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• SQL Server IO handling mechanism can be severely affected by high CPU usage

  - by sqlworkshops

  Are you using SSD or SAN / NAS based storage solution and sporadically observe SQL Server experiencing high IO wait times or from time to time your DAS / HDD becomes very slow according to SQL Server statistics? Read on… I need your help to up vote my connect item – https://connect.microsoft.com/SQLServer/feedback/details/744650/sql-server-io-handling-mechanism-can-be-severely-affected-by-high-cpu-usage. Instead of taking few seconds, queries could take minutes/hours to complete when CPU is busy.In SQL Server when a query / request needs to read data that is not in data cache or when the request has to write to disk, like transaction log records, the request / task will queue up the IO operation and wait for it to complete (task in suspended state, this wait time is the resource wait time). When the IO operation is complete, the task will be queued to run on the CPU. If the CPU is busy executing other tasks, this task will wait (task in runnable state) until other tasks in the queue either complete or get suspended due to waits or exhaust their quantum of 4ms (this is the signal wait time, which along with resource wait time will increase the overall wait time). When the CPU becomes free, the task will finally be run on the CPU (task in running state).The signal wait time can be up to 4ms per runnable task, this is by design. So if a CPU has 5 runnable tasks in the queue, then this query after the resource becomes available might wait up to a maximum of 5 X 4ms = 20ms in the runnable state (normally less as other tasks might not use the full quantum).In case the CPU usage is high, let’s say many CPU intensive queries are running on the instance, there is a possibility that the IO operations that are completed at the Hardware and Operating System level are not yet processed by SQL Server, keeping the task in the resource wait state for longer than necessary. In case of an SSD, the IO operation might even complete in less than a millisecond, but it might take SQL Server 100s of milliseconds, for instance, to process the completed IO operation. For example, let’s say you have a user inserting 500 rows in individual transactions. When the transaction log is on an SSD or battery backed up controller that has write cache enabled, all of these inserts will complete in 100 to 200ms. With a CPU intensive parallel query executing across all CPU cores, the same inserts might take minutes to complete. WRITELOG wait time will be very high in this case (both under sys.dm_io_virtual_file_stats and sys.dm_os_wait_stats). In addition you will notice a large number of WAITELOG waits since log records are written by LOG WRITER and hence very high signal_wait_time_ms leading to more query delays. However, Performance Monitor Counter, PhysicalDisk, Avg. Disk sec/Write will report very low latency times.Such delayed IO handling also occurs to read operations with artificially very high PAGEIOLATCH_SH wait time (with number of PAGEIOLATCH_SH waits remaining the same). This problem will manifest more and more as customers start using SSD based storage for SQL Server, since they drive the CPU usage to the limits with faster IOs. We have a few workarounds for specific scenarios, but we think Microsoft should resolve this issue at the product level. We have a connect item open – https://connect.microsoft.com/SQLServer/feedback/details/744650/sql-server-io-handling-mechanism-can-be-severely-affected-by-high-cpu-usage - (with example scripts) to reproduce this behavior, please up vote the item so the issue will be addressed by the SQL Server product team soon.Thanks for your help and best regards,Ramesh MeyyappanHome: www.sqlworkshops.comLinkedIn: http://at.linkedin.com/in/rmeyyappan

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• No external microphone Acer AO722

  - by Leeghwater

  The ACER AO722 comes with an external mic input, and this input is not recognised by Alsa mixer or Sound (in System Settings). There are various comments on this problem, but no real solutions. For example External Mic not working but Internal Mic works on an Acer Aspiron AO722. Using the internal mic is not an option, as I need to use skype professionally. I have tried everything in alsamixer (accessible through the Terminal Ctrl+Alt+t, command: alsamixer), and in Sound (under System Settings). I have also installed Pulseaudio. But to no avail. The headset is working normally under Skype in Windows. My AO722 came with Windows 7 on it, so I have installed Skype there too. My headset has separate connectors for ears and mic, and these go into the respective output and input on the right side of the laptop. This location: http://bernaerts.dyndns.org/linux/202-ubuntu-acer-ao722 sounds like an effective solution but it is for Ubuntu Natty 11.04. The solution suggested sounds drastic to me: replace the kernel 2.6.38-13 with version 2.6.38-12. I use Ubuntu 12.04, and my kernel is 3.2.0-30-generic-pae. Question: could I try this solution with Ubuntu 12.04? Is this a risky thing to do? I have found harware work around this problem. The audio output seems to be a combi output with also a microphone connection. I have made an adapter for this output. I used a 4 contacts 3,5 mm audio jack plug. To this plug I have soldered 2 female (common stereo) connectors, one for ears and one for the mic of my headset. The 4 contacts jack, which goes into the laptop (in audio OUTput) is wired as follows: tip = hot audio right; first sleeve after tip = hot audio left; second sleeve = common earth (for both ears and microphone); the 3rd sleeve = microphone signal input. In the connector which I could buy, the 3rd sleeve is not so much a sleeve, but part of the metal base of the connector; normally you would expect this one to be connect to earth. But connecting the mic signal to it works. Maybe ready made adapters of this kind and even headsets with a combi jack can simply be purchased; I didn't check. When I plug in the 4 contacts jack, Sound and Alsamixer immediately recognise an external microphone (even if no mic is connected to the adapter). In Sound, under the Input tab, 'Settings for internal microphone' changes into 'Setting for microphone'. The microphone comes through loud and clear, however there is a constant noise in the background. Others have reported this too. If I disconnect the external mic from the adapter, or shortcircuit the external microphone, the noise gets less but does not disappear. Therefore, it is not background noise from the room, but it comes from the computer itself. However, if you talk directly in the microphone of the headset, the noise level is acceptable for VOIP. The headset of my mobile phone Nokia C1 mobile comes wwith a 4 contacts combi 3,5mm jack plug. However, this one works (ear and mic) with the AO722 only if not inserted fully. Possibly the wiring of this headset jack is different. I cannot find detailed specs of the AO722, and don't know whether the audio 'output' was actually designed as a combi input/output. I have seen that at least one other AO model has a combi connector only. In any case, I do not believe that connecting your headset in this way will harm your computer. I would still appreciate a software solution. This must be possible, because the proper microphone input connector works under MS Windows.

