src/java.base/share/classes/sun/nio/ch/IOVecWrapper.java

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * 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.
 *
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package sun.nio.ch;

import java.nio.ByteBuffer;
import jdk.internal.misc.TerminatingThreadLocal;

/**
 * Manipulates a native array of iovec structs on Solaris:
 *
 * <pre> {@code
 * typedef struct iovec {
 *     caddr_t  iov_base;
 *     int      iov_len;
 * } iovec_t;
 * }</pre>
 *
 * @author Mike McCloskey
 * @since 1.4
 */

class IOVecWrapper {

    // Miscellaneous constants
    private static final int BASE_OFFSET = 0;
    private static final int LEN_OFFSET;
    private static final int SIZE_IOVEC;

    // The iovec array
    private final AllocatedNativeObject vecArray;

    // Number of elements in iovec array
    private final int size;

    // Buffers and position/remaining corresponding to elements in iovec array
    private final ByteBuffer[] buf;
    private final int[] position;
    private final int[] remaining;

    // Shadow buffers for cases when original buffer is substituted
    private final ByteBuffer[] shadow;

    // Base address of this array
    final long address;

    // Address size in bytes
    static final int addressSize;

    // per carrier-thread IOVecWrapper
    private static final TerminatingThreadLocal<IOVecWrapper[]> IOV_CACHE = new TerminatingThreadLocal<>() {
        @Override
        protected IOVecWrapper[] initialValue() {
            return new IOVecWrapper[1];  // one slot cache
        }
        @Override
        protected void threadTerminated(IOVecWrapper[] cache) {
            IOVecWrapper wrapper = cache[0];
            if (wrapper != null) {
                cache[0] = null;
                wrapper.vecArray.free();
            }
        }
    };

    private IOVecWrapper(int size) {
        this.size      = size;
        this.buf       = new ByteBuffer[size];
        this.position  = new int[size];
        this.remaining = new int[size];
        this.shadow    = new ByteBuffer[size];
        this.vecArray  = new AllocatedNativeObject(size * SIZE_IOVEC, false);
        this.address   = vecArray.address();
    }

    static IOVecWrapper get(int size) {
        IOVecWrapper[] cache = IOV_CACHE.get();
        IOVecWrapper wrapper = cache[0];
        if (wrapper != null) {
            cache[0] = null;
            if (wrapper.size < size) {
                // not big enough; eagerly release memory
                wrapper.vecArray.free();
                wrapper = null;
            }
        }
        return (wrapper != null) ? wrapper : new IOVecWrapper(size);
    }

    void release() {
        IOVecWrapper[] cache = IOV_CACHE.get();
        IOVecWrapper wrapper = cache[0];
        if (wrapper == null) {
            cache[0] = this;
        } else {
            // slot already used
            vecArray.free();
        }
    }

    void setBuffer(int i, ByteBuffer buf, int pos, int rem) {
        this.buf[i] = buf;
        this.position[i] = pos;
        this.remaining[i] = rem;
    }

    void setShadow(int i, ByteBuffer buf) {
        shadow[i] = buf;
    }

    ByteBuffer getBuffer(int i) {
        return buf[i];
    }

    int getPosition(int i) {
        return position[i];
    }

    int getRemaining(int i) {
        return remaining[i];
    }

    ByteBuffer getShadow(int i) {
        return shadow[i];
    }

    void clearRefs(int i) {
        buf[i] = null;
        shadow[i] = null;
    }

    void putBase(int i, long base) {
        int offset = SIZE_IOVEC * i + BASE_OFFSET;
        if (addressSize == 4)
            vecArray.putInt(offset, (int)base);
        else
            vecArray.putLong(offset, base);
    }

    void putLen(int i, long len) {
        int offset = SIZE_IOVEC * i + LEN_OFFSET;
        if (addressSize == 4)
            vecArray.putInt(offset, (int)len);
        else
            vecArray.putLong(offset, len);
    }

    static {
        addressSize = Util.unsafe().addressSize();
        LEN_OFFSET = addressSize;
        SIZE_IOVEC = (short) (addressSize * 2);
    }
}