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  • MailServer Setting

    - by Ashian
    Hi I have a mail server on windows 2003 ( MailEnable) I setup mail server to authonticate users before sending mail. (This mail server requires authentication when attempting to send to a non-local e-mail address) but from yesterday , without change any setting I got many Message Delivery Delay from mail server for email address that I never try to sending email: I afraid that I someone try to sending Spam from my mail server,How can I check this possiblity ? and fix the problem. Thanks MailEnable: Message delivery has been delayed. Message is waiting at *.info for delivery to mailin-03.mx.aol.com. The message will be retried for another 29 hours. Reason: Mail Server for aol.com could not accept your email at this time. MailEnable will keep trying to deliver this message and will notify you of any progress. The remote mail server returned the error: 421-: (DNS:NR)

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  • Puppet: Could not find init script for 'squid'

    - by chris
    I'm using Puppet to install ufdbGuard which requires Squid 2.7 (which is correctly installed and working properly). Here is the relevant class: class pns_client::squid { package { 'squid': ensure => present, before => File['/etc/squid/squid.conf'], } if $::ufdbguard_installed == "true" { $squidconf = 'puppet:///modules/pns_client/squid.conf_ufdbguard' } else { $squidconf = 'puppet:///modules/pns_client/squid.conf' } notify{$squidconf:} file { '/etc/squid/squid.conf': ensure => file, mode => 644, source => $squidconf, } service { 'squid': ensure => running, enable => true, hasrestart => true, hasstatus => true, subscribe => File['/etc/squid/squid.conf'], } } When running, I get this error: err: /Stage[main]/Pns_client::Squid/Service[squid]: Could not evaluate: Could not find init script for 'squid' This happens on all freshly-installed Debian 6 and Unbuntu 10.04/11.04 machines. Any ideas?

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  • Best way to export an icon from photoshop?

    - by Mudtail
    Hi, I'm writing a program to notify me of new email. It's mostly complete, I'm just working on the notifyicon code now. It's supposed to display the usual application icon with a box containing the count of unread emails inside it. I created icons for this in photoshop, exported them as 16x16 transparent PNGs, then converted them into windows ico files using ConvertIcon.com. Given that the image was 16x16 and the WinXP system tray uses 16x16 icons, I would assume the images would work. HOWEVER, when I start the application and get an email, the icon's all blurry: http://cyndle.com/bPJ7

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  • Can I make Puppet's module-to-file mapping to start searching at the top of the modules tree?

    - by John Siracusa
    Consider these two Puppet module files: # File modules/a/manifests/b/c.pp class a::b::c { include b::c } # File modules/b/manifests/c.pp class b::c { notify { "In b::c": } } It seems that when Puppet hits the include b::c directive in class a::b::c, it searches for the corresponding *.pp file by looking backwards from the current class and decides that it find the correct file located at ../../b/c.pp. In other words, it resolves b::c to the same *.pp file that the include b::c statement appears in: modules/a/manifests/b/c.pp I expected it (and would like it) to instead find and load the file modules/b/manifests/c.pp. Is there a way to make Puppet do this? If not, it seems to me that module names may not contain any other module names anywhere within them, which is a pretty surprising restriction.

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  • Stop Windows 7 from forcefully shutting itself down when waiting to update

    - by Kenneth
    I have had this happen to me twice now. I'll be in the middle of working on something that has resulted in me not rebooting my machine for several days. If Windows 7 is waiting to install updates it'll eventually get to a point where it forces a restart to install the updates. The problem is that it doesn't notify me or tell me that its going to do this and I've lost work as a result and most recently had a VM become corrupt and unusable. Is there a way to at least get it to prompt me before doing this? It used to...

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  • Configure akamai to ignore favicon errors [on hold]

    - by Aki
    We have hosted our services through akamai and have configured and alert in akamai to notify us of 404 errors. We dont want to serve favicon from our services (as they are rest webservices which are not consumed by humans, hence no point in serving favicons). But whenever thesewebservices are accessed from a browser the browser would send a request for the favicon, which ends up being logged as a 404 and akamai sends us an alert for this. Is there a way to configure akamai in a way that it understands that favicon 404s should not contribute to the alert?

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  • How to really change programmatically ip address without reboot (with no connection too)?

    - by DmitryI
    Really, I tried everything, and there is no solution that works for me. WMI - everything perfect, but I can't change ip address when there is no connection. O_o Are you joking me? How can I make a connection without correct Ip-address? IPHelper - not doing anything. Just adding address to the table. Not work after reboot. netsh - the stupid way I think, but ok, if you don't no another ways you can try. Before you will know, that network adapters name can contain international characters. Did someone know how it works actually, I mean inside? Registry - working after reboot. I don't want to reboot. May be someone know how to notify about reg entries changes?

