聊聊openjdk的BufferPoolMXBean-白红宇

聊聊openjdk的BufferPoolMXBean

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发布时间：2019-06-22

本文共 13212 字，大约阅读时间需要 44 分钟。

序

本文主要研究一下openjdk的BufferPoolMXBean

PlatformManagedObject

java.management/java/lang/management/PlatformManagedObject.java

public interface PlatformManagedObject {    /**     * Returns an {@link ObjectName ObjectName} instance representing     * the object name of this platform managed object.     *     * @return an {@link ObjectName ObjectName} instance representing     * the object name of this platform managed object.     */    public ObjectName getObjectName();}

PlatformManagedObject接口定义了getObjectName方法用于返回ObjectName

BufferPoolMXBean

java.management/java/lang/management/BufferPoolMXBean.java

public interface BufferPoolMXBean extends PlatformManagedObject {    /**     * Returns the name representing this buffer pool.     *     * @return  The name of this buffer pool.     */    String getName();    /**     * Returns an estimate of the number of buffers in the pool.     *     * @return  An estimate of the number of buffers in this pool     */    long getCount();    /**     * Returns an estimate of the total capacity of the buffers in this pool.     * A buffer's capacity is the number of elements it contains and the value     * returned by this method is an estimate of the total capacity of buffers     * in the pool in bytes.     *     * @return  An estimate of the total capacity of the buffers in this pool     *          in bytes     */    long getTotalCapacity();    /**     * Returns an estimate of the memory that the Java virtual machine is using     * for this buffer pool. The value returned by this method may differ     * from the estimate of the total {@link #getTotalCapacity capacity} of     * the buffers in this pool. This difference is explained by alignment,     * memory allocator, and other implementation specific reasons.     *     * @return  An estimate of the memory that the Java virtual machine is using     *          for this buffer pool in bytes, or {@code -1L} if an estimate of     *          the memory usage is not available     */    long getMemoryUsed();}

BufferPoolMXBean接口继承了PlatformManagedObject，它定义了getName、getCount、getTotalCapacity、getMemoryUsed方法

ManagementFactoryHelper

java.management/sun/management/ManagementFactoryHelper.java

public class ManagementFactoryHelper {    static {        // make sure that the management lib is loaded within        // java.lang.management.ManagementFactory        jdk.internal.misc.Unsafe.getUnsafe().ensureClassInitialized(ManagementFactory.class);    }    private static final VMManagement jvm = new VMManagementImpl();    private ManagementFactoryHelper() {};    public static VMManagement getVMManagement() {        return jvm;    }    static final String LOGGING_MXBEAN_NAME = "java.util.logging:type=Logging";    private static ClassLoadingImpl    classMBean = null;    private static MemoryImpl          memoryMBean = null;    private static ThreadImpl          threadMBean = null;    private static RuntimeImpl         runtimeMBean = null;    private static CompilationImpl     compileMBean = null;    private static BaseOperatingSystemImpl osMBean = null;    //......    private static List
    
      bufferPools = null;    public static synchronized List
     
       getBufferPoolMXBeans() {        if (bufferPools == null) {            bufferPools = new ArrayList<>(2);            bufferPools.add(createBufferPoolMXBean(SharedSecrets.getJavaNioAccess()                .getDirectBufferPool()));            bufferPools.add(createBufferPoolMXBean(sun.nio.ch.FileChannelImpl                .getMappedBufferPool()));        }        return bufferPools;    }        private static BufferPoolMXBean        createBufferPoolMXBean(final JavaNioAccess.BufferPool pool)    {        return new BufferPoolMXBean() {            private volatile ObjectName objname;  // created lazily            @Override            public ObjectName getObjectName() {                ObjectName result = objname;                if (result == null) {                    synchronized (this) {                        result = objname;                        if (result == null) {                            result = Util.newObjectName(BUFFER_POOL_MXBEAN_NAME +                                ",name=" + pool.getName());                            objname = result;                        }                    }                }                return result;            }            @Override            public String getName() {                return pool.getName();            }            @Override            public long getCount() {                return pool.getCount();            }            @Override            public long getTotalCapacity() {                return pool.getTotalCapacity();            }            @Override            public long getMemoryUsed() {                return pool.getMemoryUsed();            }        };    }    //......}

