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  • How do I setup a syslog server for my network?

    - by Solignis
    I would like to setup a syslog server to forward all log file from all of my VMs and servers. I really don't much about what is out there. So I turn to the community, Something on Linux is fine, what I want more is alert ability like emails telling me something is not right. If there was something to sort the logs by source that would be cool. Where would I want run the syslog server from? My admin WS or a server/VM? Any input would be wonderful. Thanks in advance.

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  • Hyper-V VM's cannot access Host resources, and vice-versa

    - by Agent
    I have several Hyper-V vm's running on this Win2008 R2 Server box, and up until a reboot of the host server, all the VM's were able to access shared folders on the host. Now, they can't even ping the host server. From what I've seen, I need to setup an Internal only network through Virtual Network Manager in Hyper-V. I set this up, then tried to enable the Microsoft Virtual Network Switch Protocol option in this Internal Only NIC, but I get popups saying: Your current selection will also disable the following features: Microsoft virtual network switch protocol Which is absolutely stupid, considering the protocol is what I'm ticking the checkbox to Enable! As of now, on the host, I have 2 NICs: Physical - This NIC on the host machine does have the MVNS protocol enabled Virtual Network Adapter - Created through Hyper-V Virtual Network Manager as an External type of network. Trying to enable MVNS on this NIC also produces the error above. I've tried enabling Client for Microsoft Networks on the physical NIC for IPv6, but everytime I do that, all the VMs lose Internet connectivity and I cannot RDP into them. Anything else I can try?

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  • Understanding Covariant and Contravariant interfaces in C#

    - by SLC
    I've come across these in a textbook I am reading on C#, but I am having difficulty understanding them, probably due to lack of context. Is there a good concise explanation of what they are and what they are useful for out there? Edit for clarification: Covariant interface: interface IBibble<out T> . . Contravariant interface: interface IBibble<in T> . .

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  • How to remove unwanted charecters using split in tcl

    - by Mallikarjunarao
    Here is an example Interface {} {} {} {} {} {} {} {} {} {} {} {} {} {} {} {} {} IP-Address {} {} {} {} {} OK? Method Status {} {} {} {} {} {} {} {} {} {} {} {} {} {} {} {Protocol FastEthernet0/0} {} {} {} {} {} {} {} {} {} {} {} unassigned {} {} {} {} {} YES unset {} administratively down down {} {} {} { FastEthernet0/1} {} {} {} {} {} {} {} {} {} {} {} unassigned {} {} {} {} {} YES unset {} administratively down down I want remove {} in this. I assumed all the above string interface variable set interface [string trimright [string trimleft $interface "{}"] "{}"] but it doesn't work. How to remove the {} in my example?

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  • Why am I unable to access the network shares on my own computer?

    - by DoomStone
    I am having some problems with media center computer, with Windows 7 on it. The computers IP address is 192.168.1.13, and another computer can without any problem navigate to \\192.168.1.13, but the computer itself can not. Neither \\servername nor \\localhost. If I reboot the computer a couple of times, it will work again, but this is a big problem as my computer cleans my media center library on boot and there, if it can not access \\192.168.1.13, it will think that all the files have been removed and therefore delete them from the database. I really have no idea on where to start with this problem, but if anyone has tried this before and fixed it, I would be very happy, as it would save me from having to reinstall the whole system.

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  • One huge drive (network share) from many computers, with folder priority redundancy.

    - by Exception Duck
    Not sure if this exists, but I have a huge amount of data to store (about 5-50mb files) and as it is now, I have 5 computers, each with raid 5 providing about 6TB hard drive each. This is causing some problems with the software I am using (something home made) so I'm wondering, is there some software that I can install on all those computers that will mask it as one huge drive... Running windows on those computers, from Xp 64 bit to windows server 2008 I would also like to set a priority on each folder on the redundancy it has, some folders I can live without no online backup (I have a backup in a safe of that data) but some I need full online backup system if one hard drive fails. Something open source, as I try to use that as much as I can, but all ideas welcome.

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  • Where to get the network NIC's firmware rtl_nic/rtl8105e-1.fw?

    - by Kyrol
    Im installing Debian testing version wheezy on my Asus X53Sc with Intel Centrino Wireless-N 100. Im having a problem with my wifi connection. When I try to connect to internet with the wireless connection, an error occurs: Possible missing firmware /lib/firmware/rtl_nic/rtl8105e-1.fw for module r8169. I installed successfully the iwlwifi-100-5.ucode, but now I have this error. Any ideas or suggestions to resolve the problem ?

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  • How do I set up Tomcat 7's server.xml to access a network share with an different url?

    - by jneff
    I have Apache Tomcat 7.0 installed on a Windows 2008 R2 Server. Tomcat has access to a share '\server\share' that has a documents folder that I want to access using '/foo/Documents' in my web application. My application is able to access the documents when I set the file path to '//server/share/documents/doc1.doc'. I don't want the file server's path to be exposed on my link to the file in my application. I want to be able to set the path to '/foo/Documents/doc1.doc'. In http://www3.ntu.edu.sg/home/ehchua/programming/howto/Tomcat_More.html under 'Setting the Context Root Directory and Request URL of a Webapp' item number two says that I can rename the path by putting in a context to the server.xml file. So I put <Host name="localhost" appBase="webapps" unpackWARs="true" autoDeploy="true"> <!-- SingleSignOn valve, share authentication between web applications Documentation at: /docs/config/valve.html --> <!-- <Valve className="org.apache.catalina.authenticator.SingleSignOn" /> --> <!-- Access log processes all example. Documentation at: /docs/config/valve.html Note: The pattern used is equivalent to using pattern="common" --> <Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs" prefix="localhost_access_log." suffix=".txt" pattern="%h %l %u %t &quot;%r&quot; %s %b" /> <Context path="/foo" docBase="//server/share" reloadable="false"></Context> </Host> The context at the bottum was added. Then I tried to pull the file using '/foo/Documents/doc1.doc' and it didn't work. What do I need to do to get it to work correctly? Should I be using an alias instead? Are there other security issues that this may cause?