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• Randomely loosing wireless connexion with Cubuntu 12.04

  - by statquant

  I am presently experiencing random disconnections from my wireless network. It looks like it is more and more frequent (however I have not seen any clear pattern). This is killing me... Here is some information that should help (from ubuntu forums). Thanks for reading Machine : Acer Aspire S3 statquant@euclide:~$ lsb_release -d Description: Ubuntu 12.04.1 LTS statquant@euclide:~$ uname -mr 3.2.0-33-generic x86_64 statquant@euclide:~$ sudo /etc/init.d/networking restart * Running /etc/init.d/networking restart is deprecated because it may not enable again some interfaces * Reconfiguring network interfaces... statquant@euclide:~$ lspci 02:00.0 Network controller: Atheros Communications Inc. AR9485 Wireless Network Adapter (rev 01) statquant@euclide:~$ lsusb Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Bus 001 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub Bus 002 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub Bus 001 Device 004: ID 064e:c321 Suyin Corp. Bus 002 Device 003: ID 0bda:0129 Realtek Semiconductor Corp. statquant@euclide:~$ ifconfig wlan0 Link encap:Ethernet HWaddr 74:de:2b:dd:c4:78 inet addr:192.168.1.3 Bcast:192.168.1.255 Mask:255.255.255.0 inet6 addr: fe80::76de:2bff:fedd:c478/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:913 errors:0 dropped:0 overruns:0 frame:0 TX packets:802 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:873218 (873.2 KB) TX bytes:125826 (125.8 KB) statquant@euclide:~$ iwconfig wlan0 IEEE 802.11bgn ESSID:"Bbox-D646D1" Mode:Managed Frequency:2.437 GHz Access Point: 00:19:70:80:01:6C Bit Rate=65 Mb/s Tx-Power=16 dBm Retry long limit:7 RTS thr:off Fragment thr:off Power Management:on Link Quality=56/70 Signal level=-54 dBm Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0 Tx excessive retries:0 Invalid misc:71 Missed beacon:0 statquant@euclide:~$ dmesg | grep "wlan" [ 17.495866] ADDRCONF(NETDEV_UP): wlan0: link is not ready [ 17.498950] ADDRCONF(NETDEV_UP): wlan0: link is not ready [ 20.072015] wlan0: authenticate with 00:19:70:80:01:6c (try 1) [ 20.269853] wlan0: authenticate with 00:19:70:80:01:6c (try 2) [ 20.272386] wlan0: authenticated [ 20.298682] wlan0: associate with 00:19:70:80:01:6c (try 1) [ 20.302321] wlan0: RX AssocResp from 00:19:70:80:01:6c (capab=0x431 status=0 aid=1) [ 20.302325] wlan0: associated [ 20.307307] ADDRCONF(NETDEV_CHANGE): wlan0: link becomes ready [ 30.402292] wlan0: no IPv6 routers present statquant@euclide:~$ sudo lshw -C network [sudo] password for statquant: *-network description: Wireless interface product: AR9485 Wireless Network Adapter vendor: Atheros Communications Inc. physical id: 0 bus info: pci@0000:02:00.0 logical name: wlan0 version: 01 serial: 74:de:2b:dd:c4:78 width: 64 bits clock: 33MHz capabilities: pm msi pciexpress bus_master cap_list rom ethernet physical wireless configuration: broadcast=yes driver=ath9k driverversion=3.2.0-33-generic firmware=N/A ip=192.168.1.3 latency=0 link=yes multicast=yes wireless=IEEE 802.11bgn resources: irq:17 memory:c0400000-c047ffff memory:afb00000-afb0ffff statquant@euclide:~$ iwlist scan wlan0 Scan completed : Cell 01 - Address: 00:19:70:80:01:6C Channel:6 Frequency:2.437 GHz (Channel 6) Quality=56/70 Signal level=-54 dBm Encryption key:on ESSID:"Bbox-D646D1" Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 6 Mb/s 9 Mb/s; 12 Mb/s; 18 Mb/s Bit Rates:24 Mb/s; 36 Mb/s; 48 Mb/s; 54 Mb/s Mode:Master Extra:tsf=000000125fb152bb Extra: Last beacon: 40020ms ago IE: Unknown: 000B42626F782D443634364431 IE: Unknown: 010882848B960C121824 IE: Unknown: 030106 IE: IEEE 802.11i/WPA2 Version 1 Group Cipher : TKIP Pairwise Ciphers (2) : CCMP TKIP Authentication Suites (1) : PSK IE: WPA Version 1 Group Cipher : TKIP Pairwise Ciphers (2) : CCMP TKIP Authentication Suites (1) : PSK IE: Unknown: 2A0100 IE: Unknown: 32043048606C IE: Unknown: DD180050F2020101820003A4000027A4000042435E0062322F00 IE: Unknown: 2D1A4C101BFF00000000000000000000000000000000000000000000 IE: Unknown: 3D1606080800000000000000000000000000000000000000 IE: Unknown: DD0900037F01010000FF7F IE: Unknown: DD0A00037F04010000000000 And... finally, please note that I did the following (after looking for fixes of similar problems), but unfortunately it did not work sudo modprobe -r iwlwifi sudo modprobe iwlwifi 11n_disable=1

