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• Is it really necessary to call /bin/sync twice before an unmanaged power-off?

  - by Jeremy Friesner

  Hi all, My company sells an "embedded device" which is implemented as a headless Linux box with ext4 on an internal SSD. Some of our users have a habit of doing a "save current settings" on this box, and then cutting power to the unit as soon as the unit reports that the save completed (ie two seconds later). This was causing occasional corruption of the saved files, as the data wouldn't always get flushed to the SSD before the power went out. So I tweaked my software to run /bin/sync immediately after writing the file (after closing the file handle but before notifying the user that the save completed). This appears to fix the issue, but my coworker says that one call to /bin/sync isn't sufficient, and that to be really safe I ought to run /bin/sync twice in a row. That sounds like paranoia to me... Perhaps a habit from earlier versions of Linux or unix whose sync utility didn't work reliably. Does his advice have merit, or should one call to /bin/sync suffice?

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• How to implement a simple queue properly?

  - by Stephen Hsu

  The current Go library doesn't provide the queue container. To implement a simple queue, I use circle array as the underlying data structure. It follows algorithms mentioned in TAOCP: Insert Y into queue X: X[R]<-Y; R<-(R+1)%M; if R=F then OVERFLOW. Delete Y from queue X: if F=R then UNDERFLOW; Y<-X[F]; F<-(F+1) % M. F: Front, R: Rear, M: Array length. Following is the code: package main import ( "fmt" ) type Queue struct { len int head, tail int q []int } func New(n int) *Queue { return &Queue{n, 0, 0, make([]int, n)} } func (p *Queue) Enqueue(x int) bool { p.q[p.tail] = x p.tail = (p.tail + 1) % p.len return p.head != p.tail } func (p *Queue) Dequeue() (int, bool) { if p.head == p.tail { return 0, false } x := p.q[p.head] p.head = (p.head + 1) % p.len return x, true } func main() { q := New(10) for i := 1; i < 13; i++ { fmt.Println(i, q.Enqueue(i)) } fmt.Println() for i := 1; i < 13; i++ { fmt.Println(q.Dequeue()) } } But the output is obviously wrong: 1 true 2 true 3 true 4 true 5 true 6 true 7 true 8 true 9 true 10 false 11 true 12 true 11 true 12 true 0 false 0 false 0 false 0 false 0 false 0 false 0 false 0 false 0 false 0 false I think I need one more field to make the code work properly. What do you suggest?

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• Java - Call to start method on thread : how does it route to Runnable interface's run () ?

  - by Bhaskar

  Ok , I know the two standard ways to create a new thread and run it in Java : 1 Implement Runnable in a class , define run method ,and pass an instance of the class to a new Thread. When the start method on the thread instance is called , the run method of the class instance will be invoked. 2 Let the class derive from Thread, so it can to override the method run() and then when a new instance's start method is called , the call is routed to overridden method. In both methods , basically a new Thread object is created and its start method invoked. However , while in the second method , the mechanism of the call being routed to the user defined run() method is very clear ,( its a simple runtime polymorphism in play ), I dont understand how the call to start method on the Thread object gets routed to run() method of the class implementing Runnable interface. Does the Thread class have an private field of Type Runnable which it checks first , and if it is set then invokes the run method if it set to an object ? that would be a strange mechanism IMO. How does the call to start() on a thread get routed to the run method of the Runnable interface implemented by the class whose object is passed as a parameter when contructing the thread ?

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• why toString method does not work here??

  - by user329820

  Hi this is my whole class ,I have added number 2 to the doubly linked list and then I want it to be be print in the concole but it will show this "datastructureproject.Node@f62373" thanks! package datastructureproject; public class DoublyLinkedList { private Node head = new Node(0); private Node tail = new Node(0); private int length = 0; public DoublyLinkedList() { head.setPrev(null); head.setNext(tail); tail.setPrev(head); tail.setNext(null); } public void add(int index, int value) throws IndexOutOfBoundsException { Node cursor = get(index); Node temp = new Node(value); temp.setPrev(cursor); temp.setNext(cursor.getNext()); cursor.getNext().setPrev(temp); cursor.setNext(temp); length++; } private Node get(int index) throws IndexOutOfBoundsException { if (index < 0 || index > length) { throw new IndexOutOfBoundsException(); } else { Node cursor = head; for (int i = 0; i < index; i++) { cursor = cursor.getNext(); } return cursor; } } public long size() { return length; } public boolean isEmpty() { return length == 0; } @Override public String toString() { StringBuffer result = new StringBuffer(); result.append("(head) - "); Node temp = head; while (temp.getNext() != tail) { temp = temp.getNext(); result.append(temp.getValue() + " - "); } result.append("(tail)"); return result.toString(); } public static void main(String[] args){ DoublyLinkedList list = new DoublyLinkedList(); list.add(0,2 ); System.out.println(list.get(0).toString()); } }

