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  • Java socketserver: How to handle many incoming connections?

    - by SlappyTheFish
    I am writing a simple multithreaded socketserver and I am wondering how best to handle incoming connections: create a new thread for each new connection. The number of concurrent threads would be limited and waiting connections limited by specifying a backlog add all incoming connections into a queue and have a pool of worker threads that process the queue I am inclined to go for option 2 because I really don't want to refuse any connections, even under high loads, but I am wondering if there are any considerations I should be aware of with accepting effectively unlimited connections?

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  • Yes, another thread question...

    - by Michael
    I can't understand why I am loosing control of my GUI even though I am implementing a thread to play a .wav file. Can someone pin point what is incorrect? #!/usr/bin/env python import wx, pyaudio, wave, easygui, thread, time, os, sys, traceback, threading import wx.lib.delayedresult as inbg isPaused = False isStopped = False class Frame(wx.Frame): def __init__(self): print 'Frame' wx.Frame.__init__(self, parent=None, id=-1, title="Jasmine", size=(720, 300)) #initialize panel panel = wx.Panel(self, -1) #initialize grid bag sizer = wx.GridBagSizer(hgap=20, vgap=20) #initialize buttons exitButton = wx.Button(panel, wx.ID_ANY, "Exit") pauseButton = wx.Button(panel, wx.ID_ANY, 'Pause') prevButton = wx.Button(panel, wx.ID_ANY, 'Prev') nextButton = wx.Button(panel, wx.ID_ANY, 'Next') stopButton = wx.Button(panel, wx.ID_ANY, 'Stop') #add widgets to sizer sizer.Add(pauseButton, pos=(1,10)) sizer.Add(prevButton, pos=(1,11)) sizer.Add(nextButton, pos=(1,12)) sizer.Add(stopButton, pos=(1,13)) sizer.Add(exitButton, pos=(5,13)) #initialize song time gauge #timeGauge = wx.Gauge(panel, 20) #sizer.Add(timeGauge, pos=(3,10), span=(0, 0)) #initialize menuFile widget menuFile = wx.Menu() menuFile.Append(0, "L&oad") menuFile.Append(1, "E&xit") menuBar = wx.MenuBar() menuBar.Append(menuFile, "&File") menuAbout = wx.Menu() menuAbout.Append(2, "A&bout...") menuAbout.AppendSeparator() menuBar.Append(menuAbout, "Help") self.SetMenuBar(menuBar) self.CreateStatusBar() self.SetStatusText("Welcome to Jasime!") #place sizer on panel panel.SetSizer(sizer) #initialize icon self.cd_image = wx.Image('cd_icon.png', wx.BITMAP_TYPE_PNG) self.temp = self.cd_image.ConvertToBitmap() self.size = self.temp.GetWidth(), self.temp.GetHeight() wx.StaticBitmap(parent=panel, bitmap=self.temp) #set binding self.Bind(wx.EVT_BUTTON, self.OnQuit, id=exitButton.GetId()) self.Bind(wx.EVT_BUTTON, self.pause, id=pauseButton.GetId()) self.Bind(wx.EVT_BUTTON, self.stop, id=stopButton.GetId()) self.Bind(wx.EVT_MENU, self.loadFile, id=0) self.Bind(wx.EVT_MENU, self.OnQuit, id=1) self.Bind(wx.EVT_MENU, self.OnAbout, id=2) #Load file usiing FileDialog, and create a thread for user control while running the file def loadFile(self, event): foo = wx.FileDialog(self, message="Open a .wav file...", defaultDir=os.getcwd(), defaultFile="", style=wx.FD_MULTIPLE) foo.ShowModal() self.queue = foo.GetPaths() self.threadID = 1 while len(self.queue) != 0: self.song = myThread(self.threadID, self.queue[0]) self.song.start() while self.song.isAlive(): time.sleep(2) self.queue.pop(0) self.threadID += 1 def OnQuit(self, event): self.Close() def OnAbout(self, event): wx.MessageBox("This is a great cup of tea.", "About Jasmine", wx.OK | wx.ICON_INFORMATION, self) def pause(self, event): global isPaused isPaused = not isPaused def stop(self, event): global isStopped isStopped = not isStopped class myThread (threading.Thread): def __init__(self, threadID, wf): self.threadID = threadID self.wf = wf threading.Thread.__init__(self) def run(self): global isPaused global isStopped self.waveFile = wave.open(self.wf, 'rb') #initialize stream self.p = pyaudio.PyAudio() self.stream = self.p.open(format = self.p.get_format_from_width(self.waveFile.getsampwidth()), channels = self.waveFile.getnchannels(), rate = self.waveFile.getframerate(), output = True) self.data = self.waveFile.readframes(1024) isPaused = False isStopped = False #main play loop, with pause event checking while self.data != '': # while isPaused != True: # if isStopped == False: self.stream.write(self.data) self.data = self.waveFile.readframes(1024) # elif isStopped == True: # self.stream.close() # self.p.terminate() self.stream.close() self.p.terminate() class App(wx.App): def OnInit(self): self.frame = Frame() self.frame.Show() self.SetTopWindow(self.frame) return True def main(): app = App() app.MainLoop() if __name__=='__main__': main()

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  • ActiveMQ - sending message to specific consumer

    - by archer
    Hello. Having single AMQ broker and 100 consumers connected. I would send the message to some specific consumer, so other consumers does not receive it (client-side filtering won't work). Simplest way is to create virtual destinations (name them queue:consumer-) for example and send messages there. However this will lead to 100 new queues which makes it more complex to monitor. Is there any other way to do this having single queue?

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  • Lookig for "GAE-TaskQueues" in Asp.net

    - by Fabrizio
    I normally works in asp.net. But recently I was testing Google App Engine and I found TaskQueues: it's very interesting and powerful. Does anyone know a similar service for asp.net? I know MSQueue but it's not what I need. I need something like GAE TaskQueue: I put an URL in queue and the URL is triggered (based on queue config).

