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  • Cannot use READPAST in snapshot isolation mode

    - by Marcus
    I have a process which is called from multiple threads which does the following: Start transaction Select unit of work from work table with by finding the next row where IsProcessed=0 with hints (UPDLOCK, HOLDLOCK, READPAST) Process the unit of work (C# and SQL stored procedures) Commit the transaction The idea of this is that a thread dips into the pool for the "next" piece of work, and processes it, and the locks are there to ensure that a single piece of work is not processed twice. (the order doesn't matter). All this has been working fine for months. Until today that is, when I happened to realise that despite enabling snapshot isolation and making it the default at the database level, the actual transaction creation code was manually setting an isolation level of "ReadCommitted". I duly changed that to "Snapshot", and of course immediately received the "You can only specify the READPAST lock in the READ COMMITTED or REPEATABLE READ" error message. Oops! The main reason for locking the row was to "mark the row" in such a way that the "mark" would be removed when the transaction that applied the mark was committed and the lock seemed to be the best way to do this, since this table isn't read otherwise except by these threads. If I were to use the IsProcessed flag as the lock, then presumably I would need to do the update first, and then select the row I just updated, but I would need to employ the NOLOCK flag to know whether any other thread had set the flag on a row. All sounds a bit messy. The easiest option would be to abandon the snapshot isolation mode altogether, but the design of step #3 requires it. Any bright ideas on the best way to resolve this problem? Thanks Marcus

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  • Is an LSA MSV1_0 subauthentication package needed for some impersonation use cases?

    - by Chris Sears
    Greetings, I'm working with a vendor who has implemented some code that uses a Windows LSA MSV1_0 subauthentication package (MSDN info if you're interested: http://msdn.microsoft.com/en-us/library/aa374786(VS.85).aspx ) and I'm trying to figure out if it's necessary. As far as I can tell, the subauthentication routine and filter allow for hooking or customizing the standard LSA MSV1_0 logon event processing. The issue is that I don't understand why the vendor's product would need these capabilities. I've asked them and they said they use it to perform impersonation. The product definitely does need to do impersonation, but based on my limited win32 knowledge, they could get the functionality they need using the normal auth APIs (LsaLogonUser, ImpersonateLoggedOnUser, etc) without the subauthentication package. Furthermore, I've worked with a number of similar products that all do impersonation, and this is the only one that's used a subauthentication package. If you're wondering why I would care, a previous version of the product had a bug in the subauthentication package dll that would cause lockups or bluescreens. That makes me rather nervous and has me questioning the use of such a low-level, kernel sensitive interface. I'd like to go back to the vendor and say "There's no way you could need an LSA subauth package for impersonation - take it out", but I'm not sure I understand the use cases and possible limitations of the standard win32 authentication/impersonation APIs well enough to make that claim definitively. So, to the win32 security gurus out there, is there any reason you would need an LSA MSV1_0 subauthentication package if all you were doing is impersonation? Thanks in advance for any thoughts!

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  • Java FileLock for Reading and Writing

    - by bobtheowl2
    I have a process that will be called rather frequently from cron to read a file that has certain move related commands in it. My process needs to read and write to this data file - and keep it locked to prevent other processes from touching it during this time. A completely separate process can be executed by a user to (potential) write/append to this same data file. I want these two processes to play nice and only access the file one at a time. The nio FileLock seemed to be what I needed (short of writing my own semaphore type files), but I'm having trouble locking it for reading. I can lock and write just fine, but when attempting to create lock when reading I get a NonWritableChannelException. Is it even possible to lock a file for reading? Seems like a RandomAccessFile is closer to what I need, but I don't see how to implement that. Here is the code that fails: FileInputStream fin = new FileInputStream(f); FileLock fl = fin.getChannel().tryLock(); if(fl != null) { System.out.println("Locked File"); BufferedReader in = new BufferedReader(new InputStreamReader(fin)); System.out.println(in.readLine()); ... The exception is thrown on the FileLock line. java.nio.channels.NonWritableChannelException at sun.nio.ch.FileChannelImpl.tryLock(Unknown Source) at java.nio.channels.FileChannel.tryLock(Unknown Source) at Mover.run(Mover.java:74) at java.lang.Thread.run(Unknown Source) Looking at the JavaDocs, it says Unchecked exception thrown when an attempt is made to write to a channel that was not originally opened for writing. But I don't necessarily need to write to it. When I try creating a FileOutpuStream, etc. for writing purposes it is happy until I try to open a FileInputStream on the same file.

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  • Red Box is not working

    - by palani
    Hi , I have install the Red box plugin by using the following command script/plugin install svn://rubyforge.org/var/svn/ambroseplugins/redbox . It installed successfully. and again ran the following command the following location /myapp/vendor/plugin/redbox/rake update_scripts . It shows me the following output (in /myapp/vendor/plugins/redbox) rake aborted! private method `copy' called for File:Class /home/myapp/vendor/plugins/redbox/Rakefile:28 (See full trace by running task with --trace) I don't know How to solve this ... Then i understand that "rake update_scripts" copying the Js and Css file only. so i manually copied the Redbox.js & redbox.css files into the respective places under /public folder I include the follwoing into my application.html.erb <%= stylesheet_link_tag 'redbox' % <%= javascript_include_tag :defaults % <%= javascript_include_tag 'redbox' % It included in the page successfully. The following is my view code : <%= link_to_remote_redbox('Red_box', :url = {:action= 'log'} ,:method ='get') % The popup box doesn't appear. I have no clue what is the exact error. Is that any Jquery clash? Please help me

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  • Svn import with auto-props & pre-commit hook

    - by James Tisato
    My company's svn repo has a lot of MS Word docs in it. We've implemented a policy that all .doc files must have the svn:needs-lock property set to prevent parallel access on files that are hard to merge (we've also done this for xls, ppt, pdf etc.). We've implemented the policy by distributing a svn config with auto-props set appropriately for all relevant document types. We've also set up a pre-commit hook that checks that all added files of these types have the needs-lock property set (i.e. if they forget/are too lazy to update their svn config file, they won't be able to add any docs to the repo). The problem I'm having, however, is that the pre-commit hook fails when users try to import files into the repo, e.g. some users like to add files directly thru TortoiseSVN's Repo Browser, which effectively is an svn import. Through testing on other file types, I have seen that doing an import does in fact apply the auto-props listed in my config, but they don't seem to be applied at the point that the pre-commit hook runs. When importing .doc files, the hook fails, saying that the needs-lock property is missing. Is there really much difference between adding a single file to a working copy and committing it vs importing a file directly? Do we need to tailor our precommit hook in some way to cater for this scenario?