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• Detect user logout / shutdown in Python / GTK under Linux

  - by Ivo Wetzel

  OK this is presumably a hard one, I've got an pyGTK application that has random crashes due to X Window errors that I can't catch/control. So I created a wrapper that restarts the app as soon as it detects a crash, now comes the problem, when the user logs out or shuts down the system, the app exits with status 1. But on some X errors it does so too. So I tried literally anything to catch the shutdown/logout, with no success, here's what I've tried: import pygtk import gtk import sys class Test(gtk.Window): def delete_event(self, widget, event, data=None): open("delete_event", "wb") def destroy_event(self, widget, data=None): open("destroy_event", "wb") def destroy_event2(self, widget, event, data=None): open("destroy_event2", "wb") def __init__(self): gtk.Window.__init__(self, gtk.WINDOW_TOPLEVEL) self.show() self.connect("delete_event", self.delete_event) self.connect("destroy", self.destroy_event) self.connect("destroy-event", self.destroy_event2) def foo(): open("add_event", "wb") def ex(): open("sys_event", "wb") from signal import * def clean(sig): f = open("sig_event", "wb") f.write(str(sig)) f.close() exit(0) for sig in (SIGABRT, SIGILL, SIGINT, SIGSEGV, SIGTERM): signal(sig, lambda *args: clean(sig)) def at(): open("at_event", "wb") import atexit atexit.register(at) f = Test() sys.exitfunc = ex gtk.quit_add(gtk.main_level(), foo) gtk.main() open("exit_event", "wb") Not one of these succeeds, is there any low level way to detect the system shutdown? Google didn't find anything related to that. I guess there must be a way, am I right? :/

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• Play mp3 using Python, PyQt, and Phonon

  - by KeyboardInterrupt

  I been trying all day to figure out the Qt's Phonon library with Python. My long term goal is to see if I could get it to play a mms:// stream, but since I can't find an implementation of this done anywhere, I will figure that part out myself. (figured I'd put it out there if anyone knew more about this specifically, if not no big deal.) Anyway, I figured I'd work backwards from a working example I found online. This launches a file browser and will play the mp3 file specified. I wanted to strip out the file browser stuff and get it down to the essentials of executing the script and having it play an Mp3 file with a hardcoded path. I'm assuming my problem is a misunderstanding of setCurrentSource() and specifying the data types. (see: http://www.riverbankcomputing.co.uk/static/Docs/PyQt4/html/phonon-mediasource.html#fileName) I'm keeping my question kind of broad because ANY help with understanding Phonon would be greatly appreciated. import sys from PyQt4.QtGui import QApplication, QMainWindow, QDirModel, QColumnView from PyQt4.QtGui import QFrame from PyQt4.QtCore import SIGNAL from PyQt4.phonon import Phonon class MainWindow(QMainWindow): m_model = QDirModel() def __init__(self): QMainWindow.__init__(self) self.m_fileView = QColumnView(self) self.m_media = None self.setCentralWidget(self.m_fileView) self.m_fileView.setModel(self.m_model) self.m_fileView.setFrameStyle(QFrame.NoFrame) self.connect(self.m_fileView, SIGNAL("updatePreviewWidget(const QModelIndex &)"), self.play) def play(self, index): self.delayedInit() self.m_media.setCurrentSource( Phonon.MediaSource(self.m_model.filePath(index))) self.m_media.play() def delayedInit(self): if not self.m_media: self.m_media = Phonon.MediaObject(self) audioOutput = Phonon.AudioOutput(Phonon.MusicCategory, self) Phonon.createPath(self.m_media, audioOutput) def main(): app = QApplication(sys.argv) QApplication.setApplicationName("Phonon Tutorial 2 (Python)") mw = MainWindow() mw.show() sys.exit(app.exec_()) if __name__ == '__main__': main()

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• QWebView not loading external resources

  - by Nick

  Hi. I'm working on a kiosk web browser using Qt and PyQt4. QWebView seems to work quite well except for one quirk. If a URL fails to load for any reason, I want to redirect the user to a custom error page. I've done this using the loadFinished() signal to check the result, and change the URL to the custom page if necessary using QWebView.load(). However, any page I attempt to load here fails to pull in external resources like CSS or images. Using QWebView.load() to set the initial page at startup seems to work fine, and clicking any link on the custom error page will result in the destination page loading fine. It's just the error page that doesn't work. I'm really not sure where to go next. I've included the source for an app that will replicate the problem below. It takes a URL as a command line argument - a valid URL will display correctly, a bad URL (eg. DNS resolution fails) will redirect to Google, but with the logo missing. import sys from PyQt4 import QtGui, QtCore, QtWebKit class MyWebView(QtWebKit.QWebView): def __init__(self, parent=None): QtWebKit.QWebView.__init__(self, parent) self.resize(800, 600) self.load(QtCore.QUrl(sys.argv[1])) self.connect(self, QtCore.SIGNAL('loadFinished(bool)'), self.checkLoadResult) def checkLoadResult(self, result): if (result == False): self.load(QtCore.QUrl('http://google.com')) app = QtGui.QApplication(sys.argv) main = MyWebView() main.show() sys.exit(app.exec_()) If anyone could offer some advice it would be greatly appreciated.

