8147468: Allow users to bound the size of buffers cached in the per-thread buffer caches

Summary: Introduces the jdk.nio.maxCachedBufferSize property.
Reviewed-by: alanb, bpb

src/share/classes/sun/nio/ch/Util.java

 /*
- * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2000, 2016, 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
@@ -47,6 +47,9 @@ public class Util {
     // The number of temp buffers in our pool
     private static final int TEMP_BUF_POOL_SIZE = IOUtil.IOV_MAX;
 
+    // The max size allowed for a cached temp buffer, in bytes
+    private static final long MAX_CACHED_BUFFER_SIZE = getMaxCachedBufferSize();
+
     // Per-thread cache of temporary direct buffers
     private static ThreadLocal<BufferCache> bufferCache =
         new ThreadLocal<BufferCache>()
@@ -57,6 +60,52 @@ public class Util {
         }
     };
 
+    /**
+     * Returns the max size allowed for a cached temp buffers, in
+     * bytes. It defaults to Long.MAX_VALUE. It can be set with the
+     * jdk.nio.maxCachedBufferSize property. Even though
+     * ByteBuffer.capacity() returns an int, we're using a long here
+     * for potential future-proofing.
+     */
+    private static long getMaxCachedBufferSize() {
+        String s = java.security.AccessController.doPrivileged(
+            new PrivilegedAction<String>() {
+                @Override
+                public String run() {
+                    return System.getProperty("jdk.nio.maxCachedBufferSize");
+                }
+            });
+        if (s != null) {
+            try {
+                long m = Long.parseLong(s);
+                if (m >= 0) {
+                    return m;
+                } else {
+                    // if it's negative, ignore the system property
+                }
+            } catch (NumberFormatException e) {
+                // if the string is not well formed, ignore the system property
+            }
+        }
+        return Long.MAX_VALUE;
+    }
+
+    /**
+     * Returns true if a buffer of this size is too large to be
+     * added to the buffer cache, false otherwise.
+     */
+    private static boolean isBufferTooLarge(int size) {
+        return size > MAX_CACHED_BUFFER_SIZE;
+    }
+
+    /**
+     * Returns true if the buffer is too large to be added to the
+     * buffer cache, false otherwise.
+     */
+    private static boolean isBufferTooLarge(ByteBuffer buf) {
+        return isBufferTooLarge(buf.capacity());
+    }
+
     /**
      * A simple cache of direct buffers.
      */
@@ -83,6 +132,9 @@ public class Util {
          * size (or null if no suitable buffer is found).
          */
         ByteBuffer get(int size) {
+            // Don't call this if the buffer would be too large.
+            assert !isBufferTooLarge(size);
+
             if (count == 0)
                 return null;  // cache is empty
 
@@ -120,6 +172,9 @@ public class Util {
         }
 
         boolean offerFirst(ByteBuffer buf) {
+            // Don't call this if the buffer is too large.
+            assert !isBufferTooLarge(buf);
+
             if (count >= TEMP_BUF_POOL_SIZE) {
                 return false;
             } else {
@@ -131,6 +186,9 @@ public class Util {
         }
 
         boolean offerLast(ByteBuffer buf) {
+            // Don't call this if the buffer is too large.
+            assert !isBufferTooLarge(buf);
+
             if (count >= TEMP_BUF_POOL_SIZE) {
                 return false;
             } else {
@@ -159,6 +217,15 @@ public class Util {
      * Returns a temporary buffer of at least the given size
      */
     public static ByteBuffer getTemporaryDirectBuffer(int size) {
+        // If a buffer of this size is too large for the cache, there
+        // should not be a buffer in the cache that is at least as
+        // large. So we'll just create a new one. Also, we don't have
+        // to remove the buffer from the cache (as this method does
+        // below) given that we won't put the new buffer in the cache.
+        if (isBufferTooLarge(size)) {
+            return ByteBuffer.allocateDirect(size);
+        }
+
         BufferCache cache = bufferCache.get();
         ByteBuffer buf = cache.get(size);
         if (buf != null) {
@@ -188,6 +255,13 @@ public class Util {
      * likely to be returned by a subsequent call to getTemporaryDirectBuffer.
      */
     static void offerFirstTemporaryDirectBuffer(ByteBuffer buf) {
+        // If the buffer is too large for the cache we don't have to
+        // check the cache. We'll just free it.
+        if (isBufferTooLarge(buf)) {
+            free(buf);
+            return;
+        }
+
         assert buf != null;
         BufferCache cache = bufferCache.get();
         if (!cache.offerFirst(buf)) {
@@ -203,6 +277,13 @@ public class Util {
      * cache in same order that they were obtained.
      */
     static void offerLastTemporaryDirectBuffer(ByteBuffer buf) {
+        // If the buffer is too large for the cache we don't have to
+        // check the cache. We'll just free it.
+        if (isBufferTooLarge(buf)) {
+            free(buf);
+            return;
+        }
+
         assert buf != null;
         BufferCache cache = bufferCache.get();
         if (!cache.offerLast(buf)) {

