer(), 100, MILLISECONDS);
+
+            // test that action is invoked
+            testActionInvoked(key, SelectionKey.OP_READ);
+        } finally {
+            closePipe(p);
+        }
+    }
+
+    /**
+     * Test that an action is performed when a channel is ready for writing.
+     */
+    @Test
+    public void testWritable() throws Exception {
+        Pipe p = Pipe.open();
+        try (Selector sel = Selector.open()) {
+            Pipe.SourceChannel source = p.source();
+            Pipe.SinkChannel sink = p.sink();
+            sink.configureBlocking(false);
+            SelectionKey key = sink.register(sel, SelectionKey.OP_WRITE);
+
+            // test that action is invoked
+            testActionInvoked(key, SelectionKey.OP_WRITE);
+        } finally {
+            closePipe(p);
+        }
+    }
+
+    /**
+     * Test that an action is performed when a channel is ready for both
+     * reading and writing.
+     */
+    @Test
+    public void testReadableAndWriteable() throws Exception {
+        ServerSocketChannel ssc = null;
+        SocketChannel sc = null;
+        SocketChannel peer = null;
+        try (Selector sel = Selector.open()) {
+            ssc = ServerSocketChannel.open().bind(new InetSocketAddress(0));
+            sc = SocketChannel.open(ssc.getLocalAddress());
+            sc.configureBlocking(false);
+            SelectionKey key = sc.register(sel, (SelectionKey.OP_READ |
+                                                 SelectionKey.OP_WRITE));
+
+            // accept connection and write data so the source is readable
+            peer = ssc.accept();
+            peer.write(messageBuffer());
+
+            // test that action is invoked
+            testActionInvoked(key, (SelectionKey.OP_READ | SelectionKey.OP_WRITE));
+        } finally {
+            if (ssc != null) ssc.close();
+            if (sc != null) sc.close();
+            if (peer != null) peer.close();
+        }
+    }
+
+    /**
+     * Test that the action is called for two selected channels
+     */
+    @Test
+    public void testTwoChannels() throws Exception {
+        Pipe p = Pipe.open();
+        try (Selector sel = Selector.open()) {
+            Pipe.SourceChannel source = p.source();
+            Pipe.SinkChannel sink = p.sink();
+            source.configureBlocking(false);
+            sink.configureBlocking(false);
+            SelectionKey key1 = source.register(sel, SelectionKey.OP_READ);
+            SelectionKey key2 = sink.register(sel, SelectionKey.OP_WRITE);
+
+            // write to sink to ensure that the source is readable
+            sink.write(messageBuffer());
+
+            // wait for key1 to be readable
+            sel.select();
+            assertTrue(key2.isWritable());
+            while (!key1.isReadable()) {
+                Thread.sleep(20);
+                sel.select();
+            }
+
+            var counter = new AtomicInteger();
+
+            // select(Consumer)
+            counter.set(0);
+            int n = sel.select(k -> {
+                assertTrue(k == key1 || k == key2);
+                counter.incrementAndGet();
+            });
+            assertEquals(2, n);
+            assertEquals(2, counter.get());
+
+            // select(Consumer, timeout)
+            counter.set(0);
+            n = sel.select(k -> {
+                assertTrue(k == key1 || k == key2);
+                counter.incrementAndGet();
+            }, 1000);
+            assertEquals(2, n);
+            assertEquals(2, counter.get());
+
+            // selectNow(Consumer)
+            counter.set(0);
+            n = sel.selectNow(k -> {
+                assertTrue(k == key1 || k == key2);
+                counter.incrementAndGet();
+            });
+            assertEquals(2, n);
+            assertEquals(2, counter.get());
+        } finally {
+            closePipe(p);
+        }
+    }
+
+    /**
+     * Test calling select twice, the action should be invoked each time
+     */
+    @Test
+    public void testRepeatedSelect1() throws Exception {
+        Pipe p = Pipe.open();
+        try (Selector sel = Selector.open()) {
+            Pipe.SourceChannel source = p.source();
+            Pipe.SinkChannel sink = p.sink();
+            source.configureBlocking(false);
+            SelectionKey key = source.register(sel, SelectionKey.OP_READ);
+
+            // write to sink to ensure that the source is readable
+            sink.write(messageBuffer());
+
+            // test that action is invoked
+            testActionInvoked(key, SelectionKey.OP_READ);
+            testActionInvoked(key, SelectionKey.OP_READ);
+
+        } finally {
+            closePipe(p);
+        }
+    }
+
+    /**
+     * Test calling select twice. An I/O operation is performed after the
+     * first select so the channel will not be selected by the second select.
