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  • Acquiring Table Lock in Database - Interview Question

    - by harigm
    One of my interview Questions, if multiple users across the world are accessing the application, in which it uses a Table which has a Primary Key as Auto Increment Field. The Question how can you prevent the other user getting the Same Primary key when the other user is executing? My answer was I will obtain the Lock on the table and I will make the user to wait Until that user is released with the Primary key. But the Question How do you acquire the Table lock programmatically and implement this? If there are 1000 users coming every minute to the application, if you explicity hold the lock on the table, then the application will become slower? How do you manage this? Please suggest the possible answers for the above question

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  • How to use Vendor Properties in Multiple Backgrounds?

    - by barraponto
    I want to use multiple backgrounds in css, which are currently supported by Firefox 3.61, Chrome/Safari, supposedly Opera10.5 (doesn't run on gnu/linux). It is working fine, however i would like to use linear-gradients as a background. it works ok for Firefox, doesn't work at all with Chrome, yet i can't figure out how to make it work for both at the same time. any clues? http://snook.ca/archives/html_and_css/multiple-bg-css-gradients came the closest to match what i need, but i couldn't get it to work with chrome yet.

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  • Implementing a Mutex Lock in C

    - by Adam
    I'm trying to make a really mutex in C and for some reason I'm getting cases where two threads are getting the lock at the same time, which shouldn't be possible. Any ideas why it's not working? void mutexLock(mutex_t *mutexlock, pid_t owner) { int failure; while(mutexlock->mx_state == 0 || failure || mutexlock->mx_owner != owner) { failure = 1; if (mutexlock->mx_state == 0) { asm( "test:" "movl $0x01,%%eax\n\t" // move 1 to eax "xchg %%eax,%0\n\t" // try to set the lock bit "mov %%eax,%1\n\t" // export our result to a test var "test %%eax,%%eax\n\t" "jnz test\n\t" :"=r"(mutexlock->mx_state),"=r"(failure) :"r"(mutexlock->mx_state) :"%eax" ); } if (failure == 0) { mutexlock->mx_owner = owner; //test to see if we got the lock bit } } }

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  • How to show that the double-checked-lock pattern with Dictionary's TryGetValue is not threadsafe in

    - by Amir
    Recently I've seen some C# projects that use a double-checked-lock pattern on a Dictionary. Something like this: private static readonly object _lock = new object(); private static volatile IDictionary<string, object> _cache = new Dictionary<string, object>(); public static object Create(string key) { object val; if (!_cache.TryGetValue(key, out val)) { lock (_lock) { if (!_cache.TryGetValue(key, out val)) { val = new object(); // factory construction based on key here. _cache.Add(key, val); } } } return val; } This code is incorrect, since the Dictionary can be "growing" the collection in _cache.Add() while _cache.TryGetValue (outside the lock) is iterating over the collection. It might be extremely unlikely in many situations, but is still wrong. Is there a simple program to demonstrate that this code fails? Does it make sense to incorporate this into a unit test? And if so, how?

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  • Using accelerometer to detect iPad lock switch trigger?

    - by DevDevDev
    So for complicated reasons I am managing view rotations myself, and am only implementing UIDeviceOrientationPortrait as the autorotating orientation. Anyway, when one clicks the screen lock on the iPad, the device will rotate to UIDeviceOrientationPortrait, which will cause my code to rotate, which I do not want to happen. For instance of the user is holding the device in "landscape mode", i.e. I have already manually rotated the UI to landscape mode, and he/she clicks the screen lock, it will rotate the UI to portrait mode, even though the user did not move the device at all. So somehow I need a way to differentiate between rotations to portrait mode occuring from the screen lock, and those occuring from device rotation. As such, I would like somehow to use the accelerometer to detect whether or not the device was actually 'rotated' or whether the button was clicked. Thanks!