ManagementFactoryHelper的getBufferPoolMXBeans方法会通过createBufferPoolMXBean方法创建两个BufferPoolMXBean，然后添加到bufferPools

其中一个是DirectBufferPool，一个是MappedBufferPool；他们分别使用SharedSecrets.getJavaNioAccess().getDirectBufferPool()以及sun.nio.ch.FileChannelImpl.getMappedBufferPool()来创建

createBufferPoolMXBean方法使用匿名类创建了BufferPoolMXBean的实现；createBufferPoolMXBean方法接收JavaNioAccess.BufferPool参数，其getCount、getTotalCapacity、getMemoryUsed等均是直接使用pool的相关方法

JavaNioAccess.BufferPool

java.base/jdk/internal/access/JavaNioAccess.java

public interface JavaNioAccess {    /**     * Provides access to information on buffer usage.     */    interface BufferPool {        String getName();        long getCount();        long getTotalCapacity();        long getMemoryUsed();    }    BufferPool getDirectBufferPool();}

JavaNioAccess里头定义了BufferPool接口，它定义了getName、getCount、getTotalCapacity、getMemoryUsed方法；除此之外JavaNioAccess还定义了getDirectBufferPool方法用于返回BufferPool

SharedSecrets

java.base/jdk/internal/access/SharedSecrets.java

public class SharedSecrets {    private static final Unsafe unsafe = Unsafe.getUnsafe();    private static JavaUtilJarAccess javaUtilJarAccess;    private static JavaLangAccess javaLangAccess;    private static JavaLangModuleAccess javaLangModuleAccess;    private static JavaLangInvokeAccess javaLangInvokeAccess;    private static JavaLangRefAccess javaLangRefAccess;    private static JavaIOAccess javaIOAccess;    private static JavaNetInetAddressAccess javaNetInetAddressAccess;    private static JavaNetHttpCookieAccess javaNetHttpCookieAccess;    private static JavaNetSocketAccess javaNetSocketAccess;    private static JavaNetUriAccess javaNetUriAccess;    private static JavaNetURLAccess javaNetURLAccess;    private static JavaNetURLClassLoaderAccess javaNetURLClassLoaderAccess;    private static JavaNioAccess javaNioAccess;    private static JavaIOFileDescriptorAccess javaIOFileDescriptorAccess;    private static JavaIOFilePermissionAccess javaIOFilePermissionAccess;    private static JavaSecurityAccess javaSecurityAccess;    private static JavaUtilZipFileAccess javaUtilZipFileAccess;    private static JavaUtilResourceBundleAccess javaUtilResourceBundleAccess;    private static JavaAWTAccess javaAWTAccess;    private static JavaAWTFontAccess javaAWTFontAccess;    private static JavaBeansAccess javaBeansAccess;    private static JavaObjectInputStreamAccess javaObjectInputStreamAccess;    private static JavaObjectInputFilterAccess javaObjectInputFilterAccess;    private static JavaIORandomAccessFileAccess javaIORandomAccessFileAccess;    private static JavaxCryptoSealedObjectAccess javaxCryptoSealedObjectAccess;    //......    public static void setJavaNioAccess(JavaNioAccess jna) {        javaNioAccess = jna;    }    public static JavaNioAccess getJavaNioAccess() {        if (javaNioAccess == null) {            // Ensure java.nio.Buffer is initialized, which provides the            // shared secret.            unsafe.ensureClassInitialized(java.nio.Buffer.class);        }        return javaNioAccess;    }    //......}