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  • Java Data Structure

    - by Joe
    Hi there, I'm looking for a data structure that will act like a Queue so that I can hava First In First Out behaviour, but ideally I would also be able to see if an element exists in that Queue in constant time as you can do with a HashMap, rather than the linear time that you get with a LinkedList. I thought a LinkedHashMap might do the job, but although I could make an iterator and just take and then remove the first element of the iteration to produce a sort of poll() method, I'm wondering if there is a better way. Many thanks in advance

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  • jQuery multiple selectors into dynamic attribute

    - by Jason Fletcher
    I am trying to attach an event to a separate onhover trigger. But I am having problems using multiple selectors since its dynamic. Need help ::: Upon hovering on the yellow box named 'Rings', this should trigger the animated slide event for the green box above it. http://home.jasonfletcher.info/all/alliteration/index.html $('.boxgrid1').hover(function(){ $(".cover", this).stop().animate({top:'0px'},{queue:false,duration:300}); }, function() { $(".cover", this).stop().animate({top:'247px'},{queue:false,duration:300}); });

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  • Connecting to an MQ: Newbie question

    - by deltamatrix
    Hi, I am a novice with Websphere MQ and require some novice help. I am using Websphere MQ Explorer to connect to a queue but do not know how to write the connection string. I have all the details (host, port, channel, queue manager name) but do not know how to put them together correctly as a connection string. Can any help this novice? Thanks

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  • Graph Tour with Uniform Cost Search in Java

    - by user324817
    Hi. I'm new to this site, so hopefully you guys don't mind helping a nub. Anyway, I've been asked to write code to find the shortest cost of a graph tour on a particular graph, whose details are read in from file. The graph is shown below: http://img339.imageshack.us/img339/8907/graphr.jpg This is for an Artificial Intelligence class, so I'm expected to use a decent enough search method (brute force has been allowed, but not for full marks). I've been reading, and I think that what I'm looking for is an A* search with constant heuristic value, which I believe is a uniform cost search. I'm having trouble wrapping my head around how to apply this in Java. Basically, here's what I have: Vertex class - ArrayList<Edge> adjacencies; String name; int costToThis; Edge class - final Vertex target; public final int weight; Now at the moment, I'm struggling to work out how to apply the uniform cost notion to my desired goal path. Basically I have to start on a particular node, visit all other nodes, and end on that same node, with the lowest cost. As I understand it, I could use a PriorityQueue to store all of my travelled paths, but I can't wrap my head around how I show the goal state as the starting node with all other nodes visited. Here's what I have so far, which is pretty far off the mark: public static void visitNode(Vertex vertex) { ArrayList<Edge> firstEdges = vertex.getAdjacencies(); for(Edge e : firstEdges) { e.target.costToThis = e.weight + vertex.costToThis; queue.add(e.target); } Vertex next = queue.remove(); visitNode(next); } Initially this takes the starting node, then recursively visits the first node in the PriorityQueue (the path with the next lowest cost). My problem is basically, how do I stop my program from following a path specified in the queue if that path is at the goal state? The queue currently stores Vertex objects, but in my mind this isn't going to work as I can't store whether other vertices have been visited inside a Vertex object. Help is much appreciated! Josh

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  • Where to begin with multi-threaded programming with c++?

    - by zoke
    I'm trying to implement my own IRC client as a personal proejct and I realized I needed a way to read and write from the socket at the same time. I realized I could have a reading thread which reads from the socket in the background and puts data in a queue and I could have another thread which writes data from a queue to the socket. However I have no idea on how to start with multithreaded programing or how to do it with c++. Where do I go from here?

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  • How to make hudson build only most current build.

    - by MikeU
    Question How do I setup Hudson so that if one person triggers a build, Hudson will put it on the queue and wait lets say 2 minutes, and during those 2 minutes if another build is triggered it will replace the older build on the queue with the new build? This way if there are 2 builds in those 2 minutes, Hudson will only perform the last build.

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  • WAS hosting of queues

    - by user80855
    I read that when hosting a queue endpoint all these names need to match: Hosted in IIS at: http://localhost/MyService.svc service endpoint address: http://localhost/private/MyService.svc queue: .\private$\MyService.svc So I wonder, how can you host a service with multiple endpoints to different queues? For example a service that is listening to two queues… (using two endpoints).

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  • unix DECLARE_WAIT_QUEUE_HEAD (var) var prototype?

    - by yoavstr
    hello i want to work with 2 queue in the module where i change my pointer to them therefore i need to use : //declartion wait_queue_head_t **currentQ; DECLARE_WAIT_QUEUE_HEAD (readWaitQ1); DECLARE_WAIT_QUEUE_HEAD (readWaitQ2); if(condition){ currentQ = &readWaitQ1; }else{ currentQ = &readWaitQ2; } but i get incorrect type for wake_up an other stuff using the queue. even thought i google it i couldnt find an answer can someone just give me the prototype needed?...

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  • LinkedBlockingQueue limit ignored?

    - by tgguy
    I created a Java LinkedBlockingQueue like new LinkedBlockingQueue(1) to limit the size of the queue to 1. However, in my testing, this seems to be ignored and there is often several things in the queue at any given time. Why is this?

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  • Question regarding xsd

    - by Hima
    I have an application which reads the data from the database, creates an object out of the data, marshalls it into an xml and enqueue the xml to a queue which is producer. The xml is dequeued from the queue by a consumer. I need to use xsds at two different places. For database access while reading the data from the database and For interaction between producer and consumer Can the same xsd be used in both the cases? Or do I need to use different xsds?

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  • ThreadQueue problems in "Accelerated C# 2008"

    - by Singlet
    Example for threading queue book "Accelerated C# 2008" (CrudeThreadPool class) not work correctly. If I insert long job in WorkFunction() on 2-processor machine executing for next task don't run before first is over. How to solve this problem? I want to load the processor to 100 percent public class CrudeThreadPool { static readonly int MAX_WORK_THREADS = 4; static readonly int WAIT_TIMEOUT = 2000; public delegate void WorkDelegate(); public CrudeThreadPool() { stop = 0; workLock = new Object(); workQueue = new Queue(); threads = new Thread[ MAX_WORK_THREADS ]; for( int i = 0; i < MAX_WORK_THREADS; ++i ) { threads[i] = new Thread( new ThreadStart(this.ThreadFunc) ); threads[i].Start(); } } private void ThreadFunc() { lock( workLock ) { int shouldStop = 0; do { shouldStop = Interlocked.Exchange( ref stop, stop ); if( shouldStop == 0 ) { WorkDelegate workItem = null; if( Monitor.Wait(workLock, WAIT_TIMEOUT) ) { // Process the item on the front of the queue lock( workQueue ) { workItem =(WorkDelegate) workQueue.Dequeue(); } workItem(); } } } while( shouldStop == 0 ); } } public void SubmitWorkItem( WorkDelegate item ) { lock( workLock ) { lock( workQueue ) { workQueue.Enqueue( item ); } Monitor.Pulse( workLock ); } } public void Shutdown() { Interlocked.Exchange( ref stop, 1 ); } private Queue workQueue; private Object workLock; private Thread[] threads; private int stop; } public class EntryPoint { static void WorkFunction() { Console.WriteLine( "WorkFunction() called on Thread {0}",Thread.CurrentThread.GetHashCode() ); //some long job double s = 0; for (int i = 0; i < 100000000; i++) s += Math.Sin(i); } static void Main() { CrudeThreadPool pool = new CrudeThreadPool(); for( int i = 0; i < 10; ++i ) { pool.SubmitWorkItem( new CrudeThreadPool.WorkDelegate( EntryPoint.WorkFunction) ); } pool.Shutdown(); } }

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  • C# start a static thread

    - by user595605
    I have a Queue of items I want to process in a thread, and any instance of a class can add items to the Queue to be processed. My idea for doing this is to have a static Thread in the class that processes the items, the only problem is that I don't know where to start this thread, since I can't start it in its initialization. Is there a way I can start a static thread? Or should I be changing the architecture completely?