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  • Trying to find USB device on iphone with IOKit.framework

    - by HuGeek
    Hi all, i'm working on a project were i need the usb port to communicate with a external device. I have been looking for exemple on the net (Apple and /developer/IOKit/usb exemple) and trying some other but i can't even find the device. In my code i blocking at the place where the fucntion looks for a next iterator (pointer in fact) with the function getNextIterator but never returns a good value so the code is blocking. By the way i am using toolchain and added IOKit.framework in my project. All i what right now is the communicate or do like a ping to someone on the USB bus!! I blocking in the 'FindDevice'....i can't manage to enter in the while because the variable usbDevice is always = to 0....i have tested my code in a small mac program and it works... Thanks Here is my code : IOReturn ConfigureDevice(IOUSBDeviceInterface **dev) { UInt8 numConfig; IOReturn result; IOUSBConfigurationDescriptorPtr configDesc; //Get the number of configurations result = (*dev)->GetNumberOfConfigurations(dev, &numConfig); if (!numConfig) { return -1; } // Get the configuration descriptor result = (*dev)->GetConfigurationDescriptorPtr(dev, 0, &configDesc); if (result) { NSLog(@"Couldn't get configuration descriptior for index %d (err=%08x)\n", 0, result); return -1; } ifdef OSX_DEBUG NSLog(@"Number of Configurations: %d\n", numConfig); endif // Configure the device result = (*dev)->SetConfiguration(dev, configDesc->bConfigurationValue); if (result) { NSLog(@"Unable to set configuration to value %d (err=%08x)\n", 0, result); return -1; } return kIOReturnSuccess; } IOReturn FindInterfaces(IOUSBDeviceInterface *dev, IOUSBInterfaceInterface **itf) { IOReturn kr; IOUSBFindInterfaceRequest request; io_iterator_t iterator; io_service_t usbInterface; IOUSBInterfaceInterface **intf = NULL; IOCFPlugInInterface **plugInInterface = NULL; HRESULT res; SInt32 score; UInt8 intfClass; UInt8 intfSubClass; UInt8 intfNumEndpoints; int pipeRef; CFRunLoopSourceRef runLoopSource; NSLog(@"Debut FindInterfaces \n"); request.bInterfaceClass = kIOUSBFindInterfaceDontCare; request.bInterfaceSubClass = kIOUSBFindInterfaceDontCare; request.bInterfaceProtocol = kIOUSBFindInterfaceDontCare; request.bAlternateSetting = kIOUSBFindInterfaceDontCare; kr = (*dev)->CreateInterfaceIterator(dev, &request, &iterator); usbInterface = IOIteratorNext(iterator); IOObjectRelease(iterator); NSLog(@"Interface found.\n"); kr = IOCreatePlugInInterfaceForService(usbInterface, kIOUSBInterfaceUserClientTypeID, kIOCFPlugInInterfaceID, &plugInInterface, &score); kr = IOObjectRelease(usbInterface); // done with the usbInterface object now that I have the plugin if ((kIOReturnSuccess != kr) || !plugInInterface) { NSLog(@"unable to create a plugin (%08x)\n", kr); return -1; } // I have the interface plugin. I need the interface interface res = (*plugInInterface)->QueryInterface(plugInInterface, CFUUIDGetUUIDBytes(kIOUSBInterfaceInterfaceID), (LPVOID*) &intf); (*plugInInterface)->Release(plugInInterface); // done with this if (res || !intf) { NSLog(@"couldn't create an IOUSBInterfaceInterface (%08x)\n", (int) res); return -1; } // Now open the interface. This will cause the pipes to be instantiated that are // associated with the endpoints defined in the interface descriptor. kr = (*intf)->USBInterfaceOpen(intf); if (kIOReturnSuccess != kr) { NSLog(@"unable to open interface (%08x)\n", kr); (void) (*intf)->Release(intf); return -1; } kr = (*intf)->CreateInterfaceAsyncEventSource(intf, &runLoopSource); if (kIOReturnSuccess != kr) { NSLog(@"unable to create async event source (%08x)\n", kr); (void) (*intf)->USBInterfaceClose(intf); (void) (*intf)->Release(intf); return -1; } CFRunLoopAddSource(CFRunLoopGetCurrent(), runLoopSource, kCFRunLoopDefaultMode); if (!intf) { NSLog(@"Interface is NULL!