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  • Encrypt backups with GPG to multiple tapes

    - by Dan
    Currently, I use tar to write my backups (ntbackup files) to a tape drive fed by an autoloader. Ex: tar -F /root/advancetape -cvf /dev/st0 *.bkf (/root/advancetape just has the logic to advance to the next tape if there is one available or notify to swap the tapes out) I was recently handed the requirement to encrypt our tape backups. I can easily encrypt the data with no problems using GPG. The problem I'm having is how do I write this to multiple tapes with the same logic that tar uses to advance the tapes once the current one is filled? I cannot write the encrypted file to disk first (2+TB). As far as I can tell, tar will not accept binary input from stdin (it's looking for file names). Any ideas? :(

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  • Is there any way to properly display negative time spans in Excel?

    - by Pepor
    Is there any way to make Excel show a negative time span? If I subtract two time values (say, when subtracting the actual amount of time spent on something from the amount of time planned for it) and the result is negative, Excel just fills the result cell with hashes to notify me that the result cannot be displayed as a time value. Even OpenOffice.org Calc and Google Spreadsheets can display negative time values. Is there a way to work around that issue by using conditional formatting? I really don't want to create some workaround by calculating the hours and minutes myself or anything like that.

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  • Utility for notifying a user that their roaming profile is getting too large to copy before shutdown?

    - by leeand00
    My users are having an issue with their roaming profiles getting too large and then their roaming profile is lost. I believe this is because this is because they are storing too much in their roaming profiles. Is there a program that can be installed in Windows, that will: Listen for a logoff event Check the size of their Roaming Profile against a size limit I set... If the roaming profile is too big, it will notify the user that they have to decrease the size of the profile. Does a program like this exist or does it need to written?

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  • Installed Ubuntu 11.10, getting hard disk health warnings

    - by Brad
    I'm getting hard disk health problem warnings... When I click the "examine" button the disk utility pops up. None of my drives are reporting any major issues, and the very first drive doesn't even have a SMART button. I don't really care if one of the drives is crashing, I've got everything backed up, but I just want to know how to stop these god forsaken message boxes from popping up randomly. I have already gone into the Disk Utility and checked "do not notify me if this drive is failing" on all of them except the one that doesn't have the SMART button. I've googled about as much as I can for one day.

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  • How to schedule download of windows 7 updates?

    - by atoMerz
    To put it short: I'd like to schedule my windows updates to start/stop at certain times of day. How can I do this? More explanation: This is because my internet traffic is limited by ISP and it's free only during a specific period throughout the day (2:00am-7:00am). I've set windows update setting to check for updates but notify me before downloading in order to prevent it from automatically using up my traffic. But then I have to manually tell it when to start downloading. I obviously don't want to stay up that late just to push a button. So again, how can I schedule windows updates to start/stop at specified times?

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  • Require file for mount and also update the file after mount?

    - by Andy Shinn
    I am trying to make sure a directory exists for a mount and then also update the permissions of that directory after the mount happens. I am receiving the following error: err: Failed to apply catalog: Cannot alias File[pre_eos_mount] to ["/var/tmp/eos"] at /etc/puppet/modules/mymodule/manifests/eos.pp:29; resource ["File", "/var/tmp/eos"] already declared at /etc/puppet/modules/mymodule/manifests/eos.pp:47 I would like to do something like this: file { $eos_mount : ensure = 'directory', mode = '1777', owner = 'root', group = 'root', } mount { $eos_mount : ensure = 'mounted', device = $lv_device, fstype = $fstype, options = 'defaults,noatime,nodiratime', require = File[$eos_mount], notify = File['post_eos'], } file { 'post_eos' : path = $eos_mount, ensure = 'directory', mode = '1777', owner = 'root', group = 'root', } What is a way to ensure permissions of a folder after it has been mounted?

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  • Warning popups that direct to 3rd party sites

    - by Kingamoon
    Lately, I've been getting warning popups on my browser (latest version of Chromium) that notify me that my Java version of current browser is outdated and needs to be updated. What's alarming to me is that it sends me to some sites I've never heard of like Malest.com. When I block a site, it redirects me to a different one. I don't know how to track what's causing these alerts. I ran Microsoft Security Essential and it found nothing. Any suggestions on what to do to nail down this irritating problem?

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  • How to extend a file definition from an existing module in the node?

    - by c33s
    I use an older version of the example42 mysql module, which defines the mysql.conf file but not its content. Mmy goal is to just include the mysql module and add a content definition in the node. class mysql { ... file { "mysql.conf": path => "${mysql::params::configfile}", mode => "${mysql::params::configfile_mode}", owner => "${mysql::params::configfile_owner}", group => "${mysql::params::configfile_group}", ensure => present, require => Package["mysql"], notify => Service["mysql"], } ... } node xyz { include mysql File["mysql.conf"] { content => template("mymodule/mysql.conf.erb")} } The above code produces a "Only subclasses can override parameters" What is the correct way to just add a content definition to an existing file definition?