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  • it is very important for me this problem [closed]

    - by davit-datuashvili
    please help this is very important problem for me i am going to get job and need such kind of practise implement heaps priortiy queue and so on what is wrong in my java code please tell i want insert number with heap property and return minimum element what is wrong explain please look http://stackoverflow.com/questions/2902781/priority-queue-implementation/2903288#2903288

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  • Bonding: works only for download

    - by Crazy_Bash
    I would like to install bonding with 4 links with mode 4. but only "download/receiving" works with bondig. for transmitting the system chooses one link. ifconfig bond0 Link encap:Ethernet HWaddr 90:E2:BA:0F:76:B4 inet addr:ip Bcast:ip Mask:255.255.255.248 inet6 addr: fe80::92e2:baff:fe0f:76b4/64 Scope:Link UP BROADCAST RUNNING MASTER MULTICAST MTU:1500 Metric:1 RX packets:239187413 errors:0 dropped:10944 overruns:0 frame:0 TX packets:536902370 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:14688536197 (13.6 GiB) TX bytes:799521192901 (744.6 GiB) eth2 Link encap:Ethernet HWaddr 90:E2:BA:0F:76:B4 UP BROADCAST RUNNING SLAVE MULTICAST MTU:1500 Metric:1 RX packets:54969488 errors:0 dropped:0 overruns:0 frame:0 TX packets:2537 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:3374778591 (3.1 GiB) TX bytes:314290 (306.9 KiB) eth3 Link encap:Ethernet HWaddr 90:E2:BA:0F:76:B4 UP BROADCAST RUNNING SLAVE MULTICAST MTU:1500 Metric:1 RX packets:64935805 errors:0 dropped:1 overruns:0 frame:0 TX packets:2532 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:3993499746 (3.7 GiB) TX bytes:313968 (306.6 KiB) eth4 Link encap:Ethernet HWaddr 90:E2:BA:0F:76:B4 UP BROADCAST RUNNING SLAVE MULTICAST MTU:1500 Metric:1 RX packets:57352105 errors:0 dropped:2 overruns:0 frame:0 TX packets:536894778 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:3524236530 (3.2 GiB) TX bytes:799520265627 (744.6 GiB) eth5 Link encap:Ethernet HWaddr 90:E2:BA:0F:76:B4 UP BROADCAST RUNNING SLAVE MULTICAST MTU:1500 Metric:1 RX packets:61930025 errors:0 dropped:3 overruns:0 frame:0 TX packets:2540 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:3796021948 (3.5 GiB) TX bytes:314274 (306.9 KiB) lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:62 errors:0 dropped:0 overruns:0 frame:0 TX packets:62 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:5320 (5.1 KiB) TX bytes:5320 (5.1 KiB) those are my configs: DEVICE="eth2" BOOTPROTO="none" MASTER=bond0 SLAVE=yes USERCTL=no NM_CONTROLLED="no" ONBOOT="yes" DEVICE="eth3" BOOTPROTO="none" MASTER=bond0 SLAVE=yes USERCTL=no NM_CONTROLLED="no" ONBOOT="yes" DEVICE="eth4" BOOTPROTO="none" MASTER=bond0 SLAVE=yes USERCTL=no NM_CONTROLLED="no" ONBOOT="yes" DEVICE="eth5" BOOTPROTO="none" MASTER=bond0 SLAVE=yes USERCTL=no NM_CONTROLLED="no" ONBOOT="yes" DEVICE=bond0 IPADDR=<ip> BROADCAST=<ip> NETWORK=<ip> GATEWAY=<ip> NETMASK=<ip> USERCTL=no BOOTPROTO=none ONBOOT=yes NM_CONTROLLED=no cat /proc/net/bonding/bond0 Ethernet Channel Bonding Driver: v3.7.1 (April 27, 2011) Bonding Mode: IEEE 802.3ad Dynamic link aggregation Transmit Hash Policy: layer2 (0) MII Status: up MII Polling Interval (ms): 100 Up Delay (ms): 0 Down Delay (ms): 0 802.3ad info LACP rate: slow Aggregator selection policy (ad_select): stable Active Aggregator Info: Aggregator ID: 1 Number of ports: 4 Actor Key: 17 Partner Key: 11 Partner Mac Address: 00:24:51:12:63:00 Slave Interface: eth2 MII Status: up Speed: 1000 Mbps Duplex: full Link Failure Count: 0 Permanent HW addr: 90:e2:ba:0f:76:b4 Aggregator ID: 1 Slave queue ID: 0 Slave Interface: eth3 MII Status: up Speed: 1000 Mbps Duplex: full Link Failure Count: 0 Permanent HW addr: 90:e2:ba:0f:76:b5 Aggregator ID: 1 Slave queue ID: 0 Slave Interface: eth4 MII Status: up Speed: 1000 Mbps Duplex: full Link Failure Count: 0 Permanent HW addr: 90:e2:ba:0f:76:b6 Aggregator ID: 1 Slave queue ID: 0 Slave Interface: eth5 MII Status: up Speed: 1000 Mbps Duplex: full Link Failure Count: 0 Permanent HW addr: 90:e2:ba:0f:76:b7 Aggregator ID: 1 Slave queue ID: 0 /etc/modprobe.d/bonding.conf alias bond0 bonding options bond0 mode=4 miimon=100 updelay=200 #downdelay=200 xmit_hash_policy=layer3+4 lacp_rate=1 Linux: Linux 3.0.0+ #1 SMP Fri Oct 26 07:55:47 EEST 2012 x86_64 x86_64 x86_64 GNU/Linux what i've tried: downdelay=200 xmit_hash_policy=layer3+4 lacp_rate=1 mode 6

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  • My smtp server is spammed?