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• QTcpServer not emiting signals

  - by Timothy Baldridge

  Okay, I'm sure this is simple, but I'm not seeing it: HTTPServer::HTTPServer(QObject *parent) : QTcpServer(parent) { connect(this, SIGNAL(newConnection()), this, SLOT(acceptConnection())); } void HTTPServer::acceptConnection() { qDebug() << "Got Connection"; QTcpSocket *clientconnection = this->nextPendingConnection(); connect(clientconnection, SIGNAL(disconnected()), clientconnection, SLOT(deleteLater())); HttpRequest *req = new HttpRequest(clientconnection, this); req->processHeaders(); delete req; } int main(int argc, char *argv[]) { QCoreApplication a(argc, argv); HTTPServer http(0); http.listen(QHostAddress::Any, 8011); qDebug() << "Started: " << http.isListening() << http.serverAddress() << ":" << http.serverPort(); return a.exec(); } According to the docs my acceptConnection() slot should be called whenever there is a new connection. I can connect into this tcp port with a browser or telnet, and I don't get any errors, so I know it's listening, execution never goes to my acceptConnection() function? And yes my objects inherit from QObject, I've just stripped the code down to the essential parts above. There's no build errors....

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• PyQt and unittest - how to handle signals and slots

  - by Einar

  Hello, some small application I'm developing uses a module I have written to check certain web services via a REST API. I've been trying to add unit tests to it so I don't break stuff, and I stumbled upon a problem. I use a lot of signal-slot connections to perform operations asynchronously. For example a typical test would be (pseudo-Python), with postDataDownloaded as a signal: def testConnection(self): "Test connection and posts retrieved" def length_test(): self.assertEqual(len(self.client.post_data), 5) self.client.postDataReady.connect(length_test) self.client.get_post_list(limit=5) Now, unittest will report this test to be "ok" when running, regardless of the result (as another slot is being called), even if asserts fail (I will get an unhandled AssertionError). Example when deliberatiely making the test fail: Test connection and posts retrieved ... ok [... more tests...] OK Traceback (most recent call last): [...] AssertionError: 4 != 5 The slot inside the test is merely an experiment: I get the same results if it's outside (instance method). I also have to add that the various methods I'm calling all make HTTP requests, which means they take a bit of time (I need to mock the request - in the mean time I'm using SimpleHTTPServer to fake the connections and give them proper data). Is there a way around this problem?

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• Qt, no such slot error

  - by Martin Beckett

  I'm having a strange problem with slots in Qt4.6 I have a tree control that I am trying to fire an event back to the mainwindow to edit something. I have boiled it down to this minimal example: class MainWindow : public QMainWindow { Q_OBJECT public: MainWindow(int argc, char **argv ); private Q_SLOTS: void about() {QMessageBox::about(this, "about","about"); } // Just the defaul about box void doEditFace() {QMessageBox::about(this, "test","doEditFace"); } // pretty identical .... } class TreeModel : public QAbstractItemModel { Q_OBJECT Q_SIGNALS: void editFace(); ... } In my Mainwindow() I have connect(treeModel, SIGNAL(editFace()), this, SLOT(about())); // returns true connect(treeModel, SIGNAL(editFace()), this, SLOT(doEditFace())); // returns false When I run it the second line gives a warning. Object::connect: No such slot MainWindow::doEditFace() in \src\mainwindow.cpp:588 As far as I can see the doEditFace() is in the moc_ qmeta class perfectly correctly. And the edit event fires and pops up the about box. The order doesn't matterm if I connect the about box second it still works but my slot doesnt! vS2008 windowsXP qt4.6.2

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• What are alternatives to Win32 PulseEvent() function?

  - by Bill

  The documentation for the Win32 API PulseEvent() function (kernel32.dll) states that this function is “… unreliable and should not be used by new applications. Instead, use condition variables”. However, condition variables cannot be used across process boundaries like (named) events can. I have a scenario that is cross-process, cross-runtime (native and managed code) in which a single producer occasionally has something interesting to make known to zero or more consumers. Right now, a well-known named event is used (and set to signaled state) by the producer using this PulseEvent function when it needs to make something known. Zero or more consumers wait on that event (WaitForSingleObject()) and perform an action in response. There is no need for two-way communication in my scenario, and the producer does not need to know if the event has any listeners, nor does it need to know if the event was successfully acted upon. On the other hand, I do not want any consumers to ever miss any events. In other words, the system needs to be perfectly reliable – but the producer does not need to know if that is the case or not. The scenario can be thought of as a “clock ticker” – i.e., the producer provides a semi-regular signal for zero or more consumers to count. And all consumers must have the correct count over any given period of time. No polling by consumers is allowed (performance reasons). The ticker is just a few milliseconds (20 or so, but not perfectly regular). Raymen Chen (The Old New Thing) has a blog post pointing out the “fundamentally flawed” nature of the PulseEvent() function, but I do not see an alternative for my scenario from Chen or the posted comments. Can anyone please suggest one? Please keep in mind that the IPC signal must cross process boundries on the machine, not simply threads. And the solution needs to have high performance in that consumers must be able to act within 10ms of each event.

