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• mdadm raid5 recover double disk failure - with a twist (drive order)

  - by Peter Bos

  Let me acknowledge first off that I have made mistakes, and that I have a backup for most but not all of the data on this RAID. I still have hope of recovering the rest of the data. I don't have the kind of money to take the drives to a recovery expert company. Mistake #0, not having a 100% backup. I know. I have a mdadm RAID5 system of 4x3TB. Drives /dev/sd[b-e], all with one partition /dev/sd[b-e]1. I'm aware that RAID5 on very large drives is risky, yet I did it anyway. Recent events The RAID become degraded after a two drive failure. One drive [/dev/sdc] is really gone, the other [/dev/sde] came back up after a power cycle, but was not automatically re-added to the RAID. So I was left with a 4 device RAID with only 2 active drives [/dev/sdb and /dev/sdd]. Mistake #1, not using dd copies of the drives for restoring the RAID. I did not have the drives or the time. Mistake #2, not making a backup of the superblock and mdadm -E of the remaining drives. Recovery attempt I reassembled the RAID in degraded mode with mdadm --assemble --force /dev/md0, using /dev/sd[bde]1. I could then access my data. I replaced /dev/sdc with a spare; empty; identical drive. I removed the old /dev/sdc1 from the RAID mdadm --fail /dev/md0 /dev/sdc1 Mistake #3, not doing this before replacing the drive I then partitioned the new /dev/sdc and added it to the RAID. mdadm --add /dev/md0 /dev/sdc1 It then began to restore the RAID. ETA 300 mins. I followed the process via /proc/mdstat to 2% and then went to do other stuff. Checking the result Several hours (but less then 300 mins) later, I checked the process. It had stopped due to a read error on /dev/sde1. Here is where the trouble really starts I then removed /dev/sde1 from the RAID and re-added it. I can't remember why I did this; it was late. mdadm --manage /dev/md0 --remove /dev/sde1 mdadm --manage /dev/md0 --add /dev/sde1 However, /dev/sde1 was now marked as spare. So I decided to recreate the whole array using --assume-clean using what I thought was the right order, and with /dev/sdc1 missing. mdadm --create /dev/md0 --assume-clean -l5 -n4 /dev/sdb1 missing /dev/sdd1 /dev/sde1 That worked, but the filesystem was not recognized while trying to mount. (It should have been EXT4). Device order I then checked a recent backup I had of /proc/mdstat, and I found the drive order. md0 : active raid5 sdb1[0] sde1[4] sdd1[2] sdc1[1] 8790402048 blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/4] [UUUU] I then remembered this RAID had suffered a drive loss about a year ago, and recovered from it by replacing the faulty drive with a spare one. That may have scrambled the device order a bit...so there was no drive [3] but only [0],[1],[2], and [4]. I tried to find the drive order with the Permute_array script: https://raid.wiki.kernel.org/index.php/Permute_array.pl but that did not find the right order. Questions I now have two main questions: I screwed up all the superblocks on the drives, but only gave: mdadm --create --assume-clean commands (so I should not have overwritten the data itself on /dev/sd[bde]1. Am I right that in theory the RAID can be restored [assuming for a moment that /dev/sde1 is ok] if I just find the right device order? Is it important that /dev/sde1 be given the device number [4] in the RAID? When I create it with mdadm --create /dev/md0 --assume-clean -l5 -n4 \ /dev/sdb1 missing /dev/sdd1 /dev/sde1 it is assigned the number [3]. I wonder if that is relevant to the calculation of the parity blocks. If it turns out to be important, how can I recreate the array with /dev/sdb1[0] missing[1] /dev/sdd1[2] /dev/sde1[4]? If I could get that to work I could start it in degraded mode and add the new drive /dev/sdc1 and let it resync again. It's OK if you would like to point out to me that this may not have been the best course of action, but you'll find that I realized this. It would be great if anyone has any suggestions.

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• Why are my USB 2.0 devices hanging Windows XP?

  - by BenAlabaster

  Background on the machine I'm having a problem with: The machine was inherited and appears to be circa 2003 (there's a date stamp on the power supply which leads me to this conclusion). I've got it set up as a Skype terminal for my 2 year old to keep in touch with her grandparents and other members of the family - which everyone loves. It has a DFI CM33-TL/G ATX (identified using SiSoft Sandra) motherboard hosting an Intel Celeron 1.3GHz CPU, 768Mb PC133 SDRAM, a D-LINK WDA-2320 54G Wi-Fi network card and a generic USB 2.0 expansion board based on the NEC uPD720102 chipset containing 3 external and 1 internal USB sockets. It's also hosting a 1.44Mb floppy drive on FDD0, a new 80Gb Western Digital hard drive running as master on IDE0 and a Panasonic DVD+/-RW running as master on IDE1. All this is sitting in a slimline case running off a Macron Power MPT-135 135W Flex power supply. The motherboard is running a version of Award BIOS 05/24/2002-601T-686B-6A6LID4AC-00. Could this be updated? If so, from where? I've raked through the manufacturer's website but can't find any hint of downloads for either drivers or BIOS updates. The hard disk is freshly formatted and built with Windows XP Professional/Service Pack 3 and is up to date with all current patches. In addition to Windows XP, the only other software it's running is Skype 4.1 (4.2 hangs the whole machine as soon as it starts up, requiring a hard boot to recover). It's got a Daytek MV150 15" touch screen hooked up to the on board VGA and COM1 sockets with the most current drivers from the Daytek website and the most current version of ELO-Touchsystems drivers for the touch component. The webcam is a Logitech Webcam C200 with the latest drivers from the Logitech website. The problem: If I hook any devices to the USB 2.0 sockets, it hangs the whole machine and I have to hard boot it to get it back up. If I have any devices attached to the USB 2.0 sockets when I boot up, it hangs before Windows gets to the login prompt and I have to hard boot it to recover. Workarounds found: I can plug the same devices into the on board USB 1.0 sockets and everything works fine, albeit at reduced performance. I've tried 3 different kinds of USB thumb drives, 3 different makes/models of webcams and my iPhone all with the same effect. They're recognized and don't hang the machine when I hook them to the USB 1.0 but if I hook them to the USB 2.0 ports, the machine hangs within a couple of seconds of recognizing the devices were connected. Attempted solutions: I've seen suggestions that this could be a power problem - that the PSU just doesn't have the wattage to drive these ports. While I'm doubtful this is the problem [after all the motherboard has the same standard connector regardless of the PSU wattage], I tried disabling all the on board devices that I'm not using - on board LAN, the second COM port, the AGP connector etc. through the BIOS in what I'm sure is a futile attempt to reduce the power consumption... I also modified the ACPI and power management settings. It didn't have any noticeable affect, although it didn't do any harm either. Could the wattage of the PSU really cause this problem? If it can, is there anything I need to be aware of when replacing it or do I just need to make sure it's got a higher wattage than the current one? My interpretation was that the wattage only affected the number of drives you could hook up to the power connectors, is that right? I've installed the USB card in another machine and it works without issue, so it's not a problem with the USB card itself, and Windows says the card is installed and working correctly... right up until I connect a device to it. The only thing I haven't done which I only just thought of while writing this essay is trying the USB 2.0 card in a different PCI slot, or re-ordering the wi-fi and USB cards in the slots... although I'm not sure if this will make any difference - does anyone have any experience that would suggest this might work? Other thoughts/questions: Perhaps this is an incompatibility between the USB 2.0 card and the BIOS, would re-flashing the BIOS with a newer version help? Do I need to be able to identify the manufacturer of the motherboard in order to be able to find a BIOS edition specific for this motherboard or will any version of Award BIOS function in its place? Question: Does anyone have any ideas that could help me get my USB 2.0 devices hooked up to this machine?

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• Issue with SPI (Serial Port Comm), stuck on ioctl()