    - by Milos
    I have a server and the postfix client on it. Since several days, I noticed a lot of processes running there. When checked, there are a lot of emails sent. Here is an example from the mail log: Aug 18 11:54:56 mem postfix/smtpd[9963]: connect from dslb-188-096-082-167.188.096.pools.vodafone-ip.de[188.96.82.167] Aug 18 11:54:56 mem postfix/smtpd[9301]: connect from unknown[186.113.45.4] Aug 18 11:54:56 mem postfix/smtpd[9963]: 525E7114012D: client=dslb-188-096-082-167.188.096.pools.vodafone-ip.de[188.96.82.167] Aug 18 11:54:56 mem postfix/cleanup[9970]: 525E7114012D: message-id=<B55835C9027BFA9D16CCBB556DB2F48BB82DF004000480BA-db0c3ce8aa74446411898d0d2feb3001@email.filmforthoughtinc.com> Aug 18 11:54:56 mem postfix/qmgr[2581]: 525E7114012D: from=<[email protected]>, size=10702, nrcpt=1 (queue active) Aug 18 11:54:56 mem postfix/smtpd[9301]: EC52711401DC: client=unknown[186.113.45.4] Aug 18 11:54:57 mem postfix/smtpd[9963]: disconnect from dslb-188-096-082-167.188.096.pools.vodafone-ip.de[188.96.82.167] Aug 18 11:54:57 mem postfix/cleanup[8597]: EC52711401DC: message-id=<4C905D97606B436FE50C6F738DE014D9D84F2185BA815D81-1a4dbe6fc2bfcc8183f5faf901cfa15e@email.manguerasespecializadas.com> Aug 18 11:54:57 mem postfix/smtp[9971]: 525E7114012D: to=<[email protected]>, relay=mail.mdpi.com[209.237.236.228]:25, delay=1.2, delays=0.55/0/0.45/0.16, dsn=5.1.1, status=bounced (host mail.mdpi.com[209.237.236.228] said: 550 5.1.1 <[email protected]>: Recipient address rejected: mdpi.com (in reply to RCPT TO command)) Aug 18 11:54:57 mem postfix/cleanup[10067]: 8B1E11140268: message-id=<[email protected]> Aug 18 11:54:57 mem postfix/bounce[10001]: 525E7114012D: sender non-delivery notification: 8B1E11140268 Aug 18 11:54:57 mem postfix/qmgr[2581]: 8B1E11140268: from=<>, size=12693, nrcpt=1 (queue active) Aug 18 11:54:57 mem postfix/qmgr[2581]: 525E7114012D: removed Aug 18 11:54:57 mem postfix/qmgr[2581]: EC52711401DC: from=<[email protected]>, size=10978, nrcpt=1 (queue active) Aug 18 11:54:57 mem postfix/smtp[10013]: connect to aspmx.l.google.com[2607:f8b0:400d:c03::1b]:25: Network is unreachable Aug 18 11:54:57 mem postfix/smtpd[9301]: disconnect from unknown[186.113.45.4] Aug 18 11:54:58 mem postfix/smtp[10013]: 8B1E11140268: to=<[email protected]>, relay=aspmx.l.google.com[74.125.22.26]:25, delay=0.5, delays=0.06/0/0.28/0.16, dsn=5.1.1, status=bounced (host aspmx.l.google.com[74.125.22.26] said: 550-5.1.1 The email account that you tried to reach does not exist. Please try 550-5.1.1 double-checking the recipient's email address for typos or 550-5.1.1 unnecessary spaces. Learn more at 550 5.1.1 http://support.google.com/mail/bin/answer.py?answer=6596 l7si24621420qad.26 - gsmtp (in reply to RCPT TO command)) Aug 18 11:54:58 mem postfix/qmgr[2581]: 8B1E11140268: removed Aug 18 11:54:58 mem postfix/smtp[9971]: EC52711401DC: to=<[email protected]>, relay=mail.mdpi.com[209.237.236.228]:25, delay=1.2, delays=0.66/0/0.44/0.12, dsn=5.1.1, status=bounced (host mail.mdpi.com[209.237.236.228] said: 550 5.1.1 <[email protected]>: Recipient address rejected: mdpi.com (in reply to RCPT TO command)) Aug 18 11:54:58 mem postfix/cleanup[9970]: 414361140254: message-id=<[email protected]> Aug 18 11:54:58 mem postfix/bounce[10001]: EC52711401DC: sender non-delivery notification: 414361140254 Aug 18 11:54:58 mem postfix/qmgr[2581]: 414361140254: from=<>, size=13057, nrcpt=1 (queue active) Aug 18 11:54:58 mem postfix/qmgr[2581]: EC52711401DC: removed Aug 18 11:55:01 mem postfix/smtp[10002]: 414361140254: to=<[email protected]>, relay=manguerasespecializadas.com[99.198.96.210]:25, delay=2.9, delays=0.04/0/2.1/0.84, dsn=2.0.0, status=sent (250 OK id=1XJPGs-0007BE-OI) Aug 18 11:55:01 mem postfix/qmgr[2581]: 414361140254: removed IS my server attacked, spammed? How to check that? Thank you.

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  • Use IIS Application Initialization for keeping ASP.NET Apps alive