\n"); } else { *itf = intf; } NSLog(@"End of FindInterface \n \n"); return kr; } unsigned int FindDevice(void *refCon, io_iterator_t iterator) { kern_return_t kr; io_service_t usbDevice; IOCFPlugInInterface **plugInInterface = NULL; HRESULT result; SInt32 score; UInt16 vendor; UInt16 product; UInt16 release; unsigned int count = 0; NSLog(@"Searching Device....\n"); while (usbDevice = IOIteratorNext(iterator)) { // create intermediate plug-in NSLog(@"Found a device!\n"); kr = IOCreatePlugInInterfaceForService(usbDevice, kIOUSBDeviceUserClientTypeID, kIOCFPlugInInterfaceID, &plugInInterface, &score); kr = IOObjectRelease(usbDevice); if ((kIOReturnSuccess != kr) || !plugInInterface) { NSLog(@"Unable to create a plug-in (%08x)\n", kr); continue; } // Now create the device interface result = (*plugInInterface)->QueryInterface(plugInInterface, CFUUIDGetUUIDBytes(kIOUSBDeviceInterfaceID), (LPVOID)&dev); // Don't need intermediate Plug-In Interface (*plugInInterface)->Release(plugInInterface); if (result || !dev) { NSLog(@"Couldn't create a device interface (%08x)\n", (int)result); continue; } // check these values for confirmation kr = (*dev)->GetDeviceVendor(dev, &vendor); kr = (*dev)->GetDeviceProduct(dev, &product); //kr = (*dev)->GetDeviceReleaseNumber(dev, &release); //if ((vendor != LegoUSBVendorID) || (product != LegoUSBProductID) || (release != LegoUSBRelease)) { if ((vendor != LegoUSBVendorID) || (product != LegoUSBProductID)) { NSLog(@"Found unwanted device (vendor = %d != %d, product = %d != %d, release = %d)\n", vendor, kUSBVendorID, product, LegoUSBProductID, release); (void) (*dev)-Release(dev); continue; } // Open the device to change its state kr = (*dev)->USBDeviceOpen(dev); if (kr == kIOReturnSuccess) { count++; } else { NSLog(@"Unable to open device: %08x\n", kr); (void) (*dev)->Release(dev); continue; } // Configure device kr = ConfigureDevice(dev); if (kr != kIOReturnSuccess) { NSLog(@"Unable to configure device: %08x\n", kr); (void) (*dev)->USBDeviceClose(dev); (void) (*dev)->Release(dev); continue; } break; } return count; } // USB rcx Init IOUSBInterfaceInterface** osx_usb_rcx_init (void) { CFMutableDictionaryRef matchingDict; kern_return_t result; IOUSBInterfaceInterface **intf = NULL; unsigned int device_count = 0; // Create master handler result = IOMasterPort(MACH_PORT_NULL, &gMasterPort); if (result || !gMasterPort) { NSLog(@"ERR: Couldn't create master I/O Kit port(%08x)\n", result); return NULL; } else { NSLog(@"Created Master Port.\n"); NSLog(@"Master port 0x:08X \n \n", gMasterPort); } // Set up the matching dictionary for class IOUSBDevice and its subclasses matchingDict = IOServiceMatching(kIOUSBDeviceClassName); if (!matchingDict) { NSLog(@"Couldn't create a USB matching dictionary \n"); mach_port_deallocate(mach_task_self(), gMasterPort); return NULL; } else { NSLog(@"USB matching dictionary : %08X \n", matchingDict); } CFDictionarySetValue(matchingDict, CFSTR(kUSBVendorID), CFNumberCreate(kCFAllocatorDefault, kCFNumberShortType, &LegoUSBVendorID)); CFDictionarySetValue(matchingDict, CFSTR(kUSBProductID), CFNumberCreate(kCFAllocatorDefault, kCFNumberShortType, &LegoUSBProductID)); result = IOServiceGetMatchingServices(gMasterPort, matchingDict, &gRawAddedIter); matchingDict = 0; // this was consumed by the above call // Iterate over matching devices to access already present devices NSLog(@"RawAddedIter : 0x:%08X \n", &gRawAddedIter); device_count = FindDevice(NULL, gRawAddedIter); if (device_count == 1) { result = FindInterfaces(dev, &intf); if (kIOReturnSuccess != result) { NSLog(@"unable to find interfaces on device: %08x\n", result); (*dev)-USBDeviceClose(dev); (*dev)-Release(dev); return NULL; } // osx_usb_rcx_wakeup(intf); return intf; } else if (device_count 1) { NSLog(@"too many matching devices (%d) !\n", device_count); } else { NSLog(@"no matching devices found\n"); } return NULL; } int main(int argc, char *argv[]) { int returnCode; NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; NSLog(@"Debut du programme \n \n"); osx_usb_rcx_init(); NSLog(@"Fin du programme \n \n"); return 0; // returnCode = UIApplicationMain(argc, argv, @"Untitled1App", @"Untitled1App"); // [pool release]; // return returnCode; }