  - by stef

  I'm trying to access a SPI sensor using the SPIDEV driver but my code gets stuck on IOCTL. I'm running embedded Linux on the SAM9X5EK (mounting AT91SAM9G25). The device is connected to SPI0. I enabled CONFIG_SPI_SPIDEV and CONFIG_SPI_ATMEL in menuconfig and added the proper code to the BSP file: static struct spi_board_info spidev_board_info[] { { .modalias = "spidev", .max_speed_hz = 1000000, .bus_num = 0, .chips_select = 0, .mode = SPI_MODE_3, }, ... }; spi_register_board_info(spidev_board_info, ARRAY_SIZE(spidev_board_info)); 1MHz is the maximum accepted by the sensor, I tried 500kHz but I get an error during Linux boot (too slow apparently). .bus_num and .chips_select should correct (I also tried all other combinations). SPI_MODE_3 I checked the datasheet for it. I get no error while booting and devices appear correctly as /dev/spidevX.X. I manage to open the file and obtain a valid file descriptor. I'm now trying to access the device with the following code (inspired by examples I found online). #define MY_SPIDEV_DELAY_USECS 100 // #define MY_SPIDEV_SPEED_HZ 1000000 #define MY_SPIDEV_BITS_PER_WORD 8 int spidevReadRegister(int fd, unsigned int num_out_bytes, unsigned char *out_buffer, unsigned int num_in_bytes, unsigned char *in_buffer) { struct spi_ioc_transfer mesg[2] = { {0}, }; uint8_t num_tr = 0; int ret; // Write data mesg[0].tx_buf = (unsigned long)out_buffer; mesg[0].rx_buf = (unsigned long)NULL; mesg[0].len = num_out_bytes; // mesg[0].delay_usecs = MY_SPIDEV_DELAY_USECS, // mesg[0].speed_hz = MY_SPIDEV_SPEED_HZ; mesg[0].bits_per_word = MY_SPIDEV_BITS_PER_WORD; mesg[0].cs_change = 0; num_tr++; // Read data mesg[1].tx_buf = (unsigned long)NULL; mesg[1].rx_buf = (unsigned long)in_buffer; mesg[1].len = num_in_bytes; // mesg[1].delay_usecs = MY_SPIDEV_DELAY_USECS, // mesg[1].speed_hz = MY_SPIDEV_SPEED_HZ; mesg[1].bits_per_word = MY_SPIDEV_BITS_PER_WORD; mesg[1].cs_change = 1; num_tr++; // Do the actual transmission if(num_tr > 0) { ret = ioctl(fd, SPI_IOC_MESSAGE(num_tr), mesg); if(ret == -1) { printf("Error: %d\n", errno); return -1; } } return 0; } Then I'm using this function: #define OPTICAL_SENSOR_ADDR "/dev/spidev0.0" ... int fd; fd = open(OPTICAL_SENSOR_ADDR, O_RDWR); if (fd<=0) { printf("Device not found\n"); exit(1); } uint8_t buffer1[1] = {0x3a}; uint8_t buffer2[1] = {0}; spidevReadRegister(fd, 1, buffer1, 1, buffer2); When I run it, the code get stuck on IOCTL! I did this way because, in order to read a register on the sensor, I need to send a byte with its address in it and then get the answer back without changing CS (however, when I tried using write() and read() functions, while learning, I got the same result, stuck on them). I'm aware that specifying .speed_hz causes a ENOPROTOOPT error on Atmel (I checked spidev.c) so I commented that part. Why does it get stuck? I though it can be as the device is created but it actually doesn't "feel" any hardware. As I wasn't sure if hardware SPI0 corresponded to bus_num 0 or 1, I tried both, but still no success (btw, which one is it?). UPDATE: I managed to have the SPI working! Half of it.. MOSI is transmitting the right data, but CLK doesn't start... any idea?

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• Feedback on iterating over type-safe enums

  - by Sumant

  In response to the earlier SO question "Enumerate over an enum in C++", I came up with the following reusable solution that uses type-safe enum idiom. I'm just curious to see the community feedback on my solution. This solution makes use of a static array, which is populated using type-safe enum objects before first use. Iteration over enums is then simply reduced to iteration over the array. I'm aware of the fact that this solution won't work if the enumerators are not strictly increasing. template<typename def, typename inner = typename def::type> class safe_enum : public def { typedef typename def::type type; inner val; static safe_enum array[def::end - def::begin]; static bool init; static void initialize() { if(!init) // use double checked locking in case of multi-threading. { unsigned int size = def::end - def::begin; for(unsigned int i = 0, j = def::begin; i < size; ++i, ++j) array[i] = static_cast<typename def::type>(j); init = true; } } public: safe_enum(type v = def::begin) : val(v) {} inner underlying() const { return val; } static safe_enum * begin() { initialize(); return array; } static safe_enum * end() { initialize(); return array + (def::end - def::begin); } bool operator == (const safe_enum & s) const { return this->val == s.val; } bool operator != (const safe_enum & s) const { return this->val != s.val; } bool operator < (const safe_enum & s) const { return this->val < s.val; } bool operator <= (const safe_enum & s) const { return this->val <= s.val; } bool operator > (const safe_enum & s) const { return this->val > s.val; } bool operator >= (const safe_enum & s) const { return this->val >= s.val; } }; template <typename def, typename inner> safe_enum<def, inner> safe_enum<def, inner>::array[def::end - def::begin]; template <typename def, typename inner> bool safe_enum<def, inner>::init = false; struct color_def { enum type { begin, red = begin, green, blue, end }; }; typedef safe_enum<color_def> color; template <class Enum> void f(Enum e) { std::cout << static_cast<unsigned>(e.underlying()) << std::endl; } int main() { std::for_each(color::begin(), color::end(), &f<color>); color c = color::red; }

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• Throwing a C++ exception from inside a Linux Signal handler

  - by SoapBox

  As a thought experiment more than anything I am trying to get a C++ exception thrown "from" a linux signal handler for SIGSEGV. (I'm aware this is not a solution to any real world SIGSEGV and should never actually be done, but I thought I would try it out after being asked about it, and now I can't get it out of my head until I figure out how to do it.) Below is the closest I have come, but instead of the signal being caught properly, terminate() is being called as if no try/catch block is available. Anyone know why? Or know a way I can actually get a C++ exception from a signal handler? The code (beware, the self modifying asm limits this to running on x86_64 if you're trying to test it): #include <iostream> #include <stdexcept> #include <signal.h> #include <stdint.h> #include <errno.h> #include <string.h> #include <sys/mman.h> using namespace std; uint64_t oldaddr = 0; void thrower() { cout << "Inside thrower" << endl; throw std::runtime_error("SIGSEGV"); } void segv_handler(int sig, siginfo_t *info, void *pctx) { ucontext_t *context = (ucontext_t *)pctx; cout << "Inside SIGSEGV handler" << endl; oldaddr = context->uc_mcontext.gregs[REG_RIP]; uint32_t pageSize = (uint32_t)sysconf(_SC_PAGESIZE); uint64_t bottomOfOldPage = (oldaddr/pageSize) * pageSize; mprotect((void*)bottomOfOldPage, pageSize*2, PROT_READ|PROT_WRITE|PROT_EXEC); // 48 B8 xx xx xx xx xx xx xx xx = mov rax, xxxx *((uint8_t*)(oldaddr+0)) = 0x48; *((uint8_t*)(oldaddr+1)) = 0xB8; *((int64_t*)(oldaddr+2)) = (int64_t)thrower; // FF E0 = jmp rax *((uint8_t*)(oldaddr+10)) = 0xFF; *((uint8_t*)(oldaddr+11)) = 0xE0; } void func() { try { *(uint32_t*)0x1234 = 123456789; } catch (...) { cout << "caught inside func" << endl; throw; } } int main() { cout << "Top of main" << endl; struct sigaction action, old_action; action.sa_sigaction = segv_handler; sigemptyset(&action.sa_mask); action.sa_flags = SA_SIGINFO | SA_RESTART | SA_NODEFER; if (sigaction(SIGSEGV, &action, &old_action)<0) cerr << "Error setting handler : " << strerror(errno) << endl; try { func(); } catch (std::exception &e) { cout << "Caught : " << e.what() << endl; } cout << "Bottom of main" << endl << endl; } The actual output: Top of main Inside SIGSEGV handler Inside thrower terminate called after throwing an instance of 'std::runtime_error' what(): SIGSEGV Aborted Expected output: Top of main Inside thrower caught inside func Caught : SIGSEGV Bottom of main

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• Why does jquery leak memory so badly?

  - by Thomas Lane

  This is kind of a follow-up to a question I posted last week: http://stackoverflow.com/questions/2429056/simple-jquery-ajax-call-leaks-memory-in-ie I love the jquery syntax and all of its nice features, but I've been having trouble with a page that automatically updates table cells via ajax calls leaking memory. So I created two simple test pages for experimenting. Both pages do an ajax call every .1 seconds. After each successful ajax call, a counter is incremented and the DOM is updated. The script stops after 1000 cycles. One uses jquery for both the ajax call and to update the DOM. The other uses the Yahoo API for the ajax and does a document.getElementById(...).innerHTML to update the DOM. The jquery version leaks memory badly. Running in drip (on XP Home with IE7), it starts at 9MB and finishes at about 48MB, with memory growing linearly the whole time. If I comment out the line that updates the DOM, it still finishes at 32MB, suggesting that even simple DOM updates leak a significant amount of memory. The non-jquery version starts and finishes at about 9MB, regardless of whether it updates the DOM. Does anyone have a good explanation of what is causing jquery to leak so badly? Am I missing something obvious? Is there a circular reference that I'm not aware of? Or does jquery just have some serious memory issues? Here is the source for the leaky (jquery) version: <html> <head> <script type="text/javascript" src="http://www.google.com/jsapi"></script> <script type="text/javascript"> google.load('jquery', '1.4.2'); </script> <script type="text/javascript"> var counter = 0; leakTest(); function leakTest() { $.ajax({ url: '/html/delme.x', type: 'GET', success: incrementCounter }); } function incrementCounter(data) { if (counter<1000) { counter++; $('#counter').text(counter); setTimeout(leakTest,100); } else $('#counter').text('finished.'); } </script> </head> <body> <div>Why is memory usage going up?</div> <div id="counter"></div> </body> </html> And here is the non-leaky version: <html> <head> <script type="text/javascript" src="http://yui.yahooapis.com/2.8.0r4/build/yahoo/yahoo-min.js"></script> <script type="text/javascript" src="http://yui.yahooapis.com/2.8.0r4/build/event/event-min.js"></script> <script type="text/javascript" src="http://yui.yahooapis.com/2.8.0r4/build/connection/connection_core-min.js"></script> <script type="text/javascript"> var counter = 0; leakTest(); function leakTest() { YAHOO.util.Connect.asyncRequest('GET', '/html/delme.x', {success:incrementCounter}); } function incrementCounter(o) { if (counter<1000) { counter++; document.getElementById('counter').innerHTML = counter; setTimeout(leakTest,100); } else document.getElementById('counter').innerHTML = 'finished.' } </script> </head> <body> <div>Memory usage is stable, right?</div> <div id="counter"></div> </body> </html>

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• C++/msvc6 application crashes due to heap corruption, any hints?