test/sun/nio/ch/TestMaxCachedBufferSize.java

+/*
+ * Copyright (c) 2016, 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.
+ */
+
+import java.io.IOException;
+
+import java.lang.management.BufferPoolMXBean;
+import java.lang.management.ManagementFactory;
+
+import java.nio.ByteBuffer;
+
+import java.nio.channels.FileChannel;
+
+import java.nio.file.Path;
+import java.nio.file.Paths;
+
+import static java.nio.file.StandardOpenOption.CREATE;
+import static java.nio.file.StandardOpenOption.TRUNCATE_EXISTING;
+import static java.nio.file.StandardOpenOption.WRITE;
+
+import java.util.List;
+import java.util.Random;
+
+/*
+ * @test
+ * @build TestMaxCachedBufferSize
+ * @run main/othervm TestMaxCachedBufferSize
+ * @run main/othervm -Djdk.nio.maxCachedBufferSize=0 TestMaxCachedBufferSize
+ * @run main/othervm -Djdk.nio.maxCachedBufferSize=2000 TestMaxCachedBufferSize
+ * @run main/othervm -Djdk.nio.maxCachedBufferSize=100000 TestMaxCachedBufferSize
+ * @run main/othervm -Djdk.nio.maxCachedBufferSize=10000000 TestMaxCachedBufferSize
+ *
+ * @summary Test the implementation of the jdk.nio.maxCachedBufferSize property.
+ */
+public class TestMaxCachedBufferSize {
+    private static final int DEFAULT_ITERS = 10 * 1000;
+    private static final int DEFAULT_THREAD_NUM = 4;
+
+    private static final int SMALL_BUFFER_MIN_SIZE =  4 * 1024;
+    private static final int SMALL_BUFFER_MAX_SIZE = 64 * 1024;
+    private static final int SMALL_BUFFER_DIFF_SIZE =
+                                 SMALL_BUFFER_MAX_SIZE - SMALL_BUFFER_MIN_SIZE;
+
+    private static final int LARGE_BUFFER_MIN_SIZE =      512 * 1024;
+    private static final int LARGE_BUFFER_MAX_SIZE = 4 * 1024 * 1024;
+    private static final int LARGE_BUFFER_DIFF_SIZE =
+                                 LARGE_BUFFER_MAX_SIZE - LARGE_BUFFER_MIN_SIZE;
+
+    private static final int LARGE_BUFFER_FREQUENCY = 100;
+
+    private static final String FILE_NAME_PREFIX = "nio-out-file-";
+    private static final int VERBOSE_PERIOD = 5 * 1000;
+
+    private static int iters = DEFAULT_ITERS;
+    private static int threadNum = DEFAULT_THREAD_NUM;
+
+    private static BufferPoolMXBean getDirectPool() {
+        final List<BufferPoolMXBean> pools =
+                  ManagementFactory.getPlatformMXBeans(BufferPoolMXBean.class);
+        for (BufferPoolMXBean pool : pools) {
+            if (pool.getName().equals("direct")) {
+                return pool;
+            }
+        }
+        throw new Error("could not find direct pool");
+    }
+    private static final BufferPoolMXBean directPool = getDirectPool();
+
+    // Each worker will do write operations on a file channel using
+    // buffers of various sizes. The buffer size is randomly chosen to
+    // be within a small or a large range. This way we can control
+    // which buffers can be cached (all, only the small ones, or none)
+    // by setting the jdk.nio.maxCachedBufferSize property.
+    private static class Worker implements Runnable {
+        private final int id;
+        private final Random random = new Random();
+        private long smallBufferCount = 0;
+        private long largeBufferCount = 0;
+
+        private int getWriteSize() {
+            int minSize = 0;
+            int diff = 0;
+            if (random.nextInt() % LARGE_BUFFER_FREQUENCY != 0) {
+                // small buffer
+                minSize = SMALL_BUFFER_MIN_SIZE;
+                diff = SMALL_BUFFER_DIFF_SIZE;
+                smallBufferCount += 1;
+            } else {
+                // large buffer
+                minSize = LARGE_BUFFER_MIN_SIZE;
+                diff = LARGE_BUFFER_DIFF_SIZE;
+                largeBufferCount += 1;
+            }
+            return minSize + random.nextInt(diff);
+        }
+
+        private void loop() {
+            final String fileName = String.format("%s%d", FILE_NAME_PREFIX, id);
+
+            try {
+                for (int i = 0; i < iters; i += 1) {
+                    final int writeSize = getWriteSize();
+
+                    // This will allocate a HeapByteBuffer. It should not
+                    // be a direct buffer, otherwise the write() method on
+                    // the channel below will not create a temporary
+                    // direct buffer for the write.
+                    final ByteBuffer buffer = ByteBuffer.allocate(writeSize);
+
+                    // Put some random data on it.
+                    while (buffer.hasRemaining()) {
+                        buffer.put((byte) random.nextInt());
+                    }
+                    buffer.rewind();
+
+                    final Path file = Paths.get(fileName);
+                    try (FileChannel outChannel = FileChannel.open(file, CREATE, TRUNCATE_EXISTING, WRITE)) {
+                        // The write() method will create a temporary
+                        // direct buffer for the write and attempt to cache
