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• Search engine solution for Django that actually works?

  - by prometheus

  The story so far: Decided to go with Xapian as search backend because it has all search-engine features I was looking for, knows about Unicode, stemming, has few dependencies and requires no bloated app-server installation on top of it. Tried Django and Haystack (plus xapian-haystack, the backend glue code to tie Haystack to Xapian) because it was advertised on quite some blogs as "working". Did not work. Neither django-haystack nor the xapian-haystack project provide a version combination that actually works together. MASTER from both projects yields an error from Xapian, so it's not stable at all. Haystack 1.0.1 and xapian-haystack 1.0.x/1.1.0 are not API-compatible. Plus, in a minimally working installation of Haystack 1.0.1 and xapian-haystack MASTER, any complex query yields zero results due to errors in either django-haystack or xapian-haystack (I double-verified this), maybe because the unit-tests actually test very simple cases, and no edge-cases at all. Tried Djapian. The source-code is riddled with spelling errors (mind you, in variable names, not comments), documentation is also riddled with ambiguities and outdated information that will never lead to a working installation. Not surprisingly, users rarely ask for features but how to get it working in the first place. Next on the plate: exploring Solr (installing a Java environment plus Tomcat gives me headaches, the machine is RAM- and CPU-constrained), or Lucene (slightly less headaches, but still). Before I proceed spending more time with a solution that might or might not work as advertised, I'd like to know: Did anyone ever get an actual, real-world search solution working in Django? I'm serious. I find it really frustrating reading about "large problems mostly solved", and then realizing that you will never get a working installation from the source-code because, actually, all bloggers dealing with those "mostly solved problems" never went past basic installation and copy-pasting the official tutorials. So here are the requirements: must be able to search for 10-100 terms in one query must handle + (term must be present) and - (term must not be present), AND/OR must handle arbitrary grouping (i.e. parentheses around AND/OR) must allow for Django-ORM filtering before or after fulltext-search (i.e. pre-/post-processing of results with the full set of filters that Django knows about) alternatively, there must be a facility to bulk-fetch the result set and transform it into a QuerySet should be light on the machine, so preferably no humongous JVM and Java-based app-server installation Is there anything out there that does this? I'm not interested in anecdotal evidence, or references to some blog posts that claim it should be working. I'd like to hear from someone who actually has a fully-functional setup working in the real world, under real conditions, with real queries. EDIT: Let me repeat again that I'm not so much interested in anecdotal evidence that someone, somewhere has a somewhat running installation working with unspecified properties. I already went there, I read all the blog posts, mailing lists, I contacted the authors, but when it came to actual implementation of real-world scenarios, nothing ever worked as advertised. Also, and a user below brought that point up as well, considering the TCO of any project, I'm definitely not interested in hearing that someone, somewhere was able to pull it off once a vendor parachuted in an unknown number of specialists to monkey-patch the whole installation with specific domain-knowledge that's documented nowhere. So, please, if you claim you have a working installation that actually satisfies minimum requirements for a full-fledged search (see requirements above), please provide the following so that we can all benefit from a search solution for Django that actually solves the problem: exact Linux distribution, release version, exact release version of Haystack (or equivalent) and release version of search backend, exact release version of the search engine publicly (!) available documentation how to set up all components exactly in the way that your installation was set up such that the minimal requirements above are met. Thank you.

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• Search engine solution for Django that actually works?

