ServerSocketChannel

ServerSocketChannel channel = ServerSocketChannel.open();

public static ServerSocketChannel open() throws IOException {
    return SelectorProvider.provider().openServerSocketChannel();
}

public ServerSocketChannel openServerSocketChannel() throws IOException {
    return new ServerSocketChannelImpl(this);
}

class ServerSocketChannelImpl extends ServerSocketChannel implements SelChImpl {
	private final FileDescriptor fd;
    private int fdVal;
    ServerSocket socket;
}

ServerSocketChannelImpl(SelectorProvider var1) throws IOException {
	super(var1);
	this.fd = Net.serverSocket(true);
	this.fdVal = IOUtil.fdVal(this.fd);
	this.state = 0;
}

static FileDescriptor serverSocket(boolean var0) {
    //创建FileDescriptor 并设置fd
	return IOUtil.newFD(socket0(isIPv6Available(), var0, true, fastLoopback));
}

public static FileDescriptor newFD(int var0) {
	FileDescriptor var1 = new FileDescriptor();
	setfdVal(var1, var0);
	return var1;
}

返回fd

private static native int socket0(boolean var0, boolean var1, boolean var2, boolean var3);

Java_sun_nio_ch_Net_socket0(JNIEnv *env, jclass cl, jboolean preferIPv6,
                            jboolean stream, jboolean reuse)
{
    int fd;
    int type = (stream ? SOCK_STREAM : SOCK_DGRAM);  // SOCK_STREAM: Tcp连接，提供序列化的、可靠的、双向连接的字节流。支持带外数据传输  SOCK_DGRAM： 支持UDP连接（无连接状态的消息）
#ifdef AF_INET6
    int domain = (ipv6_available() && preferIPv6) ? AF_INET6 : AF_INET;
#else
    int domain = AF_INET;
#endif

    fd = socket(domain, type, 0);  // socket  int socket(int domain, int type, int protocol);
    if (fd < 0) {
        return handleSocketError(env, errno);
    }
    .................
    }

channel.configureBlocking(false);

# ServerSocketChannelImpl
protected void implConfigureBlocking(boolean var1) throws IOException {
     IOUtil.configureBlocking(this.fd, var1);
}

# IOUtil
public static native void configureBlocking(FileDescriptor var0, boolean var1) throws IOException;

JNIEXPORT void JNICALL
Java_sun_nio_ch_IOUtil_configureBlocking(JNIEnv *env, jclass clazz,
                                         jobject fdo, jboolean blocking)
{
    if (configureBlocking(fdval(env, fdo), blocking) < 0)
        JNU_ThrowIOExceptionWithLastError(env, "Configure blocking failed");
}

static int
configureBlocking(int fd, jboolean blocking)
{
    // 非阻塞 传入的是blocking=false
    int flags = fcntl(fd, F_GETFL); // 获取文件打开方式的标志
    int newflags = blocking ? (flags & ~O_NONBLOCK) : (flags | O_NONBLOCK);

    return (flags == newflags) ? 0 : fcntl(fd, F_SETFL, newflags);
}