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  • Lists NotifyPropertyChanging

    - by Carlo
    Well BindingList and ObservableCollection work great to keep data updated and to notify when one of it's objects has changed. However, when notifying a property is about to change, I think these options are not very good. What I have to do right now to solve this (and I warn this is not elegant AT ALL), is to implement INotifyPropertyChanging on the list's type object and then tie that to the object that holds the list PropertyChanging event, or something like the following: // this object will be the type of the BindingList public class SomeObject : INotifyPropertyChanging, INotifyPropertyChanged { private int _intProperty = 0; private string _strProperty = String.Empty; public int IntProperty { get { return this._intProperty; } set { if (this._intProperty != value) { NotifyPropertyChanging("IntProperty"); this._intProperty = value; NotifyPropertyChanged("IntProperty"); } } } public string StrProperty { get { return this._strProperty; } set { if (this._strProperty != value) { NotifyPropertyChanging("StrProperty"); this._strProperty = value; NotifyPropertyChanged("StrProperty"); } } } #region INotifyPropertyChanging Members public event PropertyChangingEventHandler PropertyChanging; #endregion #region INotifyPropertyChanged Members public event PropertyChangedEventHandler PropertyChanged; #endregion public void NotifyPropertyChanging(string propertyName) { if (this.PropertyChanging != null) PropertyChanging(this, new PropertyChangingEventArgs(propertyName)); } public void NotifyPropertyChanged(string propertyName) { if (this.PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs(propertyName)); } } public class ObjectThatHoldsTheList : INotifyPropertyChanging, INotifyPropertyChanged { public BindingList<SomeObject> BindingList { get; set; } public ObjectThatHoldsTheList() { this.BindingList = new BindingList<SomeObject>(); } // this helps notifie Changing and Changed on Add private void AddItem(SomeObject someObject) { // this will tie the PropertyChanging and PropertyChanged events of SomeObject to this object // so it gets notifies because the BindingList does not notify PropertyCHANGING someObject.PropertyChanging += new PropertyChangingEventHandler(someObject_PropertyChanging); someObject.PropertyChanged += new PropertyChangedEventHandler(someObject_PropertyChanged); this.NotifyPropertyChanging("BindingList"); this.BindingList.Add(someObject); this.NotifyPropertyChanged("BindingList"); } // this helps notifies Changing and Changed on Delete private void DeleteItem(SomeObject someObject) { if (this.BindingList.IndexOf(someObject) > 0) { // this unlinks the handlers so the garbage collector can clear the objects someObject.PropertyChanging -= new PropertyChangingEventHandler(someObject_PropertyChanging); someObject.PropertyChanged -= new PropertyChangedEventHandler(someObject_PropertyChanged); } this.NotifyPropertyChanging("BindingList"); this.BindingList.Remove(someObject); this.NotifyPropertyChanged("BindingList"); } // this notifies an item in the list is about to change void someObject_PropertyChanging(object sender, PropertyChangingEventArgs e) { NotifyPropertyChanging("BindingList." + e.PropertyName); } // this notifies an item in the list has changed void someObject_PropertyChanged(object sender, PropertyChangedEventArgs e) { NotifyPropertyChanged("BindingList." + e.PropertyName); } #region INotifyPropertyChanging Members public event PropertyChangingEventHandler PropertyChanging; #endregion #region INotifyPropertyChanged Members public event PropertyChangedEventHandler PropertyChanged; #endregion public void NotifyPropertyChanging(string propertyName) { if (this.PropertyChanging != null) PropertyChanging(this, new PropertyChangingEventArgs(propertyName)); } public void NotifyPropertyChanged(string propertyName) { if (this.PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs(propertyName)); } } Sorry, I know this is a lot of code, which takes me back to my main point IT'S A LOT OF CODE to implement this. So my question is, does anyone know a better, shorter, more elegant solution? Thanks for your time and suggestions.