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  • Java Concurrency : Synchronized(this) => and this.wait() and this.notify()

    - by jens
    Hello Experts, I would appreciate your help in understand a "Concurrency Example" from: http://forums.sun.com/thread.jspa?threadID=735386 Qute Start: public synchronized void enqueue(T obj) { // do addition to internal list and then... this.notify(); } public synchronized T dequeue() { while (this.size()==0) { this.wait(); } return // something from the queue } Quote End: My Question is: Why is this code valid? = When I synchronize a method like "public synchronized" = then I synchronize on the "Instance of the Object == this". However in the example above: Calling "dequeue" I will get the "lock/monitor" on this Now I am in the dequeue method. As the list is zero, the calling thread will be "waited" From my understanding I have now a deadlock situation, as I will have no chance of ever enquing an object (from an nother thread), as the "dequeue" method is not yet finised and the dequeue "method" holds the lock on this: So I will never ever get the possibility to call "enequeue" as I will not get the "this" lock. Backround: I have exactly the same problem: I have some kind of connection pool (List of Connections) and need to block if all connections are checked. What is the correct way to synchronize the List to block, if size exceeds a limit or is zero? Thank you very much Jens

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  • Posting XML form data to a RESTful Server with Javascript or PHP

    - by pjs-worker
    Hi folks, I've been given the task of posting to a RESTful server. I'm new to the official "REST" but I've played with the concept before. However, this time I have an XML Payload example file that I am supposed to post. I'm struggling to figure out how the two relate. Can you help? Right now I can post to a specific site, say www.pcpost.com/schema/Application I can generate the URL for the inital, ie: postApplication?userid=4&... Being relatively new to web programming, I find that don't know how to take the following and interface it with the server. I'm at least familiar with Javascript and PHP. If this is impossible with those two types, I can learn whatever would be best. Thanks for your help on this. C <?xml version=\"1.0\" ?> <Application xmlns="http://www.pcpost.com/schema/Application" SchemaVersion="1.0" ProgramId="8" ApplicationDate="2009-08-29"> <Vendors> <Vendor Role="Applicant" Company="Test Company" Contact="Smith, John"/> <Vendor Role="Seller" Company="Test Company" Contact="Doe, Jane"/> <Vendor Role="Installer" Company="Test Company" Contact="Funk, Carl"/> </Vendors> <Participants> <Participant TaxStatus="Individual" Sector="Commercial"> <Roles> <Role>Host Customer</Role> </Roles> </Participants> </Application>

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  • TCL TDom: Looping through Objects

    - by pws5068
    Using TDom, I would like to cycle through a list of objects in the following format: <object> <type>Hardware</type> <name>System Name</name> <description>Basic Description of System.</description> <attributes> <vendor>Dell</vendor> <contract>MM/DD/YY</contract> <supportExpiration>MM/DD/YY</supportExpiration> <location>Building 123</location> <serial>xxx-xxx-xxxx</serial> <mac>some-mac-address</mac> </attributes> </object> <object> <type>Software</type> <name>Second Object</name> ... Then I use TDom to make a list of objects: set dom [dom parse $xml] set doc [$dom documentElement] set nodeList [$doc selectNodes /systems/object] So far I've done this to (theoretically) select every "Object" node from the list. How can I loop through them? Is it just: foreach node $nodeList { For each object, I need to retrieve the association of each attribute. From the example, I need to remember that the "name" is "System Name", "vendor" is "Dell", etc. I'm new to TCL but in other languages I would use an object or an associative list to store these. Is this possible? Can you show me an example of the syntax to select an attribute in this manner?

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  • In .NET when Aborting Thread, can this piece of code get corrupted?

    - by bosko
    Little intro: In complex multithreaded aplication (enterprise service bus EBS), I need to use Thread.Abort, because this EBS accepts user written modules which communicates with hardware security modules. So if this module gets deadlocked or hardware stops responding - i need to just unload this module and rest of this server aplication must keep runnnig. So there is abort sync mechanism which ensures that code can be aborted only in user section and this section must be marked as AbortAble. If this happen there is possibility that ThreadAbortException will be thrown in this pieace of code: public void StopAbortSection() { var id = Thread.CurrentThread.ManagedThreadId; lock (threadIdMap[id]) { .... } } If module is on AbortSection and Aplication decides to abort module, but after this decision but before actual Thread.Abort, module enters NonAbortableSection by calling this method, but lock is actualy taken on that locking object. So lock will block until Abort or abort can be executed before reaching this block by this code. But Object with this method is essential and i need to be sure that this pieace of code is safe to abort in any moment. Probably i have to mention that threadIdMap is Dictionary(int,ManualResetEvent), so locking object is instance of ManualResetEvent. I hope you now understad my question. Sorry for its largeness.

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  • SQL Concurrent test update question

    - by ptoinson
    Howdy Folks, I have a SQLServer 2008 database in which I have a table for Tags. A tag is just an id and a name. The definition of the tags table looks like: CREATE TABLE [dbo].[Tag]( [ID] [int] IDENTITY(1,1) NOT NULL, [Name] [varchar](255) NOT NULL CONSTRAINT [PK_Tag] PRIMARY KEY CLUSTERED ( [ID] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ) Name is also a unique index. further I have several processes adding data to this table at a pretty rapid rate. These processes use a stored proc that looks like: ALTER PROC [dbo].[lg_Tag_Insert] @Name varchar(255) AS DECLARE @ID int SET @ID = (select ID from Tag where Name=@Name ) if @ID is null begin INSERT Tag(Name) VALUES (@Name) RETURN SCOPE_IDENTITY() end else begin return @ID end My issues is that, other than being a novice at concurrent database design, there seems to be a race condition that is causing me to occasionally get an error that I'm trying to enter duplicate keys (Name) into the DB. The error is: Cannot insert duplicate key row in object 'dbo.Tag' with unique index 'IX_Tag_Name'. This makes sense, I'm just not sure how to fix this. If it where code I would know how to lock the right areas. SQLServer is quite a different beast. First question is what is the proper way to code this 'check, then update pattern'? It seems I need to get an exclusive lock on the row during the check, rather than a shared lock, but it's not clear to me the best way to do that. Any help in the right direction will be greatly appreciated. Thanks in advance.

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  • How to program critical section for reader-writer systems?

    - by Srinivas Nayak
    Hi, Lets say, I have a reader-writer system where reader and writer are concurrently running. 'a' and 'b' are two shared variables, which are related to each other, so modification to them needs to be an atomic operation. A reader-writer system can be of the following types: rr ww r-w r-ww rr-w rr-ww where [ r : single reader rr: multiple reader w : single writer ww: multiple writer ] Now, We can have a read method for a reader and a write method for a writer as follows. I have written them system type wise. rr read_method { read a; read b; } ww write_method { lock(m); write a; write b; unlock(m); } r-w r-ww rr-w rr-ww read_method { lock(m); read a; read b; unlock(m); } write_method { lock(m); write a; write b; unlock(m); } For multiple reader system, shared variable access doesn't need to be atomic. For multiple writer system, shared variable access need to be atomic, so locked with 'm'. But, for system types 3 to 6, is my read_method and write_method correct? How can I improve? Sincerely, Srinivas Nayak

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  • Delete throws "deleted object would be re-saved by cascade"