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  • Problem on getting the vendor id and product id of a usb device

    - by new
    Hi... my application comes and prints this "\?\usb#vid_04f2&pid_0111#5&1ba5a77f&0&2#{a5dcbf1 0-6530-11d2-901f-00c04fb951ed}" again it goes to while loop .... here it gets breaked in the else statement... Qt Code: if (GetLastError() == ERROR_INSUFFICIENT_BUFFER) { // Change the buffer size. if (buffer) LocalFree(buffer); buffer = (LPTSTR)LocalAlloc(LPTR,buffersize); } else { qDebug ()<<"Here it quits the application"; // Insert error handling here. break; } Any ideas in this.... full source code comes here static GUID GUID_DEVINTERFACE_USB_DEVICE = { 0xA5DCBF10L, 0x6530, 0x11D2, { 0x90, 0x1F, 0x00, 0xC0, 0x4F, 0xB9, 0x51, 0xED } }; HANDLE hInfo = SetupDiGetClassDevs(&GUID_DEVINTERFACE_USB_DEVICE,NULL,NULL, DIGCF_PRESENT | DIGCF_INTERFACEDEVICE); if ( hInfo == INVALID_HANDLE_VALUE ) { qDebug ()<<"invalid"; } else { qDebug ()<<"valid handle"; SP_DEVINFO_DATA DeviceInfoData; DeviceInfoData.cbSize = sizeof(SP_DEVINFO_DATA); SP_INTERFACE_DEVICE_DATA Interface_Info; Interface_Info.cbSize = sizeof(Interface_Info); BYTE Buf[1024]; DWORD i; DWORD InterfaceNumber= 0; PSP_DEVICE_INTERFACE_DETAIL_DATA pspdidd = (PSP_DEVICE_INTERFACE_DETAIL_DATA) Buf; for (i=0;SetupDiEnumDeviceInfo(hInfo,i,&DeviceInfoData);i++) { DWORD DataT; LPTSTR buffer = NULL; DWORD buffersize = 0; while (!SetupDiGetDeviceRegistryProperty( hInfo, &DeviceInfoData,SPDRP_DEVICEDESC, &DataT,(PBYTE)buffer,buffersize, &buffersize)) { if (GetLastError() == ERROR_INSUFFICIENT_BUFFER) { // Change the buffer size. if (buffer) LocalFree(buffer); buffer = (LPTSTR)LocalAlloc(LPTR,buffersize); } else { // Insert error handling here. break; } qDebug ()<<(TEXT("Device Number %i is: %s\n"),i, buffer); if (buffer) LocalFree(buffer); if ( GetLastError() != NO_ERROR && GetLastError() != ERROR_NO_MORE_ITEMS ) { // Insert error handling here. qDebug ()<<"return false"; } InterfaceNumber = 0; // this just returns the first one, you can iterate on this if (SetupDiEnumDeviceInterfaces(hInfo, NULL, &GUID_DEVINTERFACE_USB_DEVICE, InterfaceNumber, &Interface_Info)) { printf("Got interface"); DWORD needed; pspdidd->cbSize = sizeof(*pspdidd); SP_DEVICE_INTERFACE_DETAIL_DATA *pDetData = NULL; DWORD dwDetDataSize = sizeof (SP_DEVICE_INTERFACE_DETAIL_DATA) + 256; pDetData = (SP_DEVICE_INTERFACE_DETAIL_DATA*) malloc (dwDetDataSize); pDetData->cbSize = sizeof (SP_DEVICE_INTERFACE_DETAIL_DATA); SetupDiGetDeviceInterfaceDetail(hInfo,&Interface_Info, pDetData,dwDetDataSize, NULL,&DeviceInfoData); qDebug ()<<pDetData->DevicePath; qDebug ()<<QString::fromWCharArray(pDetData->DevicePath); free(pDetData); } else { printf("\nNo interface"); //ErrorExit((LPTSTR) "SetupDiEnumDeviceInterfaces"); if ( GetLastError() == ERROR_NO_MORE_ITEMS) printf(", since there are no more items found."); else printf(", unknown reason."); } // Cleanup SetupDiDestroyDeviceInfoList(hInfo); } } }

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  • Oracle global lock across process

    - by Jimm
    I would like to synchronize access to a particular insert. Hence, if multiple applications execute this "one" insert, the inserts should happen one at a time. The reason behind synchronization is that there should only be ONE instance of this entity. If multiple applications try to insert the same entity,only one should succeed and others should fail. One option considered was to create a composite unique key, that would uniquely identify the entity and rely on unique constraint. For some reasons, the dba department rejected this idea. Other option that came to my mind was to create a stored proc for the insert and if the stored proc can obtain a global lock, then multiple applications invoking the same stored proc, though in their seperate database sessions, it is expected that the stored proc can obtain a global lock and hence serialize the inserts. My question is it possible to for a stored proc in oracle version 10/11, to obtain such a lock and any pointers to documentation would be helpful.