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  • Synchronizing issue: I want the main thread to be run before another thread but it sometimes doesn´t

    - by Rox
    I have done my own small concurrency framework (just for learning purposes) inspired by the java.util.concurrency package. This is about the Callable/Future mechanism. My code below is the whole one and is compilable and very easy to understand. My problem is that sometimes I run into a deadlock where the first thread (the main thread) awaits for a signal from the other thread. But then the other thread has already notified the main thread before the main thread went into waiting state, so the main thread cannot wake up. FutureTask.get() should always be run before FutureTask.run() but sometimes the run() method (which is called by new thread) runs before the get() method (which is called by main thread). I don´t know how I can prevent that. This is a pseudo code of how I want the two threads to be run. //From main thread: Executor.submit().get() (in get() the main thread waits for new thread to notify) ->submit() calls Executor.execute(FutureTask object) -> execute() starts new thread -> new thread shall notify `main thread` I cannot understand how the new thread can start up and run faster than the main thread that actually starts the new thread. Main.java: public class Main { public static void main(String[] args) { new ExecutorServiceExample(); } public Main() { ThreadExecutor executor = new ThreadExecutor(); Integer i = executor.submit(new Callable<Integer>() { @Override public Integer call() { return 10; } }).get(); System.err.println("Value: "+i); } } ThreadExecutor.java: public class ThreadExecutor { public ThreadExecutor() {} protected <V> RunnableFuture<V> newTaskFor(Callable c) { return new FutureTask<V>(c); } public <V> Future<V> submit(Callable<V> task) { if (task == null) throw new NullPointerException(); RunnableFuture<V> ftask = newTaskFor(task); execute(ftask); return ftask; } public void execute(Runnable r) { new Thread(r).start(); } } FutureTask.java: import java.util.concurrent.locks.Condition; import java.util.concurrent.locks.ReentrantLock; import java.util.logging.Level; import java.util.logging.Logger; public class FutureTask<V> implements RunnableFuture<V> { private Callable<V> callable; private volatile V result; private ReentrantLock lock = new ReentrantLock(); private Condition condition = lock.newCondition(); public FutureTask(Callable callable) { if (callable == null) throw new NullPointerException(); this.callable = callable; } @Override public void run() { acquireLock(); System.err.println("RUN"+Thread.currentThread().getName()); V v = this.callable.call(); set(v); condition.signal(); releaseLock(); } @Override public V get() { acquireLock(); System.err.println("GET "+Thread.currentThread().getName()); try { condition.await(); } catch (InterruptedException ex) { Logger.getLogger(FutureTask.class.getName()).log(Level.SEVERE, null, ex); } releaseLock(); return this.result; } public void set(V v) { this.result = v; } private void acquireLock() { lock.lock(); } private void releaseLock() { lock.unlock(); } } And the interfaces: public interface RunnableFuture<V> extends Runnable, Future<V> { @Override void run(); } public interface Future<V> { V get(); } public interface Callable<V> { V call(); }

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  • Unnecessary Java context switches

    - by Paul Morrison
    I have a network of Java Threads (Flow-Based Programming) communicating via fixed-capacity channels - running under WindowsXP. What we expected, based on our experience with "green" threads (non-preemptive), would be that threads would switch context less often (thus reducing CPU time) if the channels were made bigger. However, we found that increasing channel size does not make any difference to the run time. What seems to be happening is that Java decides to switch threads even though channels aren't full or empty (i.e. even though a thread doesn't have to suspend), which costs CPU time for no apparent advantage. Also changing Thread priorities doesn't make any observable difference. My question is whether there is some way of persuading Java not to make unnecessary context switches, but hold off switching until it is really necessary to switch threads - is there some way of changing Java's dispatching logic? Or is it reacting to something I didn't pay attention to?! Or are there other asynchronism mechanisms, e.g. Thread factories, Runnable(s), maybe even daemons (!). The answer appears to be non-obvious, as so far none of my correspondents has come up with an answer (including most recently two CS profs). Or maybe I'm missing something that's so obvious that people can't imagine my not knowing it... I've added the send and receive code here - not very elegant, but it seems to work...;-) In case you are wondering, I thought the goLock logic in 'send' might be causing the problem, but removing it temporarily didn't make any difference. I have added the code for send and receive... public synchronized Packet receive() { if (isDrained()) { return null; } while (isEmpty()) { try { wait(); } catch (InterruptedException e) { close(); return null; } if (isDrained()) { return null; } } if (isDrained()) { return null; } if (isFull()) { notifyAll(); // notify other components waiting to send } Packet packet = array[receivePtr]; array[receivePtr] = null; receivePtr = (receivePtr + 1) % array.length; //notifyAll(); // only needed if it was full usedSlots--; packet.setOwner(receiver); if (null == packet.getContent()) { traceFuncs("Received null packet"); } else { traceFuncs("Received: " + packet.toString()); } return packet; } synchronized boolean send(final Packet packet, final OutputPort op) { sender = op.sender; if (isClosed()) { return false; } while (isFull()) { try { wait(); } catch (InterruptedException e) { indicateOneSenderClosed(); return false; } sender = op.sender; } if (isClosed()) { return false; } try { receiver.goLock.lockInterruptibly(); } catch (InterruptedException ex) { return false; } try { packet.clearOwner(); array[sendPtr] = packet; sendPtr = (sendPtr + 1) % array.length; usedSlots++; // move this to here if (receiver.getStatus() == StatusValues.DORMANT || receiver.getStatus() == StatusValues.NOT_STARTED) { receiver.activate(); // start or wake up if necessary } else { notifyAll(); // notify receiver // other components waiting to send to this connection may also get // notified, // but this is handled by while statement } sender = null; Component.network.active = true; } finally { receiver.goLock.unlock(); } return true; }

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  • What's the best-practice way to update an Adapter's underlying data?