+     */
+    @Test
+    public void testRepeatedSelect2() throws Exception {
+        Pipe p = Pipe.open();
+        try (Selector sel = Selector.open()) {
+            Pipe.SourceChannel source = p.source();
+            Pipe.SinkChannel sink = p.sink();
+            source.configureBlocking(false);
+            SelectionKey key = source.register(sel, SelectionKey.OP_READ);
+
+            // write to sink to ensure that the source is readable
+            sink.write(messageBuffer());
+
+            // test that action is invoked
+            testActionInvoked(key, SelectionKey.OP_READ);
+
+            // read all bytes
+            int n;
+            ByteBuffer bb = ByteBuffer.allocate(100);
+            do {
+                n = source.read(bb);
+                bb.clear();
+            } while (n > 0);
+
+            // test that action is not invoked
+            testActionInvoked(key, 0);
+        } finally {
+            closePipe(p);
+        }
+    }
+
+    /**
+     * Test timeout
+     */
+    @Test
+    public void testTimeout() throws Exception {
+        Pipe p = Pipe.open();
+        try (Selector sel = Selector.open()) {
+            Pipe.SourceChannel source = p.source();
+            Pipe.SinkChannel sink = p.sink();
+            source.configureBlocking(false);
+            source.register(sel, SelectionKey.OP_READ);
+            long start = millisTime();
+            int n = sel.select(k -> assertTrue(false), 1000L);
+            expectDuration(start, 500, Long.MAX_VALUE);
+            assertEquals(0, n);
+        } finally {
+            closePipe(p);
+        }
+    }
+
+    /**
+     * Test wakeup prior to select
+     */
+    @Test
+    public void testWakeupBeforeSelect() throws Exception {
+        // select(Consumer)
+        try (Selector sel = Selector.open()) {
+            sel.wakeup();
+            int n = sel.select(k -> assertTrue(false));
+            assertEquals(0, n);
+        }
+
+        // select(Consumer, timeout)
+        try (Selector sel = Selector.open()) {
+            sel.wakeup();
+            long start = millisTime();
+            int n = sel.select(k -> assertTrue(false), 60*1000);
+            expectDuration(start, 0, 20_000);
+            assertEquals(0, n);
+        }
+    }
+
+    /**
+     * Test wakeup during select
+     */
+    @Test
+    public void testWakeupDuringSelect() throws Exception {
+        // select(Consumer)
+        try (Selector sel = Selector.open()) {
+            scheduleWakeup(sel, 1, SECONDS);
+            int n = sel.select(k -> assertTrue(false));
+            assertEquals(0, n);
+        }
+
+        // select(Consumer, timeout)
+        try (Selector sel = Selector.open()) {
+            scheduleWakeup(sel, 1, SECONDS);
+            long start = millisTime();
+            int n = sel.select(k -> assertTrue(false), 60*1000);
+            expectDuration(start, 0, 20_000);
+            assertEquals(0, n);
+        }
+    }
+
+    /**
+     * Test invoking select with interrupted status set
+     */
+    @Test
+    public void testInterruptBeforeSelect() throws Exception {
+        // select(Consumer)
+        try (Selector sel = Selector.open()) {
+            Thread.currentThread().interrupt();
+            int n = sel.select(k -> assertTrue(false));
+            assertEquals(0, n);
+            assertTrue(Thread.currentThread().isInterrupted());
+            assertTrue(sel.isOpen());
+        } finally {
+            Thread.currentThread().interrupted();  // clear interrupted status
+        }
+
+        // select(Consumer, timeout)
+        try (Selector sel = Selector.open()) {
+            Thread.currentThread().interrupt();
+            long start = millisTime();
+            int n = sel.select(k -> assertTrue(false), 60*1000);
+            expectDuration(start, 0, 20_000);
+            assertEquals(0, n);
+            assertTrue(Thread.currentThread().isInterrupted());
+            assertTrue(sel.isOpen());
+        } finally {
+            Thread.currentThread().interrupted();  // clear interrupted status
+        }
+    }
+
+    /**
+     * Test interrupt thread during select
+     */
+    @Test
+    public void testInterruptDuringSelect() throws Exception {
+        // select(Consumer)
+        try (Selector sel = Selector.open()) {
+            scheduleInterrupt(Thread.currentThread(), 1, SECONDS);
+            int n = sel.select(k -> assertTrue(false));
+            assertEquals(0, n);
+            assertTrue(Thread.currentThread().isInterrupted());
+            assertTrue(sel.isOpen());
+        } finally {
+            Thread.currentThread().interrupted();  // clear interrupted status
+        }
+
+        // select(Consumer, timeout)
+        try (Selector sel = Selector.open()) {
+            scheduleInterrupt(Thread.currentThread(), 1, SECONDS);
+            int n = sel.select(k -> assertTrue(false), 60*1000);
+            assertEquals(0, n);