    - by Rick Strahl
    I've been working quite a bit with Windows Services in the recent months, and well, it turns out that Windows Services are quite a bear to debug, deploy, update and maintain. The process of getting services set up,  debugged and updated is a major chore that has to be extensively documented and or automated specifically. On most projects when a service is built, people end up scrambling for the right 'process' to use for administration. Web app deployment and maintenance on the other hand are common and well understood today, as we are constantly dealing with Web apps. There's plenty of infrastructure and tooling built into Web Tools like Visual Studio to facilitate the process. By comparison Windows Services or anything self-hosted for that matter seems convoluted.In fact, in a recent blog post I mentioned that on a recent project I'd been using self-hosting for SignalR inside of a Windows service, because the application is in fact a 'service' that also needs to send out lots of messages via SignalR. But the reality is that it could just as well be an IIS application with a service component that runs in the background. Either way you look at it, it's either a Windows Service with a built in Web Server, or an IIS application running a Service application, neither of which follows the standard Service or Web App template.Personally I much prefer Web applications. Running inside of IIS I get all the benefits of the IIS platform including service lifetime management (crash and restart), controlled shutdowns, the whole security infrastructure including easy certificate support, hot-swapping of code and the the ability to publish directly to IIS from within Visual Studio with ease.Because of these benefits we set out to move from the self hosted service into an ASP.NET Web app instead.The Missing Link for ASP.NET as a Service: Auto-LoadingI've had moments in the past where I wanted to run a 'service like' application in ASP.NET because when you think about it, it's so much easier to control a Web application remotely. Services are locked into start/stop operations, but if you host inside of a Web app you can write your own ticket and control it from anywhere. In fact nearly 10 years ago I built a background scheduling application that ran inside of ASP.NET and it worked great and it's still running doing its job today.The tricky part for running an app as a service inside of IIS then and now, is how to get IIS and ASP.NET launched so your 'service' stays alive even after an Application Pool reset. 7 years ago I faked it by using a web monitor (my own West Wind Web Monitor app) I was running anyway to monitor my various web sites for uptime, and having the monitor ping my 'service' every 20 seconds to effectively keep ASP.NET alive or fire it back up after a reload. I used a simple scheduler class that also includes some logic for 'self-reloading'. Hacky for sure, but it worked reliably.Luckily today it's much easier and more integrated to get IIS to launch ASP.NET as soon as an Application Pool is started by using the Application Initialization Module. The Application Initialization Module basically allows you to turn on Preloading on the Application Pool and the Site/IIS App, which essentially fires a request through the IIS pipeline as soon as the Application Pool has been launched. This means that effectively your ASP.NET app becomes active immediately, Application_Start is fired making sure your app stays up and running at all times. All the other features like Application Pool recycling and auto-shutdown after idle time still work, but IIS will then always immediately re-launch the application.Getting started with Application InitializationAs of IIS 8 Application Initialization is part of the IIS feature set. For IIS 7 and 7.5 there's a separate download available via Web Platform Installer. Using IIS 8 Application Initialization is an optional install component in Windows or the Windows Server Role Manager: This is an optional component so make sure you explicitly select it.IIS Configuration for Application InitializationInitialization needs to be applied on the Application Pool as well as the IIS Application level. As of IIS 8 these settings can be made through the IIS Administration console.Start with the Application Pool:Here you need to set both the Start Automatically which is always set, and the StartMode which should be set to AlwaysRunning. Both have to be set - the Start Automatically flag is set true by default and controls the starting of the application pool itself while Always Running flag is required in order to launch the application. Without the latter flag set the site settings have no effect.Now on the Site/Application level you can specify whether the site should pre load: Set the Preload Enabled flag to true.At this point ASP.NET apps should auto-load. This is all that's needed to pre-load the site if all you want is to get your site launched automatically.If you want a little more control over the load process you can add a few more settings to your web.config file that allow you to show a static page while the App is starting up. This can be useful if startup is really slow, so rather than displaying blank screen while the user is fiddling their thumbs you can display a static HTML page instead: <system.webServer> <applicationInitialization remapManagedRequestsTo="Startup.htm" skipManagedModules="true"> <add initializationPage="ping.ashx" /> </applicationInitialization> </system.webServer>This allows you to specify a page to execute in a dry run. IIS basically fakes request and pushes it directly into the IIS pipeline without hitting the network. You specify a page and IIS will fake a request to that page in this case ping.ashx which just returns a simple OK string - ie. a fast pipeline request. This request is run immediately after Application Pool restart, and while this request is running and your app is warming up, IIS can display an alternate static page - Startup.htm above. So instead of showing users an empty loading page when clicking a link on your site you can optionally show some sort of static status page that says, "we'll be right back".  I'm not sure if that's such a brilliant idea since this can be pretty disruptive in some cases. Personally I think I prefer letting people wait, but at least get the response they were supposed to get back rather than a random page. But it's there if you need it.Note that the web.config stuff is optional. If you don't provide it IIS hits the default site link (/) and even if there's no matching request at the end of that request it'll still fire the request through the IIS pipeline. Ideally though you want to make sure that an ASP.NET endpoint is hit either with your default page, or by specify the initializationPage to ensure ASP.NET actually gets hit since it's possible for IIS fire unmanaged requests only for static pages (depending how your pipeline is configured).What about AppDomain Restarts?In addition to full Worker Process recycles at the IIS level, ASP.NET also has to deal with AppDomain shutdowns which can occur for a variety of reasons:Files are updated in the BIN folderWeb Deploy to your siteweb.config is changedHard application crashThese operations don't cause the worker process to restart, but they do cause ASP.NET to unload the current AppDomain and start up a new one. Because the features above only apply to Application Pool restarts, AppDomain restarts could also cause your 'ASP.NET service' to stop processing in the background.In order to keep the app running on AppDomain recycles, you can resort to a simple ping in the Application_End event:protected void Application_End() { var client = new WebClient(); var url = App.AdminConfiguration.MonitorHostUrl + "ping.aspx"; client.DownloadString(url); Trace.WriteLine("Application Shut Down Ping: " + url); }which fires any ASP.NET url to the current site at the very end of the pipeline shutdown which in turn ensures that the site immediately starts back up.Manual Configuration in ApplicationHost.configThe above UI corresponds to the following ApplicationHost.config settings. If you're using IIS 7, there's no UI for these flags so you'll have to manually edit them.When you install the Application Initialization component into IIS it should auto-configure the module into ApplicationHost.config. Unfortunately for me, with Mr. Murphy in his best form for me, the module registration did not occur and I had to manually add it.