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• why does setting stderr=subprocess.STDOUT fix a subprocess.check_output call?

  - by ShankarG

  I have a python script running on a small server that is called in three different ways - from within another python script, by cron, or by gammu-smsd (an SMS daemon with the wonderful mobile utility [gammu]). The script is for maintenance and contained the following kludge to measure used space on the system (presumably this is possible from within Python, but this was quick and dirty): reportdict['Used Space'] = subprocess.check_output(["df / | tail -1 | awk '{ print $5; }'"], shell=True)[0:-1] Oddly enough this line would only fail when the script was called by a shell script running from gammu-smsd. The line would fail with a CalledProcessError exception saying "returned exit status 2", even though the output attribute of the CalledProcessError object contained the correct output. The only command in the sequence of shell commands that would give such an error status would be awk, with status 2 indicating a fatal error. If the python script with this line was called by cron, by another python script, or from the command line, this line would work fine. I broke my head trying to fix the environment for the script, thinking this must be the problem. Finally though I put in stderr=subprocess.STDOUT, like so: reportdict['Used Space'] = subprocess.check_output(["df / | tail -1 | awk '{ print $5; }'"], stderr=subprocess.STDOUT, shell=True)[0:-1] This was a debug measure to help me figure out if some output was coming on stderr. But after this the script started working, even when called from gammu-smsd! Why might this be the case? I ask for future reference when using subprocess...

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• Javascript function working strangely during the first call in CHROME ?

  - by Sohil

  HI all, Below mentioned javascript code works fine in all browsers including chrome(from second call onwards). function call(val){ url = window.location.href; indexnum = url.lastIndexOf("/"); str = url.slice(indexnum+1); window.location.href = url.replace(str, "sample.php?src_q=") + val; } I am calling this function on onclick of a link as below <?php echo "<a href='#' onclick='javascript:call(\"$fieldvalue\");'>$fieldvalue</a>" ?> Normal Behaviour : In all browser after clicking on the link new formed url is url://localhost/mysite/sample.php?src_q=val Strange Behaviour : When I click on the link for the first time in chrome value of variable val gets replaced by url and its value as follows http://localhost/mysite/sample.php?src_q=http://localhost/mysite/val This strange behaviour happens during the first click in chrome. From the second call onwards in the same tab, the value of variable val works fine and I get desired url. I tried to google on it, but couldn't found any explanation. Thanks in advance.

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• How to call WCF Service Method Asycroniously from Class file?

  - by stackuser1

  I've added WCF Service reference to my asp.net application and configured that reference to support asncronious calls. From asp.net code behind files, i'm able to call the service methods asyncroniously like the bellow sample code. protected void Button1_Click(object sender, EventArgs e) { PageAsyncTask pat = new PageAsyncTask(BeiginGetDataAsync, EndDataRetrieveAsync, null, null); Page.RegisterAsyncTask(pat); } IAsyncResult BeiginGetDataAsync(object sender, EventArgs e, AsyncCallback async, object extractData) { svc = new Service1Client(); return svc.BeginGetData(656,async, extractData); } void EndDataRetrieveAsync(IAsyncResult ar) { Label1.Text = svc.EndGetData(ar); } and in page directive added Async="true" In this scenario it is working fine. But from UI i'm not supposed to call the service methods directly. I need to call all service methods from a static class and from code behind file i need to invoke the static method. In this scenario what exactlly do i need to do?

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• How to call Struts1 Action from Ajax or JavaScript?

  - by Dj.