  - by prometheus

  The story so far: Decided to go with Xapian as search backend because it has all search-engine features I was looking for, knows about Unicode, stemming, has few dependencies and requires no bloated app-server installation on top of it. Tried Django and Haystack (plus xapian-haystack, the backend glue code to tie Haystack to Xapian) because it was advertised on quite some blogs as "working". Did not work. Neither django-haystack nor the xapian-haystack project provide a version combination that actually works together. MASTER from both projects yields an error from Xapian, so it's not stable at all. Haystack 1.0.1 and xapian-haystack 1.0.x/1.1.0 are not API-compatible. Plus, in a minimally working installation of Haystack 1.0.1 and xapian-haystack MASTER, any complex query yields zero results due to errors in either django-haystack or xapian-haystack (I double-verified this), maybe because the unit-tests actually test very simple cases, and no edge-cases at all. Tried Djapian. The source-code is riddled with spelling errors (mind you, in variable names, not comments), documentation is also riddled with ambiguities and outdated information that will never lead to a working installation. Not surprisingly, users rarely ask for features but how to get it working in the first place. Next on the plate: exploring Solr (installing a Java environment plus Tomcat gives me headaches, the machine is RAM- and CPU-constrained), or Lucene (slightly less headaches, but still). Before I proceed spending more time with a solution that might or might not work as advertised, I'd like to know: Did anyone ever get an actual, real-world search solution working in Django? I'm serious. I find it really frustrating reading about "large problems mostly solved", and then realizing that you will never get a working installation from the source-code because, actually, all bloggers dealing with those "mostly solved problems" never went past basic installation and copy-pasting the official tutorials. So here are the requirements: must be able to search for 10-100 terms in one query must handle + (term must be present) and - (term must not be present), AND/OR must handle arbitrary grouping (i.e. parentheses around AND/OR) must allow for Django-ORM filtering before or after fulltext-search (i.e. pre-/post-processing of results with the full set of filters that Django knows about) alternatively, there must be a facility to bulk-fetch the result set and transform it into a QuerySet should be light on the machine, so preferably no humongous JVM and Java-based app-server installation Is there anything out there that does this? I'm not interested in anecdotal evidence, or references to some blog posts that claim it should be working. I'd like to hear from someone who actually has a fully-functional setup working in the real world, under real conditions, with real queries. EDIT: Let me repeat again that I'm not so much interested in anecdotal evidence that someone, somewhere has a somewhat running installation working with unspecified properties. I already went there, I read all the blog posts, mailing lists, I contacted the authors, but when it came to actual implementation of real-world scenarios, nothing ever worked as advertised. Also, and a user below brought that point up as well, considering the TCO of any project, I'm definitely not interested in hearing that someone, somewhere was able to pull it off once a vendor parachuted in an unknown number of specialists to monkey-patch the whole installation with specific domain-knowledge that's documented nowhere. So, please, if you claim you have a working installation that actually satisfies minimum requirements for a full-fledged search (see requirements above), please provide the following so that we can all benefit from a search solution for Django that actually solves the problem: exact Linux distribution, release version, exact release version of Haystack (or equivalent) and release version of search backend, exact release version of the search engine publicly (!) available documentation how to set up all components exactly in the way that your installation was set up such that the minimal requirements above are met. Thank you.

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• Cocoa Basic HTTP Authentication : Advice Needed..

  - by Kristiaan

  Hello all, im looking to read the contents of a webpage that is secured with a user name and password. this is a mac OS X application NOT an iphone app so most of the things i have read on here or been suggested to read do not seem to work. Also i am a total beginner with Xcode and Obj C i was told to have a look at a website that provided sample code to http auth however so far i have had little luck in getting this working. below is the main code for the button press in my application, there is also another unit called Base64 below that has some code in i had to change to even get it compiling (no idea if what i changed is correct mind you). NSURL *url = [NSURL URLWithString:@"my URL"]; NSString *userName = @"UN"; NSString *password = @"PW"; NSError *myError = nil; // create a plaintext string in the format username:password NSMutableString *loginString = (NSMutableString*)[@"" stringByAppendingFormat:@"%@:%@", userName, password]; // employ the Base64 encoding above to encode the authentication tokens char *encodedLoginData = [base64 encode:[loginString dataUsingEncoding:NSUTF8StringEncoding]]; // create the contents of the header NSString *authHeader = [@"Basic " stringByAppendingFormat:@"%@", [NSString stringWithCString:encodedLoginData length:strlen(encodedLoginData)]]; //NSString *authHeader = [@"Basic " stringByAppendingFormat:@"%@", loginString];//[NSString stringWithString:loginString length:strlen(loginString)]]; NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL: url cachePolicy: NSURLRequestReloadIgnoringCacheData timeoutInterval: 3]; // add the header to the request. Here's the $$$!!! [request addValue:authHeader forHTTPHeaderField:@"Authorization"]; // perform the reqeust NSURLResponse *response; NSData *data = [NSURLConnection sendSynchronousRequest: request returningResponse: &response error: &myError]; //*error = myError; // POW, here's the content of the webserver's response. NSString *result = [NSString stringWithCString:[data bytes] length:[data length]]; [myTextView setString:result]; code from the BASE64 file #import "base64.h" static char *alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+-"; @implementation Base64 +(char *)encode:(NSData *)plainText { // create an adequately sized buffer for the output. every 3 bytes // become four basically with padding to the next largest integer // divisible by four. char * encodedText = malloc((((([plainText length] % 3) + [plainText length]) / 3) * 4) + 1); char* inputBuffer = malloc([plainText length]); inputBuffer = (char *)[plainText bytes]; int i; int j = 0; // encode, this expands every 3 bytes to 4 for(i = 0; i < [plainText length]; i += 3) { encodedText[j++] = alphabet[(inputBuffer[i] & 0xFC) >> 2]; encodedText[j++] = alphabet[((inputBuffer[i] & 0x03) << 4) | ((inputBuffer[i + 1] & 0xF0) >> 4)]; if(i + 1 >= [plainText length]) // padding encodedText[j++] = '='; else encodedText[j++] = alphabet[((inputBuffer[i + 1] & 0x0F) << 2) | ((inputBuffer[i + 2] & 0xC0) >> 6)]; if(i + 2 >= [plainText length]) // padding encodedText[j++] = '='; else encodedText[j++] = alphabet[inputBuffer[i + 2] & 0x3F]; } // terminate the string encodedText[j] = 0; return encodedText;//outputBuffer; } @end when executing the code it stops on the following line with a EXC_BAD_ACCESS ?!?!? NSString *authHeader = [@"Basic " stringByAppendingFormat:@"%@", [NSString stringWithCString:encodedLoginData length:strlen(encodedLoginData)]]; any help would be appreciated as i am a little clueless on this problem, not being very literate with Cocoa, objective c, xcode is only adding fuel to this fire for me.