    - by skyler
    I'm running into an IllegalStateException updating an underlying List to an Adapter (might be an ArrayAdapter or an extension of BaseAdapter, I don't remember). I do not have or remember the text of the exception at the moment, but it says something to the effect of the List's content changing without the Adapter having been notified of the change. This List /may/ be updated from another thread other than the UI thread (main). After I update this list (adding an item), I call notifyDataSetChanged. The issue seems to be that the Adapter, or ListView attached to the Adapter attempts to update itself before this method is invoked. When this happens, the IllegalStateException is thrown. If I set the ListView's visibility to GONE before the update, then VISIBLE again, no error occurs. But this isn't always practical. I read somewhere that you cannot modify the underlying this from another thread--this would seem to limit an MVC pattern, as with this particular List, I want to add items from different threads. I assumed that as long as I called notifyDataSetChanged() I'd be safe--that the Adapter didn't revisit the underlying List until this method was invoked but this doesn't seem to be the case. I suppose what I'm asking is, can it be safe to update the underlying List from threads other than the UI? Additionally, if I want to modify the data within an Adapter, do I modify the underlying List or the Adapter itself (via its add(), etc. methods). Modifying the data through the Adapter seems wrong. I came across a thread on another site from someone who seems to be having a similar problem to mine: http://osdir.com/ml/Android-Developers/2010-04/msg01199.html (this is from where I grabbed the Visibility.GONE and .VISIBLE idea). To give you a better idea of my particular problem, I'll describe a bit of how my List, Adapter, etc. are set up. I've an object named Queue that contains a LinkedList. Queue extends Observable, and when things are added to its internal list through its methods, I call setChanged() and notifyListeners(). This Queue object can have items added or removed from any number of threads. I have a single "queue view" Activity that contains an Adapter. This Activity, in its onCreate() method, registers an Observer listener to my Queue object. In the Observer's update() method I call notifyDataSetChanged() on the Adapter. I added a lot of log output and determined that when this IllegalStateExcption occurs that my Observer callback was never invoked. So it's as if the Adapter noticed the List's change before the Observer had a chance to notify its Observers, and call my method to notify the Adapter that the contents had changed. So I suppose what I'm asking is, is this a good way to rig-up an Adapter? Is this a problem because I'm updating the Adapter's contents from a thread other than the UI thread? If this is the case, I may have a solution in mind (give the Queue object a Handler to the UI thread when it's created, and make all List modifications using that Handler, but this seems improper). I realize that this is a very open-ended post, but I'm a bit lost on this and would appreciate any comments on what I've written.

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  • External Monitors shut off when Laptop Lid closes

    - by John Lanz
    I have researched the solution... gconftool-2 --type string --set /apps/gnome-power-manager/buttons/lid_ac "nothing" does not fix it. I have two external monitors and when I close my lid the settings are reset and the laptop's monitor is set to the default. Thanks! gsettings list-recursively org.gnome.settings-daemon.plugins.power org.gnome.settings-daemon.plugins.power active true org.gnome.settings-daemon.plugins.power button-hibernate 'nothing' org.gnome.settings-daemon.plugins.power button-power 'nothing' org.gnome.settings-daemon.plugins.power button-sleep 'nothing' org.gnome.settings-daemon.plugins.power button-suspend 'nothing' org.gnome.settings-daemon.plugins.power critical-battery-action 'suspend' org.gnome.settings-daemon.plugins.power idle-brightness 30 org.gnome.settings-daemon.plugins.power idle-dim-ac false org.gnome.settings-daemon.plugins.power idle-dim-battery true org.gnome.settings-daemon.plugins.power idle-dim-time 10 org.gnome.settings-daemon.plugins.power lid-close-ac-action 'nothing' org.gnome.settings-daemon.plugins.power lid-close-battery-action 'nothing' org.gnome.settings-daemon.plugins.power notify-perhaps-recall true org.gnome.settings-daemon.plugins.power percentage-action 2 org.gnome.settings-daemon.plugins.power percentage-critical 3 org.gnome.settings-daemon.plugins.power percentage-low 10 org.gnome.settings-daemon.plugins.power priority 1 org.gnome.settings-daemon.plugins.power sleep-display-ac 600 org.gnome.settings-daemon.plugins.power sleep-display-battery 600 org.gnome.settings-daemon.plugins.power sleep-inactive-ac false org.gnome.settings-daemon.plugins.power sleep-inactive-ac-timeout 0 org.gnome.settings-daemon.plugins.power sleep-inactive-ac-type 'suspend' org.gnome.settings-daemon.plugins.power sleep-inactive-battery true org.gnome.settings-daemon.plugins.power sleep-inactive-battery-timeout 0 org.gnome.settings-daemon.plugins.power sleep-inactive-battery-type 'suspend' org.gnome.settings-daemon.plugins.power time-action 120 org.gnome.settings-daemon.plugins.power time-critical 300 org.gnome.settings-daemon.plugins.power time-low 1200 org.gnome.settings-daemon.plugins.power use-time-for-policy true