<globalModules> <add name="ApplicationInitializationModule" image="%windir%\System32\inetsrv\warmup.dll" /> </globalModules>Most likely you won't need ever need to add this, but if things are not working it's worth to check if the module is actually registered.Next you need to configure the ApplicationPool and the Web site. The following are the two relevant entries in ApplicationHost.config.<system.applicationHost> <applicationPools> <add name="West Wind West Wind Web Connection" autoStart="true" startMode="AlwaysRunning" managedRuntimeVersion="v4.0" managedPipelineMode="Integrated"> <processModel identityType="LocalSystem" setProfileEnvironment="true" /> </add> </applicationPools> <sites> <site name="Default Web Site" id="1"> <application path="/MPress.Workflow.WebQueueMessageManager" applicationPool="West Wind West Wind Web Connection" preloadEnabled="true"> <virtualDirectory path="/" physicalPath="C:\Clients\…" /> </application> </site> </sites> </system.applicationHost>On the Application Pool make sure to set the autoStart and startMode flags to true and AlwaysRunning respectively. On the site make sure to set the preloadEnabled flag to true.And that's all you should need. You can still set the web.config settings described above as well.ASP.NET as a Service?In the particular application I'm working on currently, we have a queue manager that runs as standalone service that polls a database queue and picks out jobs and processes them on several threads. The service can spin up any number of threads and keep these threads alive in the background while IIS is running doing its own thing. These threads are newly created threads, so they sit completely outside of the IIS thread pool. In order for this service to work all it needs is a long running reference that keeps it alive for the life time of the application.In this particular app there are two components that run in the background on their own threads: A scheduler that runs various scheduled tasks and handles things like picking up emails to send out outside of IIS's scope and the QueueManager. Here's what this looks like in global.asax:public class Global : System.Web.HttpApplication { private static ApplicationScheduler scheduler; private static ServiceLauncher launcher; protected void Application_Start(object sender, EventArgs e) { // Pings the service and ensures it stays alive scheduler = new ApplicationScheduler() { CheckFrequency = 600000 }; scheduler.Start(); launcher = new ServiceLauncher(); launcher.Start(); // register so shutdown is controlled HostingEnvironment.RegisterObject(launcher); }}By keeping these objects around as static instances that are set only once on startup, they survive the lifetime of the application. The code in these classes is essentially unchanged from the Windows Service code except that I could remove the various overrides required for the Windows Service interface (OnStart,OnStop,OnResume etc.). Otherwise the behavior and operation is very similar.In this application ASP.NET serves two purposes: It acts as the host for SignalR and provides the administration interface which allows remote management of the 'service'. I can start and stop the service remotely by shutting down the ApplicationScheduler very easily. I can also very easily feed stats from the queue out directly via a couple of Web requests or (as we do now) through the SignalR service.Registering a Background Object with ASP.NETNotice also the use of the HostingEnvironment.RegisterObject(). This function registers an object with ASP.NET to let it know that it's a background task that should be notified if the AppDomain shuts down. RegisterObject() requires an interface with a Stop() method that's fired and allows your code to respond to a shutdown request. Here's what the IRegisteredObject::Stop() method looks like on the launcher:public void Stop(bool immediate = false) { LogManager.Current.LogInfo("QueueManager Controller Stopped."); Controller.StopProcessing(); Controller.Dispose(); Thread.Sleep(1500); // give background threads some time HostingEnvironment.UnregisterObject(this); }Implementing IRegisterObject should help with reliability on AppDomain shutdowns. Thanks to Justin Van Patten for pointing this out to me on Twitter.RegisterObject() is not required but I would highly recommend implementing it on whatever object controls your background processing to all clean shutdowns when the AppDomain shuts down.Testing it outI'm still in the testing phase with this particular service to see if there are any side effects. But so far it doesn't look like it. With about 50 lines of code I was able to replace the Windows service startup to Web start up - everything else just worked as is. An honorable mention goes to SignalR 2.0's oWin hosting, because with the new oWin based hosting no code changes at all were required, merely a couple of configuration file settings and an assembly directive needed, to point at the SignalR startup class. Sweet!It also seems like SignalR is noticeably faster running inside of IIS compared to self-host. Startup feels faster because of the preload.Starting and Stopping the 'Service'Because the application is running as a Web Server, it's easy to have a Web interface for starting and stopping the services running inside of the service. For our queue manager the SignalR service and front monitoring app has a play and stop button for toggling the queue.If you want more administrative control and have it work more like a Windows Service you can also stop the application pool explicitly from the command line which would be equivalent to stopping and restarting a service.To start and stop from the command line you can use the IIS appCmd tool. To stop:> %windir%\system32\inetsrv\appcmd stop apppool /apppool.name:"Weblog"and to start> %windir%\system32\inetsrv\appcmd start apppool /apppool.name:"Weblog"Note that when you explicitly force the AppPool to stop running either in the UI (on the ApplicationPools page use Start/Stop) or via command line tools, the application pool will not auto-restart immediately. You have to manually start it back up.What's not to like?There are certainly a lot of benefits to running a background service in IIS, but… ASP.NET applications do have more overhead in terms of memory footprint and startup time is a little slower, but generally for server applications this is not a big deal. If the application is stable the service should fire up and stay running indefinitely. A lot of times this kind of service interface can simply be attached to an existing Web application, or if scalability requires be offloaded to its own Web server.Easier to work withBut the ultimate benefit here is that it's much easier to work with a Web app as opposed to a service. While developing I can simply turn off the auto-launch features and launch the service on demand through IIS simply by hitting a page on the site. If I want to shut down an IISRESET -stop will shut down the service easily enough. I can then attach a debugger anywhere I want and this works like any other ASP.NET application. Yes you end up on a background thread for debugging but Visual Studio handles that just fine and if you stay on a single thread this is no different than debugging any other code.SummaryUsing ASP.NET to run background service operations is probably not a super common scenario, but it probably should be something that is considered carefully when building services. Many applications have service like features and with the auto-start functionality of the Application Initialization module, it's easy to build this functionality into ASP.NET. Especially when combined with the notification features of SignalR it becomes very, very easy to create rich services that can also communicate their status easily to the outside world.Whether it's existing applications that need some background processing for scheduling related tasks, or whether you just create a separate site altogether just to host your service it's easy to do and you can leverage the same tool chain you're already using for other Web projects. If you have lots of service projects it's worth considering… give it some thought…© Rick Strahl, West Wind Technologies, 2005-2013Posted in ASP.NET  SignalR  IIS   Tweet !function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="//platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs"); (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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  • CodePlex Daily Summary for Saturday, April 24, 2010