  I need to call an action on load of a JSP. To keep track of number of users who visited that page. I hav an action VisitorCounterAction. Where il update the database. On load of the JSP im calling an ajax function callCounter(); { alert("callCounter"); if (window.XMLHttpRequest) {// code for IE7+, Firefox, Chrome, Opera, Safari xmlhttp=new XMLHttpRequest(); } else {// code for IE6, IE5 xmlhttp=new ActiveXObject("Microsoft.XMLHTTP"); } // i need some correction here xmlhttp.open("GET",VisitorCounterAction,false); xmlhttp.send(null); alert("callCounter returned from Action"); } I am getting an exception as: /web/guest/content?p_p_id=31&p_p_lifecycle=0&p_p_state=pop_up&p_p_mode=view&_31_struts_action=%2Fimage_gallery%2Fview_slide_show&_31_folderId=10605 generates exception: null Please help me with this. Or any other way to call the Action. I can't reload the page as it'll call onload function again. Thanks, Dj

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• How do I call overloaded Java methods in Clojure.

  - by Pat Wallace

  For this example Java class: package foo; public class TestInterop { public String test(int i) { return "Test(int)"; } public String test(Object i) { return "Test(Object)"; } } When I start Clojure and try to call the test(int) method, the test(Object) method is called instead, because Clojure automatically boxes the integer into a java.lang.Integer object. How do I force Clojure to call the test(int) method? user=> (.test (new foo.TestInterop) 10) "Test(Object)" I want to call methods like Component.add(Component comp, int index) in AWT, but instead keep calling add(Component comp, Object constraints), so the buttons on my toolbar always appear in the wrong order.

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• How is method group overload resolution different to method call overload resolution?

  - by thecoop

  The following code doesn't compile (error CS0123: No overload for 'System.Convert.ToString(object)' matches delegate 'System.Converter<T,string>'): class A<T> { void Method(T obj) { Converter<T, string> toString = Convert.ToString; } } however, this does: class A<T> { void Method(T obj) { Converter<T, string> toString = o => Convert.ToString(o); } } intellisense gives o as a T, and the Convert.ToString call as using Convert.ToString(object). In c# 3.5, delegates can be created from co/contra-variant methods, so the ToString(object) method can be used as a Converter<T, string>, as T is always guarenteed to be an object. So, the first example (method group overload resolution) should be finding the only applicable method string Convert.ToString(object o), the same as the method call overload resolution. Why is the method group & method call overload resolution producing different results?

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• How do I fire an asynchronous call in asp classic and ignore the response?

  - by Hexate

  Here's the gist: I have a call I want to make in asp, and I do not care about the response. I just want to fire the call and I do not want the page to wait for the response. According to the documentation, it should look something like this: dim xmlhttp : set xmlhttp = Server.CreateObject("MSXML2.ServerXMLHTTP") xmlhttp.Open "POST", url, true '' setting the 'asynchronous' option to 'true' xmlhttp.setRequestHeader "Content-Type", "application/soap+xml; charset=utf-8" xmlhttp.setRequestHeader "Content-Length", Len(XMLData) xmlhttp.send XMLData This works peachy when calling synchronously, but when I flip the ansynchronous option to 'true', nothing fires. What I can gather from the internet is that users do something like the following: While xmlhttp.readyState <> 4 xmlhttp.waitForResponse 1000 Wend Am I crazy in that this does not really seem like an asynchrous call anymore though if you are waiting for a response? putting the line xmlhttp.waitForResponse 1 right after the send will cause the request to fire, but again, I don't want to wait a second. Any thoughts?

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• call my web services from other app with javascript?

  - by Dejan.S

  Hi. I got .asmx a web service on my app. I need to call a method from an other app to get statistics from my app. I need it to return XML. the call to the webmethod is done with javascript soap. There is a default hellow world webmethod and calling that work but it seem that when i try to call a method where i need to pass parameters and it need to execute code it wont work and just return my error message. any ideas on what can be wrong. am I using the wrong web method?

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• Using C++, how to call a base class method from a derived class method and apply this to an object passed as an argument?