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  • C#/.NET Little Wonders: The EventHandler and EventHandler&lt;TEventArgs&gt; delegates

    - by James Michael Hare
    Once again, in this series of posts I look at the parts of the .NET Framework that may seem trivial, but can help improve your code by making it easier to write and maintain. The index of all my past little wonders posts can be found here. In the last two weeks, we examined the Action family of delegates (and delegates in general), and the Func family of delegates and how they can be used to support generic, reusable algorithms and classes. So this week, we are going to look at a handy pair of delegates that can be used to eliminate the need for defining custom delegates when creating events: the EventHandler and EventHandler<TEventArgs> delegates. Events and delegates Before we begin, let’s quickly consider events in .NET.  According to the MSDN: An event in C# is a way for a class to provide notifications to clients of that class when some interesting thing happens to an object. So, basically, you can create an event in a type so that users of that type can subscribe to notifications of things of interest.  How is this different than some of the delegate programming that we talked about in the last two weeks?  Well, you can think of an event as a special access modifier on a delegate.  Some differences between the two are: Events are a special access case of delegates They behave much like delegates instances inside the type they are declared in, but outside of that type they can only be (un)subscribed to. Events can specify add/remove behavior explicitly If you want to do additional work when someone subscribes or unsubscribes to an event, you can specify the add and remove actions explicitly. Events have access modifiers, but these only specify the access level of those who can (un)subscribe A public event, for example, means anyone can (un)subscribe, but it does not mean that anyone can raise (invoke) the event directly.  Events can only be raised by the type that contains them In contrast, if a delegate is visible, it can be invoked outside of the object (not even in a sub-class!). Events tend to be for notifications only, and should be treated as optional Semantically speaking, events typically don’t perform work on the the class directly, but tend to just notify subscribers when something of note occurs. My basic rule-of-thumb is that if you are just wanting to notify any listeners (who may or may not care) that something has happened, use an event.  However, if you want the caller to provide some function to perform to direct the class about how it should perform work, make it a delegate. Declaring events using custom delegates To declare an event in a type, we simply use the event keyword and specify its delegate type.  For example, let’s say you wanted to create a new TimeOfDayTimer that triggers at a given time of the day (as opposed to on an interval).  We could write something like this: 1: public delegate void TimeOfDayHandler(object source, ElapsedEventArgs e); 2:  3: // A timer that will fire at time of day each day. 4: public class TimeOfDayTimer : IDisposable 5: { 6: // Event that is triggered at time of day. 7: public event TimeOfDayHandler Elapsed; 8:  9: // ... 10: } The first thing to note is that the event is a delegate type, which tells us what types of methods may subscribe to it.  The second thing to note is the signature of the event handler delegate, according to the MSDN: The standard signature of an event handler delegate defines a method that does not return a value, whose first parameter is of type Object and refers to the instance that raises the event, and whose second parameter is derived from type EventArgs and holds the event data. If the event does not generate event data, the second parameter is simply an instance of EventArgs. Otherwise, the second parameter is a custom type derived from EventArgs and supplies any fields or properties needed to hold the event data. So, in a nutshell, the event handler delegates should return void and take two parameters: An object reference to the object that raised the event. An EventArgs (or a subclass of EventArgs) reference to event specific information. Even if your event has no additional information to provide, you are still expected to provide an EventArgs instance.  In this case, feel free to pass the EventArgs.Empty singleton instead of creating new instances of EventArgs (to avoid generating unneeded memory garbage). The EventHandler delegate Because many events have no additional information to pass, and thus do not require custom EventArgs, the signature of the delegates for subscribing to these events is typically: 1: // always takes an object and an EventArgs reference 2: public delegate void EventHandler(object sender, EventArgs e) It would be insane to recreate this delegate for every class that had a basic event with no additional event data, so there already exists a delegate for you called EventHandler that has this very definition!  