    - by Greg
    I have following model: <class name="Person" table="Person" optimistic-lock="version"> <id name="Id" type="Int32" unsaved-value="0"> <generator class="native" /> </id> <!-- plus some properties here --> </class> <class name="Event" table="Event" optimistic-lock="version"> <id name="Id" type="Int32" unsaved-value="0"> <generator class="native" /> </id> <!-- plus some properties here --> </class> <class name="PersonEventRegistration" table="PersonEventRegistration" optimistic-lock="version"> <id name="Id" type="Int32" unsaved-value="0"> <generator class="native" /> </id> <property name="IsComplete" type="Boolean" not-null="true" /> <property name="RegistrationDate" type="DateTime" not-null="true" /> <many-to-one name="Person" class="Person" column="PersonId" foreign-key="FK_PersonEvent_PersonId" cascade="all-delete-orphan" /> <many-to-one name="Event" class="Event" column="EventId" foreign-key="FK_PersonEvent_EventId" cascade="all-delete-orphan" /> </class> There are no properties pointing to PersonEventRegistration either in Person nor in Event. When I try to delete an entry from PersonEventRegistration, I get the following error: "deleted object would be re-saved by cascade" The problem is, I don't store this object in any other collection - the delete code looks like this: public bool UnregisterFromEvent(Person person, Event entry) { var registrationEntry = this.session .CreateCriteria<PersonEventRegistration>() .Add(Restrictions.Eq("Person", person)) .Add(Restrictions.Eq("Event", entry)) .Add(Restrictions.Eq("IsComplete", false)) .UniqueResult<PersonEventRegistration>(); bool result = false; if (null != registrationEntry) { using (ITransaction tx = this.session.BeginTransaction()) { this.session.Delete(registrationEntry); tx.Commit(); result = true; } } return result; } What am I doing wrong here?

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  • Atomic int writes on file

    - by Waneck
    Hello! I'm writing an application that will have to be able to handle many concurrent accesses to it, either by threads as by processes. So no mutex'es or locks should be applied to this. To make the use of locks go down to a minimum, I'm designing for the file to be "append-only", so all data is first appended to disk, and then the address pointing to the info it has updated, is changed to refer to the new one. So I will need to implement a small lock system only to change this one int so it refers to the new address. How is the best way to do it? I was thinking about maybe putting a flag before the address, that when it's set, the readers will use a spin lock until it's released. But I'm afraid that it isn't at all atomic, is it? e.g. a reader reads the flag, and it is unset on the same time, a writer writes the flag and changes the value of the int the reader may read an inconsistent value! I'm looking for locking techniques but all I find is either for thread locking techniques, or to lock an entire file, not fields. Is it not possible to do this? How do append-only databases handle this? Thanks! Cauê

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  • How did this happen?? Git error? Some other fluke?

    - by marfarma
    Every file in this Rails project is duplicated with a -e and again with a -e-e tacked onto the end of it, like the following. It's that way in my GitHub repository too. But I can't figure out how it happened. Any clue? Google searching comes up empty. -rw-r--r--@ 1 usrname staff 959 Jan 7 02:13 Gemfile -rw-r--r-- 1 usrname staff 958 Jan 5 01:10 Gemfile-e -rw-r--r-- 1 usrname staff 958 Jan 5 01:09 Gemfile-e-e -rw-r--r-- 1 usrname staff 6650 Jan 7 02:13 Gemfile.lock -rw-r--r-- 1 usrname staff 6650 Jan 5 01:10 Gemfile.lock-e -rw-r--r-- 1 usrname staff 6650 Jan 5 01:09 Gemfile.lock-e-e lrwxr-xr-x 1 usrname staff 18 Jan 5 00:37 README.rdoc - doc/README_FOR_APP -rw-r--r-- 1 usrname staff 283 Jan 5 01:10 Rakefile -rw-r--r-- 1 usrname staff 283 Jan 5 01:10 Rakefile-e -rw-r--r-- 1 usrname staff 283 Jan 5 01:09 Rakefile-e-e drwxr-xr-x 6 usrname staff 204 Jan 5 00:37 app drwxr-xr-x 5 usrname staff 170 Jan 5 01:10 autotest drwxr-xr-x 28 usrname staff 952 Jan 5 01:15 config -rw-r--r-- 1 usrname staff 173 Jan 5 01:10 config.ru -rw-r--r-- 1 usrname staff 173 Jan 5 01:10 config.ru-e -rw-r--r-- 1 usrname staff 173 Jan 5 01:09 config.ru-e-e

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  • Rails - strip xml import from whitespace and line break

    - by val_to_many
    Hey folks, I am stuck with something quite simple but really annoying: I have an xml file with one node, where the content includes line breaks and whitspaces. Sadly I can't change the xml. <?xml version="1.0" encoding="utf-8" ?> <ProductFeed> ACME Ltd. Fooproduct Foo Root :: Bar Category I get to the node and can read from it without trouble: url = "http://feeds.somefeed/feed.xml.gz" @source = open((url), :http_basic_authentication=>["USER", "PW"]) @gz = Zlib::GzipReader.new(@source) @result = @gz.read @doc = Nokogiri::XML(@result) @doc.xpath("/ProductFeed/Vendors/Vendor").each do |manuf| vendor = manuf.css("Name").first.text manuf.xpath("//child::Product").each do |product| product_name = product.css("Name").text foocat = product.css("Category").text puts "#{vendor} ---- #{product_name} ---- #{foocat} " end end This results in: ACME Ltd. ---- Fooproduct ---- Foo Root :: Bar Category Obviously there are line breaks and tab stops or spaces in the string returned by product.css("Category").text. Does anyone know how to strip the result from linebreaks and taps or spaces right here? Alternatively I could do that in the next step, where I do a find on 'foocat' like barcat = Category.find_by_foocat(foocat) Thanks for helping! Val