  - by David Alfonso

  Hello all, let me say first that I'm writing this question after months of trying to find out the root of a crash happening in our application. I'll try to detail as much as possible what I've already found out about it. About the application It runs on Windows XP Professional SP2. It's built with Microsoft Visual C++ 6.0 with Service Pack 6. It's MFC based. It uses several external dlls (e.g. Xerces, ZLib or ACE). It has high performance requirements. It does a lot of network and hard disk I/O, but it's also cpu intensive. It has an exception handling mechanism which generates a minidump when an unhandled exception occurs. Facts about the crash It only happens on multiprocessor/multicore machines and under heavy loads of work. It happens at random (neither we nor our client have found a pattern yet). We cannot reproduce the crash on our testing lab. It only happens on some production systems (but always in multicore machines) It always ends up crashing at the same point, although the complete stack is not always the same. Let me add the stack of the crashing thread (obtained using WinDbg, sorry we don't have symbols) ChildEBP RetAddr Args to Child WARNING: Stack unwind information not available. Following frames may be wrong. 030af6c8 7c9206eb 77bfc3c9 01a80000 00224bc3 MyApplication+0x2a85b9 030af960 7c91e9c0 7c92901b 00000ab4 00000000 ntdll!RtlAllocateHeap+0xeac (FPO: [Non-Fpo]) 030af98c 7c9205c8 00000001 00000000 00000000 ntdll!ZwWaitForSingleObject+0xc (FPO: [3,0,0]) 030af9c0 7c920551 01a80898 7c92056d 313adfb0 ntdll!RtlpFreeToHeapLookaside+0x22 (FPO: [2,0,4]) 030afa8c 4ba3ae96 000307da 00130005 00040012 ntdll!RtlFreeHeap+0x1e9 (FPO: [Non-Fpo]) 030afacc 77bfc2e3 0214e384 3087c8d8 02151030 0x4ba3ae96 030afb00 7c91e306 7c80bfc1 00000948 00000001 msvcrt!free+0xc8 (FPO: [Non-Fpo]) 030afb20 0042965b 030afcc0 0214d780 02151218 ntdll!ZwReleaseSemaphore+0xc (FPO: [3,0,0]) 030afb7c 7c9206eb 02e6c471 02ea0000 00000008 MyApplication+0x2965b 030afe60 7c9205c8 02151248 030aff38 7c920551 ntdll!RtlAllocateHeap+0xeac (FPO: [Non-Fpo]) 030afe74 7c92056d 0210bfb8 02151250 02151250 ntdll!RtlpFreeToHeapLookaside+0x22 (FPO: [2,0,4]) 030aff38 77bfc2de 01a80000 00000000 77bfc2e3 ntdll!RtlFreeHeap+0x647 (FPO: [Non-Fpo]) 7c92056d c5ffffff ce7c94be ff7c94be 00ffffff msvcrt!free+0xc3 (FPO: [Non-Fpo]) 7c920575 ff7c94be 00ffffff 12000000 907c94be 0xc5ffffff 7c920579 00ffffff 12000000 907c94be 90909090 0xff7c94be *** WARNING: Unable to verify checksum for xerces-c_2_7.dll *** ERROR: Symbol file could not be found. Defaulted to export symbols for xerces-c_2_7.dll - 7c92057d 12000000 907c94be 90909090 8b55ff8b MyApplication+0xbfffff 7c920581 907c94be 90909090 8b55ff8b 08458bec xerces_c_2_7 7c920585 90909090 8b55ff8b 08458bec 04408b66 0x907c94be 7c920589 8b55ff8b 08458bec 04408b66 0004c25d 0x90909090 7c92058d 08458bec 04408b66 0004c25d 90909090 0x8b55ff8b The address MyApplication+0x2a85b9 corresponds to a call to erase() of a std::list. What I have tried so far Reviewing all the code related to the point where the crash ends happening. Trying to enable pageheap on our testing lab though nothing useful has been found by now. We have substituted the std::list for a C array and then it crashes in other part of the code (although it is related code, it's not in the code where the old list resided). Coincidentally, now it crashes in another erase, though this time of a std::multiset. Let me copy the stack contained in the dump: ntdll.dll!_RtlpCoalesceFreeBlocks@16() + 0x124e bytes ntdll.dll!_RtlFreeHeap@12() + 0x91f bytes msvcrt.dll!_free() + 0xc3 bytes MyApplication.exe!006a4fda() [Frames below may be incorrect and/or missing, no symbols loaded for MyApplication.exe] MyApplication.exe!0069f305() ntdll.dll!_NtFreeVirtualMemory@16() + 0xc bytes ntdll.dll!_RtlpSecMemFreeVirtualMemory@16() + 0x1b bytes ntdll.dll!_ZwWaitForSingleObject@12() + 0xc bytes ntdll.dll!_RtlpFreeToHeapLookaside@8() + 0x26 bytes ntdll.dll!_RtlFreeHeap@12() + 0x114 bytes msvcrt.dll!_free() + 0xc3 bytes c5ffffff() Possible solutions (that I'm aware of) which cannot be applied "Migrate the application to a newer compiler": We are working on this but It's not a solution at the moment. "Enable pageheap (normal or full)": We can't enable pageheap on production machines as this affects performance heavily. I think that's all I remember now, if I have forgotten something I'll add it asap. If you can give me some hint or propose some possible solution, don't hesitate to answer! Thank you in advance for your time and advice.

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• evaluating cost/benefits of using extension methods in C# => 3.0

  - by BillW

  Hi, In what circumstances (usage scenarios) would you choose to write an extension rather than sub-classing an object ? < full disclosure : I am not an MS employee; I do not know Mitsu Furota personally; I do know the author of the open-source Componax library mentioned here, but I have no business dealings with him whatsoever; I am not creating, or planning to create any commercial product using extensions : in sum : this post is from pure intellectal curiousity related to my trying to (continually) become aware of "best practices" I find the idea of extension methods "cool," and obviously you can do "far-out" things with them as in the many examples you can in Mitsu Furota's (MS) blog postslink text. A personal friend wrote the open-source Componax librarylink text, and there's some remarkable facilities in there; but he is in complete command of his small company with total control over code guidelines, and every line of code "passes through his hands." While this is speculation on my part : I think/guess other issues might come into play in a medium-to-large software team situation re use of Extensions. Looking at MS's guidelines at link text, you find : In general, you will probably be calling extension methods far more often than implementing your own. ... In general, we recommend that you implement extension methods sparingly and only when you have to. Whenever possible, client code that must extend an existing type should do so by creating a new type derived from the existing type. For more information, see Inheritance (C# Programming Guide). ... When the compiler encounters a method invocation, it first looks for a match in the type's instance methods. If no match is found, it will search for any extension methods that are defined for the type, and bind to the first extension method that it finds. And at Ms's link text : Extension methods present no specific security vulnerabilities. They can never be used to impersonate existing methods on a type, because all name collisions are resolved in favor of the instance or static method defined by the type itself. Extension methods cannot access any private data in the extended class. Factors that seem obvious to me would include : I assume you would not write an extension unless you expected it be used very generally and very frequently. On the other hand : couldn't you say the same thing about sub-classing ? Knowing we can compile them into a seperate dll, and add the compiled dll, and reference it, and then use the extensions : is "cool," but does that "balance out" the cost inherent in the compiler first having to check to see if instance methods are defined as described above. Or the cost, in case of a "name clash," of using the Static invocation methods to make sure your extension is invoked rather than the instance definition ? How frequent use of Extensions would affect run-time performance or memory use : I have no idea. So, I'd appreciate your thoughts, or knowing about how/when you do, or don't do, use Extensions, compared to sub-classing. thanks, Bill

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• jquery intercept

  - by zurna

  In another question's discussion, I became aware of intercepting clicks and updating area without refreshing the whole page. Problem is, the following code seems correct to me and I dont receive any errors but data taken from another page is not displayed at all. Please advise. main page $('ul.thumbs li.pagination a').live('click', function() { var pageNumber = parseInt($(this).text().replace(/[^0-9]/g, '')); $(function ViewImages() { $.ajax({ type: "GET", url: "/FLPM/cp/images.cs.asp?Process=ViewImages&PAGEID=" + pageNumber, success: function(data) { $("#ViewImages").html(data); }, error: function (XMLHttpRequest, textStatus, errorThrown) { $("#ViewImages").html('.'); } }); }); return false; }); <div id="ViewImages"> </div> page where data lays <ul class="thumbs"> <li> <a href="#" class="thumb"><img src="/FLPM/media/news/images/5P2B4K5M_sm.jpg" alt="Forest Flowers" class="floatLeft" /></a> <br /> <a href="?Process=DeleteImage&IMAGEID=21" class="thumb"><span class="floatLeft">DELETE</span></a> </li> <li> <a href="#" class="thumb"><img src="/FLPM/media/news/images/6Z3L5U6W_sm.jpg" alt="Forest" class="floatLeft" /></a> <br /> <a href="?Process=DeleteImage&IMAGEID=20" class="thumb"><span class="floatLeft">DELETE</span></a> </li> <li> <a href="#" class="thumb"><img src="/FLPM/media/news/images/8O5A7J8M_sm.jpg" alt="Dock" class="floatLeft" /></a> <br /> <a href="?Process=DeleteImage&IMAGEID=19" class="thumb"><span class="floatLeft">DELETE</span></a> </li> <li> <a href="#" class="thumb"><img src="/FLPM/media/news/images/9Q6B3Q4S_sm.jpg" alt="Desert Landscape" class="floatLeft" /></a> <br /> <a href="?Process=DeleteImage&IMAGEID=18" class="thumb"><span class="floatLeft">DELETE</span></a> </li> <li> <a href="#" class="thumb"><img src="/FLPM/media/news/images/5B2N4W5Z_sm.jpg" alt="Creek" class="floatLeft" /></a> <br /> <a href="?Process=DeleteImage&IMAGEID=17" class="thumb"><span class="floatLeft">DELETE</span></a> </li> <li class="pagination">1.&nbsp;</li> <li class="pagination"><a href="2">2.</a>&nbsp;</li> </ul>

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• How can I get SQL Server transactions to use record-level locks?