Feel free to use it to define any events which supply no additional event information: 1: public class Cache 2: { 3: // event that is raised whenever the cache performs a cleanup 4: public event EventHandler OnCleanup; 5:  6: // ... 7: } This will handle any event with the standard EventArgs (no additional information).  But what of events that do need to supply additional information?  Does that mean we’re out of luck for subclasses of EventArgs?  That’s where the generic for of EventHandler comes into play… The generic EventHandler<TEventArgs> delegate Starting with the introduction of generics in .NET 2.0, we have a generic delegate called EventHandler<TEventArgs>.  Its signature is as follows: 1: public delegate void EventHandler<TEventArgs>(object sender, TEventArgs e) 2: where TEventArgs : EventArgs This is similar to EventHandler except it has been made generic to support the more general case.  Thus, it will work for any delegate where the first argument is an object (the sender) and the second argument is a class derived from EventArgs (the event data). For example, let’s say we wanted to create a message receiver, and we wanted it to have a few events such as OnConnected that will tell us when a connection is established (probably with no additional information) and OnMessageReceived that will tell us when a new message arrives (probably with a string for the new message text). So for OnMessageReceived, our MessageReceivedEventArgs might look like this: 1: public sealed class MessageReceivedEventArgs : EventArgs 2: { 3: public string Message { get; set; } 4: } And since OnConnected needs no event argument type defined, our class might look something like this: 1: public class MessageReceiver 2: { 3: // event that is called when the receiver connects with sender 4: public event EventHandler OnConnected; 5:  6: // event that is called when a new message is received. 7: public event EventHandler<MessageReceivedEventArgs> OnMessageReceived; 8:  9: // ... 10: } Notice, nowhere did we have to define a delegate to fit our event definition, the EventHandler and generic EventHandler<TEventArgs> delegates fit almost anything we’d need to do with events. Sidebar: Thread-safety and raising an event When the time comes to raise an event, we should always check to make sure there are subscribers, and then only raise the event if anyone is subscribed.  This is important because if no one is subscribed to the event, then the instance will be null and we will get a NullReferenceException if we attempt to raise the event. 1: // This protects against NullReferenceException... or does it? 2: if (OnMessageReceived != null) 3: { 4: OnMessageReceived(this, new MessageReceivedEventArgs(aMessage)); 5: } The above code seems to handle the null reference if no one is subscribed, but there’s a problem if this is being used in multi-threaded environments.  For example, assume we have thread A which is about to raise the event, and it checks and clears the null check and is about to raise the event.  However, before it can do that thread B unsubscribes to the event, which sets the delegate to null.  Now, when thread A attempts to raise the event, this causes the NullReferenceException that we were hoping to avoid! To counter this, the simplest best-practice method is to copy the event (just a multicast delegate) to a temporary local variable just before we raise it.  Since we are inside the class where this event is being raised, we can copy it to a local variable like this, and it will protect us from multi-threading since multicast delegates are immutable and assignments are atomic: 1: // always make copy of the event multi-cast delegate before checking 2: // for null to avoid race-condition between the null-check and raising it. 3: var handler = OnMessageReceived; 4: 5: if (handler != null) 6: { 7: handler(this, new MessageReceivedEventArgs(aMessage)); 8: } The very slight trade-off is that it’s possible a class may get an event after it unsubscribes in a multi-threaded environment, but this is a small risk and classes should be prepared for this possibility anyway.  For a more detailed discussion on this, check out this excellent Eric Lippert blog post on Events and Races. Summary Generic delegates give us a lot of power to make generic algorithms and classes, and the EventHandler delegate family gives us the flexibility to create events easily, without needing to redefine delegates over and over.  Use them whenever you need to define events with or without specialized EventArgs.   Tweet Technorati Tags: .NET, C#, CSharp, Little Wonders, Generics, Delegates, EventHandler