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  • SQLite transaction doesn't work as expected

    - by troll
    I prepared 2 files, "1.php" and "2.php". "1.php" is like this. <?php $dbh = new PDO('sqlite:test1'); $dbh->beginTransaction(); print "aaa<br>"; sleep(55); $dbh->commit(); print "bbb"; ?> and "2.php" is like this. <?php $dbh = new PDO('sqlite:test1'); $dbh->beginTransaction(); print "ccc<br>"; $dbh->commit(); print "ddd"; ?> and I excute "1.php". It starts a transaction and waits 55 seconds. So when I immediately excute "2.php", my expectation is this: "1.php" is getting transaction and "1" holds a database lock "2" can not begin a transaction "2" can not get database lock so "2" have to wait 55 seconds BUT, but the test went another way. When I excute "2",then "2" immediately returned it's result "2" did not wait so I have to think that "1" could not get transaction, or could not get database lock. Can anyone help?

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  • File Locked by Services (after service code reading the text file)

    - by rvpals
    I have a windows services written in C# .NET. The service is running on a internal timer, every time the interval hits, it will go and try to read this log file into a String. My issue is every time the log file is read, the service seem to lock the log file. The lock on that log file will continue until I stop the windows service. At the same time the service is checking the log file, the same log file needs to be continuously updated by another program. If the file lock is on, the other program could not update the log file. Here is the code I use to read the text log file. private string ReadtextFile(string filename) { string res = ""; try { System.IO.FileStream fs = new System.IO.FileStream(filename, System.IO.FileMode.Open, System.IO.FileAccess.Read); System.IO.StreamReader sr = new System.IO.StreamReader(fs); res = sr.ReadToEnd(); sr.Close(); fs.Close(); } catch (System.Exception ex) { HandleEx(ex); } return res; } Thank you.

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  • Any way to turn off quips in OOWeb?