  - by Joe White

  We have an application that was originally written as a desktop app, lo these many years ago. It starts a transaction whenever you open an edit screen, and commits if you click OK, or rolls back if you click Cancel. This worked okay for a desktop app, but now we're trying to move to ADO.NET and SQL Server, and the long-running transactions are problematic. I found that we'll have a problem when multiple users are all trying to edit (different subsets of) the same table at the same time. In our old database, each user's transaction would acquire record-level locks to every record they modified during their transaction; since different users were editing different records, everyone gets their own locks and everything works. But in SQL Server, as soon as one user edits a record inside a transaction, SQL Server appears to get a lock on the entire table. When a second user tries to edit a different record in the same table, the second user's app simply locks up, because the SqlConnection blocks until the first user either commits or rolls back. I'm aware that long-running transactions are bad, and I know that the best solution would be to change these screens so that they no longer keep transactions open for a long time. But since that would mean some invasive and risky changes, I also want to research whether there's a way to get this code up and running as-is, just so I know what my options are. How can I get two different users' transactions in SQL Server to lock individual records instead of the entire table? Here's a quick-and-dirty console app that illustrates the issue. I've created a database called "test1", with one table called "Values" that just has ID (int) and Value (nvarchar) columns. If you run the app, it asks for an ID to modify, starts a transaction, modifies that record, and then leaves the transaction open until you press ENTER. I want to be able to start the program and tell it to update ID 1; let it get its transaction and modify the record; start a second copy of the program and tell it to update ID 2; have it able to update (and commit) while the first app's transaction is still open. Currently it freezes at step 4, until I go back to the first copy of the app and close it or press ENTER so it commits. The call to command.ExecuteNonQuery blocks until the first connection is closed. public static void Main() { Console.Write("ID to update: "); var id = int.Parse(Console.ReadLine()); Console.WriteLine("Starting transaction"); using (var scope = new TransactionScope()) using (var connection = new SqlConnection(@"Data Source=localhost\sqlexpress;Initial Catalog=test1;Integrated Security=True")) { connection.Open(); var command = connection.CreateCommand(); command.CommandText = "UPDATE [Values] SET Value = 'Value' WHERE ID = " + id; Console.WriteLine("Updating record"); command.ExecuteNonQuery(); Console.Write("Press ENTER to end transaction: "); Console.ReadLine(); scope.Complete(); } } Here are some things I've already tried, with no change in behavior: Changing the transaction isolation level to "read uncommitted" Specifying a "WITH (ROWLOCK)" on the UPDATE statement

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• Languages and VMs: Features that are hard to optimize and why

  - by mrjoltcola

  I'm doing a survey of features in preparation for a research project. Name a mainstream language or language feature that is hard to optimize, and why the feature is or isn't worth the price paid, or instead, just debunk my theories below with anecdotal evidence. Before anyone flags this as subjective, I am asking for specific examples of languages or features, and ideas for optimization of these features, or important features that I haven't considered. Also, any references to implementations that prove my theories right or wrong. Top on my list of hard to optimize features and my theories (some of my theories are untested and are based on thought experiments): 1) Runtime method overloading (aka multi-method dispatch or signature based dispatch). Is it hard to optimize when combined with features that allow runtime recompilation or method addition. Or is it just hard, anyway? Call site caching is a common optimization for many runtime systems, but multi-methods add additional complexity as well as making it less practical to inline methods. 2) Type morphing / variants (aka value based typing as opposed to variable based) Traditional optimizations simply cannot be applied when you don't know if the type of someting can change in a basic block. Combined with multi-methods, inlining must be done carefully if at all, and probably only for a given threshold of size of the callee. ie. it is easy to consider inlining simple property fetches (getters / setters) but inlining complex methods may result in code bloat. The other issue is I cannot just assign a variant to a register and JIT it to the native instructions because I have to carry around the type info, or every variable needs 2 registers instead of 1. On IA-32 this is inconvenient, even if improved with x64's extra registers. This is probably my favorite feature of dynamic languages, as it simplifies so many things from the programmer's perspective. 3) First class continuations - There are multiple ways to implement them, and I have done so in both of the most common approaches, one being stack copying and the other as implementing the runtime to use continuation passing style, cactus stacks, copy-on-write stack frames, and garbage collection. First class continuations have resource management issues, ie. we must save everything, in case the continuation is resumed, and I'm not aware if any languages support leaving a continuation with "intent" (ie. "I am not coming back here, so you may discard this copy of the world"). Having programmed in the threading model and the contination model, I know both can accomplish the same thing, but continuations' elegance imposes considerable complexity on the runtime and also may affect cache efficienty (locality of stack changes more with use of continuations and co-routines). The other issue is they just don't map to hardware. Optimizing continuations is optimizing for the less-common case, and as we know, the common case should be fast, and the less-common cases should be correct. 4) Pointer arithmetic and ability to mask pointers (storing in integers, etc.) Had to throw this in, but I could actually live without this quite easily. My feelings are that many of the high-level features, particularly in dynamic languages just don't map to hardware. Microprocessor implementations have billions of dollars of research behind the optimizations on the chip, yet the choice of language feature(s) may marginalize many of these features (features like caching, aliasing top of stack to register, instruction parallelism, return address buffers, loop buffers and branch prediction). Macro-applications of micro-features don't necessarily pan out like some developers like to think, and implementing many languages in a VM ends up mapping native ops into function calls (ie. the more dynamic a language is the more we must lookup/cache at runtime, nothing can be assumed, so our instruction mix is made up of a higher percentage of non-local branching than traditional, statically compiled code) and the only thing we can really JIT well is expression evaluation of non-dynamic types and operations on constant or immediate types. It is my gut feeling that bytecode virtual machines and JIT cores are perhaps not always justified for certain languages because of this. I welcome your answers.

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• Lock free multiple readers single writer

  - by dummzeuch

  I have got an in memory data structure that is read by multiple threads and written by only one thread. Currently I am using a critical section to make this access threadsafe. Unfortunately this has the effect of blocking readers even though only another reader is accessing it. There are two options to remedy this: use TMultiReadExclusiveWriteSynchronizer do away with any blocking by using a lock free approach For 2. I have got the following so far (any code that doesn't matter has been left out): type TDataManager = class private FAccessCount: integer; FData: TDataClass; public procedure Read(out _Some: integer; out _Data: double); procedure Write(_Some: integer; _Data: double); end; procedure TDataManager.Read(out _Some: integer; out _Data: double); var Data: TDAtaClass; begin InterlockedIncrement(FAccessCount); try // make sure we get both values from the same TDataClass instance Data := FData; // read the actual data _Some := Data.Some; _Data := Data.Data; finally InterlockedDecrement(FAccessCount); end; end; procedure TDataManager.Write(_Some: integer; _Data: double); var NewData: TDataClass; OldData: TDataClass; ReaderCount: integer; begin NewData := TDataClass.Create(_Some, _Data); InterlockedIncrement(FAccessCount); OldData := TDataClass(InterlockedExchange(integer(FData), integer(NewData)); // now FData points to the new instance but there might still be // readers that got the old one before we exchanged it. ReaderCount := InterlockedDecrement(FAccessCount); if ReaderCount = 0 then // no active readers, so we can safely free the old instance FreeAndNil(OldData) else begin /// here is the problem end; end; Unfortunately there is the small problem of getting rid of the OldData instance after it has been replaced. If no other thread is currently within the Read method (ReaderCount=0), it can safely be disposed and that's it. But what can I do if that's not the case? I could just store it until the next call and dispose it there, but Windows scheduling could in theory let a reader thread sleep while it is within the Read method and still has got a reference to OldData. If you see any other problem with the above code, please tell me about it. This is to be run on computers with multiple cores and the above methods are to be called very frequently. In case this matters: I am using Delphi 2007 with the builtin memory manager. I am aware that the memory manager probably enforces some lock anyway when creating a new class but I want to ignore that for the moment. Edit: It may not have been clear from the above: For the full lifetime of the TDataManager object there is only one thread that writes to the data, not several that might compete for write access. So this is a special case of MREW.

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• Source code versioning with comments (organizational practice) - leave or remove?