  - by Chris

  I can't figure out how to call a base class method from a derived class method but concurrently applying this method call at an object passed as argument. What I mean is this: class Animal { virtual void eat(Animal& to_be_eaten) = 0; }; class Carnivores: public Animal { virtual void eat(Animal& to_be_eaten) { /*implementation here*/} }; class Wolf : public Carnivores { virtual void eat(Animal& to_be_eaten) { /*call eat method(of Base class) of Base to_be_eaten here*/ } } I thought of something like this dynamic_cast<Carnivores&>(to_be_eaten).eat(*this) //and got a segmentation fault Is there any way for this to be done? Thank you! New edit:: Updated the code

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• Making all links inside of a div call the same function?

  - by Brandon

  I'm trying to make a notification area that will show alerts. return this.each(function() { jQuery('<div class="' + o['className'] + '">' + o.msg + ' + '<a href="#" onclick="$(this).parent().remove(); dismiss(' + o["id"] + ');">X</a>' + '</div>') .appendTo(this); }); This just takes a message pulled from the database, and shows it to the user. If the user clicks the X then it will call dismiss() which will mark it as being read in the database. The thing is, if the message itself contains a link to another page or external site, I also want to call dismiss() before the user leaves the page. Is there anyway to alter this javascript to take all a elements (the X and any links that would appear in the message) and change the onclick to call the function?

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• Call non-static method in server side(aspx.cs) from client side use javascript (aspx).....

  - by Pramulia

  how Call non-static method in server side(aspx.cs) from client side using javascript (aspx)....? As far as I know I can call static method in server side from client side... server side : [System.Web.Services.WebMethod] public static void method1() { } client side : <script language="JavaScript"> function keyUP() { PageMethods.method1(); } </script> <asp:ScriptManager ID="ScriptManager1" runat="server" EnablePageMethods="true"> </asp:ScriptManager> It works. Now how do I call non-static method from client side...?

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• Catch and Show an error from a WCF service call in javascript.

  - by cw

  Hello, I'm calling a WCF service through javascript and right now it's not showing any errors that might occur on the service side to the user. I have the code below and am looking for a better way to inform the user an error has occured, including the call stack and error message if possible. The service itself throws a FaultException if an error has occured. However, I want to catch that error in the javascript call and show it to the user. Here is the js code to call the service function Save() { var saveInfo = $("._saveInfo").val() app.namspace.interfacetoservice.Save( saveInfo, function(results) { if (results == true) { window.close(); } else { alert("error saving"); } } ); } Thanks for the help!

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• .net example of using client certificates in web service call?

  - by Rory

  I'd like to use client certificates to verify the identity of administrative callers to my web service. Then I can issue certificates only to the people I want to call my web service and be pretty sure noone else can call it. This is in a very controlled scenario where only one or two people will get the client certificate, so distribution isn't a hard problem. This article provides a good example of how to call a web service using a client certificate. But how can I check details of the client certificate from within my web service? This old article talks about configuring IIS to do it, but I'd like to do it programmatically within my app. I think? thanks for any suggestions!

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• Why doesn't Perl threading work when I call readdir beforehand?

  - by Kevin

  Whenever I call readdir before I create a thread, I get an error that looks like this: perl(2820,0x7fff70c33ca0) malloc: * error for object 0x10082e600: pointer being freed was not allocated * set a breakpoint in malloc_error_break to debug Abort trap What's strange is that it happens when I call readdir before I create a thread (i.e. readdir is not called in any concurrent code). I don't even use the results from readdir, just making the call to it seems to screw things up. When I get rid of it, things seem to work fine. Some example code is below: opendir(DIR, $someDir); my @allFiles = readdir(DIR); close(DIR); my $thread = threads-create(\&sub1); $thread-join(); sub sub1 { print "in thread\n" }

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• How can I call an Actionscript function when the .swf is referenced by jQuery?

  - by Arms

  I have an .swf that I am embedding into HTML using the jQuery SWF Object plugin (http://jquery.thewikies.com/swfobject). I have a number of functions within the .swf that I need to call from within javascript functions. I've made these actionscript functions accessible to javascript by calling flash.external.ExternalInterface.addCallback(). Yet nothing happens when I make the call. I've had this happen before and it seems to be that when you reference the .swf from jQuery, you can't call flash functions. Is there anyway around this (aside from not using jQuery)? Thanks.