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• iPhone app memory leak with UIImage animation? Problem testing on device

  - by user157733

  I have an animation which works fine in the simulator but crashes on the device. I am getting the following error... Program received signal: “0”. The Debugger has exited due to signal 10 (SIGBUS) A bit of investigating suggests that the UIImages are not getting released and I have a memory leak. I am new to this so can someone tell me if this is the likely cause? If you could also tell me how to solve it then that would be amazing. The images are 480px x 480px and about 25kb each. My code is below... NSArray *rainImages = [NSArray arrayWithObjects: [UIImage imageNamed:@"rain-loop0001.png"], [UIImage imageNamed:@"rain-loop0002.png"], [UIImage imageNamed:@"rain-loop0003.png"], [UIImage imageNamed:@"rain-loop0004.png"], [UIImage imageNamed:@"rain-loop0005.png"], [UIImage imageNamed:@"rain-loop0006.png"], //more looping images [UIImage imageNamed:@"rain-loop0045.png"], [UIImage imageNamed:@"rain-loop0046.png"], [UIImage imageNamed:@"rain-loop0047.png"], [UIImage imageNamed:@"rain-loop0048.png"], [UIImage imageNamed:@"rain-loop0049.png"], [UIImage imageNamed:@"rain-loop0050.png"], nil]; rainImage.animationImages = rainImages; rainImage.animationDuration = 4.15/2; rainImage.animationRepeatCount = 0; [rainImage startAnimating]; [rainImage release]; Thanks

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• Break on EXC_BAD_ACCESS in XCode?

  - by jasonh

  I'm new to iPhone development and XCode in general and have no idea how to begin troubleshooting an EXC_BAD_ACCESS signal. How can I get XCode to break at the exact line that is causing the error? I can't seem to get XCode to stop on the line causing the problem, but I do see the following lines in my debug console: Sun Oct 25 15:12:14 jasonsmacbook TestProject[1289] : CGContextSetStrokeColorWithColor: invalid context Sun Oct 25 15:12:14 jasonsmacbook TestProject[1289] : CGContextSetLineWidth: invalid context Sun Oct 25 15:12:14 jasonsmacbook TestProject[1289] : CGContextAddPath: invalid context Sun Oct 25 15:12:14 jasonsmacbook TestProject[1289] : CGContextDrawPath: invalid context 2009-10-25 15:12:14.680 LanderTest[1289:207] *** -[CFArray objectAtIndex:]: message sent to deallocated instance 0x3c4e610 Now, I am attempting to draw to the context I retrieve from UIGraphicsGetCurrentContext() and pass to the object that I want to draw with. Further trial and error debugging and I found that an NSMutableArray I have a property for on my class was a zombie. I went into the init function for the class and here's the code I was using: if ((self = [super init])) { NSMutableArray *array = [NSMutableArray array]; self.terrainBlocks = array; [array release]; } return self; } I removed the [array release] line and it no longer gives me the EXC_BAD_ACCESS signal, but I'm now confused about why this works. I thought that when I used the property, it automatically retained it for me, and thus I should release it from within init so that I don't have a leak. I'm thoroughly confused about how this works and all the guides and Stackoverflow questions I've read only confuse me more about how to set properties within my init method. There seems to be no consensus as to which way is the best.

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• Small-o(n^2) implementation of Polynomial Multiplication

  - by AlanTuring

  I'm having a little trouble with this problem that is listed at the back of my book, i'm currently in the middle of test prep but i can't seem to locate anything regarding this in the book. Anyone got an idea? A real polynomial of degree n is a function of the form f(x)=a(n)x^n+?+a1x+a0, where an,…,a1,a0 are real numbers. In computational situations, such a polynomial is represented by a sequence of its coefficients (a0,a1,…,an). Assuming that any two real numbers can be added/multiplied in O(1) time, design an o(n^2)-time algorithm to compute, given two real polynomials f(x) and g(x) both of degree n, the product h(x)=f(x)g(x). Your algorithm should **not** be based on the Fast Fourier Transform (FFT) technique. Please note it needs to be small-o(n^2), which means it complexity must be sub-quadratic. The obvious solution that i have been finding is indeed the FFT, but of course i can't use that. There is another method that i have found called convolution, where if you take polynomial A to be a signal and polynomial B to be a filter. A passed through B yields a shifted signal that has been "smoothed" by A and the resultant is A*B. This is supposed to work in O(n log n) time. Of course i am completely unsure of implementation. If anyone has any ideas of how to achieve a small-o(n^2) implementation please do share, thanks.

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• Good patterns for loose coupling in Java?

  - by Eye of Hell

  Hello. I'm new to java, and while reading documentation so far i can't find any good ways for programming with loose coupling between objects. For majority of languages i know (C++, C#, python, javascript) i can manage objects as having 'signals' (notification about something happens/something needed) and 'slots' (method that can be connected to signal and process notification/do some work). In all mentioned languages i can write something like this: Object1 = new Object1Class(); Object2 = new Object2Class(); Connect( Object1.ItemAdded, Object2.OnItemAdded ); Now if object1 calls/emits ItemAdded, the OnItemAdded method of Object2 will be called. Such loose coupling technique is often referred as 'delegates', 'signal-slot' or 'inversion of control'. Compared to interface pattern, technique mentioned don't need to group signals into some interfaces. Any object's methods can be connected to any delegate as long as signatures match ( C++Qt even extends this by allowing only partial signature match ). So i don't need to write additional interface code for each methods / groups of methods, provide default implementation for interface methods not used etc. And i can't see anything like this in Java :(. Maybe i'm looking a wrong way?