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  • What tools can I use to locate the IP of a machine on my network?

    - by user134918
    I am logged in to a remote Windows Server machine and am trying to attach it to a VPN for a LAN that I am also connected to locally from another Windows machine using Remotr Desktop. I can connect the remote machine to the VPN but when I do so, I lose my remote desktop connection. I am now in a situation where I know/think that the remote machine is on my LAN, but do not know what its current IP is and can therefor not connect to it again. I do not have any control over the infrastructure, all I have is a remote machine that I do control, and another machine that I also control that is connected to the same LAN as I'm trying to get the remote machine on using the existing VPN. What tools are available for Windows to allow me to locate the machine on my LAN again? I am imagining that there must be a tool that broadcasts the machines new IP using multicast, or tries to log in to a server component running somewhere with a know IP. Effectively, I am looking for some software that I can run on my remote machine, as well as my local machine, to allow me to discover the new IP address (on the LAN) assigned to the remote machine after connecting to the VPN.

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  • What's a good box to serve files on my local network, cross platform?

    - by rogpeppe
    I've installed CAT5e cable and gigabit switches in my house with the goal of having an "always-on" file server in the loft, accessible to both my macbook and my partner's Windows box. I'd like to find a solution which: uses minimal power. allows me to access as much disk bandwidth as possible. provides glitch-free file access to both MacOS and Windows. is as cheap as possible, while remaining reliable. Optional, but desirable extras: software or hardware RAID; open source solutions. A SheevaPlug with eSATA seems one possibility, but I'm sure there are any number of other good options.

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  • How to share a internet connection in a network with openSuse 12.2?

    - by eneepo
    I have to computer and opensuse 12.2 on both of them: Internet 192.168.2.1 | eth0 eth1 First Computer 192.168.2.2 192.168.2.10 | eth0 Second Computer 192.168.2.11 I am following the instruction on http://www.swerdna.net.au/suseics.html but as soon as I enable eth1 on first computer I lose connection with internet. I follow all the instructions I don't know which part I'm miss-configuring.

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  • How can I monitor network usage by process on Mac OS X?

    - by psmith
    Is there any way to find out which process using how much internet bandwidth on Mac OS X Lion? I'm on mobile internet now, which is not very fast, so it would be nice if I can tell that for example, Chrome using 10kB/s, and Skype using 2kB/s. I can see the total amount of traffic in Activity Monitor, but it is not enough for me. I'd like to use an existing application, not interested to write an app like this. And I'm not interested in the actual traffic, only the number of bytes transferred and received by each processes.

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  • Linux: Three default gateways?

    - by Daniel
    My server has three default gateways, how can that be? Shouldn't there be one default gw? I have three NICs, each attached to a separate subnet: server1:~# route Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 10.5.0.0 * 255.255.255.224 U 0 0 0 eth3 localnet * 255.255.255.224 U 0 0 0 eth0 192.168.8.0 * 255.255.255.192 U 0 0 0 eth1 default 10.5.0.1 0.0.0.0 UG 0 0 0 eth3 default 192.168.8.1 0.0.0.0 UG 0 0 0 eth1 default 10.1.0.1 0.0.0.0 UG 0 0 0 eth0 Sometimes, I can't ping a host on the Internet, sometimes I can. What I want is traffic to the Internet (0.0.0.0) routed through a specific NIC. Can I just add a route for 0.0.0.0 and default gw to one of the eth0-3 interfaces? Will it break my connection? I'm using Debian, here is my /etc/network/interfaces: # This file describes the network interfaces available on your system # and how to activate them. For more information, see interfaces(5). # The loopback network interface auto lo iface lo inet loopback # The primary network interface allow-hotplug eth0 iface eth0 inet static address 10.1.0.4 netmask 255.255.255.224 network 10.1.0.0 broadcast 10.1.0.31 gateway 10.1.0.1 allow-hotplug eth1 iface eth1 inet static address 192.168.8.4 netmask 255.255.255.192 network 192.168.8.0 broadcast 192.168.8.63 gateway 192.168.8.1 allow-hotplug eth3 iface eth3 inet static address 10.5.0.4 netmask 255.255.255.224 network 10.5.0.0 broadcast 10.5.0.31 gateway 10.5.0.1

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  • vmware server 64 bit on ubuntu 9.10 64 bit with P2V windows 2003 SBS poor network speed

    - by RobertHC
    configuration is ubuntu 2.6.31-21 64 bit vmware 2.0.2 64 bit last release hardware is core 2 quad with 8GB ram guest is win 2003 server SBS 32 bit Dear friends, we have a converted physical to virtual windows sbs 2003, converted with last converter available nowadays http://www.vmware.com/products/converter/ vCenter converter. Running the P2V 2K3 SBS on vmware server, it does boot fine, but we do note an abnormal CPU activity and a poor lan speed. As attempts we did what follow. We removed all unneeded peripherals, we removed one NIC (phisycal server was 2 nics), we changed the vmx to ged the nic recognized as intel instead than amd, we removed 1 cpu (physical was 2 cpu), we removed anything was reported as failed driver from system events monitor. Nothing to do, no way and funny results. Let's read some tests results. All are made with the same file copied in different source folders. Copying from client side (both directions copy, to/from server) results are i.e. 10 seconds, copying the same files from server side (again from and to server) results are different... from client to server, speed is round about (bit more) 10 seconds, but from server to client direction is slower: double the time. Beeing very fast and launching a simultaneous copy "from server to client"+"from client to server", this made from the server side, results in a stuck traffic... 45 seconds to do the copy. vmware tools are installed and e1000 driver has been updated. With one processor CPU activity is still going up and down but much less than with two. Because of test, we installed win 2k8 STD 64 bit. We repeated all the above tests with exactly the same file result is just one: always 5 seconds (this matches the lan speed) Any idea about this issue is welcome and thank you if any. Kind regards R.