    - by Misha Koshelev
    http://ooweb.sourceforge.net/tutorial.html Not really a question, but I can't seem to stop writing stuff like this. Maybe someone will find it useful. I know rewriting an HTTP server is not the way to turn off the quips ;) /* Copyright 2010 Misha Koshelev. All Rights Reserved. */ package com.mksoft.common; import java.io.BufferedReader; import java.io.InputStreamReader; import java.io.IOException; import java.io.PrintWriter; import java.io.UnsupportedEncodingException; import java.net.URLDecoder; import java.text.SimpleDateFormat; import java.util.Date; import java.util.LinkedHashMap; import java.net.ServerSocket; import java.net.Socket; /** * Simple HTTP Server. * * @author Misha Koshelev */ public class HttpServer extends Thread { /* * Constants */ /** * 404 Not Found Result */ protected final static String result404NotFound="<html><head><title>404 Not Found</title></head><body bgcolor='#ffffff'><h1>404 Not Found</h1></body></html>"; /* * Variables */ /** * Port on which HTTP server handles requests. */ protected int port; public int getPort() { return port; } public void setPort(int _port) { port=_port; } /* * Constructors */ public HttpServer(int _port) { setPort(_port); } /* * Helpers */ /** * Errors */ protected void error(String message) { System.err.println(message); System.err.flush(); } /** * Debugging */ protected boolean debugOutput=true; protected void debug(String message) { if (debugOutput) { error(message); } } /** * Lock object */ private Object lock=new Object(); /** * Should we quit? */ protected boolean doQuit=false; /** * Are we done? */ protected boolean areWeDone=false; /** * Process POST request headers */ protected String processPostRequest(String url,LinkedHashMap<String,String> headers,String inputLine) { debug("HttpServer.processPostRequest: url=\""+url); if (debugOutput) { for (String key: headers.keySet()) { debug("HttpServer.processPostRequest: headers."+key+"=\""+headers.get(key)+"\""); } } debug("HttpServer.processPostRequest: inputLine=\""+inputLine+"\""); try { inputLine=new URLDecoder().decode(inputLine,"UTF-8"); } catch (UnsupportedEncodingException uee) { uee.printStackTrace(); } String[] keyValues=inputLine.split("&"); LinkedHashMap<String,String> post=new LinkedHashMap<String,String>(); for (int i=0;i<keyValues.length;i++) { String keyValue=keyValues[i]; int equals=keyValue.indexOf('='); String key=keyValue.substring(0,equals); String value=keyValue.substring(equals+1); post.put(key,value); } return post(url,headers,post); } /** * Server loop (here for exception handling purposes) */ protected void serverLoop() throws IOException { /* Start server socket */ ServerSocket serverSocket=null; try { serverSocket=new ServerSocket(getPort()); } catch (IOException ioe) { ioe.printStackTrace(); System.exit(1); } Socket clientSocket=null; while (true) { /* Quit if necessary */ if (doQuit) { break; } /* Accept incoming connections */ try { clientSocket=serverSocket.accept(); } catch (IOException ioe) { ioe.printStackTrace(); System.exit(1); } /* Read request */ BufferedReader in=null; String inputLine=null; String firstLine=null; String blankLine=null; LinkedHashMap<String,String> headers=new LinkedHashMap<String,String>(); try { in=new BufferedReader(new InputStreamReader(clientSocket.getInputStream())); while (true) { if (blankLine==null) { inputLine=in.readLine(); } else { /* POST request, read Content-length bytes */ int contentLength=new Integer(headers.get("Content-Length")).intValue(); StringBuilder sb=new StringBuilder(contentLength); for (int i=0;i<contentLength;i++) { sb.append((char)in.read()); } inputLine=sb.toString(); break; } if (firstLine==null) { firstLine=inputLine; } else if (blankLine==null) { if (inputLine.equals("")) { if (firstLine.startsWith("GET ")) { break; } blankLine=inputLine; } else { int colon=inputLine.indexOf(": "); String key=inputLine.substring(0,colon); String value=inputLine.substring(colon+2); headers.put(key,value); } } } } catch (IOException ioe) { ioe.printStackTrace(); } /* Process request */ String result=null; firstLine=firstLine.replaceAll(" HTTP/.*",""); if (firstLine.startsWith("GET ")) { result=get(firstLine.replaceFirst("GET ",""),headers); } else if (firstLine.startsWith("POST ")) { result=processPostRequest(firstLine.replaceFirst("POST ",""),headers,inputLine); } else { error("HttpServer.ServerLoop: Unhandled request \""+firstLine+"\""); } debug("HttpServer.ServerLoop: result=\""+result+"\""); /* Send response */ PrintWriter out=null; try { out=new PrintWriter(clientSocket.getOutputStream(),true); } catch (IOException ioe) { ioe.printStackTrace(); } if (result!=null) { out.println("HTTP/1.1 200 OK"); } else { out.println("HTTP/1.0 404 Not Found"); result=result404NotFound; } Date now=new Date(); out.println("Date: "+new SimpleDateFormat("EEE, d MMM yyyy HH:mm:ss z").format(now)); out.println("Content-Type: text/html; charset=UTF-8"); out.println("Content-Length: "+result.length()); out.println(""); out.print(result); /* Clean up */ out.close(); if (in!=null) { in.close(); } clientSocket.close(); } serverSocket.close(); areWeDone=true; synchronized(lock) { lock.notifyAll(); } } /* * Methods */ /** * Run server on port specified in constructor. */ public void run() { try { serverLoop(); } catch (IOException ioe) { ioe.printStackTrace(); System.exit(1); } } /** * Process GET request (should be overwritten). */ public String get(String url,LinkedHashMap<String,String> headers) { debug("HttpServer.get: url=\""+url+"\""); if (debugOutput) { for (String key: headers.keySet()) { debug("HttpServer.get: headers."+key+"=\""+headers.get(key)+"\""); } } if (url.equals("/")) { return "<html><head><title>HttpServer GET Test Page</title></head>\r\n"+ "<body bgcolor='#ffffff'>\r\n"+ "<center><h1>HttpServer GET Test Page</h1></center>\r\n"+ "<hr />\r\n"+ "<center><table>\r\n"+ "<form method='post' action='/'>\r\n"+ "<tr><td align=right>Test 1:</td>\r\n"+ " <td><input type='text' name='text 1' value='test me !!! !@#$'></td></tr>\r\n"+ "<tr><td align=right>Test 2:</td>\r\n"+ " <td><input type='text' name='text 2' value='type smthng'></td></tr>\r\n"+ "<tr><td>&nbsp;</td>\r\n"+ " <td align=right><input type='submit' value='Submit'></td></tr>\r\n"+ "</form>\r\n"+ "</table></center>\r\n"+ "<hr />\r\n"+ "<center><a href='/quit'>Shutdown Server</a></center>\r\n"+ "</html>"; } else if (url.equals("/quit")) { quit(); return ""; } else { return null; } } /** * Process POST request (should be overwritten). */ public String post(String url,LinkedHashMap<String,String> headers,LinkedHashMap<String,String> post) { debug("HttpServer.post: url=\""+url+"\""); if (debugOutput) { for (String key: headers.keySet()) { debug("HttpServer.post: headers."+key+"=\""+headers.get(key)+"\""); } } if (url.equals("/")) { String result="<html><head><title>HttpServer Post Test Page</title></head>\r\n"+ "<body bgcolor='#ffffff'>\r\n"+ "<center><h1>HttpServer Post Test Page</h1></center>\r\n"+ "<hr />\r\n"+ "<center><table>\r\n"+ "<tr><th>Key</th><th>Value</th></tr>\r\n"; for (String key: post.keySet()) { result+="<tr><td align=right>"+key+"</td><td align=left>"+post.get(key)+"</td></tr>\r\n"; } result+="</table></center>\r\n"+ "</html>"; return result; } else { return null; } } /** * Wait for server to quit. */ public void waitForCompletion() { while (areWeDone==false) { synchronized(lock) { try { lock.wait(); } catch (InterruptedException ie) { } } } } /** * Shutdown server. */ public void quit() { doQuit=true; } }

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  • Have I found a security problem in an API or do I just not understand SSL?

    - by jamieb
    I'm working on building a set of Python bindings around an XML-based API provided by a vendor. The vendor requires that all transactions be conducted over SSL. Using a Linux box, I created a key file and a CSR for my application. Using their self-service web portal, I then generate a certificate using that CSR. Both the key file and the certificate are used when making the SSL request to the API. I'm now working on designing exception classes to make error messages more verbose (and, hopefully, more useful to developers using my bindings). Part of my testing has included altering the key file: transpose a couple characters here, replace 4 or 5 with random characters there, etc. To my surprise, altering the key file had no effect! As long as I didn't change the total length of it, the API didn't complain about a bad key file. The only way I was able to throw an error was by swapping in a completely different key from another application. At that point, the API complained about the Common Name not matching. Is this normal behavior or has the vendor not properly implemented SSL?