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• Creating a service (SERVICE_ACCEPT_SESSIONCHANGE)

  - by Ron

  Hi there, I am trying to create a service following the example documented in the link below: http://msdn.microsoft.com/en-us/library/bb540475(v=VS.85).aspx What I am interested in is to be able to catch user "lock" and "unlock" workstation events. Using the code on from the example provided, I modified the following: Line 15: Original: VOID WINAPI SvcCtrlHandler( DWORD ); Modified: DWORD WINAPI SvcCtrlHandler( DWORD, DWORD, LPVOID, LPVOID ); Line 141: Original: gSvcStatusHandle = RegisterServiceCtrlHandler( SVCNAME, SvcCtrlHandler); Modified: gSvcStatusHandle = RegisterServiceCtrlHandlerEx( SVCNAME, SvcCtrlHandler, NULL); Line 244: Original: SvcStatus.dwControlsAccepted = SERVICE_ACCEPT_STOP; Modified: gSvcStatus.dwControlsAccepted = SERVICE_ACCEPT_STOP|SERVICE_ACCEPT_SESSIONCHANGE; Line 266: Original: VOID WINAPI SvcCtrlHandler( DWORD dwCtrl ) { // Handle the requested control code. switch(dwCtrl) { case SERVICE_CONTROL_STOP: ReportSvcStatus(SERVICE_STOP_PENDING, NO_ERROR, 0); // Signal the service to stop. SetEvent(ghSvcStopEvent); ReportSvcStatus(gSvcStatus.dwCurrentState, NO_ERROR, 0); return; case SERVICE_CONTROL_INTERROGATE: break; default: break; } }` Modified: DWORD WINAPI SvcCtrlHandler( DWORD dwControl, DWORD dwEventType, LPVOID lpEventData, LPVOID lpContext ) { DWORD dwErrorCode = NO_ERROR; switch(dwControl) { case SERVICE_CONTROL_STOP: ReportSvcStatus(SERVICE_STOP_PENDING, NO_ERROR, 0); // Signal the service to stop. SetEvent(ghSvcStopEvent); ReportSvcStatus(gSvcStatus.dwCurrentState, NO_ERROR, 0); break; case SERVICE_CONTROL_INTERROGATE: break; case SERVICE_CONTROL_SESSIONCHANGE: ReportSvcStatus(gSvcStatus.dwCurrentState, NO_ERROR, 0); break; default: break; } return dwErrorCode; } With the changes above, my service compiled and install fine. But when I try to start my service on my Windows 2000 machine, it does not start properly (it will be stuck on the "starting" status) Can anyone please advise? Thank you in advance, Ron

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• gdb reverse debugging error

  - by Werner

  Hi, i started to try reverse debugging with gdb 7, followin the tutorial: http://www.sourceware.org/gdb/wiki/ProcessRecord/Tutorial and I thought, great! Then I started to debug a real program which gives an error at the end. So I run it with gdb, and I put a breakpoint just before the place I think the error appears. Then I type "record" in order to start to recrd actions for future reverse-debugging. But after some steps I get Process record doesn't support instruction 0xf0d at address 0x2aaaab4c4b4e. Process record: failed to record execution log. Program received signal SIGTRAP, Trace/breakpoint trap. 0x00002aaaab4c4b4e in memcpy () from /lib64/libc.so.6 (gdb) n Single stepping until exit from function memcpy, which has no line number information. Process record doesn't support instruction 0xf0d at address 0x2aaaab4c4b4e. Process record: failed to record execution log. Program received signal SIGABRT, Aborted. 0x00002aaaab4c4b4e in memcpy () from /lib64/libc.so.6 Before I look at in in detail, I wonder if this feature is still buggy, or if I should start to record from the beginning. Where this "record" error happens, just an object is created as a copy of other: Thanks

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• Is it approproate it use django signals withing the same app

  - by Alex Lebedev

  Trying to add email notification to my app in the cleanest way possible. When certain fields of a model change, app should send a notification to a user. Here's my old solution: from django.contrib.auth import User class MyModel(models.Model): user = models.ForeignKey(User) field_a = models.CharField() field_b = models.CharField() def save(self, *args, **kwargs): old = self.__class__.objects.get(pk=self.pk) if self.pk else None super(MyModel, self).save(*args, **kwargs) if old and old.field_b != self.field_b: self.notify("b-changed") # Sevelar more events here # ... def notify(self, event) subj, text = self._prepare_notification(event) send_mail(subj, body, settings.DEFAULT_FROM_EMAIL, [self.user.email], fail_silently=True) This worked fine while I had one or two notification types, but after that just felt wrong to have so much code in my save() method. So, I changed code to signal-based: from django.db.models import signals def remember_old(sender, instance, **kwargs): """pre_save hanlder to save clean copy of original record into `old` attribute """ instance.old = None if instance.pk: try: instance.old = sender.objects.get(pk=instance.pk) except ObjectDoesNotExist: pass def on_mymodel_save(sender, instance, created, **kwargs): old = instance.old if old and old.field_b != instance.field_b: self.notify("b-changed") # Sevelar more events here # ... signals.pre_save.connect(remember_old, sender=MyModel, dispatch_uid="mymodel-remember-old") signals.post_save.connect(on_mymodel_save, sender=MyModel, dispatch_uid="mymodel-on-save") The benefit is that I can separate event handlers into different module, reducing size of models.py and I can enable/disable them individually. The downside is that this solution is more code and signal handlers are separated from model itself and unknowing reader can miss them altogether. So, colleagues, do you think it's worth it?

