Hi Lucy, in general I support the addition of SO_REUSEPORT to the set of standard socket options. However for me the problem is not that this new option is not supported on all platforms, but instead that it has such different semantics on different platforms. If you look at the code, you'll see that we already implicitly set SO_REUSEPORT on Mac and AIX for datagram sockets for which we set SO_REUSEADDR. So maybe we have to rethink this, once SO_REUSEPORT becomes available as a standard socket option.
I like the new wording you've posted for JavaDoc of SO_REUSEPORT, but I think the sentence: * Although SO_REUSEADDR option already enables similar * functionality, SO_REUSEPORT prevents port hijacking and * distributes the involving datagrams evenly across all of the * receiving threads. refers to a Linux-specific implementation detail which shouldn't be mentioned in the general documentation. You already have the sentence "The exact semantics of this socket option are socket type and system dependent" which should let everybody think twice before using this option. I'm also not sure about the link to the Linux article but I again think it is inappropriate in a general API documentation (otherwise we would have to add links for every platform which supports SO_REUSEPORT). As far as I can see (and please correct me if I'm wrong) you actually only add the new option for Linux platforms. But this socket option is also supported on Solaris (>= 11), MacOS X, AIX. So could you please enable it on the other platforms as well. Finally I want to mention the good stackoverflow article at http://stackoverflow.com/questions/14388706/socket-options-so-reuseaddr-and-so-reuseport-how-do-they-differ-do-they-mean-t which covers the topic SO_REUSEADDR vs. SO_REUSEPORT quite well. And I've collected the man-page entries for SO_REUSEADDR and SO_REUSEPORT for the systems I have (unfortunately, I couldn't find an updated Linux man-page which mentions SO_REUSEPORT): Linux ===== SO_REUSEADDR Indicates that the rules used in validating addresses supplied in a bind(2) call should allow reuse of local addresses. For AF_INET sockets this means that a socket may bind, except when there is an active listening socket bound to the address. When the listening socket is bound to INADDR_ANY with a specific port then it is not possi- ble to bind to this port for any local address. Argument is an integer boolean flag. Linux will only allow port reuse with the SO_REUSEADDR option when this option was set both in the previous program that performed a bind(2) to the port and in the program that wants to reuse the port. This differs from some implementations (e.g., FreeBSD) where only the later program needs to set the SO_REUSEADDR option. Typically this difference is invisi- ble, since, for example, a server program is designed to always set this option. MacOS X ======= SO_REUSEADDR enables local address reuse SO_REUSEPORT enables duplicate address and port bindings SO_REUSEADDR indicates that the rules used in validating addresses supplied in a bind(2) call should allow reuse of local addresses. SO_REUSEPORT allows completely duplicate bindings by multiple processes if they all set SO_REUSEPORT before bind- ing the port. This option permits multiple instances of a program to each receive UDP/IP multicast or broadcast datagrams destined for the bound port. Solaris ======= SO_REUSEADDR enable/disable local address reuse SO_REUSEPORT enable/disable local port reuse for PF_INET/PF_INET6 socket The SO_REUSEADDR/SO_REUSEPORT options indi- cate that the rules used in validating addresses and ports supplied in a bind(3SOCKET) call should allow reuse of local addresses or ports. AIX === SO_REUSEADDR Specifies that the rules used in validating addresses supplied by a bind subroutine should allow reuse of a local port. A particular IP address can only be bound once to the same port. This option enables or disables reuse of local ports. SO_REUSEADDR allows an application to explicitly deny subsequent bind subroutine to the port/address of the socket with SO_REUSEADDR set. This allows an application to block other applications from binding with the bind subroutine. SO_REUSEPORT Specifies that the rules used in validating addresses supplied by a bind subroutine should allow reuse of a local port/address combination. Each binding of the port/address combination must specify the SO_REUSEPORT socket option. This option enables or disables the reuse of local port/address combinations. HPUX ==== SO_REUSEADDR (int; boolean; AF_INET sockets only) If enabled, allows a local address to be reused in subsequent calls to bind(). Default: disallowed. SO_REUSEPORT (int; boolean; AF_INET sockets only) If enabled, allows a local address and port to be reused in subsequent calls to bind(). Default: disallowed. Setting the SO_REUSEADDR option allows the local socket address to be reused in subsequent calls to bind(). This permits multiple SOCK_STREAM sockets to be bound to the same local address, as long as all existing sockets with the desired local address are in a connected state before bind() is called for a new socket. For SOCK_DGRAM sockets, SO_REUSEADDR allows multiple sockets to receive UDP multicast datagrams addressed to the bound port number. For all SOCK_DGRAM sockets bound to the same local address, SO_REUSEADDR must be set before calling bind(). Setting the SO_REUSEPORT option allows multiple SOCK_DGRAM sockets to share the same address and port. Each one of those sockets, including the first one to use that port, must specify this option before calling bind(). Regards, Volker On Mon, Nov 23, 2015 at 9:00 AM, Alan Bateman <alan.bate...@oracle.com> wrote: > > > On 23/11/2015 04:12, Lu, Yingqi wrote: > > Hi Alan, > > > > One more question please J I want to make sure I understand correctly on > your following suggestion. In order to use supportedOptions method to test > SO_REUSEPORT, I will need to first write a native function to check if > SO_REUSEPORT is supported. Then, in the defaultOptions method, I do a > conditional add for StandardSocketOptions.SO_REUSEPORT if it is supported on > the platform? Is this a preferred way to implement? Please let me know! > > > Yes as supportedOptions() shouldn't return SO_REUSEPORT in the set when it's > not supported. It might be simplest to put that code in sun.nio.ch.Net, > maybe isReusePortSupported or some such method. In the implementation > (Net.c) then you can return true or false depending on the platform and > maybe kernel version. > > -Alan