+            assertTrue(Thread.currentThread().isInterrupted());
+            assertTrue(sel.isOpen());
+        } finally {
+            Thread.currentThread().interrupted();  // clear interrupted status
+        }
+    }
+
+    /**
+     * Test invoking select on a closed selector
+     */
+    @Test
+    public void testClosedSelector1() throws Exception {
+        Selector sel = Selector.open();
+        sel.close();
+        assertThrows(ClosedSelectorException.class,
+                     () -> sel.select(k -> assertTrue(false)));
+    }
+    @Test
+    public void testClosedSelector2() throws Exception {
+        Selector sel = Selector.open();
+        sel.close();
+        assertThrows(ClosedSelectorException.class,
+                     () -> sel.select(k -> assertTrue(false), 1000));
+    }
+    @Test
+    public void testClosedSelector3() throws Exception {
+        Selector sel = Selector.open();
+        sel.close();
+        assertThrows(ClosedSelectorException.class,
+                     () -> sel.selectNow(k -> assertTrue(false)));
+    }
+
+    /**
+     * Test closing selector while in a selection operation
+     */
+    @Test
+    public void testCloseDuringSelect() throws Exception {
+        // select(Consumer)
+        try (Selector sel = Selector.open()) {
+            scheduleClose(sel, 3, SECONDS);
+            int n = sel.select(k -> assertTrue(false));
+            assertEquals(0, n);
+            assertFalse(sel.isOpen());
+        }
+
+        // select(Consumer, timeout)
+        try (Selector sel = Selector.open()) {
+            long before = System.nanoTime();
+            scheduleClose(sel, 3, SECONDS);
+            long start = System.nanoTime();
+            int n = sel.select(k -> assertTrue(false), 60*1000);
+            long after = System.nanoTime();
+            long selectDuration = (after - start) / 1000000;
+            long scheduleDuration = (start - before) / 1000000;
+            assertEquals(0, n);
+            assertTrue(selectDuration > 2000 && selectDuration < 10*1000,
+                    "select took " + selectDuration + " ms schedule took " +
+                    scheduleDuration + " ms");
+            assertFalse(sel.isOpen());
+        }
+    }
+
+    /**
+     * Test action closing selector
+     */
+    @Test
+    public void testActionClosingSelector() throws Exception {
+        Pipe p = Pipe.open();
+        try (Selector sel = Selector.open()) {
+            Pipe.SourceChannel source = p.source();
+            Pipe.SinkChannel sink = p.sink();
+            source.configureBlocking(false);
+            SelectionKey key = source.register(sel, SelectionKey.OP_READ);
+
+            // write to sink to ensure that the source is readable
+            sink.write(messageBuffer());
+
+            // should relay ClosedSelectorException
+            assertThrows(ClosedSelectorException.class,
+                () -> sel.select(k -> {
+                    assertTrue(k == key);
+                    try {
+                        sel.close();
+                    } catch (IOException ioe) { }
+                })
+            );
+        } finally {
+            closePipe(p);
+        }
+    }
+
+    /**
+     * Test that the action is invoked while synchronized on the selector and
+     * its selected-key set.
+     */
+    @Test
+    public void testLocks() throws Exception {
+        Pipe p = Pipe.open();
+        try (Selector sel = Selector.open()) {
+            Pipe.SourceChannel source = p.source();
+            Pipe.SinkChannel sink = p.sink();
+            source.configureBlocking(false);
+            SelectionKey key = source.register(sel, SelectionKey.OP_READ);
+
+            // write to sink to ensure that the source is readable
+            sink.write(messageBuffer());
+
+            // select(Consumer)
+            sel.select(k -> {
+                assertSame(key, k);
+                assertTrue(Thread.holdsLock(sel));
+                assertFalse(Thread.holdsLock(sel.keys()));
+                assertTrue(Thread.holdsLock(sel.selectedKeys()));
+            });
+
+            // select(Consumer, timeout)
+            sel.select(k -> {
+                assertSame(key, k);
+                assertTrue(Thread.holdsLock(sel));
+                assertFalse(Thread.holdsLock(sel.keys()));
+                assertTrue(Thread.holdsLock(sel.selectedKeys()));
+            }, 1000L);
+
+            // selectNow(Consumer)
+            sel.selectNow(k -> {
+                assertSame(key, k);
+                assertTrue(Thread.holdsLock(sel));
+                assertFalse(Thread.holdsLock(sel.keys()));
+                assertTrue(Thread.holdsLock(sel.selectedKeys()));
+            });
+        } finally {
+            closePipe(p);
+        }
+    }
+
+    /**
+     * Test that selection operations remove cancelled keys from the selector's
+     * key and selected-key sets.