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  • oracle access on vmware fusion

    - by gaudi_br
    Hello, I'm running snow leopard and I'm doing some development that requires some network knowledge. I've installed vmware fusion 3.0 and I've set up a virtual machine with windows 2003 server. I need to mimic the exact configuration of another server in the network, so I really need to run the versions I'll be mentioning here. Besides, I set up two network configurations on the VM: one NAT config (so that I can have internet access) and one host-only config (because I need to use another server's mac adress and my local area network might have a problem with it) From the installation of windows 2003, I then installed oracle 10.2.0.1. During the installation I received a warning about the primary ip-address of the system being dhcp assigned, but I ignored it (maybe it was a mistake)... Now, from experience, unless the DHCP assigned address changes, I should be able to access the guest system's database from the host system, so I went to safari and tried to access the oracle em. As it turns out, because my computer is on a company network, the company's DNS doesn't know about the virtual machine, unless of course I switch to a bridged network config. However, I don't want to do that because I don't to mix up the domains. So I guess the question is, how can I define my own dns or router, or whatever it is that I need to define so that whenever I try the guest system's ip address form the host, it will use the vmnet1 or vmnet8 interface define by vmware and bypass the dns configuration of my local area network. I'd also like to know what to do incase I want to change ip addresses on the guest machine without having oracle go haywire (I've noticed a few folders on the structure which are specific for the very first IP Address)... Any help would be appreciated. Thanks in advance.

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  • How can I find a computer on my network that is doing mass mailings?

    - by Alex Ciarlill
    I was notified by my isp that one of my machines is sending out spam. This happened about 3 months ago on windows machine running cygwin that was hacked due to an SSH vuln. The hackers setup IIS and SMTP. I cleared out the machine and all the services are disabled so I think that machine is okay I am wondering if there is any other way to identify which machine it could be coming from? The ISP has NO useful information such as source port, destination port, destination IP... nothing. I am running DD-WRT on my router, Windows 7 PC and a Windows XP PC.

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  • How to redirect / route VPN traffic to back standing local network?

    - by Milkywayfarer
    There are two computers one "HOME" with Ubuntu 10.10 installed, and another "WORK" with WinXP installed. WORK PC is behind draconian firewall. However, let's imagine, that there is VPN connection installed between this 2 work stations, for example, with teamviewer, hamachi, openvpn, or by some other mean (by the way, what is the best mean for such purposes?). One is interested in working with WORK's LAN resources from his HOME computer via VPN. So my question is about configuration required to be done on WinXP machine (or, maybe on both machines), to make such interaction possible? I'm guessing that some routing stuff should be performed somewhere. But I don't know what exactly and how to do?

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  • How do i network ten branch office with voip, video calling and files sharing.

    - by Oluwalogbon
    Am an IT person, have done some networking job for my organization like Lan and wireless within the area, configure windows server to manage staff account My company has ten branch (In each state) in my country and am giving a task to connect dose branch together, which there will be VOIP, Video calling and sharing of files within the branch. I need someone to help me with this project..what and what did I need to put in place

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  • Diagnosing PC crashes (most often while using shared folders or torrents)

    - by Dyppl
    For the last few weeks my PC (pretty old P4 with WinXP SP3) has been crashing randomly. It just suddenly reboots instanteneously. It feels hardware-related but I wasn't able to determine wether it's software or hardware that causes it. I did notice a pattern though: it's more likely to crash when I copy a lot of files over network or have uTorrent running, but sometimes it crashes when I am not doing anything with it. Copying files from it over network causes it to crash in 1 to 10 minutes almost every time. Using torrents causes it to crash every 1-3 hours. With neither or that on it crashes every 24 hours or so. I ruled out the following probable causes: PSU (I bought a new one and turned off most of the drives so the power is sufficient 100%) Bad HDD or interface cable on my SATA disk from which I was originally copying the data over network (bought new SATA cable and later yanked out the HDD completely, PC still crashes without it) Video adapter (AGP slot is now empty, using the onboard VGA at the moment) Network adapter (removed it from PCI, using onboard LAN) CPU (I think: I changed the termopaste and it's temperature is below 50C) RAM (I think: I ran Memtest86 and it didn't show any errors) At the moment I only have only one system HDD and DVD drives, a mouse and a keyboard plugged in. The fact that it crashes most often when I use network extensively makes me think that maybe it's software related (I removed the network adapter from PCI and now am using an onboard one, so network hardware is unlikely to cause problems). I am now pondering system reinstall but it's not a pleasant solution so I decided to ask wether there are better ideas first. If someone can share a good diagnostic tool it would be great because I didn't find anything good. Thanks in advance, I hope that "help to diagnose" questions aren't entirely banned here. EDIT: Motherboard is actually ~4 years old as I replaced it back in 2007

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  • Why are interfaces unusable in PHP?