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• Qt support for VNC

  - by muchala123

  i want to test whether qt is supporting VNC or not. For that i have written a small layout program using Qt library. the source code for the layout program is as follows: layout.cpp #include <QApplication> #include <QHBoxLayout> #include <QSlider> #include <QSpinBox> int main(int argc, char *argv[]) { QApplication app(argc, argv); QWidget *window = new QWidget; window->setWindowTitle("Enter The Age of the person"); QSpinBox *spinBox = new QSpinBox; QSlider *slider = new QSlider(Qt::Horizontal); spinBox->setRange(0, 130); slider->setRange(0, 130); QObject::connect(spinBox, SIGNAL(valueChanged(int)), slider, SLOT(setValue(int))); QObject::connect(slider, SIGNAL(valueChanged(int)), spinBox, SLOT(setValue(int))); spinBox->setValue(35); QHBoxLayout *layout = new QHBoxLayout; layout->addWidget(spinBox); layout->addWidget(slider); window->setLayout(layout); window->show(); return app.exec(); } i want to run this as server application on my linux PC.For that what i configured Qt and installed like this. ./configure -qt-gfx-vnc make make install The program is working fine. But if i run the application as VNC server application like ./layout -qws -display VNC:0 i am encountering an error.it says that "_X11TransSocketINETConnect() can't get address for VNC:6000: Temporary failure in name resolution".. pls help me what i need to do. Thanks

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• Why doesn't gcc remove this check of a non-volatile variable?

  - by Thomas

  This question is mostly academic. I ask out of curiosity, not because this poses an actual problem for me. Consider the following incorrect C program. #include <signal.h> #include <stdio.h> static int running = 1; void handler(int u) { running = 0; } int main() { signal(SIGTERM, handler); while (running) ; printf("Bye!\n"); return 0; } This program is incorrect because the handler interrupts the program flow, so running can be modified at any time and should therefore be declared volatile. But let's say the programmer forgot that. gcc 4.3.3, with the -O3 flag, compiles the loop body (after one initial check of the running flag) down to the infinite loop .L7: jmp .L7 which was to be expected. Now we put something trivial inside the while loop, like: while (running) putchar('.'); And suddenly, gcc does not optimize the loop condition anymore! The loop body's assembly now looks like this (again at -O3): .L7: movq stdout(%rip), %rsi movl $46, %edi call _IO_putc movl running(%rip), %eax testl %eax, %eax jne .L7 We see that running is re-loaded from memory each time through the loop; it is not even cached in a register. Apparently gcc now thinks that the value of running could have changed. So why does gcc suddenly decide that it needs to re-check the value of running in this case?

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• Wait on multiple condition variables on Linux without unnecessary sleeps?

  - by Joseph Garvin

  I'm writing a latency sensitive app that in effect wants to wait on multiple condition variables at once. I've read before of several ways to get this functionality on Linux (apparently this is builtin on Windows), but none of them seem suitable for my app. The methods I know of are: Have one thread wait on each of the condition variables you want to wait on, which when woken will signal a single condition variable which you wait on instead. Cycling through multiple condition variables with a timed wait. Writing dummy bytes to files or pipes instead, and polling on those. #1 & #2 are unsuitable because they cause unnecessary sleeping. With #1, you have to wait for the dummy thread to wake up, then signal the real thread, then for the real thread to wake up, instead of the real thread just waking up to begin with -- the extra scheduler quantum spent on this actually matters for my app, and I'd prefer not to have to use a full fledged RTOS. #2 is even worse, you potentially spend N * timeout time asleep, or your timeout will be 0 in which case you never sleep (endlessly burning CPU and starving other threads is also bad). For #3, pipes are problematic because if the thread being 'signaled' is busy or even crashes (I'm in fact dealing with separate process rather than threads -- the mutexes and conditions would be stored in shared memory), then the writing thread will be stuck because the pipe's buffer will be full, as will any other clients. Files are problematic because you'd be growing it endlessly the longer the app ran. Is there a better way to do this? Curious for answers appropriate for Solaris as well.

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• QT QSslError being signaled with the error code set to NoError

  - by Nantucket

  My Problem I compiled OpenSSL into QT to enable OpenSSL support. Everything appeared to go correctly in the compile. However, when I try to use the official HTTP example application that can be found here, everytime I try to download an https page, it will signal two QSslError, each with contents NoError. The types of QSslErrors, including NoError, are documented here, poorly. There is no explanation on why they even included an error type called NoError, or what it means. Bizarrely, the NoError error code seems to be true, as it downloads the remote https document perfectly even while signaling the error. Does anyone have any idea what this means and what could possibly be causing it? Optional Background Reading Here is the relevant part of the code from the example app (this is connected to the network connection's sslErrors signal by the constructor): void HttpWindow::sslErrors(QNetworkReply*,const QList<QSslError> &errors) { QString errorString; foreach (const QSslError &error, errors) { if (!errorString.isEmpty()) errorString += ", "; errorString += error.errorString(); } if (QMessageBox::warning(this, tr("HTTP"), tr("One or more SSL errors has occurred: %1").arg(errorString), QMessageBox::Ignore | QMessageBox::Abort) == QMessageBox::Ignore) { reply->ignoreSslErrors(); } } I have tried the old version of this example, and it produced the same result. I have tried OpenSSL 1.0.0a and 0.9.8o. I have tried tried compiling OpenSSL myself, I have tried using pre-compiled versions of OpenSSL from the net. All produce the same result. If this were my first time using QT with SSL, I would almost think this is the intended result (even though their example application is popping up error warning message windows), if not for the fact that last time I played with QT, using what would now be an old version of QT with an old version of SSL, I distinctly remember everything working fine with no error windows. My system is running Windows 7 x64.