+     */
+    @Test
+    public void testCancel() throws Exception {
+        Pipe p = Pipe.open();
+        try (Selector sel = Selector.open()) {
+            Pipe.SinkChannel sink = p.sink();
+            Pipe.SourceChannel source = p.source();
+
+            // write to sink to ensure that the source is readable
+            sink.write(messageBuffer());
+
+            source.configureBlocking(false);
+            SelectionKey key1 = source.register(sel, SelectionKey.OP_READ);
+            // make sure pipe source is readable before we do following checks.
+            // this is sometime necessary on windows where pipe is implemented
+            // as a pair of connected socket, so there is no guarantee that written
+            // bytes on sink side is immediately available on source side.
+            sel.select();
+
+            sink.configureBlocking(false);
+            SelectionKey key2 = sink.register(sel, SelectionKey.OP_WRITE);
+            sel.selectNow();
+
+            assertTrue(sel.keys().contains(key1));
+            assertTrue(sel.keys().contains(key2));
+            assertTrue(sel.selectedKeys().contains(key1));
+            assertTrue(sel.selectedKeys().contains(key2));
+
+            // cancel key1
+            key1.cancel();
+            int n = sel.selectNow(k -> assertTrue(k == key2));
+            assertEquals(1, n);
+            assertFalse(sel.keys().contains(key1));
+            assertTrue(sel.keys().contains(key2));
+            assertFalse(sel.selectedKeys().contains(key1));
+            assertTrue(sel.selectedKeys().contains(key2));
+
+            // cancel key2
+            key2.cancel();
+            n = sel.selectNow(k -> assertTrue(false));
+            assertEquals(0, n);
+            assertFalse(sel.keys().contains(key1));
+            assertFalse(sel.keys().contains(key2));
+            assertFalse(sel.selectedKeys().contains(key1));
+            assertFalse(sel.selectedKeys().contains(key2));
+        } finally {
+            closePipe(p);
+        }
+    }
+
+    /**
+     * Test an action invoking select()
+     */
+    @Test
+    public void testReentrantSelect1() throws Exception {
+        Pipe p = Pipe.open();
+        try (Selector sel = Selector.open()) {
+            Pipe.SinkChannel sink = p.sink();
+            Pipe.SourceChannel source = p.source();
+            source.configureBlocking(false);
+            source.register(sel, SelectionKey.OP_READ);
+
+            // write to sink to ensure that the source is readable
+            scheduleWrite(sink, messageBuffer(), 100, MILLISECONDS);
+
+            int n = sel.select(k -> {
+                try {
+                    sel.select();
+                    assertTrue(false);
+                } catch (IOException ioe) {
+                    throw new RuntimeException(ioe);
+                } catch (IllegalStateException expected) {
+                }
+            });
+            assertEquals(1, n);
+        } finally {
+            closePipe(p);
+        }
+    }
+
+    /**
+     * Test an action invoking selectNow()
+     */
+    @Test
+    public void testReentrantSelect2() throws Exception {
+        Pipe p = Pipe.open();
+        try (Selector sel = Selector.open()) {
+            Pipe.SinkChannel sink = p.sink();
+            Pipe.SourceChannel source = p.source();
+
+            // write to sink to ensure that the source is readable
+            scheduleWrite(sink, messageBuffer(), 100, MILLISECONDS);
+
+            source.configureBlocking(false);
+            source.register(sel, SelectionKey.OP_READ);
+            int n = sel.select(k -> {
+                try {
+                    sel.selectNow();
+                    assertTrue(false);
+                } catch (IOException ioe) {
+                    throw new RuntimeException(ioe);
+                } catch (IllegalStateException expected) {
+                }
+            });
+            assertEquals(1, n);
+        } finally {
+            closePipe(p);
+        }
+    }
+
+    /**
+     * Test an action invoking select(Consumer)
+     */
+    @Test
+    public void testReentrantSelect3() throws Exception {
+        Pipe p = Pipe.open();
+        try (Selector sel = Selector.open()) {
+            Pipe.SinkChannel sink = p.sink();