    CodePlex Daily Summary for Saturday, April 24, 2010New ProjectsAutoWorkLoad: Is an application intended to load hours to accounting system such as TimeTracker automatically.Chemistry Add-in for Word: The Chemistry Add-in for Word makes it easier for students, chemists, and researchers to insert and modify chemical information, such as labels, fo...Exceptional Visualizer: A Debugger Visualizer for VS 2008 that allows for effective visual tracing of an Exception stack. Useful for Unity Resolution Exceptions as seen i...FTE Owner Requirement: FIM 2010 Activity: Forefront Identity Manager 2010 (FIM) activity designed to ensure that group object has at least one assigned Full Time Employee owner. This policy...Globus CB: Group project 2009-2010Highlighterr for Visual C++ 2010: A simple code syntax highlighter to change the colors of classes, structs, interfaces, macros and typedefs in the Visual C++ 2010 IDE. It is implem...HTML to word (.doc): easy to export your HTML code to Microsoft Word (.doc extension)IETT Hat Güzergah Importer: http://www.iett.gov.tr sitesinden otobüs hat ve güzergahlarını indirerek RegEx ile parse eder. Elde ettiği verileri SQL Server'a kaydeder.Industrial Dashboard: WCF service that allows executing SQL Server stored procedures straight from javascript code, enabling sending and receiving structured data withou...iSafePDF: iSafePDF is a PDF protection software. it allows you to encrypt PDF document, signe them using a certificate and timestamp the signature. all those...Kordinat Dönüştürücü: * UTM Koordinatlardan DDD koordinatlara iki yönlü dönüşüm. * Google Earth üzerinde koordinat, polygon ve ruhsat gösterimi. * Türkiye Paftalarının...LinkedIn® for Windows Mobile: LinkedIn® for Windows Mobile brings your LinkedIn® account to your Window Mobile powered phone. See networkupdates / connections / profile etc. Macrosome: An F# project demonstrates recording and replaying user operations.Markov Text Generator: Markov Text Generator.MEFedMVVM: Library for building MEF MVVM applications for Silverlight and WPF. By using this library you can easily build MVVM application. *UNDER Constructi...Mercurial to Team Foundation Server Work Item Hook: This is a Mercurial hook that will mark Team Foundation Server work items as resolved with a specific format in the commit description.Metaball WPF HLSL: Metaballs in WPF 3 with pixel shaders.Project Audiophile: Project Audiophile is a suite of applications and libraries built for .Net and Mono for the purposes of listening and organising music.RSS Application Updater: A Libbrary that helps you to update your app from your web site's feed. works very good with drupal .Sherwood Content Management Suite: A project that aims to provide a powerful and flexible tool for aggregating data from different data sources. Add your own plugins to store wanted ...Sonic.Net: Sonic.Net is a .Net Library designed to facilitate development of rich client applications both in Silverlight and WPF. Sonic.Net makes use of all ...StoichiometriCS: Stoichiometric Chemical Equation Solver.Vate Game Engine: Vate is a new XNA Game Engine. For more information about this project, please visit http://blog.aphysoft.com.Yahoo OpenID YQL Demo: This is demo program how to use Yahoo OpenID and Yahoo Query Language (YQL)New ReleasesBasic Sprite Sheet Creator: Sprite Tool V1.11: I had a small error when using multiple animations without the one pixel border that I overlooked when rewriting the code. It should be completely ...Braintree Client Library: Braintree-2.0.0: Updated IsSuccess() on transaction results to return false on declined transactions Search results now implement IEnumerable and will automatical...BV Commerce 5 Import Export Tools: Version 5.7.0 (for BV Commerce 5.7): Updated version compatible with BV Commerce 5.7. Do not use on earlier versions.Chemistry Add-in for Word: Chemistry Add-in for Word Beta 2: This is the source code release of the Chemistry Add-in for Word Beta 2. System Requirements To run this software, you’ll need the following: Wind...Controlled Vocabulary: 1.0.0.5: System Requirements Outlook 2007 / 2010 .Net Framework 3.5 VSTO 2010 Runtime Installation 1. Close Outlook (Use Task Manager to ensure no running ...DotNetNuke® Store: 02.01.33 RC: What's New in this release? Bugs corrected: - Fixed a bug related to encryption cookie. New Features: - Adden token pair [IFLOGGED] [/IFLOGGED] us...EdiliOS: Beta 0.2.1: Aggiunto supporto a FidoCadJ, editor FidoCad multipiattaforma di Davide Bucci, con Libreria di Ingegneria Civile integrata.Event Scavenger: Admin tool Version 3.1.1: Fixed the Admin tool that fails on editing general settings. Only Admin tool is affected.Exceptional Visualizer: Exception Visualizer: A Debugger Visualizer to help with long chains of exceptions where digging through the inner exceptions is hard to do. Specifically, this release ...fracback: Binaries: Use at your own riskFree Silverlight & WPF Chart Control - Visifire: Visifire for SL 4 and WPF Charts 3.5.1 Released: Hi, This release contains fix for the following bug: Chart threw exception with DateTime axis if IntervalType property was set as ‘Minutes’ in Ax...Free Silverlight & WPF Chart Control - Visifire: Visifire Silverlight and WPF Charts 3.0.8 Released: Hi, This release contains fix for the following bug: * Chart threw exception with DateTime axis if IntervalType property was set as ‘Minutes’...GeoUtility Library: GeoUtility Library 3.1.5.0: Please Note: This is an open source version. The commercial version offers much more functionality. Help files (english/german) are only available ...Highlighterr for Visual C++ 2010: Highlighterr for Visual C++ 2010 Test Release 1.0: To install the extension, download the and then double-click on the Highlighterr.vsix file. This should bring up a dialog saying something about wh...Highlighterr for Visual C++ 2010: Highlighterr for Visual C++ 2010 Test Release 1.01: The lack of support for /* */ comments was annoying me, so I added it. To install the extension, download the and then double-click on the Highlig...Home Access Plus+: v4.0.1.0: v4.0.1.0 Beta Change Log: Fixed an issue with laptops and the booking system (CSS and code fixes) Moved filters to top Added some Javascript to...HTML to word (.doc): FullSourceDownload: the full source contain: bin/AppWebdx7wusqu.dll Default.aspx htw.ascx htw.ascx.vb Web.configIndustrial Dashboard: 3.0 Beta: Added Example with Dojox.DataGrid Added Example with Ext.js ChartiSafePDF: iSafePDF v1.2: This is the first public release, this version support : PDF signature, timestamped signature, multi-signature, PDF encryption and meta-data modifi...linq.js - LINQ for JavaScript: ver 2.0.0.0: all code rewrite from scratch. enumerator support Dispose. namespace changed E, Linq.Enumerable -> Enumerable delete methods ToJSON ToTable Trace...LogikBug's IoC Container: Third Release: This project is dependent upon Microsoft.Practices.ServiceLocation and must be referenced when referencing LogikBug.Injection. Click here to view d...Macrosome: 0.0.1 preview: Key pointsOnly mouse clicks supported Just for preview: not stable How to useStart from Macrosome.Wpf.exe Click "Record" button will start oper...Mercurial to Team Foundation Server Work Item Hook: Version 0.1: This is the first version of the Mercurial to Team Foundation Server hook. It currently supports only adding comments to existing work items.MOSSDAL: MOSS Data Access Layer for data from the Sharepoint Lists Service: MOSSDAL Silverlight Framework Release 1: This is the first release of MOSSDAL for silverlight. For the MOSSDAL Framework for .NET release 1 click hereMOSSDAL: MOSS Data Access Layer for data from the Sharepoint Lists Service: MOSSDAL Silverlight Sample Release 1: This is the first release of the MOSSDAL framework samples for Silverlight. For the MOSSDAL .NET Release 1 Sample click hereMyWSAT - ASP.NET Membership Administration Tool: MyWSAT v3.5.1: MyWSAT 3.5.1 Update Notes - April 23rd 2010 1.) Fixed standard profile problem in web.config as well as on all the forms the profiles are used. The...NetPE: NetPE v1.0: Initial Release of NetPE. Features: -View & Editing Portable Executable -Hex editor -Full Metadata Support -Disassemble Cil/x86 codeNSIS Autorun: NSIS Autorun 0.1.1: NSIS Autorun 0.1.1 This release includes source code, application binary, and example materials.Over Store: OverStore Release 1.17.0.0: Version 1.17.0.0 - AdoNetStorage: AdoNetStorage refactored. Detailed Log messages added on each event. Database resource management moved to A...RoTwee: RoTwee (11.0.0.3): Fix for "17385 Remove saved degree val from code"Silverlight 4.0 Popup Menu: Popup Menu for Silverlight 4.0: This is the first project release. Added drop shadow and fade in effects. Left click and hover events are also supported.Silverlight 4.0 Popup Menu: Popup menu for Silverlight 4.0 Version 0.8: - Placed the invoker for the 'Opening' event handler within a dispatcher. This ensures that the visual tree is created before it is accessed.sNPCedit: sNPCedit v0.9: + Some changes in GUI and Behaviour + Added: Search functionSonic.Net: Sonic.Net v1.0.0: Sonic.Net v1.0.0 Targets Net 3.5 sp1 and Sinverlight 3 Includes: sonic.UnityConfiguration.Silverlight sonic.UnityConfiguration.WpfSurvey - web survey & form engine: Survey™ 1.2.1: Survey™ 1.2.1 release (based on the original Nsurvey 1.9.1. source files) New Features & fixes: 1. Final bits of code rewritten to become 100% ...SysPad: 4.10.10.2: Release Notes A folder management and scratchpad utility; especially useful in a business network setting that utilizes numerous, commonly used fol...Third Hand - Use your voice to control Visual Studio: Update for VS2010: Added support for VS2010, and minor improvements when using the grid.TiledLib: TiledLib 1.2: - Added overload of Map.Draw that specifies the area to draw - Added demo of a camera control for a mapXMLPreprocess: 2.0.12: What's new in this release: This release contains a number of enhancements based on feedback given through the discussion forums and issue tracker....Xrns2XMod: Xrns2Xmod 0.8: Added >> Real preliminary sound conversion for XM >> Some code optimizations Note Some samples might not be converted due to a flac parsing error ...Yahoo OpenID YQL Demo: Yahoo YQL .Net Demo: This is a demo program for using YQL with C#.netYahoo OpenID YQL Demo: YQL Demo: This is a demo program using Yahoo YQL with C#.NetYahoo OpenID YQL Demo: YQLDemo using .Net: This is a demo program for using Yahoo YQL with C#.NetMost Popular ProjectsRawrWBFS ManagerAJAX Control ToolkitSilverlight ToolkitMicrosoft SQL Server Product Samples: Databasepatterns & practices – Enterprise LibraryWindows Presentation Foundation (WPF)ASP.NETMicrosoft SQL Server Community & SamplesPHPExcelMost Active Projectspatterns & practices – Enterprise LibraryRawrBlogEngine.NETParticle Plot PivotNB_Store - Free DotNetNuke Ecommerce Catalog ModuleDotNetZip LibraryGMap.NET - Great Maps for Windows Forms & Presentationturing machine simulatorIonics Isapi Rewrite Filterpatterns & practices: Composite WPF and Silverlight

