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   /*
    * Copyright 2015 The Netty Project
    *
    * The Netty Project licenses this file to you under the Apache License,
    * version 2.0 (the "License"); you may not use this file except in compliance
    * with the License. You may obtain a copy of the License at:
    *
    *   https://www.apache.org/licenses/LICENSE-2.0
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
   * License for the specific language governing permissions and limitations
   * under the License.
   */
  package io.netty.channel.unix;
  
  
  import java.io.File;
  import java.io.IOException;
  import java.nio.ByteBuffer;
  import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
  
  import static io.netty.channel.unix.Errors.ioResult;
  import static io.netty.channel.unix.Errors.newIOException;
  import static io.netty.channel.unix.Limits.IOV_MAX;
  import static io.netty.util.internal.ObjectUtil.checkNotNull;
  import static io.netty.util.internal.ObjectUtil.checkPositiveOrZero;
  import static java.lang.Math.min;
  
  /**
   * Native {@link FileDescriptor} implementation which allows to wrap an {@code int} and provide a
   * {@link FileDescriptor} for it.
   */
  public class FileDescriptor {
  
      private static final AtomicIntegerFieldUpdater<FileDescriptor> stateUpdater =
              AtomicIntegerFieldUpdater.newUpdater(FileDescriptor.class, "state");
  
      private static final int STATE_CLOSED_MASK = 1;
      private static final int STATE_INPUT_SHUTDOWN_MASK = 1 << 1;
      private static final int STATE_OUTPUT_SHUTDOWN_MASK = 1 << 2;
      private static final int STATE_ALL_MASK = STATE_CLOSED_MASK |
                                                STATE_INPUT_SHUTDOWN_MASK |
                                                STATE_OUTPUT_SHUTDOWN_MASK;
  
      /**
       * Bit map = [Output Shutdown | Input Shutdown | Closed]
       */
      volatile int state;
      final int fd;
  
      public FileDescriptor(int fd) {
          checkPositiveOrZero(fd, "fd");
          this.fd = fd;
      }
  
      /**
       * Return the int value of the filedescriptor.
       */
      public final int intValue() {
          return fd;
      }
  
      protected boolean markClosed() {
          for (;;) {
              int state = this.state;
              if (isClosed(state)) {
                  return false;
              }
              // Once a close operation happens, the channel is considered shutdown.
              if (casState(state, state | STATE_ALL_MASK)) {
                  return true;
              }
          }
      }
  
      /**
       * Close the file descriptor.
       */
      public void close() throws IOException {
          if (markClosed()) {
              int res = close(fd);
              if (res < 0) {
                  throw newIOException("close", res);
              }
          }
      }
  
      /**
       * Returns {@code true} if the file descriptor is open.
       */
      public boolean isOpen() {
          return !isClosed(state);
      }
  
      public final int write(ByteBuffer buf, int pos, int limit) throws IOException {
          int res = write(fd, buf, pos, limit);
          if (res >= 0) {
             return res;
         }
         return ioResult("write", res);
     }
 
     public final int writeAddress(long address, int pos, int limit) throws IOException {
         int res = writeAddress(fd, address, pos, limit);
         if (res >= 0) {
             return res;
         }
         return ioResult("writeAddress", res);
     }
 
     public final long writev(ByteBuffer[] buffers, int offset, int length, long maxBytesToWrite) throws IOException {
         long res = writev(fd, buffers, offset, min(IOV_MAX, length), maxBytesToWrite);
         if (res >= 0) {
             return res;
         }
         return ioResult("writev", (int) res);
     }
 
     public final long writevAddresses(long memoryAddress, int length) throws IOException {
         long res = writevAddresses(fd, memoryAddress, length);
         if (res >= 0) {
             return res;
         }
         return ioResult("writevAddresses", (int) res);
     }
 
     public final int read(ByteBuffer buf, int pos, int limit) throws IOException {
         int res = read(fd, buf, pos, limit);
         if (res > 0) {
             return res;
         }
         if (res == 0) {
             return -1;
         }
         return ioResult("read", res);
     }
 
     public final int readAddress(long address, int pos, int limit) throws IOException {
         int res = readAddress(fd, address, pos, limit);
         if (res > 0) {
             return res;
         }
         if (res == 0) {
             return -1;
         }
         return ioResult("readAddress", res);
     }
 
     @Override
     public String toString() {
         return "FileDescriptor{" +
                 "fd=" + fd +
                 '}';
     }
 
     @Override
     public boolean equals(Object o) {
         if (this == o) {
             return true;
         }
         if (!(o instanceof FileDescriptor)) {
             return false;
         }
 
         return fd == ((FileDescriptor) o).fd;
     }
 
     @Override
     public int hashCode() {
         return fd;
     }
 
     /**
      * Open a new {@link FileDescriptor} for the given path.
      */
     public static FileDescriptor from(String path) throws IOException {
         int res = open(checkNotNull(path, "path"));
         if (res < 0) {
             throw newIOException("open", res);
         }
         return new FileDescriptor(res);
     }
 
     /**
      * Open a new {@link FileDescriptor} for the given {@link File}.
      */
     public static FileDescriptor from(File file) throws IOException {
         return from(checkNotNull(file, "file").getPath());
     }
 
     /**
      * @return [0] = read end, [1] = write end
      */
     public static FileDescriptor[] pipe() throws IOException {
         long res = newPipe();
         if (res < 0) {
             throw newIOException("newPipe", (int) res);
         }
         return new FileDescriptor[]{new FileDescriptor((int) (res >>> 32)), new FileDescriptor((int) res)};
     }
 
     final boolean casState(int expected, int update) {
         return stateUpdater.compareAndSet(this, expected, update);
     }
 
     static boolean isClosed(int state) {
         return (state & STATE_CLOSED_MASK) != 0;
     }
 
     static boolean isInputShutdown(int state) {
         return (state & STATE_INPUT_SHUTDOWN_MASK) != 0;
     }
 
     static boolean isOutputShutdown(int state) {
         return (state & STATE_OUTPUT_SHUTDOWN_MASK) != 0;
     }
 
     static int inputShutdown(int state) {
         return state | STATE_INPUT_SHUTDOWN_MASK;
     }
 
     static int outputShutdown(int state) {
         return state | STATE_OUTPUT_SHUTDOWN_MASK;
     }
 
     private static native int open(String path);
     private static native int close(int fd);
 
     private static native int write(int fd, ByteBuffer buf, int pos, int limit);
     private static native int writeAddress(int fd, long address, int pos, int limit);
     private static native long writev(int fd, ByteBuffer[] buffers, int offset, int length, long maxBytesToWrite);
     private static native long writevAddresses(int fd, long memoryAddress, int length);
 
     private static native int read(int fd, ByteBuffer buf, int pos, int limit);
     private static native int readAddress(int fd, long address, int pos, int limit);
 
     private static native long newPipe();
 }