  - by ADTC

  Before you start admonishing me with "DON'T DO IT," "BAD PRACTICE!" and "Learn to use proper source code control", please hear me out first. I am fully aware that the practice of commenting out old code and leaving it there forever is very bad and I hate such practice myself. But here's the situation I'm in. A few months ago I joined a company as software developer. I had worked in the company for few months as an intern, about a year before joining recently. Our company uses source code version control (CVS) but not properly. Here's what happened both in my internship and my current permanent position. Each time I was assigned to work on a project (legacy, about 8-10 years old). Instead of creating a CVS account and letting me check out code and check in changes, a senior colleague exported the code from CVS, zipped it up and passed it to me. While this colleague checks in all changes in bulk every few weeks, our usual practice is to do fine-grained versioning in the actual source code itself (each file increments in versions independent from the rest). Whenever a change is made to a file, old code is commented out, new code entered below it, and this whole section is marked with a version number. Finally a note about the changes is placed at the top of the file in a section called Modification History. Finally the changed files are placed in a shared folder, ready and waiting for the bulk check-in. /* * Copyright notice blah blah * Some details about file (project name, file name etc) * Modification History: * Date Version Modified By Description * 2012-10-15 1.0 Joey Initial creation * 2012-10-22 1.1 Chandler Replaced old code with new code */ code .... //v1.1 start //old code new code //v1.1 end code .... Now the problem is this. In the project I'm working on, I needed to copy some new source code files from another project (new in the sense that they didn't exist in destination project before). These files have a lot of historical commented out code and comment-based versioning including usually long or very long Modification History section. Since the files are new to this project I decided to clean them up and remove unnecessary code including historical code, and start fresh at version 1.0. (I still have to continue the practice of comment-based versioning despite hating it. And don't ask why not start at version 0.1...) I have done similar something during my internship and no one said anything. My supervisor has seen the work a few times and didn't say I shouldn't do such clean-up (if at all it was noticed). But a same-level colleague saw this and said it's not recommended as it may cause downtime in the future and increase maintenance costs. An example is when changes are made in another project on the original files and these changes need to be propagated to this project. With code files drastically different, it could cause confusion to an employee doing the propagation. It makes sense to me, and is a valid point. I couldn't find any reason to do my clean-up other than the inconvenience of a ridiculously messy code. So, long story short: Given the practice in our company, should I not do such clean-up when copying new files from project to project? Is it better to make changes on the (copy of) original code with full history in comments? Or what justification can I give for doing the clean-up? PS to mods: Hope you allow this question some time even if for any reason you determine it to be unfit in SO. I apologize in advance if anything is inappropriate including tags.

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• Array not showing in Jlist but filled in console

  - by OVERTONE

  Hey there. been a busy debugger today. ill give ths short version. ive made an array list that takes names from a database. then i put the contents of the arraylist into an array of strings. now i want too display the arrays contents in a JList. the weird thing is it was working earlier. and ive two methods. ones just a little practice too make sure i was adding to the Jlist correctly. so heres the key codes. this is the layout of my code. variables constructor methods in my variables i have these 3 defined String[] contactListNames = new String[5]; ArrayList<String> rowNames = new ArrayList<String>(); JList contactList = new JList(contactListNames); simple enough. in my constructor i have them again. contactListNames = new String[5]; contactList = new JList(contactListNames); //i dont have the array list defined though. printSqlDetails(); // the prinSqldetails was too make sure that the connectionw as alright. and its working fine. fillContactList(); // this is the one thats causing me grief. its where all the work happens. // fillContactListTest(); // this was the tester that makes sure its adding to the list alright. heres the code for fillContactListTest() public void fillContactListTest() { for(int i = 0;i<3;i++) { try { String contact; System.out.println(" please fill the list at index "+ i); Scanner in = new Scanner(System.in); contact = in.next(); contactListNames[i] = contact; in.nextLine(); } catch(Exception e) { e.printStackTrace(); } } } heres the main one thats supposed too work. public void fillContactList() { int i =0; createConnection(); ArrayList<String> rowNames = new ArrayList<String>(); try { Statement stmt = conn.createStatement(); ResultSet namesList = stmt.executeQuery("SELECT name FROM Users"); try { while (namesList.next()) { rowNames.add(namesList.getString(1)); contactListNames =(String[])rowNames.toArray(new String[rowNames.size()]); // this used to print out contents of array list // System.out.println("" + rowNames); while(i<contactListNames.length) { System.out.println(" " + contactListNames[i]); i++; } } } catch(SQLException q) { q.printStackTrace(); } conn.commit(); stmt.close(); conn.close(); } catch(SQLException e) { e.printStackTrace(); } } i really need help here. im at my wits end. i just cant see why the first method would add to the JList no problem. but the second one wont. both the contactListNames array and array list can print fine and have the names in them. but i must be transfering them too the jlist wrong. please help p.s im aware this is long. but trust me its the short version.

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• Why are my USB 2.0 devices crashing Windows XP?

  - by BenAlabaster

  Background on the machine I'm having a problem with: The machine was inherited and appears to be circa 2003 (there's a date stamp on the power supply which leads me to this conclusion). I've got it set up as a Skype terminal for my 2 year old to keep in touch with her grandparents and other members of the family - which everyone loves. It has a generic ATX motherboard with no identifying markings other than one stamp that says "Rev.B". CPU-Z identifies the motherboard model as VT8601 but doesn't provide me with any manufacturer name. On board it has 1 x 10/100 LAN, 2 x USB 1.0, VGA, PS/2 for KB and mouse, parallel port, 2 x serial ports, 2 x IDE, 1 x floppy, 2 x SDRAM slots, 1 x CPU housing that is seating a 1.3GHz Intel Celeron CPU, 3 x PCI, 1 x AGP - although you can only use 2 of the PCI slots if you use the AGP slot due to the physical layout of the board. It's got 768Mb PC133 SDRAM - 1 x 512Mb & 1 x 256Mb installed as well as a D-LINK WDA-2320 54G Wi-Fi network card and a generic USB 2.0 expansion board containing 3 x external + 1 x internal USB connectors. It has a DVD+/-RW running as master on IDE1 and a 1.44Mb 3.5" floppy drive connected to the floppy connector. It has an 80Gb Western Digital hard drive running as master on IDE0. All this is sitting in a slimline case. I don't know the wattage of the PSU, but can post this later if this proves to be helpful. The motherboard is running a version of Award BIOS for which I don't have the version number to hand but can again post this later if it would be helpful. The hard disk is freshly formatted and built with Windows XP Professional/Service Pack 3 and is up to date with all current patches. In addition to Windows XP, the only other software it's running is Skype 4.1 (4.2 hangs the whole machine as soon as it starts up, requiring a hard boot to recover). It's got a Daytek MV150 15" touch screen hooked up to the on board VGA and COM1 sockets with the most current drivers from the Daytek website and the most current version of ELO-Touchsystems drivers for the touch component. The webcam is a Logitech Webcam C200 with the latest drivers from the Logitech website. The problem: If I hook any devices to the USB 2.0 sockets, it hangs the whole machine and I have to hard boot it to get it back up. If I have any devices attached to the USB 2.0 sockets when I boot up, it hangs before Windows gets to the login prompt and I have to hard boot it to recover. Workarounds found: I can plug the same devices into the on board USB 1.0 sockets and everything works fine, albeit at reduced performance. I've tried 3 different kinds of USB thumb drives, 3 different makes/models of webcams and my iPhone all with the same effect. They're recognized and don't hang the machine when I hook them to the USB 1.0 but if I hook them to the USB 2.0 ports, the machine hangs within a couple of seconds of recognizing the devices were connected. Attempted solutions: I've seen suggestions that this could be a power problem - that the PSU just doesn't have the wattage to drive these ports. While I'm doubtful this is the problem [after all the motherboard has the same standard connector regardless of the PSU wattage], I tried disabling all the on board devices that I'm not using - on board LAN, the second COM port, the AGP connector etc. through the BIOS in what I'm sure is a futile attempt to reduce the power consumption... I also modified the ACPI and power management settings. It didn't have any noticeable affect, although it didn't do any harm either. Could the wattage of the PSU really cause this problem? If it can, is there anything I need to be aware of when replacing it or do I just need to make sure it's got a higher wattage than the current one? My interpretation was that the wattage only affected the number of drives you could hook up to the power connectors, is that right? I've installed the USB card in another machine and it works without issue, so it's not a problem with the USB card itself, and Windows says the card is installed and working correctly... right up until I connect a device to it. The only thing I haven't done which I only just thought of while writing this essay is trying the USB 2.0 card in a different PCI slot, or re-ordering the wi-fi and USB cards in the slots... although I'm not sure if this will make any difference - does anyone have any experience that would suggest this might work? Other thoughts/questions: Perhaps this is an incompatibility between the USB 2.0 card and the BIOS, would re-flashing the BIOS with a newer version help? Do I need to be able to identify the manufacturer of the motherboard in order to be able to find a BIOS edition specific for this motherboard or will any version of Award BIOS function in its place? Question: Does anyone have any ideas that could help me get my USB 2.0 devices hooked up to this machine?

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• Geolocation through Android's GPS Provider on a website?