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  • Optimized Image Loading in a UIScrollView

    - by Michael Gaylord
    I have a UIScrollView that has a set of images loaded side-by-side inside it. You can see an example of my app here: http://www.42restaurants.com. My problem comes in with memory usage. I want to lazy load the images as they are about to appear on the screen and unload images that aren't on screen. As you can see in the code I work out at a minimum which image I need to load and then assign the loading portion to an NSOperation and place it on an NSOperationQueue. Everything works great apart from a jerky scrolling experience. I don't know if anyone has any ideas as to how I can make this even more optimized, so that the loading time of each image is minimized or so that the scrolling is less jerky. - (void)scrollViewDidScroll:(UIScrollView *)scrollView{ [self manageThumbs]; } - (void) manageThumbs{ int centerIndex = [self centerThumbIndex]; if(lastCenterIndex == centerIndex){ return; } if(centerIndex >= totalThumbs){ return; } NSRange unloadRange; NSRange loadRange; int totalChange = lastCenterIndex - centerIndex; if(totalChange > 0){ //scrolling backwards loadRange.length = fabsf(totalChange); loadRange.location = centerIndex - 5; unloadRange.length = fabsf(totalChange); unloadRange.location = centerIndex + 6; }else if(totalChange < 0){ //scrolling forwards unloadRange.length = fabsf(totalChange); unloadRange.location = centerIndex - 6; loadRange.length = fabsf(totalChange); loadRange.location = centerIndex + 5; } [self unloadImages:unloadRange]; [self loadImages:loadRange]; lastCenterIndex = centerIndex; return; } - (void) unloadImages:(NSRange)range{ UIScrollView *scrollView = (UIScrollView *)[[self.view subviews] objectAtIndex:0]; for(int i = 0; i < range.length && range.location + i < [scrollView.subviews count]; i++){ UIView *subview = [scrollView.subviews objectAtIndex:(range.location + i)]; if(subview != nil && [subview isKindOfClass:[ThumbnailView class]]){ ThumbnailView *thumbView = (ThumbnailView *)subview; if(thumbView.loaded){ UnloadImageOperation *unloadOperation = [[UnloadImageOperation alloc] initWithOperableImage:thumbView]; [queue addOperation:unloadOperation]; [unloadOperation release]; } } } } - (void) loadImages:(NSRange)range{ UIScrollView *scrollView = (UIScrollView *)[[self.view subviews] objectAtIndex:0]; for(int i = 0; i < range.length && range.location + i < [scrollView.subviews count]; i++){ UIView *subview = [scrollView.subviews objectAtIndex:(range.location + i)]; if(subview != nil && [subview isKindOfClass:[ThumbnailView class]]){ ThumbnailView *thumbView = (ThumbnailView *)subview; if(!thumbView.loaded){ LoadImageOperation *loadOperation = [[LoadImageOperation alloc] initWithOperableImage:thumbView]; [queue addOperation:loadOperation]; [loadOperation release]; } } } } EDIT: Thanks for the really great responses. Here is my NSOperation code and ThumbnailView code. I tried a couple of things over the weekend but I only managed to improve performance by suspending the operation queue during scrolling and resuming it when scrolling is finished. Here are my code snippets: //In the init method queue = [[NSOperationQueue alloc] init]; [queue setMaxConcurrentOperationCount:4]; //In the thumbnail view the loadImage and unloadImage methods - (void) loadImage{ if(!loaded){ NSString *filename = [NSString stringWithFormat:@"%03d-cover-front", recipe.identifier, recipe.identifier]; NSString *directory = [NSString stringWithFormat:@"RestaurantContent/%03d", recipe.identifier]; NSString *path = [[NSBundle mainBundle] pathForResource:filename ofType:@"png" inDirectory:directory]; UIImage *image = [UIImage imageWithContentsOfFile:path]; imageView = [[ImageView alloc] initWithImage:image andFrame:CGRectMake(0.0f, 0.0f, 176.0f, 262.0f)]; [self addSubview:imageView]; [self sendSubviewToBack:imageView]; [imageView release]; loaded = YES; } } - (void) unloadImage{ if(loaded){ [imageView removeFromSuperview]; imageView = nil; loaded = NO; } } Then my load and unload operations: - (id) initWithOperableImage:(id<OperableImage>) anOperableImage{ self = [super init]; if (self != nil) { self.image = anOperableImage; } return self; } //This is the main method in the load image operation - (void)main { [image loadImage]; } //This is the main method in the unload image operation - (void)main { [image unloadImage]; }

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