    - by streetparade
    I mean an interface definition without defining the return type makes it unusable? This makes more Clear Interface run { public function getInteger(); } class MyString implements run { public function myNumber() { } public function getInteger() { return "Not a number"; } } In Java every Interface has a return type like Integer,String,Void I know that PHP is unfortunately a loosly typed Language but isnt there a Solution for that Problem? Is it Possible to defining a Interface with a Return type like Integer?

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  • Error 1606. Could not access network location %SystemDrive%\inetpub\wwwroot\ while installing on IIS

    - by Mark
    I'm trying to port our software installer which currently supports Windows 2000 and Windows 2003 to a Windows 2008 environment. Currently, the installer gets an error which reads "Error 1606. Could not access network location %SystemDrive%\inetpub\wwwroot." %SystemDrive% is without a doubt C:\, and C:\inetpub\wwwroot\ has the correct accessibility. It is interesting that if I hardcode the path in the following keys in the registry to C:\inetpub\wwwroot\, without using the environment variable, the installer works correctly. • HKLM/Software/Wow6432Node/Microsoft/InetStp/PathWWWRoot • KHLM/Software/Microsoft/InetStp/PathWWWRoot. This seems like a very poor hack. I do not want to tell our clients that they need to hack their registry before they will be able to install our product. Another option is to change the registry behind the scenes, do our install, and revert the registry keys to their original values at the end of the install, but obviously I don't like this solution either. I find it hard to believe that Microsoft would have done this without reason, so there must be an alternate approach to get these installers to work without modifying the registry. Any tips appreciated.