+            Pipe.SourceChannel source = p.source();
+
+            // write to sink to ensure that the source is readable
+            scheduleWrite(sink, messageBuffer(), 100, MILLISECONDS);
+
+            source.configureBlocking(false);
+            source.register(sel, SelectionKey.OP_READ);
+            int n = sel.select(k -> {
+                try {
+                    sel.select(x -> assertTrue(false));
+                    assertTrue(false);
+                } catch (IOException ioe) {
+                    throw new RuntimeException(ioe);
+                } catch (IllegalStateException expected) {
+                }
+            });
+            assertEquals(1, n);
+        } finally {
+            closePipe(p);
+        }
+    }
+
+    /**
+     * Negative timeout
+     */
+    @Test
+    public void testNegativeTimeout() throws Exception {
+        try (Selector sel = Selector.open()) {
+            assertThrows(IllegalArgumentException.class,
+                         () -> sel.select(k -> { }, -1L));
+        }
+    }
+
+    /**
+     * Null action
+     */
+    @Test
+    public void testNull1() throws Exception {
+        try (Selector sel = Selector.open()) {
+            assertThrows(NullPointerException.class,
+                         () -> sel.select(null));
+        }
+    }
+    @Test
+    public void testNull2() throws Exception {
+        try (Selector sel = Selector.open()) {
+            assertThrows(NullPointerException.class,
+                         () -> sel.select(null, 1000));
+        }
+    }
+    @Test
+    public void testNull3() throws Exception {
+        try (Selector sel = Selector.open()) {
+            assertThrows(NullPointerException.class,
+                         () -> sel.selectNow(null));
+        }
+    }
+
+
+    // -- support methods ---
+
+    private static final ScheduledExecutorService POOL = Executors.newScheduledThreadPool(1);
+
+    @AfterAll
+    static void shutdownThreadPool() {
+        POOL.shutdown();
+    }
+
+    void scheduleWakeup(Selector sel, long delay, TimeUnit unit) {
+        POOL.schedule(() -> sel.wakeup(), delay, unit);
+    }
+
+    void scheduleInterrupt(Thread t, long delay, TimeUnit unit) {
+        POOL.schedule(() -> t.interrupt(), delay, unit);
+    }
+
+    void scheduleClose(Closeable c, long delay, TimeUnit unit) {
+        POOL.schedule(() -> {
+            try {
+                c.close();
+            } catch (IOException ioe) {
+                ioe.printStackTrace();
+            }
+        }, delay, unit);
+    }
+
+    void scheduleWrite(WritableByteChannel sink, ByteBuffer buf, long delay, TimeUnit unit) {
+        POOL.schedule(() -> {
+            try {
+                sink.write(buf);
+            } catch (IOException ioe) {
+                ioe.printStackTrace();
+            }
+        }, delay, unit);
+    }
+
+    static void closePipe(Pipe p) {
+        try { p.sink().close(); } catch (IOException ignore) { }
+        try { p.source().close(); } catch (IOException ignore) { }
+    }
+
+    static ByteBuffer messageBuffer() {
+        try {
+            return ByteBuffer.wrap("message".getBytes("UTF-8"));
+        } catch (Exception e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    /**
+     * Returns the current time in milliseconds.
+     */
+    private static long millisTime() {
+        long now = System.nanoTime();
+        return TimeUnit.MILLISECONDS.convert(now, TimeUnit.NANOSECONDS);
+    }
+
+    /**
+     * Check the duration of a task. The method will fail with an
+     * AssertionError if the millisecond duration does not satisfy:
+     *
+     *     duration >= min && duration <= max
+     *
+     * Note that the inequalities are not strict, i.e., are inclusive.
+     *
+     * @param start start time, in milliseconds
+     * @param min minimum expected duration, in milliseconds
+     * @param max maximum expected duration, in milliseconds
+     */
+    private static void expectDuration(long start, long min, long max) {
+        long duration = millisTime() - start;
+        assertTrue(duration >= min,
+                "Duration " + duration + "ms, expected >= " + min + "ms");
+        assertTrue(duration <= max,
+                "Duration " + duration + "ms, expected <= " + max + "ms");
+    }
+}