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• QT4 Designer - Implement Widget

  - by MOnsDaR

  I'm currently trying to get into QT4 and figure out a workflow for myself. While trying to create a widget which allows the user to connect to a hostname:port some questions appeared. The widget itself contains a LineEdit for entering the hostname, a SpinBox for entering the port and a PushButton which should emit a connect(QString hostname, unsigned int port) signal. In QTDesigner I created the necessary Form. It is saved as a .ui-File. Now the big question is how could I implement the widget? Is there a place in QTDesigner where I could add my signal to the Widget? Where could I add custom Properties? I've learned in another tutorial, which showed how to create a Widget in C++, how signals, slots, Q_PROPERTIES etc are defined and added to the widget. But there is no sourcecode in QTDesigner. Another option would be to generate sourcecode using uic. But the header says, that another generate would overwrite any changes to the sourcefiles. So how can I create a QT-widget completely with my own signals, slots and properties by using the QTDesigner for creating the UI and not having to recode everything whenever the UI is changing. Is there some kind of Roundtrip-Engineering? If thats not possible: Whats the sense of creating a Widget with QTDesigner then?

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• Validation on ManyToManyField before Save in Models.py

  - by Heyl1

  I have the following models: class Application(models.Model): users = models.ManyToManyField(User, through='Permission') folder = models.ForeignKey(Folder) class Folder(models.Model): company = models.ManyToManyField(Compnay) class UserProfile(models.Model): user = models.OneToOneField(User, related_name='profile') company = models.ManyToManyField(Company) What I would like to do is to check whether one of the users of the Application has the same company as the Application (via Folder). If this is the case the Application instance should not be saved. The problem is that the ManyToManyFields aren't updated until after the 'post-save' signal. The only option seems to be the new m2m_changed signal. But I'm not sure how I then roll back the save that has already happened. Another option would be to rewrite the save function (in models.py, because I'm talking about the admin here), but I'm not sure how I could access the manytomanyfield content. Finally I've read something about rewriting the save function in the admin of the model in admin.py, however I still wouldn't know how you would access the manytomanyfield content. I have been searching for this everywhere but nothing I come across seems to work for me. If anything is unclear, please tell me. Thanks for your help! Heleen

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• Can get members, but not count of NSMutableArray

  - by Curyous

  I'm filling an NSMutableArray from a CoreData call. I can get the first object, but when I try to get the count, the app crashes with Program received signal: “EXC_BAD_ACCESS”. How can I get the count? Here's the relevant code - I've put a comment on the line where it crashes. - (void)viewDidLoad { [super viewDidLoad]; managedObjectContext = [[MySingleton sharedInstance] managedObjectContext]; if (managedObjectContext != nil) { charactersRequest = [[NSFetchRequest alloc] init]; charactersEntity = [NSEntityDescription entityForName:@"Character" inManagedObjectContext:managedObjectContext]; [charactersEntity retain]; [charactersRequest setEntity:charactersEntity]; [charactersRequest retain]; NSError *error; characters = [[managedObjectContext executeFetchRequest:charactersRequest error:&error] mutableCopy]; if (characters == nil) { NSLog(@"Did not get results for characters: %@", error.localizedDescription); } else { [characters retain]; NSLog(@"Found some character(s)."); Character* character = (Character *)[characters objectAtIndex:0]; NSLog(@"Name of first one: %@", character.name); NSLog(@"Found %@ character(s).", characters.count); // Crashes on this line with - Program received signal: “EXC_BAD_ACCESS”. } } } And previous declarations from the header file: @interface CrowdViewController : UITableViewController { NSManagedObjectContext *managedObjectContext; NSFetchRequest *charactersRequest; NSEntityDescription *charactersEntity; NSMutableArray *characters; } I'm a bit perplexed and would really appreciate finding out what is going on.

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• PyQt - QLabel inheriting

  - by Ockonal

  Hello, i wanna inherit QLabel to add there click event processing. I'm trying this code: class NewLabel(QtGui.QLabel): def __init__(self, parent): QtGui.QLabel.__init__(self, parent) def clickEvent(self, event): print 'Label clicked!' But after clicking I have no line 'Label clicked!' EDIT: Okay, now I'm using not 'clickEvent' but 'mousePressEvent'. And I still have a question. How can i know what exactly label was clicked? For example, i have 2 edit box and 2 labels. Labels content are pixmaps. So there aren't any text in labels, so i can't discern difference between labels. How can i do that? EDIT2: I made this code: class NewLabel(QtGui.QLabel): def __init__(self, firstLabel): QtGui.QLabel.__init__(self, firstLabel) def mousePressEvent(self, event): print 'Clicked' #myLabel = self.sender() # None =) self.emit(QtCore.SIGNAL('clicked()'), "Label pressed") In another class: self.FirstLang = NewLabel(Form) QtCore.QObject.connect(self.FirstLang, QtCore.SIGNAL('clicked()'), self.labelPressed) Slot in the same class: def labelPressed(self): print 'in labelPressed' print self.sender() But there isn't sender object in self. What i did wrong?

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