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• Is SQL Server DRI (ON DELETE CASCADE) slow?

  - by Aaronaught

  I've been analyzing a recurring "bug report" (perf issue) in one of our systems related to a particularly slow delete operation. Long story short: It seems that the CASCADE DELETE keys were largely responsible, and I'd like to know (a) if this makes sense, and (b) why it's the case. We have a schema of, let's say, widgets, those being at the root of a large graph of related tables and related-to-related tables and so on. To be perfectly clear, deleting from this table is actively discouraged; it is the "nuclear option" and users are under no illusions to the contrary. Nevertheless, it sometimes just has to be done. The schema looks something like this: Widgets | +--- Anvils (1:1) | | | +--- AnvilTestData (1:N) | +--- WidgetHistory (1:N) | +--- WidgetHistoryDetails (1:N) Nothing too scary, really. A Widget can be different types, an Anvil is a special type, so that relationship is 1:1 (or more accurately 1:0..1). Then there's a large amount of data - perhaps thousands of rows of AnvilTestData per Anvil collected over time, dealing with hardness, corrosion, exact weight, hammer compatibility, usability issues, and impact tests with cartoon heads. Then every Widget has a long, boring history of various types of transactions - production, inventory moves, sales, defect investigations, RMAs, repairs, customer complaints, etc. There might be 10-20k details for a single widget, or none at all, depending on its age. So, unsurprisingly, there's a CASCADE DELETE relationship at every level here. If a Widget needs to be deleted, it means something's gone terribly wrong and we need to erase any records of that widget ever existing, including its history, test data, etc. Again, nuclear option. Relations are all indexed, statistics are up to date. Normal queries are fast. The system tends to hum along pretty smoothly for everything except deletes. Getting to the point here, finally, for various reasons we only allow deleting one widget at a time, so a delete statement would look like this: DELETE FROM Widgets WHERE WidgetID = @WidgetID Pretty simple, innocuous looking delete... that takes over 2 minutes to run, for a widget with no data! After slogging through execution plans I was finally able to pick out the AnvilTestData and WidgetHistoryDetails deletes as the sub-operations with the highest cost. So I experimented with turning off the CASCADE (but keeping the actual FK, just setting it to NO ACTION) and rewriting the script as something very much like the following: DECLARE @AnvilID int SELECT @AnvilID = AnvilID FROM Anvils WHERE WidgetID = @WidgetID DELETE FROM AnvilTestData WHERE AnvilID = @AnvilID DELETE FROM WidgetHistory WHERE HistoryID IN ( SELECT HistoryID FROM WidgetHistory WHERE WidgetID = @WidgetID) DELETE FROM Widgets WHERE WidgetID = @WidgetID Both of these "optimizations" resulted in significant speedups, each one shaving nearly a full minute off the execution time, so that the original 2-minute deletion now takes about 5-10 seconds - at least for new widgets, without much history or test data. Just to be absolutely clear, there is still a CASCADE from WidgetHistory to WidgetHistoryDetails, where the fanout is highest, I only removed the one originating from Widgets. Further "flattening" of the cascade relationships resulted in progressively less dramatic but still noticeable speedups, to the point where deleting a new widget was almost instantaneous once all of the cascade deletes to larger tables were removed and replaced with explicit deletes. I'm using DBCC DROPCLEANBUFFERS and DBCC FREEPROCCACHE before each test. I've disabled all triggers that might be causing further slowdowns (although those would show up in the execution plan anyway). And I'm testing against older widgets, too, and noticing a significant speedup there as well; deletes that used to take 5 minutes now take 20-40 seconds. Now I'm an ardent supporter of the "SELECT ain't broken" philosophy, but there just doesn't seem to be any logical explanation for this behaviour other than crushing, mind-boggling inefficiency of the CASCADE DELETE relationships. So, my questions are: Is this a known issue with DRI in SQL Server? (I couldn't seem to find any references to this sort of thing on Google or here in SO; I suspect the answer is no.) If not, is there another explanation for the behaviour I'm seeing? If it is a known issue, why is it an issue, and are there better workarounds I could be using?