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  • Test For CSS3 Radial Gradient Vendor Syntax

    - by Scott Christopherson
    I'm having an issue where I'm trying to update the background gradient of an element with JavaScript based on values I specify. I tried this route: elem.style.backgroundImage = '-webkit-gradient(radial, '+x+' '+y+', 0, '+x+' '+y+', 800, from(#ccc), to(#333)), -moz-radial-gradient('+x+'px '+y+'px, circle cover, #ccc 0, #333 100%)'; Since Webkit and Gecko have two different syntaxes for CSS3 gradients, I need to specify both. However, the above code doesn't work. It works if I only have just the Gecko syntax or just the Webkit syntax, not both. I think you can check for CSS gradient support, but my question is, is there a way to check which syntax needs to be used without browser sniffing? Keep in mind that I need to set my gradients this way since the x and y coordinates of the gradient change dynamically. Hope this makes sense, thanks.

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  • is it possible to lock oracle 10g database table with C#/(ADO?).NET 2.0

    - by matti
    I have a table that contains a maximum value that needs to be get and set by multiple programs. How can I lock the table for a while when old value is got and new is updated in C#? In other words: string sql = "lock table MaxValueTable in exclusive mode"; using (DbCommand cmd = cnctn.CreateCommand()) { cmd.CommandText = sql; // execute command somehow!! } maxValue = GetMaxValue(); SetMaxValue(maxValue + X); sql = "lock table MaxValueTable in share mode"; using (DbCommand cmd = cnctn.CreateCommand()) { cmd.CommandText = sql; // execute command somehow!! } -BR: Matti

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  • net c# lock statement in data access layer

    - by Pedro Rivera
    I saw a code where they have the data access layer like this: public class CustomerDA{ private static readonly object _sync = new object(); private static readonly CustomerDA _mutex = new CustomerDA(); private CustomerDA(){ } public CustomerDA GetInstance(){ lock(_sync){ return _mutex; } } public DataSet GetCustomers(){ //database SELECT //return a DataSet } public int UpdateCustomer(some parameters){ //update some user } } public class CustomerBO{ public DataSet GetCustomers(){ //some bussiness logic return CustomerDA.GetInstance().GetCustomers(); } } I was using it, but start thinking... "and what if had to build a facebook like application where there are hundreds of thousands of concurrent users? would I be blocking each user from doing his things until the previous user ends his database stuff? and for the Update method, is it useful to LOCK THREADS in the app when database engines already manage concurrency at database server level?" Then I started to think about moving the lock to the GetCustomers and UpdateCustomer methods, but think again: "is it useful at all?"

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  • innodb lock wait timeout

    - by shantanuo
    As per the documentation link given below: When a lock wait timeout occurs, the current statement is not executed. The current transaction is not rolled back. (Until MySQL 5.0.13 InnoDB rolled back the entire transaction if a lock wait timeout happened. You can restore this behavior by starting the server with the --innodb_rollback_on_timeout option, available as of MySQL 5.0.32. http://dev.mysql.com/doc/refman/5.0/en/innodb-parameters.html#sysvar_innodb_lock_wait_timeout Does it mean that when a lock wait timeout occurs, it compromises the transactional integrity? "roollback on timeout" was the default behaviour till 5.0.13 and I guess that was the correct way to handle such situations. Does anyone think that this should be the default behaviour and the user should not be asked to add a parameter for a functionality that is taken for granted?

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  • Timer applications running under lock on Windows Phone 7

    - by cpedros
    Under the current Windows Phone 7 Application Certification Requirements (pdf) applications running under lock must "stop any ... active timers" (section 6.3.1). However looking out on Marketplace there are a number of timer/stopwatch apps claiming to run under lock and also allow lock to be disabled in their settings. How are these apps certified or is there some loosening on the restrictions by Microsoft if the app allows the user to make that decision? Also some of these apps also suggest they continue even when the app is exited or when the device off. Is it the case that they are not truly running under these circumstances, i.e. the timers either start where they left off when reactivated, or perhaps use the OS time to work out the time elapsed between tombstoning and reactivation? In these circumstance I also presume it is not possible for the app to notify the user when the timer completes?