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  • value types in the vm

    - by john.rose
    value types in the vm p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Times} p.p2 {margin: 0.0px 0.0px 14.0px 0.0px; font: 14.0px Times} p.p3 {margin: 0.0px 0.0px 12.0px 0.0px; font: 14.0px Times} p.p4 {margin: 0.0px 0.0px 15.0px 0.0px; font: 14.0px Times} p.p5 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Courier} p.p6 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Courier; min-height: 17.0px} p.p7 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Times; min-height: 18.0px} p.p8 {margin: 0.0px 0.0px 0.0px 36.0px; text-indent: -36.0px; font: 14.0px Times; min-height: 18.0px} p.p9 {margin: 0.0px 0.0px 12.0px 0.0px; font: 14.0px Times; min-height: 18.0px} p.p10 {margin: 0.0px 0.0px 12.0px 0.0px; font: 14.0px Times; color: #000000} li.li1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Times} li.li7 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Times; min-height: 18.0px} span.s1 {font: 14.0px Courier} span.s2 {color: #000000} span.s3 {font: 14.0px Courier; color: #000000} ol.ol1 {list-style-type: decimal} Or, enduring values for a changing world. Introduction A value type is a data type which, generally speaking, is designed for being passed by value in and out of methods, and stored by value in data structures. The only value types which the Java language directly supports are the eight primitive types. Java indirectly and approximately supports value types, if they are implemented in terms of classes. For example, both Integer and String may be viewed as value types, especially if their usage is restricted to avoid operations appropriate to Object. In this note, we propose a definition of value types in terms of a design pattern for Java classes, accompanied by a set of usage restrictions. We also sketch the relation of such value types to tuple types (which are a JVM-level notion), and point out JVM optimizations that can apply to value types. This note is a thought experiment to extend the JVM’s performance model in support of value types. The demonstration has two phases.  Initially the extension can simply use design patterns, within the current bytecode architecture, and in today’s Java language. But if the performance model is to be realized in practice, it will probably require new JVM bytecode features, changes to the Java language, or both.  We will look at a few possibilities for these new features. An Axiom of Value In the context of the JVM, a value type is a data type equipped with construction, assignment, and equality operations, and a set of typed components, such that, whenever two variables of the value type produce equal corresponding values for their components, the values of the two variables cannot be distinguished by any JVM operation. Here are some corollaries: A value type is immutable, since otherwise a copy could be constructed and the original could be modified in one of its components, allowing the copies to be distinguished. Changing the component of a value type requires construction of a new value. The equals and hashCode operations are strictly component-wise. If a value type is represented by a JVM reference, that reference cannot be successfully synchronized on, and cannot be usefully compared for reference equality. A value type can be viewed in terms of what it doesn’t do. We can say that a value type omits all value-unsafe operations, which could violate the constraints on value types.  These operations, which are ordinarily allowed for Java object types, are pointer equality comparison (the acmp instruction), synchronization (the monitor instructions), all the wait and notify methods of class Object, and non-trivial finalize methods. The clone method is also value-unsafe, although for value types it could be treated as the identity function. Finally, and most importantly, any side effect on an object (however visible) also counts as an value-unsafe operation. A value type may have methods, but such methods must not change the components of the value. It is reasonable and useful to define methods like toString, equals, and hashCode on value types, and also methods which are specifically valuable to users of the value type. Representations of Value Value types have two natural representations in the JVM, unboxed and boxed. An unboxed value consists of the components, as simple variables. For example, the complex number x=(1+2i), in rectangular coordinate form, may be represented in unboxed form by the following pair of variables: /*Complex x = Complex.valueOf(1.0, 2.0):*/ double x_re = 1.0, x_im = 2.0; These variables might be locals, parameters, or fields. Their association as components of a single value is not defined to the JVM. Here is a sample computation which computes the norm of the difference between two complex numbers: double distance(/*Complex x:*/ double x_re, double x_im,         /*Complex y:*/ double y_re, double y_im) {     /*Complex z = x.minus(y):*/     double z_re = x_re - y_re, z_im = x_im - y_im;     /*return z.abs():*/     return Math.sqrt(z_re*z_re + z_im*z_im); } A boxed representation groups component values under a single object reference. The reference is to a ‘wrapper class’ that carries the component values in its fields. (A primitive type can naturally be equated with a trivial value type with just one component of that type. In that view, the wrapper class Integer can serve as a boxed representation of value type int.) The unboxed representation of complex numbers is practical for many uses, but it fails to cover several major use cases: return values, array elements, and generic APIs. The two components of a complex number cannot be directly returned from a Java function, since Java does not support multiple return values. The same story applies to array elements: Java has no ’array of structs’ feature. (Double-length arrays are a possible workaround for complex numbers, but not for value types with heterogeneous components.) By generic APIs I mean both those which use generic types, like Arrays.asList and those which have special case support for primitive types, like String.valueOf and PrintStream.println. Those APIs do not support unboxed values, and offer some problems to boxed values. Any ’real’ JVM type should have a story for returns, arrays, and API interoperability. The basic problem here is that value types fall between primitive types and object types. Value types are clearly more complex than primitive types, and object types are slightly too complicated. Objects are a little bit dangerous to use as value carriers, since object references can be compared for pointer equality, and can be synchronized on. Also, as many Java programmers have observed, there is often a performance cost to using wrapper objects, even on modern JVMs. Even so, wrapper classes are a good starting point for talking about value types. If there were a set of structural rules and restrictions which would prevent value-unsafe operations on value types, wrapper classes would provide a good notation for defining value types. This note attempts to define such rules and restrictions. Let’s Start Coding Now it is time to look at some real code. Here is a definition, written in Java, of a complex number value type. @ValueSafe public final class Complex implements java.io.Serializable {     // immutable component structure:     public final double re, im;     private Complex(double re, double im) {         this.re = re; this.im = im;     }     // interoperability methods:     public String toString() { return "Complex("+re+","+im+")"; }     public List<Double> asList() { return Arrays.asList(re, im); }     public boolean equals(Complex c) {         return re == c.re && im == c.im;     }     public boolean equals(@ValueSafe Object x) {         return x instanceof Complex && equals((Complex) x);     }     public int hashCode() {         return 31*Double.valueOf(re).hashCode()                 + Double.valueOf(im).hashCode();     }     // factory methods:     public static Complex valueOf(double re, double im) {         return new Complex(re, im);     }     public Complex changeRe(double re2) { return valueOf(re2, im); }     public Complex changeIm(double im2) { return valueOf(re, im2); }     public static Complex cast(@ValueSafe Object x) {         return x == null ? ZERO : (Complex) x;     }     // utility methods and constants:     public Complex plus(Complex c)  { return new Complex(re+c.re, im+c.im); }     public Complex minus(Complex c) { return new Complex(re-c.re, im-c.im); }     public double abs() { return Math.sqrt(re*re + im*im); }     public static final Complex PI = valueOf(Math.PI, 0.0);     public static final Complex ZERO = valueOf(0.0, 0.0); } This is not a minimal definition, because it includes some utility methods and other optional parts.  