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• Two network interfaces and two IP addresses on the same subnet in Linux

  - by Scott Duckworth

  I recently ran into a situation where I needed two IP addresses on the same subnet assigned to one Linux host so that we could run two SSL/TLS sites. My first approach was to use IP aliasing, e.g. using eth0:0, eth0:1, etc, but our network admins have some fairly strict settings in place for security that squashed this idea: They use DHCP snooping and normally don't allow static IP addresses. Static addressing is accomplished by using static DHCP entries, so the same MAC address always gets the same IP assignment. This feature can be disabled per switchport if you ask and you have a reason for it (thankfully I have a good relationship with the network guys and this isn't hard to do). With the DHCP snooping disabled on the switchport, they had to put in a rule on the switch that said MAC address X is allowed to have IP address Y. Unfortunately this had the side effect of also saying that MAC address X is ONLY allowed to have IP address Y. IP aliasing required that MAC address X was assigned two IP addresses, so this didn't work. There may have been a way around these issues on the switch configuration, but in an attempt to preserve good relations with the network admins I tried to find another way. Having two network interfaces seemed like the next logical step. Thankfully this Linux system is a virtual machine, so I was able to easily add a second network interface (without rebooting, I might add - pretty cool). A few keystrokes later I had two network interfaces up and running and both pulled IP addresses from DHCP. But then the problem came in: the network admins could see (on the switch) the ARP entry for both interfaces, but only the first network interface that I brought up would respond to pings or any sort of TCP or UDP traffic. After lots of digging and poking, here's what I came up with. It seems to work, but it also seems to be a lot of work for something that seems like it should be simple. Any alternate ideas out there? Step 1: Enable ARP filtering on all interfaces: # sysctl -w net.ipv4.conf.all.arp_filter=1 # echo "net.ipv4.conf.all.arp_filter = 1" >> /etc/sysctl.conf From the file networking/ip-sysctl.txt in the Linux kernel docs: arp_filter - BOOLEAN 1 - Allows you to have multiple network interfaces on the same subnet, and have the ARPs for each interface be answered based on whether or not the kernel would route a packet from the ARP'd IP out that interface (therefore you must use source based routing for this to work). In other words it allows control of which cards (usually 1) will respond to an arp request. 0 - (default) The kernel can respond to arp requests with addresses from other interfaces. This may seem wrong but it usually makes sense, because it increases the chance of successful communication. IP addresses are owned by the complete host on Linux, not by particular interfaces. Only for more complex setups like load- balancing, does this behaviour cause problems. arp_filter for the interface will be enabled if at least one of conf/{all,interface}/arp_filter is set to TRUE, it will be disabled otherwise Step 2: Implement source-based routing I basically just followed directions from http://lartc.org/howto/lartc.rpdb.multiple-links.html, although that page was written with a different goal in mind (dealing with two ISPs). Assume that the subnet is 10.0.0.0/24, the gateway is 10.0.0.1, the IP address for eth0 is 10.0.0.100, and the IP address for eth1 is 10.0.0.101. Define two new routing tables named eth0 and eth1 in /etc/iproute2/rt_tables: ... top of file omitted ... 1 eth0 2 eth1 Define the routes for these two tables: # ip route add default via 10.0.0.1 table eth0 # ip route add default via 10.0.0.1 table eth1 # ip route add 10.0.0.0/24 dev eth0 src 10.0.0.100 table eth0 # ip route add 10.0.0.0/24 dev eth1 src 10.0.0.101 table eth1 Define the rules for when to use the new routing tables: # ip rule add from 10.0.0.100 table eth0 # ip rule add from 10.0.0.101 table eth1 The main routing table was already taken care of by DHCP (and it's not even clear that its strictly necessary in this case), but it basically equates to this: # ip route add default via 10.0.0.1 dev eth0 # ip route add 130.127.48.0/23 dev eth0 src 10.0.0.100 # ip route add 130.127.48.0/23 dev eth1 src 10.0.0.101 And voila! Everything seems to work just fine. Sending pings to both IP addresses works fine. Sending pings from this system to other systems and forcing the ping to use a specific interface works fine (ping -I eth0 10.0.0.1, ping -I eth1 10.0.0.1). And most importantly, all TCP and UDP traffic to/from either IP address works as expected. So again, my question is: is there a better way to do this? This seems like a lot of work for a seemingly simple problem.