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  • Unit Testing a rails 2.3.5 plugin

    - by brad
    I'm writing a new plugin for a rails 2.3.5 app. I've included an app directory (which makes it an engine) so i can easily load some extra routes. Not sure if that affects anything. Anyway, in the test directory i have two files: test_helper.rb and my_plugin_test.rb These files were generated automatically using script/generate plugin my_plugin When I go to vendor/plugins/my_plugin directory and run rake test they don't seem to run. I get the following console output: (in /Users/me/Repos/my_app/source/trunk/vendor/plugins/my_plugin) /Users/me/.rvm/rubies/jruby-1.4.0/bin/jruby -I"lib:lib:test" "/Users/me/.rvm/gems/jruby-1.4.0/gems/rake-0.8.7/lib/rake/rake_test_loader.rb" "test/my_plugin_test.rb" So it obviously sees my test file, but none of the tests inside get run, I just get back to my console prompt. What am I missing here? I figured the generated code would work out of the box Here are the two files test_helper.rb require 'rubygems' require 'active_support' require 'active_support/test_case' my_plugin_test.rb require 'test_helper' class MyPluginTest < ActiveSupport::TestCase # Replace this with your real tests. test "the truth" do assert true end test "Factories are supported" do assert_not_nil Factory end end File structure vendor - plugins - my_plugin - app - config - routes.rb - generators - my_plugin - some generator files.rb - lib - my_plugin.rb - my_plugin - my_plugin_lib_file.rb - rails - init.rb - Rakefile - tasks - my_plugin_tasks.rake - test - test_helper.rb - my_plugin_test.rb

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  • Correct way to generate order numbers in SQL Server

    - by Anton Gogolev
    This question certainly applies to a much broader scope, but here it is. I have a basic ecommerce app, where users can, naturally enough, place orders. Said orders need to have a unique number, which I'm trying to generate right now. Each order is Vendor-specific. Basically, I have an OrderNumberInfo (VendorID, OrderNumber) table. Now whenever a customer places an order I need to increment OrderNumber for a particuar Vendor and return that value. Naturally, I don't want other processes to interfere with me, so I need to exclusively lock this row somehow: begin tranaction declare @n int select @n = OrderNumber from OrderNumberInfo where VendorID = @vendorID update OrderNumberInfo set OrderNumber = @n + 1 where OrderNumber = @n and VendorID = @vendorID commit transaction Now, I've read about select ... with (updlock rowlock), pessimistic locking, etc., but just cannot fit all this in a coherent picture: How do these hints play with SQL Server 2008s' snapshot isolation? Do they perform row-level, page-level or even table-level locks? How does this tolerate multiple users trying to generate numbers for a single Vendor? What isolation levels are appropriate here? And generally - what is the way to do such things?

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  • How to deserialize implementation classes in OSGi

    - by Daniel Schneller
    In an eRCP OSGi based application the user can push a button and go to a lock screen similar to that of Windows or Mac OS X. When this happens, the current state of the application is serialized to a file and control is handed over to the lock screen. In this mobile application memory is very tight, so we need to get rid of the original view/controller when the lock screen comes up. This works fine and we end up with a binary serialized file. Once the user logs back in, the file is read in again and the original state of the application restored. This works fine as well, except when the controller that was serialized contained a reference to an object which comes from a different bundle. In my concrete case the original controller (from bundle A) can call a web service and gets a result back. Nothing fancy, just some Strings and Numbers in a simple value holder class. However the controller only sees this as a Result interface; the actual runtime object (ResultImpl) is defined and created in a different bundle (bundle B, the webservice client implementation) and returned via a service call. When the deserialization now tries to thaw the controller from the file, it throws a ClassNotFound exception, complaining about not being able to deserialize the result object, because deserialization is called from bundle A, which cannot see the ResultImpl class from bundle B. Any ideas on how to work around that? The only thing I could come up with is to clone all the individual values into another object, defined in the controller's bundle, but this seems like quite a hassle.

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  • How to improve multi-threaded access to Cache (custom implementation)

    - by Andy
    I have a custom Cache implementation, which allows to cache TCacheable<TKey> descendants using LRU (Least Recently Used) cache replacement algorithm. Every time an element is accessed, it is bubbled up to the top of the LRU queue using the following synchronized function: // a single instance is created to handle all TCacheable<T> elements public class Cache() { private object syncQueue = new object(); private void topQueue(TCacheable<T> el) { lock (syncQueue) if (newest != el) { if (el.elder != null) el.elder.newer = el.newer; if (el.newer != null) el.newer.elder = el.elder; if (oldest == el) oldest = el.newer; if (oldest == null) oldest = el; if (newest != null) newest.newer = el; el.newer = null; el.elder = newest; newest = el; } } } The bottleneck in this function is the lock() operator, which limits cache access to just one thread at a time. Question: Is it possible to get rid of lock(syncQueue) in this function while still preserving the queue integrity?

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  • Sharing a COM port over TCP

    - by guinness
    What would be a simple design pattern for sharing a COM port over TCP to multiple clients? For example, a local GPS device that could transmit co-ordinates to remote hosts in realtime. So I need a program that would open the serial port and accept multiple TCP connections like: class Program { public static void Main(string[] args) { SerialPort sp = new SerialPort("COM4", 19200, Parity.None, 8, StopBits.One); Socket srv = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); srv.Bind(new IPEndPoint(IPAddress.Any, 8000)); srv.Listen(20); while (true) { Socket soc = srv.Accept(); new Connection(soc); } } } I would then need a class to handle the communication between connected clients, allowing them all to see the data and keeping it synchronized so client commands are received in sequence: class Connection { static object lck = new object(); static List<Connection> cons = new List<Connection>(); public Socket socket; public StreamReader reader; public StreamWriter writer; public Connection(Socket soc) { this.socket = soc; this.reader = new StreamReader(new NetworkStream(soc, false)); this.writer = new StreamWriter(new NetworkStream(soc, true)); new Thread(ClientLoop).Start(); } void ClientLoop() { lock (lck) { connections.Add(this); } while (true) { lock (lck) { string line = reader.ReadLine(); if (String.IsNullOrEmpty(line)) break; foreach (Connection con in cons) con.writer.WriteLine(line); } } lock (lck) { cons.Remove(this); socket.Close(); } } } The problem I'm struggling to resolve is how to facilitate communication between the SerialPort instance and the threads. I'm not certain that the above code is the best way forward, so does anybody have another solution (the simpler the better)?

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