The essential elements are as follows: The class is marked as a value type with an annotation. The class is final, because it does not make sense to create subclasses of value types. The fields of the class are all non-private and final.  (I.e., the type is immutable and structurally transparent.) From the supertype Object, all public non-final methods are overridden. The constructor is private. Beyond these bare essentials, we can observe the following features in this example, which are likely to be typical of all value types: One or more factory methods are responsible for value creation, including a component-wise valueOf method. There are utility methods for complex arithmetic and instance creation, such as plus and changeIm. There are static utility constants, such as PI. The type is serializable, using the default mechanisms. There are methods for converting to and from dynamically typed references, such as asList and cast. The Rules In order to use value types properly, the programmer must avoid value-unsafe operations.  A helpful Java compiler should issue errors (or at least warnings) for code which provably applies value-unsafe operations, and should issue warnings for code which might be correct but does not provably avoid value-unsafe operations.  No such compilers exist today, but to simplify our account here, we will pretend that they do exist. A value-safe type is any class, interface, or type parameter marked with the @ValueSafe annotation, or any subtype of a value-safe type.  If a value-safe class is marked final, it is in fact a value type.  All other value-safe classes must be abstract.  The non-static fields of a value class must be non-public and final, and all its constructors must be private. Under the above rules, a standard interface could be helpful to define value types like Complex.  Here is an example: @ValueSafe public interface ValueType extends java.io.Serializable {     // All methods listed here must get redefined.     // Definitions must be value-safe, which means     // they may depend on component values only.     List<? extends Object> asList();     int hashCode();     boolean equals(@ValueSafe Object c);     String toString(); } //@ValueSafe inherited from supertype: public final class Complex implements ValueType { … The main advantage of such a conventional interface is that (unlike an annotation) it is reified in the runtime type system.  It could appear as an element type or parameter bound, for facilities which are designed to work on value types only.  More broadly, it might assist the JVM to perform dynamic enforcement of the rules for value types. Besides types, the annotation @ValueSafe can mark fields, parameters, local variables, and methods.  (This is redundant when the type is also value-safe, but may be useful when the type is Object or another supertype of a value type.)  Working forward from these annotations, an expression E is defined as value-safe if it satisfies one or more of the following: The type of E is a value-safe type. E names a field, parameter, or local variable whose declaration is marked @ValueSafe. E is a call to a method whose declaration is marked @ValueSafe. E is an assignment to a value-safe variable, field reference, or array reference. E is a cast to a value-safe type from a value-safe expression. E is a conditional expression E0 ? E1 : E2, and both E1 and E2 are value-safe. Assignments to value-safe expressions and initializations of value-safe names must take their values from value-safe expressions. A value-safe expression may not be the subject of a value-unsafe operation.  In particular, it cannot be synchronized on, nor can it be compared with the “==” operator, not even with a null or with another value-safe type. In a program where all of these rules are followed, no value-type value will be subject to a value-unsafe operation.  Thus, the prime axiom of value types will be satisfied, that no two value type will be distinguishable as long as their component values are equal. More Code To illustrate these rules, here are some usage examples for Complex: Complex pi = Complex.valueOf(Math.PI, 0); Complex zero = pi.changeRe(0);  //zero = pi; zero.re = 0; ValueType vtype = pi; @SuppressWarnings("value-unsafe")   Object obj = pi; @ValueSafe Object obj2 = pi; obj2 = new Object();  // ok List<Complex> clist = new ArrayList<Complex>(); clist.add(pi);  // (ok assuming List.add param is @ValueSafe) List<ValueType> vlist = new ArrayList<ValueType>(); vlist.add(pi);  // (ok) List<Object> olist = new ArrayList<Object>(); olist.add(pi);  // warning: "value-unsafe" boolean z = pi.equals(zero); boolean z1 = (pi == zero);  // error: reference comparison on value type boolean z2 = (pi == null);  // error: reference comparison on value type boolean z3 = (pi == obj2);  // error: reference comparison on value type synchronized (pi) { }  // error: synch of value, unpredictable result synchronized (obj2) { }  // unpredictable result Complex qq = pi; qq = null;  // possible NPE; warning: “null-unsafe" qq = (Complex) obj;  // warning: “null-unsafe" qq = Complex.cast(obj);  // OK @SuppressWarnings("null-unsafe")   Complex empty = null;  // possible NPE qq = empty;  // possible NPE (null pollution) The Payoffs It follows from this that either the JVM or the java compiler can replace boxed value-type values with unboxed ones, without affecting normal computations.  Fields and variables of value types can be split into their unboxed components.  Non-static methods on value types can be transformed into static methods which take the components as value parameters. Some common questions arise around this point in any discussion of value types. Why burden the programmer with all these extra rules?  Why not detect programs automagically and perform unboxing transparently?  The answer is that it is easy to break the rules accidently unless they are agreed to by the programmer and enforced.  Automatic unboxing optimizations are tantalizing but (so far) unreachable ideal.  In the current state of the art, it is possible exhibit benchmarks in which automatic unboxing provides the desired effects, but it is not possible to provide a JVM with a performance model that assures the programmer when unboxing will occur.  This is why I’m writing this note, to enlist help from, and provide assurances to, the programmer.  Basically, I’m shooting for a good set of user-supplied “pragmas” to frame the desired optimization. Again, the important thing is that the unboxing must be done reliably, or else programmers will have no reason to work with the extra complexity of the value-safety rules.  There must be a reasonably stable performance model, wherein using a value type has approximately the same performance characteristics as writing the unboxed components as separate Java variables. There are some rough corners to the present scheme.  Since Java fields and array elements are initialized to null, value-type computations which incorporate uninitialized variables can produce null pointer exceptions.  One workaround for this is to require such variables to be null-tested, and the result replaced with a suitable all-zero value of the value type.  That is what the “cast” method does above. Generically typed APIs like List<T> will continue to manipulate boxed values always, at least until we figure out how to do reification of generic type instances.  Use of such APIs will elicit warnings until their type parameters (and/or relevant members) are annotated or typed as value-safe.  Retrofitting List<T> is likely to expose flaws in the present scheme, which we will need to engineer around.  Here are a couple of first approaches: public interface java.util.List<@ValueSafe T> extends Collection<T> { … public interface java.util.List<T extends Object|ValueType> extends Collection<T> { … (The second approach would require disjunctive types, in which value-safety is “contagious” from the constituent types.) With more transformations, the return value types of methods can also be unboxed.  