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  • Performing time consuming operation on STL container within a lock

    - by Ashley
    I have an unordered_map of an unordered_map which stores a pointer of objects. The unordered map is being shared by multiple threads. I need to iterate through each object and perform some time consuming operation (like sending it through network etc) . How could I lock the multiple unordered_map so that it won't blocked for too long? typedef std::unordered_map<string, classA*>MAP1; typedef std::unordered_map<int, MAP1*>MAP2; MAP2 map2; pthread_mutex_lock(&mutexA) //how could I lock the maps? Could I reduce the lock granularity? for(MAP2::iterator it2 = map2.begin; it2 != map2.end; it2++) { for(MAP1::iterator it1 = *(it2->second).begin(); it1 != *(it2->second).end(); it1++) { //perform some time consuming operation on it1->second eg sendToNetwork(*(it1->second)); } } pthread_mutex_unlock(&mutexA)

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  • Lock thread using somthing other than a object

    - by Scott Chamberlain
    when using a lock does the thing you are locking on have to be a object. For example is this legal static DateTime NextCleanup = DateTime.Now; const TimeSpan CleanupInterval = new TimeSpan(1, 0, 0); private static void DoCleanup() { lock ((object)NextCleanup) { if (NextCleanup < DateTime.Now) { NextCleanup = DateTime.Now.Add(CleanupInterval); System.Threading.ThreadPool.QueueUserWorkItem(new System.Threading.WaitCallback(cleanupThread)); } } return; } EDIT-- From reading SLaks' responce I know the above code would be not valid but would this be? static MyClass myClass = new MyClass(); private static void DoCleanup() { lock (myClass) { // } return; }

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  • Why boost::recursive_mutex is not working as expected?

    - by Kjir
    I have a custom class that uses boost mutexes and locks like this (only relevant parts): template<class T> class FFTBuf { public: FFTBuf(); [...] void lock(); void unlock(); private: T *_dst; int _siglen; int _processed_sums; int _expected_sums; int _assigned_sources; bool _written; boost::recursive_mutex _mut; boost::unique_lock<boost::recursive_mutex> _lock; }; template<class T> FFTBuf<T>::FFTBuf() : _dst(NULL), _siglen(0), _expected_sums(1), _processed_sums(0), _assigned_sources(0), _written(false), _lock(_mut, boost::defer_lock_t()) { } template<class T> void FFTBuf<T>::lock() { std::cerr << "Locking" << std::endl; _lock.lock(); std::cerr << "Locked" << std::endl; } template<class T> void FFTBuf<T>::unlock() { std::cerr << "Unlocking" << std::endl; _lock.unlock(); } If I try to lock more than once the object from the same thread, I get an exception (lock_error): #include "fft_buf.hpp" int main( void ) { FFTBuf<int> b( 256 ); b.lock(); b.lock(); b.unlock(); b.unlock(); return 0; } This is the output: sb@dex $ ./src/test Locking Locked Locking terminate called after throwing an instance of 'boost::lock_error' what(): boost::lock_error zsh: abort ./src/test Why is this happening? Am I understanding some concept incorrectly?

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  • Lock a mutex multiple times in the same thread

    - by Megacan
    Hi, I'm developing an application on an embedded linux OS (uClinux) and I need to be able to lock the mutex more than once (by the same thread). I have a mutex and a mutexattr defined and initialized as follows: pthread_mutexattr_t waiting_barcode_mutexattr; pthread_mutex_t waiting_barcode_mutex; pthread_mutexattr_init(&waiting_barcode_mutexattr); pthread_mutexattr_settype(&waiting_barcode_mutexattr, PTHREAD_MUTEX_RECURSIVE); pthread_mutex_init(&waiting_barcode_mutex, &waiting_barcode_mutexattr); But when I try to acquire the lock twice it blocks on the second lock: pthread_mutex_lock(&waiting_barcode_mutex); pthread_mutex_lock(&waiting_barcode_mutex); Am I initializing it wrong or is there a better way of accomplishing the same? Thanks in advance.