+                        // it. It's important that buffer is not a
+                        // direct buffer, otherwise the temporary buffer
+                        // will not be created.
+                        long res = outChannel.write(buffer);
+                    }
+
+                    if ((i + 1) % VERBOSE_PERIOD == 0) {
+                        System.out.printf(
+                          " Worker %3d | %8d Iters | Small %8d Large %8d | Direct %4d / %7dK\n",
+                          id, i + 1, smallBufferCount, largeBufferCount,
+                          directPool.getCount(), directPool.getTotalCapacity() / 1024);
+                    }
+                }
+            } catch (IOException e) {
+                throw new Error("I/O error", e);
+            }
+        }
+
+        @Override
+        public void run() {
+            loop();
+        }
+
+        public Worker(int id) {
+            this.id = id;
+        }
+    }
+
+    public static void checkDirectBuffers(long expectedCount, long expectedMax) {
+        final long directCount = directPool.getCount();
+        final long directTotalCapacity = directPool.getTotalCapacity();
+        System.out.printf("Direct %d / %dK\n",
+                          directCount, directTotalCapacity / 1024);
+
+        // Note that directCount could be < expectedCount. This can
+        // happen if a GC occurs after one of the worker threads exits
+        // since its thread-local DirectByteBuffer could be cleaned up
+        // before we reach here.
+        if (directCount > expectedCount) {
+            throw new Error(String.format(
+                "inconsistent direct buffer total count, expected = %d, found = %d",
+                expectedCount, directCount));
+        }
+
+        if (directTotalCapacity > expectedMax) {
+            throw new Error(String.format(
+                "inconsistent direct buffer total capacity, expectex max = %d, found = %d",
+                expectedMax, directTotalCapacity));
+        }
+    }
+
+    public static void main(String[] args) {
+        final String maxBufferSizeStr = System.getProperty("jdk.nio.maxCachedBufferSize");
+        final long maxBufferSize =
+            (maxBufferSizeStr != null) ? Long.valueOf(maxBufferSizeStr) : Long.MAX_VALUE;
+
+        // We assume that the max cannot be equal to a size of a
+        // buffer that can be allocated (makes sanity checking at the
+        // end easier).
+        if ((SMALL_BUFFER_MIN_SIZE <= maxBufferSize &&
+                                     maxBufferSize <= SMALL_BUFFER_MAX_SIZE) ||
+            (LARGE_BUFFER_MIN_SIZE <= maxBufferSize &&
+                                     maxBufferSize <= LARGE_BUFFER_MAX_SIZE)) {
+            throw new Error(String.format("max buffer size = %d not allowed",
+                                          maxBufferSize));
+        }
+
+        System.out.printf("Threads %d | Iterations %d | MaxBufferSize %d\n",
+                          threadNum, iters, maxBufferSize);
+        System.out.println();
+
+        final Thread[] threads = new Thread[threadNum];
+        for (int i = 0; i < threadNum; i += 1) {
+            threads[i] = new Thread(new Worker(i));
+            threads[i].start();
+        }
+
+        try {
+            for (int i = 0; i < threadNum; i += 1) {
+                threads[i].join();
+            }
+        } catch (InterruptedException e) {
+            throw new Error("join() interrupted!", e);
+        }
+
+        // There is an assumption here that, at this point, only the
+        // cached DirectByteBuffers should be active. Given we
+        // haven't used any other DirectByteBuffers in this test, this
+        // should hold.
+        //
+        // Also note that we can only do the sanity checking at the
+        // end and not during the run given that, at any time, there
+        // could be buffers currently in use by some of the workers
+        // that will not be cached.
+
+        System.out.println();
+        if (maxBufferSize < SMALL_BUFFER_MAX_SIZE) {
+            // The max buffer size is smaller than all buffers that
+            // were allocated. No buffers should have been cached.
+            checkDirectBuffers(0, 0);
+        } else if (maxBufferSize < LARGE_BUFFER_MIN_SIZE) {
+            // The max buffer size is larger than all small buffers
+            // but smaller than all large buffers that were
+            // allocated. Only small buffers could have been cached.
+            checkDirectBuffers(threadNum,
+                               (long) threadNum * (long) SMALL_BUFFER_MAX_SIZE);
+        } else {
+            // The max buffer size is larger than all buffers that
+            // were allocated. All buffers could have been cached.
+            checkDirectBuffers(threadNum,
+                               (long) threadNum * (long) LARGE_BUFFER_MAX_SIZE);
+        }
+    }
+}