  - by Corey Ogburn

  I'm trying to get the geolocation of the mobile device in a regular website, not a webview of an application or anything native like that. I'm getting a location, but it's highly inaccurate, the accuracy comes back as 3230 or some other outrageous number. I'm assuming that's in meters, either way it's not nearly accurate enough. By comparison, the same webpage on a laptop gets an accuracy of 30-40. My first thought was that it was using the Network Provider instead of the GPS Provider, telling me where I am based on tower location and reach. A little research later I found enableHighAccuracy and set it true in the options that I pass. After including that, I still notice no difference. Here's the test page's HTML/javascript: <html> <head> <script type="text/javascript" src="http://ecn.dev.virtualearth.net/mapcontrol/mapcontrol.ashx?v=7.0"></script> <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.3/jquery.min.js"></script> <script type="text/javascript"> function OnLoad() { $("#Status").text("Init"); if (navigator.geolocation) { $("#Status").text("Supports Geolocation"); navigator.geolocation.getCurrentPosition(HandleLocation, LocationError, { enableHighAccuracy: true }); $("#Status").text("Sent position request..."); } else { $("#Status").text("Doesn't support geolocation"); } } function HandleLocation(position) { $("#Status").text("Received response:"); $("#Position").text("(" + position.coords.latitude + ", " + position.coords.longitude + ") accuracy: " + position.coords.accuracy); var loc = new Microsoft.Maps.Location(position.coords.latitude, position.coords.longitude); GetMap(loc); } function LocationError(error) { switch(error.code) { case error.PERMISSION_DENIED: alert("Location not provided"); break; case error.POSITION_UNAVAILABLE: alert("Current location not available"); break; case error.TIMEOUT: alert("Timeout"); break; default: alert("unknown error"); break; } } function GetMap(loc) { var map = new Microsoft.Maps.Map(document.getElementById("mapDiv"), {credentials: "Aj59meaCR1e7rNgkfQy7j08Pd3mzfP1r04hGesGmLe2a3ZwZ3iGecwPX2SNPWq5a", center: loc, mapTypeId: Microsoft.Maps.MapTypeId.road, zoom: 15}); } </script> </head> <body onload="javascript:OnLoad()"> <div id="Status"></div> <div id="Position"></div><br/> <div id='mapDiv' style="position:relative; width:600px; height:400px;"></div> </body> </html> I'm testing this on a rooted MyTouch 3G running Cyanogen 6.1 stable, Android 2.2 and GPS is enabled. In case rooting was a problem, I have also had various friends and coworkers try the webpage on their non-rooted 2.0+ Android devices. Each phone had various effects on the accuracy, but none were better than 1000, I attribute this to the different carriers. I have not (but eventually will) tested with iPhone or other location-aware cell phones.

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• Why are my USB 2.0 devices hanging Windows XP?

  - by BenAlabaster

  Background on the machine I'm having a problem with: The machine was inherited and appears to be circa 2003 (there's a date stamp on the power supply which leads me to this conclusion). I've got it set up as a Skype terminal for my 2 year old to keep in touch with her grandparents and other members of the family - which everyone loves. It has a generic ATX motherboard with no identifying markings other than one stamp that says "Rev.B". CPU-Z identifies the motherboard model as VT8601 but doesn't provide me with any manufacturer name. On board it has 1 x 10/100 LAN, 2 x USB 1.0, VGA, PS/2 for KB and mouse, parallel port, 2 x serial ports, 2 x IDE, 1 x floppy, 2 x SDRAM slots, 1 x CPU housing that is seating a 1.3GHz Intel Celeron CPU, 3 x PCI, 1 x AGP - although you can only use 2 of the PCI slots if you use the AGP slot due to the physical layout of the board. It's got 768Mb PC133 SDRAM - 1 x 512Mb & 1 x 256Mb installed as well as a D-LINK WDA-2320 54G Wi-Fi network card and a generic USB 2.0 expansion board containing 3 x external + 1 x internal USB connectors - it has a NEC uPD720102 chipset. It has a DVD+/-RW running as master on IDE1 and a 1.44Mb 3.5" floppy drive connected to the floppy connector. It has an 80Gb Western Digital hard drive running as master on IDE0. All this is sitting in a slimline case. I don't know the wattage of the PSU, but can post this later if this proves to be helpful. The motherboard is running a version of Award BIOS for which I don't have the version number to hand but can again post this later if it would be helpful. The hard disk is freshly formatted and built with Windows XP Professional/Service Pack 3 and is up to date with all current patches. In addition to Windows XP, the only other software it's running is Skype 4.1 (4.2 hangs the whole machine as soon as it starts up, requiring a hard boot to recover). It's got a Daytek MV150 15" touch screen hooked up to the on board VGA and COM1 sockets with the most current drivers from the Daytek website and the most current version of ELO-Touchsystems drivers for the touch component. The webcam is a Logitech Webcam C200 with the latest drivers from the Logitech website. The problem: If I hook any devices to the USB 2.0 sockets, it hangs the whole machine and I have to hard boot it to get it back up. If I have any devices attached to the USB 2.0 sockets when I boot up, it hangs before Windows gets to the login prompt and I have to hard boot it to recover. Workarounds found: I can plug the same devices into the on board USB 1.0 sockets and everything works fine, albeit at reduced performance. I've tried 3 different kinds of USB thumb drives, 3 different makes/models of webcams and my iPhone all with the same effect. They're recognized and don't hang the machine when I hook them to the USB 1.0 but if I hook them to the USB 2.0 ports, the machine hangs within a couple of seconds of recognizing the devices were connected. Attempted solutions: I've seen suggestions that this could be a power problem - that the PSU just doesn't have the wattage to drive these ports. While I'm doubtful this is the problem [after all the motherboard has the same standard connector regardless of the PSU wattage], I tried disabling all the on board devices that I'm not using - on board LAN, the second COM port, the AGP connector etc. through the BIOS in what I'm sure is a futile attempt to reduce the power consumption... I also modified the ACPI and power management settings. It didn't have any noticeable affect, although it didn't do any harm either. Could the wattage of the PSU really cause this problem? If it can, is there anything I need to be aware of when replacing it or do I just need to make sure it's got a higher wattage than the current one? My interpretation was that the wattage only affected the number of drives you could hook up to the power connectors, is that right? I've installed the USB card in another machine and it works without issue, so it's not a problem with the USB card itself, and Windows says the card is installed and working correctly... right up until I connect a device to it. The only thing I haven't done which I only just thought of while writing this essay is trying the USB 2.0 card in a different PCI slot, or re-ordering the wi-fi and USB cards in the slots... although I'm not sure if this will make any difference - does anyone have any experience that would suggest this might work? Other thoughts/questions: Perhaps this is an incompatibility between the USB 2.0 card and the BIOS, would re-flashing the BIOS with a newer version help? Do I need to be able to identify the manufacturer of the motherboard in order to be able to find a BIOS edition specific for this motherboard or will any version of Award BIOS function in its place? Question: Does anyone have any ideas that could help me get my USB 2.0 devices hooked up to this machine? Edit: Updated the USB 2.0 info with reference to actual card - http://www.xpcgear.com/lpnec4u.html

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• Dynamically loading modules in Python (+ multi processing question)

  - by morpheous

  I am writing a Python package which reads the list of modules (along with ancillary data) from a configuration file. I then want to iterate through each of the dynamically loaded modules and invoke a do_work() function in it which will spawn a new process, so that the code runs ASYNCHRONOUSLY in a separate process. At the moment, I am importing the list of all known modules at the beginning of my main script - this is a nasty hack I feel, and is not very flexible, as well as being a maintenance pain. This is the function that spawns the processes. I will like to modify it to dynamically load the module when it is encountered. The key in the dictionary is the name of the module containing the code: def do_work(work_info): for (worker, dataset) in work_info.items(): #import the module defined by variable worker here... # [Edit] NOT using threads anymore, want to spawn processes asynchronously here... #t = threading.Thread(target=worker.do_work, args=[dataset]) # I'll NOT dameonize since spawned children need to clean up on shutdown # Since the threads will be holding resources #t.daemon = True #t.start() Question 1 When I call the function in my script (as written above), I get the following error: AttributeError: 'str' object has no attribute 'do_work' Which makes sense, since the dictionary key is a string (name of the module to be imported). When I add the statement: import worker before spawning the thread, I get the error: ImportError: No module named worker This is strange, since the variable name rather than the value it holds are being used - when I print the variable, I get the value (as I expect) whats going on? Question 2 As I mentioned in the comments section, I realize that the do_work() function written in the spawned children needs to cleanup after itself. My understanding is to write a clean_up function that is called when do_work() has completed successfully, or an unhandled exception is caught - is there anything more I need to do to ensure resources don't leak or leave the OS in an unstable state? Question 3 If I comment out the t.daemon flag statement, will the code stil run ASYNCHRONOUSLY?. The work carried out by the spawned children are pretty intensive, and I don't want to have to be waiting for one child to finish before spawning another child. BTW, I am aware that threading in Python is in reality, a kind of time sharing/slicing - thats ok Lastly is there a better (more Pythonic) way of doing what I'm trying to do? [Edit] After reading a little more about Pythons GIL and the threading (ahem - hack) in Python, I think its best to use separate processes instead (at least IIUC, the script can take advantage of multiple processes if they are available), so I will be spawning new processes instead of threads. I have some sample code for spawning processes, but it is a bit trivial (using lambad functions). I would like to know how to expand it, so that it can deal with running functions in a loaded module (like I am doing above). This is a snippet of what I have: def do_mp_bench(): q = mp.Queue() # Not only thread safe, but "process safe" p1 = mp.Process(target=lambda: q.put(sum(range(10000000)))) p2 = mp.Process(target=lambda: q.put(sum(range(10000000)))) p1.start() p2.start() r1 = q.get() r2 = q.get() return r1 + r2 How may I modify this to process a dictionary of modules and run a do_work() function in each loaded module in a new process?