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• Chaining CSS classes in IE6 - Trying to find a jQuery solution?

  - by Mike Baxter

  Right, perhaps I ask the impossible? I consider myself fairly new to Javscript and jQuery, but that being said, I have written some fairly complex code recently so I am definitely getting there... however I am now possed with a rather interesting issue at my current freelance contract. The previous web coder has taken a Grid-960 approach to the HTML and as a result has used chained classes to style many of the elements. The example below is typical of what can be found in the code: <div class='blocks four-col-1 orange highlight'>Some content</div> And in the css there will be different declarations for: (not actual css... but close enough) .blocks {margin-right:10px;} .orange {background-image:url(someimage.jpg);} .highlight {font-weight:bold;} .four-col-1 {width:300px;} and to make matters worse... this is in the CSS: .blocks.orange.highlight {background-colour:#dd00ff;} Anyone not familiar with this particular bug can read more on it here: http://www.ryanbrill.com/archives/multiple-classes-in-ie/ it is very real and very annoying. Without wanting to go into the merrits of not chaining classes (I told them this, but it is no longer feasible to change their approach... 100 hand coded pages into a 150 page website, no CMS... sigh) and without the luxury of being able to change the way these blocks are styled... can anyone advise me on the complexity and benefits between any of my below proposed approaches or possible other options that would adequately solve this problem. Potential Solution 1 Using conditional comments I am considering loading a jquery script only for IE6 that: Reads the class of all divs in a certain section of the page and pushes to an array creates empty boxes off screen with only one of the classes applied at a time Reads the applied CSS values for each box Re-applies these styles to the individual box, somehow bearing in mind the order in which they are called and overwriting conflicting instructions as required Potential Solution 2 read the class of all divs in a certain section of the page and push to an array Scan the document for links to style sheets Ajax grab the stylesheets and traverse looking for matching names to those in class array Apply styles as needed Potential Solution 3 Create an IE6 only stylesheet containing the exact style to be applied as a unique name (ie: class='blocks orange highlight' becomes class='blocks-orange-highlight') Traverse the document in IE6 and convert all spaces in class declarations to hyphens and reapply classes based on new style name Summary: Solution 1 allows the people at this company to apply any styles in the future and the script will adjust as needed. However it does not allow for the chained style to be added, only the individual style... it is also processor intensive and time consuming, but also the most likely to be converted into a plugin that could be used the world over Solution 2 is a potential nightmare to code. But again will allow for an endless number of updates without breaking Solution 3 will require someone at the companty to hardcode the new styles every time they make a change, and if they don't, IE6 will break. Ironically the site, whilst needing to conform to IE6 in a limited manner, does not need to run wihtout javascript (they've made the call... have JS or go away), so consider all jQuery and JS solutions to be 'game on'. Did I mention how much i hate IE6? Anyway... any thoughts or comments would be appreciated. I will continue to develop my own solution and if I discover one that can be turned into a jQuery plugin I will post it here in the comments. Regards, Mike.