SharedSecrets提供了JavaNioAccess的getter及setter

Buffer

java.base/java/nio/Buffer.java

public abstract class Buffer {    // Cached unsafe-access object    static final Unsafe UNSAFE = Unsafe.getUnsafe();    /**     * The characteristics of Spliterators that traverse and split elements     * maintained in Buffers.     */    static final int SPLITERATOR_CHARACTERISTICS =        Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.ORDERED;    // Invariants: mark <= position <= limit <= capacity    private int mark = -1;    private int position = 0;    private int limit;    private int capacity;    // Used by heap byte buffers or direct buffers with Unsafe access    // For heap byte buffers this field will be the address relative to the    // array base address and offset into that array. The address might    // not align on a word boundary for slices, nor align at a long word    // (8 byte) boundary for byte[] allocations on 32-bit systems.    // For direct buffers it is the start address of the memory region. The    // address might not align on a word boundary for slices, nor when created    // using JNI, see NewDirectByteBuffer(void*, long).    // Should ideally be declared final    // NOTE: hoisted here for speed in JNI GetDirectBufferAddress    long address;    //......    static {        // setup access to this package in SharedSecrets        SharedSecrets.setJavaNioAccess(            new JavaNioAccess() {                @Override                public JavaNioAccess.BufferPool getDirectBufferPool() {                    return Bits.BUFFER_POOL;                }            });    }}

抽象类Buffer有个static代码块，里头创建了匿名JavaNioAccess，然后设置到了SharedSecrets中；其中匿名JavaNioAccess的getDirectBufferPool方法返回的是Bits.BUFFER_POOL

FileChannelImpl

java.base/sun/nio/ch/FileChannelImpl.java

public class FileChannelImpl    extends FileChannel{    // Memory allocation size for mapping buffers    private static final long allocationGranularity;    // Access to FileDescriptor internals    private static final JavaIOFileDescriptorAccess fdAccess =        SharedSecrets.getJavaIOFileDescriptorAccess();    // Used to make native read and write calls    private final FileDispatcher nd;    // File descriptor    private final FileDescriptor fd;    //......    // -- Memory-mapped buffers --    private static class Unmapper        implements Runnable    {        // may be required to close file        private static final NativeDispatcher nd = new FileDispatcherImpl();        // keep track of mapped buffer usage        static volatile int count;        static volatile long totalSize;        static volatile long totalCapacity;        private volatile long address;        private final long size;        private final int cap;        private final FileDescriptor fd;        private Unmapper(long address, long size, int cap,                         FileDescriptor fd)        {            assert (address != 0);            this.address = address;            this.size = size;            this.cap = cap;            this.fd = fd;            synchronized (Unmapper.class) {                count++;                totalSize += size;                totalCapacity += cap;            }        }        public void run() {            if (address == 0)                return;            unmap0(address, size);            address = 0;            // if this mapping has a valid file descriptor then we close it            if (fd.valid()) {                try {                    nd.close(fd);                } catch (IOException ignore) {                    // nothing we can do                }            }            synchronized (Unmapper.class) {                count--;                totalSize -= size;                totalCapacity -= cap;            }        }    }    //......    /**     * Invoked by sun.management.ManagementFactoryHelper to create the management     * interface for mapped buffers.     */    public static JavaNioAccess.BufferPool getMappedBufferPool() {        return new JavaNioAccess.BufferPool() {            @Override            public String getName() {                return "mapped";            }            @Override            public long getCount() {                return Unmapper.count;            }            @Override            public long getTotalCapacity() {                return Unmapper.totalCapacity;            }            @Override            public long getMemoryUsed() {                return Unmapper.totalSize;            }        };    }    //......}

FileChannelImpl定义了getMappedBufferPool方法，返回的是匿名JavaNioAccess.BufferPool，其相关返回实现直接使用Unmapper的对应方法；Unmapper实现了Runnable接口

小结

BufferPoolMXBean接口继承了PlatformManagedObject，它定义了getName、getCount、getTotalCapacity、getMemoryUsed方法

ManagementFactoryHelper的getBufferPoolMXBeans方法会通过createBufferPoolMXBean方法创建两个BufferPoolMXBean，然后添加到bufferPools；其中一个是DirectBufferPool，一个是MappedBufferPool；他们分别使用SharedSecrets.getJavaNioAccess().getDirectBufferPool()以及sun.nio.ch.FileChannelImpl.getMappedBufferPool()来创建

createBufferPoolMXBean方法接收JavaNioAccess.BufferPool参数；抽象类Buffer有个static代码块，里头创建了匿名JavaNioAccess，然后设置到了SharedSecrets中；其中匿名JavaNioAccess的getDirectBufferPool方法返回的是Bits.BUFFER_POOL；FileChannelImpl定义了getMappedBufferPool方法，返回的是匿名JavaNioAccess.BufferPool，其相关返回实现直接使用Unmapper的对应方法；Unmapper实现了Runnable接口