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• How to design a data model that deals with (real) contracts?

  - by Geoffrey

  I was looking for some advice on designing a data model for contract administration. The general life cycle of a contract is thus: Contract is created and in a "draft" state. It is viewable internally and changes may be made. Contract goes out to vendor, status is set to "pending" Contract is rejected by vendor. At this state, nothing can be done to the contract. No statuses may be added to the collection. Contract is accepted by vendor. At this state, nothing can be done to the contract. No statuses may be added to the collection. I obviously want to avoid a situation where the contract is accepted and, say, the amount is changed. Here are my classes: [EnforceNoChangesAfterDraftState] public class VendorContract { public virtual Vendor Vendor { get; set; } public virtual decimal Amount { get; set; } public virtual VendorContact VendorContact { get; set; } public virtual string CreatedBy { get; set; } public virtual DateTime CreatedOn { get; set; } public virtual FileStore Contract { get; set; } public virtual IList<VendorContractStatus> ContractStatus { get; set; } } [EnforceCorrectWorkflow] public class VendorContractStatus { public virtual VendorContract VendorContract { get; set; } public virtual FileStore ExecutedDocument { get; set; } public virtual string Status { get; set; } public virtual string Reason { get; set; } public virtual string CreatedBy { get; set; } public virtual DateTime CreatedOn { get; set; } } I've omitted the filestore class, which is basically a key/value lookup to find the document based on its guid. The VendorContractStatus is mapped as a many-to-one in Nhibernate. I then use a custom validator as described here. If anything but draft is returned in the VendorContractStatus collection, no changes are allowed. Furthermore the VendorContractStatus must follow the correct workflow (you can add a rejected after a pending, but you can't add anything else to the collection if a reject or accepted exists, etc.). All sounds alright? Well a colleague has argued that we should simply add an "IsDraft" bool property to VendorContract and not accept updates if IsDraft is false. Then we should setup a method inside of VendorContractStatus for updating the status, if something gets added after a draft, it sets the IsDraft property of VendorContract to false. I do not like this as it feels like I'm dirtying up the POCOs and adding logic that should persist in the validation area, that no rules should really exist in these classes and they shouldn't be aware of their states. Any thoughts on this and what is the better practice from a DDD perspective? From my view, if in the future we want more complex rules, my way will be more maintainable over the long run. Say we have contracts over a certain amount to be approved by a manager. I would think it would be better to have a one-to-one mapping with a VendorContractApproval class, rather than adding IsApproved properties, but that's just speculation. This might be splitting hairs, but this is the first real gritty enterprise software project we've done. Any advice would be appreciated!

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• Little Regular Expression (against HTML) help

  - by Marcos Placona

  Hi, I have the following HTML <p>Some text <a title="link" href="http://link.com/" target="_blank">my link</a> more text <a title="link" href="http://link.com/" target="_blank">more link</a>.</p> <p>Another paragraph.</p> <p>[code:cf]</p> <p>&lt;cfset ArrFruits = ["Orange", "Apple", "Peach", "Blueberry", </p> <p>"Blackberry", "Strawberry", "Grape", "Mango", </p> <p>"Clementine", "Cherry", "Plum", "Guava", </p> <p>"Cranberry"]&gt;</p> <p>[/code]</p> <p>Another line</p> <p><img src="http://image.jpg" alt="Array" /> </p> <p>More text</p> <p>[code:cf]</p> <p>&lt;table border="1"&gt;</p> <p> &lt;cfoutput&gt;</p> <p> &lt;cfloop array="#GroupsOf(ArrFruits, 5)#" index="arrFruitsIX"&gt;</p> <p>  &lt;tr&gt;</p> <p> &lt;cfloop array="#arrFruitsIX#" index="arrFruit"&gt;</p> <p>     &lt;td&gt;#arrFruit#&lt;/td&gt;</p> <p> &lt;/cfloop&gt;</p> <p>  &lt;/tr&gt;</p> <p> &lt;/cfloop&gt;</p> <p> &lt;/cfoutput&gt;</p> <p>&lt;/table&gt;</p> <p>[/code]</p> <p>With an output that looks like:</p> <p><img src="another_image.jpg" alt="" width="342" height="85" /></p> What I'm trying to do, is write a regular expression that will remove all the or , and whenever it finds a , it will replace it with a line-break. So far, my pattern looks like this: /\<p\>(.*?)(<\/p>)/g And I'm replacing the matches with: $1\n It all looks good, but it's also replacing the contents inside the [code][/code] tags, which in this case should not replace the tags at all, so as a result, i would lkike to get rid of the tags, when the content isn't inside the [code] tags. I can't ever get negation right, I know it will be something along the lines of \<p\>^\[code*\](.*?)(<\/p>) But obviously this doesn't work :-) Could anyone please lend me a hand with this regex? BTW, I know I shouldn't be using regular expressions to parse HTML at all. I'm fully aware of that, but still, for this specific case, I'd like to use regex. Thanks in advance

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• Using dynamic enum as type in a parameter of a method

  - by samar

  Hi Experts, What i am trying to achieve here is a bit tricky. Let me brief on a little background first before going ahead. I am aware that we can use a enum as a type to a parameter of a method. For example I can do something like this (a very basic example) namespace Test { class DefineEnums { public enum MyEnum { value1 = 0, value2 = 1 } } class UseEnums { public void UseDefinedEnums(DefineEnums.MyEnum _enum) { //Any code here. } public void Test() { // "value1" comes here with the intellisense. UseDefinedEnums(DefineEnums.MyEnum.value1); } } } What i need to do is create a dynamic Enum and use that as type in place of DefineEnums.MyEnum mentioned above. I tried the following. 1. Used a method which i got from the net to create a dynamic enum from a list of strings. And created a static class which i can use. using System; using System.Collections.Generic; using System.Reflection; using System.Reflection.Emit; namespace Test { public static class DynamicEnum { public static Enum finished; static List<string> _lst = new List<string>(); static DynamicEnum() { _lst.Add("value1"); _lst.Add("value2"); finished = CreateDynamicEnum(_lst); } public static Enum CreateDynamicEnum(List<string> _list) { // Get the current application domain for the current thread. AppDomain currentDomain = AppDomain.CurrentDomain; // Create a dynamic assembly in the current application domain, // and allow it to be executed and saved to disk. AssemblyName aName = new AssemblyName("TempAssembly"); AssemblyBuilder ab = currentDomain.DefineDynamicAssembly( aName, AssemblyBuilderAccess.RunAndSave); // Define a dynamic module in "TempAssembly" assembly. For a single- // module assembly, the module has the same name as the assembly. ModuleBuilder mb = ab.DefineDynamicModule(aName.Name, aName.Name + ".dll"); // Define a public enumeration with the name "Elevation" and an // underlying type of Integer. EnumBuilder eb = mb.DefineEnum("Elevation", TypeAttributes.Public, typeof(int)); // Define two members, "High" and "Low". //eb.DefineLiteral("Low", 0); //eb.DefineLiteral("High", 1); int i = 0; foreach (string item in _list) { eb.DefineLiteral(item, i); i++; } // Create the type and save the assembly. return (Enum)Activator.CreateInstance(eb.CreateType()); //ab.Save(aName.Name + ".dll"); } } } Tried using the class but i am unable to find the "finished" enum defined above. i.e. I am not able to do the following public static void TestDynEnum(Test.DynamicEnum.finished _finished) { // Do anything here with _finished. } I guess the post has become too long but i hope i have made it quite clear. Please help! Thanks in advance! Regards, Samar

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• Running code when all threads are finished processing.

  - by rich97

  Quick note: Java and Android noob here, I'm open to you telling me I'm stupid (as long as you tell me why.) I have an android application which requires me start multiple threads originating from various classes and only advance to the next activity once all threads have done their job. I also want to add a "failsafe" timeout in case one the the threads takes too long (HTTP request taking too long or something.) I searched Stack Overflow and found a post saying that I should create a class to keep a running total of open threads and then use a timer to poll for when all the threads are completed. I think I've created a working class to do this for me, it's untested as of yet but has no errors showing in eclipse. Is this a correct implementation? Are there any APIs that I should be made aware of (such as classes in the Java or Android APIs that could be used in place of the abstract classes at the bottom of the class?) package com.dmp.geofix.libs; import java.util.ArrayList; import java.util.Iterator; import java.util.Timer; import java.util.TimerTask; public class ThreadMonitor { private Timer timer = null; private TimerTask timerTask = null; private OnSuccess onSuccess = null; private OnError onError = null; private static ArrayList<Thread> threads; private final int POLL_OPEN_THREADS = 100; private final int TIMEOUT = 10000; public ThreadMonitor() { timerTask = new PollThreadsTask(); } public ThreadMonitor(OnSuccess s) { timerTask = new PollThreadsTask(); onSuccess = s; } public ThreadMonitor(OnError e) { timerTask = new PollThreadsTask(); onError = e; } public ThreadMonitor(OnSuccess s, OnError e) { timerTask = new PollThreadsTask(); onSuccess = s; onError = e; } public void start() { Iterator<Thread> i = threads.iterator(); while (i.hasNext()) { i.next().start(); } timer = new Timer(); timer.schedule(timerTask, 0, POLL_OPEN_THREADS); } public void finish() { Iterator<Thread> i = threads.iterator(); while (i.hasNext()) { i.next().interrupt(); } threads.clear(); timer.cancel(); } public void addThread(Thread t) { threads.add(t); } public void removeThread(Thread t) { threads.remove(t); t.interrupt(); } class PollThreadsTask extends TimerTask { private int timeElapsed = 0; @Override public void run() { timeElapsed += POLL_OPEN_THREADS; if (timeElapsed <= TIMEOUT) { if (threads.isEmpty() == false) { if (onSuccess != null) { onSuccess.run(); } } } else { if (onError != null) { onError.run(); } finish(); } } } public abstract class OnSuccess { public abstract void run(); } public abstract class OnError { public abstract void run(); } }

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• How to map code points to unicode characters depending on the font used?