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  • Windows 7 Group Policy to display message for login tries left before account lock

    - by Vivek
    My requirement is to display the the remaining count left on the login screen when user trying to login using Windows 7 OS before account lock in case user enter invalid password. I am having Active Directory on Windows 2008 R2 server. I set the maximum Lockout count = 5 in GPO policy. Example: If user try login first 1 attempt is failed, next time enter password and login shold show message for remaining attemps left.( my case count 4 left) Please let me know as this is urgent for me.

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  • X window (or whole linux system) replace Caps Lock with ESC *and* Control

    - by gcb
    on windows there are several key maps applications that replaces Caps lock with ESC on a single 'press and relase' and with a Control signal if hold and another key is pressed. Is there any way to do something similar on linux? Ideally on the whole system, but if it is only for X window it is fine too. i'm currently writting scripts with the xautomation package tools. but i guess there is already a better way to do that via configurations.

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  • clients auto-lock feature for inactvity timeout not working

    - by Swaminathan Shanmugam
    In our sbs 2003 domain environment, the clients' pc's inactive for default period will be locked out automatically and only Ctrl+ Alt + Del & client password combination will unlock the client's pcs. Recently around 9 months before, all our client's pc's joined the new sbs 2011 but (usually all are locking with Win+L key combination manually)the auto lock feature is not working from the beginning onwards. Now only I am brought up with this issue by clients. Please help me set that option!

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  • Location of lock screen

    - by ICTdesk.net
    Does anybody know if it is possible to change a setting so that the Windows XP Lock Screen is not centered, but let's say in right or left top/down corner or maybe even a give x or y coordinate?

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  • How to version lock packages in Ubuntu?

    - by Sandra
    On CentOS exists the yum versionlock option, where you can lock a package to a specific version, so it is never upgraded past that. I would like that puppet-server-2.7.19-1 puppet-2.7.19-1 stays on 2.7, and never upgraded to 3.0. Puppet Labs have released 3.0 and put it into the stable repo, so 2.7 will get upgraded to 3.0, which is not backwards compatible. Does Ubuntu have something similar to yum versionlock?

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  • Which folder lock application will meet this requirement?

    - by user1540992
    I want any third party(either commercial or Open source) folder lock application that protects file with password without hiding the files. The locked folder should be displayed to user as password protected folder, when user try to open the folder, it should ask password. When the user enters correct password it should open, otherwise it should throw an error. Is there any application with this quality? I searched a lot, but I could not find any.

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  • Set Windows 7 Lock Screen Background

    - by helpsplz
    I've googled this a bit, but have yet to find anything. I have 2 monitors. when I lock my screen via win+L, it turns 1 of them to the background color selected in background options, and the other one is the win 7 login screen. I would like to keep my current wallpaper as the background and on the two monitors if possible when the pc is locked.

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  • Booby Traps and Locked-in Kids: An Interview with a Safecracker

    - by Jason Fitzpatrick
    While most of our articles focus on security of the digital sort, this interview with a professional safecracker is an interesting look the physical side of securing your goods. As part of their Interviews with People Who Have Interesting or Unusual Jobs series over at McSweeney’s, they interviewed Ken Doyle, a professional a locksmithing and safecracking veteran with 30 years of industry experience. The interview is both entertaining and an interesting read. One of the more unusual aspects of safecracking he highlights: Q: Do you ever look inside? A: I NEVER look. It’s none of my business. Involving yourself in people’s private affairs can lead to being subpoenaed in a lawsuit or criminal trial. Besides, I’d prefer not knowing about a client’s drug stash, personal porn, or belly button lint collection. When I’m done I gather my tools and walk to the truck to write my invoice. Sometimes I’m out of the room before they open it. I don’t want to be nearby if there is a booby trap. Q: Why would there be a booby trap? A: The safe owner intentionally uses trip mechanisms, explosives or tear gas devices to “deter” unauthorized entry into his safe. It’s pretty stupid because I have yet to see any signs warning a would-be culprit about the danger. HTG Explains: Why Linux Doesn’t Need Defragmenting How to Convert News Feeds to Ebooks with Calibre How To Customize Your Wallpaper with Google Image Searches, RSS Feeds, and More

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