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• Can NSUserDefaults be used for pausing the application during a phone call ?

  - by Anil Kumar

  Friends, currently I dont have iphone to test and using Simulator for testing purposes. I am Just curious to know whether an application continues to run even after a phone call.. here i have no option to test this from simulator. If it terminates then how can i pause things.. and continue after a phone call. Is NSUserDefaults can be used for my case. As far I understood NSuserDefaults are used to store data that is required when the App is next time loaded. But here I dont want my App to terminate instead pause until Call ends and continue as uninterrupted later. Please clear me about this. Sorry I am still a beginner so I request for no harsh replies if my question looks stupid. Thanks in Advance

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• Why I have to call 'exit' after redirection through header('Location..') in PHP?

  - by Nicolò Martini

  You know that if you want to redirect an user in PHP you can use the header function: header('Location: http://smowhere.com'); It is also well known that it is a good practice to put also an exit; after the header call, to prevent execution of other php code. So my question is: could the code after the header-location call be effectively executed? In which cases? Can a malicious user be able to completely ignore the header('Location..') call? How?

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• how to call a javascript function in the top frame?

  - by Rory

  This seems really simple, but how do I call a javascript function that's defined in the top-level html, from a child frame? top html doc - 1st level frame - 2nd level frame my top html doc has a function called testFn(). In the 2nd level frame I have a button with onclick="top.testFn();" but this doesn't call the testFn(). In Firebug if I use a watch to execute top.testFn(); it says TypeError: testFn() is not a function. Should this all just work - in which case it's a problem with my documents, or is there some other way to call functions in the top-level window?

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• Best way to call other class view in iphone?

  - by aman-gupta

  Hi, Generally i call my other class view by creating a pointer of delegate and then call the other class by using its link as below:- First Way :- Mydelegate *ptr = (Mydelegate *)[[UIApplication sharedApplication]delegate]; [self.navigationController pushViewController:ptr.NextClasspointer animated:YES]; Second Way :- Create a pointer of that class which u want to call :-- NextClass *nextptr = [[NextClass alloc]initWithnibName:@"NextClass" bundle:nil]; [self.navigationController pushViewController:nextptr animated:YES]; [nextptr release]; nextptr = nil; These above two methods i generally used but my problem is that which one is best for big project so that my stack problem will be removed I mean memory issue will be solved.And is it necessary to release pointer in first and second case is the way i release is correct or wrong Please help me Thanks in Advance

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• What happens if an asynchronous delegate call never returns?

  - by RichardHowells

  I found a decent looking example of how to call a delegate asynchronously with a timeout... http://www.eggheadcafe.com/tutorials/aspnet/847c94bf-4b8d-4a66-9ae5-5b61f049019f/basics-make-any-method-c.aspx. In summary it uses WaitOne with a timeout to determine if the call does not return before the timeout expires. I also know that you should have an EndInvoke to match each BeginInvoke. So what happens if the wait timeout expires? We (presumably) DON'T want to call EndInvoke as that will block. The code can go on to do 'other things', but have we leaked anything? Is there some poor thread someplace blocked waiting for a return that's never going to happen? Have we leaked some memory where the result-that-will-never-return was going to be placed?

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• How can I delete a row in the view only if the AJAX call & db deletion was successful?

  - by user1760663

  I have a table where each row has a button for deletion. Actually I delete the row everytime without checking if the ajax call was successfull. How can I achieve that, so that the row will only be deleted if the ajax call was ok. Here is my clickhandler on each row $("body").on('click', ".ui-icon-trash" ,function(){ var $closestTr = $(this).closest('tr'); // This will give the closest tr // If the class element is the child of tr deleteRowFromDB(oTable, closestTr); $closestTr.remove() ; // Will delete that }); And here my ajax call function deleteRowFromDB(oTable, sendallproperty){ var deleteEntryRoute = #{jsRoute @Application.deleteConfigurationEntry() /} console.log("route is: " + deleteEntryRoute.url) $.ajax({ url: deleteEntryRoute.url({id: sendallproperty}), type: deleteEntryRoute.method, data: 'id=' + sendallproperty });

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