  - by Alex Schröder

  The client prints labels and has been using a set of symbolic (?) fonts to do this. The application uses a single byte database (Oracle with Latin-1). The old application I am replacing was not Unicode aware. It somehow did OK. The replacement application I am writing is supposed to handle the old data. The symbols picked from the charmap application often map to particular Unicode characters, but sometimes they don't. What looks like the Moon using the LAB3 font, for example, is in fact U+2014 (EM DASH). When users paste this character into a Swing text field, the character has the code point 8212. It was "moved" into the Private Use Area (by Windows? Java?). When saving this character to the database, Oracle decides that it cannot be safely encoded and replaces it with the dreaded ¿. Thus, I started shifting the characters by 8000: -= 8000 when saving, += 8000 when displaying the field. Unfortunately I discovered that other characters were not shifted by the same amount. In one particular font, for example, ž has the code point 382, so I shifted it by +/-256 to "fix" it. By now I'm dreading the discovery of more strange offsets and I wonder: Can I get at this mapping using Java? Perhaps the TTF font has a list of the 255 glyphs it encodes and what Unicode characters those correspond to and I can do it "right"? Right now I'm using the following kludge: static String fromDatabase(String str, String fontFamily) { if (str != null && fontFamily != null) { Font font = new Font(fontFamily, Font.PLAIN, 1); boolean changed = false; char[] chars = str.toCharArray(); for (int i = 0; i < chars.length; i++) { if (font.canDisplay(chars[i] + 0xF000)) { // WE8MSWIN1252 + WinXP chars[i] += 0xF000; changed = true; } else if (chars[i] >= 128 && font.canDisplay(chars[i] + 8000)) { // WE8ISO8859P1 + WinXP chars[i] += 8000; changed = true; } else if (font.canDisplay(chars[i] + 256)) { // ž in LAB1 Eastern = 382 chars[i] += 256; changed = true; } } if (changed) str = new String(chars); } return str; } static String toDatabase(String str, String fontFamily) { if (str != null && fontFamily != null) { boolean changed = false; char[] chars = str.toCharArray(); for (int i = 0; i < chars.length; i++) { int chr = chars[i]; if (chars[i] > 0xF000) { // WE8MSWIN1252 + WinXP chars[i] -= 0xF000; changed = true; } else if (chars[i] > 8000) { // WE8ISO8859P1 + WinXP chars[i] = (char) (chars[i] - 8000); changed = true; } else if (chars[i] > 256) { // ž in LAB1 Eastern = 382 chars[i] = (char) (chars[i] - 256); changed = true; } } if (changed) return new String(chars); } return str; }

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• What does a WinForm application need to be designed for usability, and be robust, clean, and profess

  - by msorens

  One of the principal problems impeding productivity in software implementation is the classic conundrum of “reinventing the wheel”. Of late I am a .NET developer and even the wonderful wizardry of .NET and Visual Studio covers only a portion of this challenging issue. Below I present my initial thoughts both on what is available and what should be available from .NET on a WinForm, focusing on good usability. That is, aspects of an application exposed to the user and making the user experience easier and/or better. (I do include a couple items not visible to the user because I feel strongly about them, such as diagnostics.) I invite you to contribute to these lists. LIST A: Components provided by .NET These are substantially complete components provided by .NET, i.e. those requiring at most trivial coding to use. “About” dialog -- add it with a couple clicks then customize. Persist settings across invocations -- .NET has the support; just use a few lines of code to glue them together. Migrate settings with a new version -- a powerful one, available with one line of code. Tooltips (and infotips) -- .NET includes just plain text tooltips; third-party libraries provide richer ones. Diagnostic support -- TraceSources, TraceListeners, and more are built-in. Internationalization -- support for tailoring your app to languages other than your own. LIST B: Components not provided by .NET These are not supplied at all by .NET or supplied only as rudimentary elements requiring substantial work to be realized. Splash screen -- a small window present during program startup with your logo, loading messages, etc. Tip of the day -- a mini-tutorial presented one bit at a time each time the user starts your app. Check for available updates -- facility to query a server to see if the user is running the latest version of your app, then provide a simple way to upgrade if a new version is found. Maximize to multiple monitors -- the canonical window allows you to maximize to a single monitor only; in my apps I allow maximizing across multiple monitors with a click. Taskbar notifier -- flash the taskbar when your backgrounded app has new info for the user. Options dialogs -- multi-page dialogs letting the user customize the app settings to his/her own preferences. Progress indicator -- for long running operations give the user feedback on how far there is left to go. Memory gauge -- an indicator (either absolute or percentage) of how much memory is used by your app. LIST C: Stylistic and/or tiny bits of functionality This list includes bits of functionality that are too tiny to merit being called a component, along with stylistic concerns (that admittedly do overlap with the Windows User Experience Interaction Guidelines). Design a form for resizing -- unless you are restricting your form to be a fixed size, use anchors and docking so that it does what is reasonable when enlarged or shrunk by the user. Set tab order on a form -- repeated tab presses by the user should advance from field to field in a logical order rather than the default order in which you added fields. Adjust controls to be aware of operating modes -- When starting a background operation with, for example, a “Go” button, disable that “Go” button until the operation completes. Provide access keys for all menu items (per UXGuide). Provide shortcut keys for commonly used menu items (per UXGuide). Set up some (global or important or common) shortcut keys without associating to menu items. Allow some menu items to be invoked with or without modifier keys (shift, control, alt) where the modifier key is useful to vary the operation slightly. Hook up Escape and Enter on child forms to do what is reasonable. Decorate any library classes with documentation-comments and attributes -- this allows Visual Studio to leverage them for Intellisense and property descriptions. Spell check your code! What else would you include?

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• RavenDB - Can I create/query an index, from an application that doesn't share the CLR objects that were persisted?

  - by Jaz Lalli

  This post goes some way to answering this question (I'll include the answer later), but I was hoping for some further details. We have a number of applications that each need to access/manipulate data from Raven in their own way. Data is only written via the main web application. Other apps include batch-style tasks, reporting etc. In an attempt to keep each of these as de-coupled as possible, they are separate solutions. That being the case, how can I, from the reporting application, create indexes over the existing data, using my locally defined types? The answer from the linked question states As long as the structure of the classes you are deserializing into partially matches the structure of the data, it shouldn't make a difference. The RavenDB server doesn't care at all what classes you use in the client. You certainly could share a dll, or even share a portable dll if you are targeting a different platform. But you are correct that it is not necessary. However, you should be aware of the Raven-Clr-Type metadata value. The RavenDB client sets this when storing the original document. It is consumed back by the client to assist with deserialization, but it is not fully enforced It's the first part of that that I wanted clarification on. Do the object graphs for the docs on the server and types in my application have to match exactly? If the Click document on the server is { "Visit": { "Version": "0", "Domain": "www.mydomain.com", "Page": "/index", "QueryString": "", "IPAddress": "127.0.0.1", "Guid": "10cb6886-cb5c-46f8-94ed-4b0d45a5e9ca", "MetaData": { "Version": "1", "CreatedDate": "2012-11-09T15:11:03.5669038Z", "UpdatedDate": "2012-11-09T15:11:03.5669038Z", "DeletedDate": null } }, "ResultId": "Results/1", "ProductCode": "280", "MetaData": { "Version": "1", "CreatedDate": "2012-11-09T15:14:26.1332596Z", "UpdatedDate": "2012-11-09T15:14:26.1332596Z", "DeletedDate": null } } Is it possible (and if so, how?), to create a Map index from my application, which defines the Click class as follows? class Click { public Guid Guid {get;set;} public int ProductCode {get;set;} public DateTime CreatedDate {get;set;} } Or would my class have to be look like this? (where the custom types are defined as a sub-set of the properties on the document above, with matching property names) class Click { public Visit Visit {get;set;} public int ProductCode {get;set;} public MetaData MetaData {get;set;} } UPDATE Following on from the answer below, here's the code I managed to get working. Index public class Clicks_ByVisitGuidAndProductCode : AbstractIndexCreationTask { public override IndexDefinition CreateIndexDefinition() { return new IndexDefinition { Map = "from click in docs.Clicks select new {Guid = click.Visit.Guid, ProductCode = click.ProductCode, CreatedDate = click.MetaData.CreatedDate}", TransformResults = "results.Select(click => new {Guid = click.Visit.Guid, ProductCode = click.ProductCode, CreatedDate = click.MetaData.CreatedDate})" }; } } Query var query = _documentSession.Query<ReportClick, Clicks_ByVisitGuidAndProductCode>() .Customize(x => x.WaitForNonStaleResultsAsOfNow()) .Where(x => x.CreatedDate >= start.Date && x.CreatedDate < end.Date); where Click is public class Click { public Guid Guid { get; set; } public int ProductCode { get; set; } public DateTime CreatedDate { get; set; } } Many thanks @MattJohnson.

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