This may require significant bytecode-level transformations, and would work best in the presence of a bytecode representation for multiple value groups, which I have proposed elsewhere under the title “Tuples in the VM”. But for starters, the JVM can apply this transformation under the covers, to internally compiled methods.  This would give a way to express multiple return values and structured return values, which is a significant pain-point for Java programmers, especially those who work with low-level structure types favored by modern vector and graphics processors.  The lack of multiple return values has a strong distorting effect on many Java APIs. Even if the JVM fails to unbox a value, there is still potential benefit to the value type.  Clustered computing systems something have copy operations (serialization or something similar) which apply implicitly to command operands.  When copying JVM objects, it is extremely helpful to know when an object’s identity is important or not.  If an object reference is a copied operand, the system may have to create a proxy handle which points back to the original object, so that side effects are visible.  Proxies must be managed carefully, and this can be expensive.  On the other hand, value types are exactly those types which a JVM can “copy and forget” with no downside. Array types are crucial to bulk data interfaces.  (As data sizes and rates increase, bulk data becomes more important than scalar data, so arrays are definitely accompanying us into the future of computing.)  Value types are very helpful for adding structure to bulk data, so a successful value type mechanism will make it easier for us to express richer forms of bulk data. Unboxing arrays (i.e., arrays containing unboxed values) will provide better cache and memory density, and more direct data movement within clustered or heterogeneous computing systems.  They require the deepest transformations, relative to today’s JVM.  There is an impedance mismatch between value-type arrays and Java’s covariant array typing, so compromises will need to be struck with existing Java semantics.  It is probably worth the effort, since arrays of unboxed value types are inherently more memory-efficient than standard Java arrays, which rely on dependent pointer chains. It may be sufficient to extend the “value-safe” concept to array declarations, and allow low-level transformations to change value-safe array declarations from the standard boxed form into an unboxed tuple-based form.  Such value-safe arrays would not be convertible to Object[] arrays.  Certain connection points, such as Arrays.copyOf and System.arraycopy might need additional input/output combinations, to allow smooth conversion between arrays with boxed and unboxed elements. Alternatively, the correct solution may have to wait until we have enough reification of generic types, and enough operator overloading, to enable an overhaul of Java arrays. Implicit Method Definitions The example of class Complex above may be unattractively complex.  I believe most or all of the elements of the example class are required by the logic of value types. If this is true, a programmer who writes a value type will have to write lots of error-prone boilerplate code.  On the other hand, I think nearly all of the code (except for the domain-specific parts like plus and minus) can be implicitly generated. Java has a rule for implicitly defining a class’s constructor, if no it defines no constructors explicitly.  Likewise, there are rules for providing default access modifiers for interface members.  Because of the highly regular structure of value types, it might be reasonable to perform similar implicit transformations on value types.  Here’s an example of a “highly implicit” definition of a complex number type: public class Complex implements ValueType {  // implicitly final     public double re, im;  // implicitly public final     //implicit methods are defined elementwise from te fields:     //  toString, asList, equals(2), hashCode, valueOf, cast     //optionally, explicit methods (plus, abs, etc.) would go here } In other words, with the right defaults, a simple value type definition can be a one-liner.  The observant reader will have noticed the similarities (and suitable differences) between the explicit methods above and the corresponding methods for List<T>. Another way to abbreviate such a class would be to make an annotation the primary trigger of the functionality, and to add the interface(s) implicitly: public @ValueType class Complex { … // implicitly final, implements ValueType (But to me it seems better to communicate the “magic” via an interface, even if it is rooted in an annotation.) Implicitly Defined Value Types So far we have been working with nominal value types, which is to say that the sequence of typed components is associated with a name and additional methods that convey the intention of the programmer.  A simple ordered pair of floating point numbers can be variously interpreted as (to name a few possibilities) a rectangular or polar complex number or Cartesian point.  The name and the methods convey the intended meaning. But what if we need a truly simple ordered pair of floating point numbers, without any further conceptual baggage?  Perhaps we are writing a method (like “divideAndRemainder”) which naturally returns a pair of numbers instead of a single number.  Wrapping the pair of numbers in a nominal type (like “QuotientAndRemainder”) makes as little sense as wrapping a single return value in a nominal type (like “Quotient”).  What we need here are structural value types commonly known as tuples. For the present discussion, let us assign a conventional, JVM-friendly name to tuples, roughly as follows: public class java.lang.tuple.$DD extends java.lang.tuple.Tuple {      double $1, $2; } Here the component names are fixed and all the required methods are defined implicitly.  The supertype is an abstract class which has suitable shared declarations.  The name itself mentions a JVM-style method parameter descriptor, which may be “cracked” to determine the number and types of the component fields. The odd thing about such a tuple type (and structural types in general) is it must be instantiated lazily, in response to linkage requests from one or more classes that need it.  The JVM and/or its class loaders must be prepared to spin a tuple type on demand, given a simple name reference, $xyz, where the xyz is cracked into a series of component types.  (Specifics of naming and name mangling need some tasteful engineering.) Tuples also seem to demand, even more than nominal types, some support from the language.  (This is probably because notations for non-nominal types work best as combinations of punctuation and type names, rather than named constructors like Function3 or Tuple2.)  At a minimum, languages with tuples usually (I think) have some sort of simple bracket notation for creating tuples, and a corresponding pattern-matching syntax (or “destructuring bind”) for taking tuples apart, at least when they are parameter lists.  Designing such a syntax is no simple thing, because it ought to play well with nominal value types, and also with pre-existing Java features, such as method parameter lists, implicit conversions, generic types, and reflection.  That is a task for another day. Other Use Cases Besides complex numbers and simple tuples there are many use cases for value types.  Many tuple-like types have natural value-type representations. These include rational numbers, point locations and pixel colors, and various kinds of dates and addresses. Other types have a variable-length ‘tail’ of internal values. The most common example of this is String, which is (mathematically) a sequence of UTF-16 character values. Similarly, bit vectors, multiple-precision numbers, and polynomials are composed of sequences of values. Such types include, in their representation, a reference to a variable-sized data structure (often an array) which (somehow) represents the sequence of values. The value type may also include ’header’ information. Variable-sized values often have a length distribution which favors short lengths. In that case, the design of the value type can make the first few values in the sequence be direct ’header’ fields of the value type. In the common case where the header is enough to represent the whole value, the tail can be a shared null value, or even just a null reference. Note that the tail need not be an immutable object, as long as the header type encapsulates it well enough. This is the case with String, where the tail is a mutable (but never mutated) character array. Field types and their order must be a globally visible part of the API.  