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  • How do I set up pairing email addresses?

    - by James A. Rosen
    Our team uses the Ruby gem hitch to manage pairing. You set it up with a group email address (e.g. [email protected]) and then tell it who is pairing: $ hitch james tiffany Hitch then sets your Git author configuration so that our commits look like commit 629dbd4739eaa91a720dd432c7a8e6e1a511cb2d Author: James and Tiffany <[email protected]> Date: Thu Oct 31 13:59:05 2013 -0700 Unfortunately, we've only been able to come up with two options: [email protected] doesn't exist. The downside is that if Travis CI tries to notify us that we broke the build, we don't see it. [email protected] does exist and forwards to all the developers. Now the downside is that everyone gets spammed with every broken build by every pair. We have too many possible pair to do any of the following: set up actual [email protected] email addresses or groups (n^2 email addresses) set up forwarding rules for [email protected] (n^2 forwarding rules) set up forwarding rules for [email protected] (n forwarding rules for each of n developers) Does anyone have a system that works for them?

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  • UEFI/GPT Win 7 Load Failure in Dual Boot and no GRUB2 [Ubuntu 12.04]

    - by cristian_jordache
    Configuration: MBB: ASRock X79 Extreme6 Win 7 installed on a INTEL 40GB SSD (GPT partitioned) Ubuntu 14.04 on a CORSAIR 30GB SSD (Ext4 and SWAP) I had Windows 7 installed previously in UEFI mode, using 3 partitions (GPT) and works fine if left alone. In UEFI BIOS settings I can see sometimes a "Windows Boot Manager" and other times (?) a "UEFI Intel" entry for INTEL HDD and Windows will boot properly selecting the one available at that time. I installed Ubuntu 14.04 after Win 7 w/o changing any UEFI BIOS settings and it works fine only if the BIOS is set w/ the Ubuntu partition as the first drive to boot, in AHCI mode. If both SSD drives are connected, the Win7 Intel boot drive can be chosen as first boot device but only as an "AHCI Intel drive" (No "Windows Boot Manager" nor "UEFI Intel device" options available in BIOS Boot menu) and Win7 will not load properly as long as the Ubuntu Crucial SSD is NOT PHYSICALLY DISCONNECTED. Windows will try, start booting for few seconds but will fail replacing Win7 logo and that startup animation with w/ the "old" white progress bar and then and will notify that there is a issue and prompt the user to try to Load Win 7 in Normal Mode again or try a Recovery Mode to fix it. If I let Windows INTEL HDD boot via BIOS/UEFI - Windows Boot manager selection, I may see the purple screen of Grub2 loaded for a while, but there's no selection for Ubuntu or Windows and/or then machine is not booting, showing a black screen and a small command prompt cursor blinking on top. So far the only option I see to have Ubuntu boot side by side w/ Win 7 is to reformat the Win7 SDD and set it boot in legacy BIOS mode with a MBR instead of GPT. Per my understanding this is a quite complex issue to fix (Rod Smith's answer was pretty helpful: UEFI boot on my Asus k52f) but any other suggestions are welcome. I find a bit odd that I can boot properly Windows7 SSD or an Ubuntu DVD using a DVD drive set in UEFI-BIOS in "AHCI mode" and w/ using "UEFI/Windows Boot Manager" booting option but I cannot boot a secondary SSD-HDD w/ Ubuntu having the same BIOS/UEFI Boot configuration. Looks like plugging the second SSD [the Ubuntu partition] is interfering with boot options in UEFI-BIOS.

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  • Windows Azure Upgrade Domain

    - by kaleidoscope
    Windows Azure automatically divides your role instances into some “logical” domains called upgrade domains. During upgrade, Azure is updating these domains one by one. This is a by design behavior to avoid nasty situations. Some of the last feature additions and enhancements on the platform was the ability to notify your role instances in case of “environment” changes, like adding or removing being most common. In such case, all your roles get a notification of this change. Imagine if you had 50 or 60 role instances, getting notified all at once and start doing various actions to react to this change. It will be a complete disaster for your service. The way to address this problem is upgrade domains. During upgrade Windows Azure updates them one by one and only the associated role instances to a specific domain get notified of the changes taking place. Only a small number of your role instances will get notified, react and the rest will remain intact providing a seamless upgrade experience and no service disruption or downtime. http://www.kefalidis.me/archive/2009/11/27/windows-azure-ndash-what-is-an-upgrade-domain.aspx   Lokesh, M

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  • Copy wrongs and Copyright

    - by Tony Davis
    Recently, a Chinese blog website copied, wholesale and without permission, a Simple-Talk article on troubleshooting locking and blocking. Our initial reaction was exasperation and anger, tempered slightly by the fact that there was, at the top, a clear link to the original, and the book from which it was extracted. On the day the copy was posted, our original article saw a 30K spike in visits, so the site clearly has a substantial following! This made us pause for thought. Indeed, we wondered whether it might not be more profitable, and certainly more enjoyable, to notify the offender of similar content and serve a "put up" notice, rather than the usual DMCA "take down" . The DMCA request, issued to protect our and our authors' assets, is a necessary but tiresome, chore. So often, simple communication and negotiation could have averted the need for it. We are, after all, in the business of presenting knowledge, information and help to the SQL Server Community. If only they had asked! Of course, one's attitude changes according to the motivation behind the copying of content. One of the motivations seems to be pure vanity; they do it to try to enhance their CV, or their company's expertise, by pretending to expertise they don't possess. There is a class of plagiariser, however, that is doing it purely for money, getting advertising revenue by attracting hapless readers to their site. Not content with stealing content, sites can invest in services that provide 'load-testing' for websites that is so realistic that even the search engines can be fooled. Stolen content, fake visitors, swindled advertisers. Zero-tolerance is really the only way of dealing with plagiarism, and action will only be completely effective once Bing, Google, and the other search engines strike out from their listings the rogue sites that refuse to take down plagiarised content. It is, after all in everyone else's interests. Cheers, Tony.

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