The structure of the value type must be transparent enough to have a globally consistent unboxed representation, so that all callers and callees agree about the type and order of components  that appear as parameters, return types, and array elements.  This is a trade-off between efficiency and encapsulation, which is forced on us when we remove an indirection enjoyed by boxed representations.  A JVM-only transformation would not care about such visibility, but a bytecode transformation would need to take care that (say) the components of complex numbers would not get swapped after a redefinition of Complex and a partial recompile.  Perhaps constant pool references to value types need to declare the field order as assumed by each API user. This brings up the delicate status of private fields in a value type.  It must always be possible to load, store, and copy value types as coordinated groups, and the JVM performs those movements by moving individual scalar values between locals and stack.  If a component field is not public, what is to prevent hostile code from plucking it out of the tuple using a rogue aload or astore instruction?  Nothing but the verifier, so we may need to give it more smarts, so that it treats value types as inseparable groups of stack slots or locals (something like long or double). My initial thought was to make the fields always public, which would make the security problem moot.  But public is not always the right answer; consider the case of String, where the underlying mutable character array must be encapsulated to prevent security holes.  I believe we can win back both sides of the tradeoff, by training the verifier never to split up the components in an unboxed value.  Just as the verifier encapsulates the two halves of a 64-bit primitive, it can encapsulate the the header and body of an unboxed String, so that no code other than that of class String itself can take apart the values. Similar to String, we could build an efficient multi-precision decimal type along these lines: public final class DecimalValue extends ValueType {     protected final long header;     protected private final BigInteger digits;     public DecimalValue valueOf(int value, int scale) {         assert(scale >= 0);         return new DecimalValue(((long)value << 32) + scale, null);     }     public DecimalValue valueOf(long value, int scale) {         if (value == (int) value)             return valueOf((int)value, scale);         return new DecimalValue(-scale, new BigInteger(value));     } } Values of this type would be passed between methods as two machine words. Small values (those with a significand which fits into 32 bits) would be represented without any heap data at all, unless the DecimalValue itself were boxed. (Note the tension between encapsulation and unboxing in this case.  It would be better if the header and digits fields were private, but depending on where the unboxing information must “leak”, it is probably safer to make a public revelation of the internal structure.) Note that, although an array of Complex can be faked with a double-length array of double, there is no easy way to fake an array of unboxed DecimalValues.  (Either an array of boxed values or a transposed pair of homogeneous arrays would be reasonable fallbacks, in a current JVM.)  Getting the full benefit of unboxing and arrays will require some new JVM magic. Although the JVM emphasizes portability, system dependent code will benefit from using machine-level types larger than 64 bits.  For example, the back end of a linear algebra package might benefit from value types like Float4 which map to stock vector types.  This is probably only worthwhile if the unboxing arrays can be packed with such values. More Daydreams A more finely-divided design for dynamic enforcement of value safety could feature separate marker interfaces for each invariant.  An empty marker interface Unsynchronizable could cause suitable exceptions for monitor instructions on objects in marked classes.  More radically, a Interchangeable marker interface could cause JVM primitives that are sensitive to object identity to raise exceptions; the strangest result would be that the acmp instruction would have to be specified as raising an exception. @ValueSafe public interface ValueType extends java.io.Serializable,         Unsynchronizable, Interchangeable { … public class Complex implements ValueType {     // inherits Serializable, Unsynchronizable, Interchangeable, @ValueSafe     … It seems possible that Integer and the other wrapper types could be retro-fitted as value-safe types.  This is a major change, since wrapper objects would be unsynchronizable and their references interchangeable.  It is likely that code which violates value-safety for wrapper types exists but is uncommon.  It is less plausible to retro-fit String, since the prominent operation String.intern is often used with value-unsafe code. We should also reconsider the distinction between boxed and unboxed values in code.  The design presented above obscures that distinction.  As another thought experiment, we could imagine making a first class distinction in the type system between boxed and unboxed representations.  Since only primitive types are named with a lower-case initial letter, we could define that the capitalized version of a value type name always refers to the boxed representation, while the initial lower-case variant always refers to boxed.  For example: complex pi = complex.valueOf(Math.PI, 0); Complex boxPi = pi;  // convert to boxed myList.add(boxPi); complex z = myList.get(0);  // unbox Such a convention could perhaps absorb the current difference between int and Integer, double and Double. It might also allow the programmer to express a helpful distinction among array types. As said above, array types are crucial to bulk data interfaces, but are limited in the JVM.  Extending arrays beyond the present limitations is worth thinking about; for example, the Maxine JVM implementation has a hybrid object/array type.  Something like this which can also accommodate value type components seems worthwhile.  On the other hand, does it make sense for value types to contain short arrays?  And why should random-access arrays be the end of our design process, when bulk data is often sequentially accessed, and it might make sense to have heterogeneous streams of data as the natural “jumbo” data structure.  These considerations must wait for another day and another note. More Work It seems to me that a good sequence for introducing such value types would be as follows: Add the value-safety restrictions to an experimental version of javac. Code some sample applications with value types, including Complex and DecimalValue. Create an experimental JVM which internally unboxes value types but does not require new bytecodes to do so.  Ensure the feasibility of the performance model for the sample applications. Add tuple-like bytecodes (with or without generic type reification) to a major revision of the JVM, and teach the Java compiler to switch in the new bytecodes without code changes. A staggered roll-out like this would decouple language changes from bytecode changes, which is always a convenient thing. A similar investigation should be applied (concurrently) to array types.  In this case, it seems to me that the starting point is in the JVM: Add an experimental unboxing array data structure to a production JVM, perhaps along the lines of Maxine hybrids.  No bytecode or language support is required at first; everything can be done with encapsulated unsafe operations and/or method handles. Create an experimental JVM which internally unboxes value types but does not require new bytecodes to do so.  Ensure the feasibility of the performance model for the sample applications. Add tuple-like bytecodes (with or without generic type reification) to a major revision of the JVM, and teach the Java compiler to switch in the new bytecodes without code changes. That’s enough musing me for now.  Back to work!

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