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• Allocation algorithm help, using Python.

  - by Az

  Hi there, I've been working on this general allocation algorithm for students. The pseudocode for it (a Python implementation) is: for a student in a dictionary of students: for student's preference in a set of preferences (ordered from 1 to 10): let temp_project be the first preferred project check if temp_project is available if so, allocate it to them and make the project UNavailable to others Quite simply this will try to allocate projects by starting from their most preferred. The way it works, out of a set of say 100 projects, you list 10 you would want to do. So the 10th project wouldn't be the "least preferred overall" but rather the least preferred in their chosen set, which isn't so bad. Obviously if it can't allocate a project, a student just reverts to the base case which is an allocation of None, with a rank of 11. What I'm doing is calculating the allocation "quality" based on a weighted sum of the ranks. So the lower the numbers (i.e. more highly preferred projects), the better the allocation quality (i.e. more students have highly preferred projects). That's basically what I've currently got. Simple and it works. Now I'm working on this algorithm that tries to minimise the allocation weight locally (this pseudocode is a bit messy, sorry). The only reason this will probably work is because my "search space" as it is, isn't particularly large (just a very general, anecdotal observation, mind you). Since the project is only specific to my Department, we have their own limits imposed. So the number of students can't exceed 100 and the number of preferences won't exceed 10. for student in a dictionary/list/whatever of students: where i = 0 take the (i)st student, (i+1)nd student for their ranks: allocate the projects and set local_weighting to be sum(student_i.alloc_proj_rank, student_i+1.alloc_proj_rank) these are the cases: if local_weighting is 2 (i.e. both ranks are 1): then i += 1 and and continue above if local weighting is = N>2 (i.e. one or more ranks are greater than 1): let temp_local_weighting be N: pick student with lowest rank and then move him to his next rank and pick the other student and reallocate his project after this if temp_local_weighting is < N: then allocate those projects to the students move student with lowest rank to the next rank and reallocate other if temp_local_weighting < previous_temp_allocation: let these be the new allocated projects try moving for the lowest rank and reallocate other else: if this weighting => previous_weighting let these be the allocated projects i += 1 and move on for the rest of the students So, questions: This is sort of a modification of simulated annealing, but any sort of comments on this would be appreciated. How would I keep track of which student is (i) and which student is (i+1) If my overall list of students is 100, then the thing would mess up on (i+1) = 101 since there is none. How can I circumvent that? Any immediate flaws that can be spotted? Extra info: My students dictionary is designed as such: students[student_id] = Student(student_id, student_name, alloc_proj, alloc_proj_rank, preferences) where preferences is in the form of a dictionary such that preferences[rank] = {project_id}

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• How should I clean up hung grandchild processes when an alarm trips in Perl?

  - by brian d foy

  I have a parallelized automation script which needs to call many other scripts, some of which hang because they (incorrectly) wait for standard input. That's not a big deal because I catch those with alarm. The trick is to shut down those hung grandchild processes when the child shuts down. I thought various incantations of SIGCHLD, waiting, and process groups could do the trick, but they all block and the grandchildren aren't reaped. My solution, which works, just doesn't seem like it is the right solution. I'm not especially interested in the Windows solution just yet, but I'll eventually need that too. Mine only works for Unix, which is fine for now. I wrote a small script that takes the number of simultaneous parallel children to run and the total number of forks: $ fork_bomb <parallel jobs> <number of forks> $ fork_bomb 8 500 This will probably hit the per-user process limit within a couple of minutes. Many solutions I've found just tell you to increase the per-user process limit, but I need this to run about 300,000 times, so that isn't going to work. Similarly, suggestions to re-exec and so on to clear the process table aren't what I need. I'd like to actually fix the problem instead of slapping duct tape over it. I crawl the process table looking for the child processes and shut down the hung processes individually in the SIGALRM handler, which needs to die because the rest of real code has no hope of success after that. The kludgey crawl through the process table doesn't bother me from a performance perspective, but I wouldn't mind not doing it: use Parallel::ForkManager; use Proc::ProcessTable; my $pm = Parallel::ForkManager->new( $ARGV[0] ); my $alarm_sub = sub { kill 9, map { $_->{pid} } grep { $_->{ppid} == $$ } @{ Proc::ProcessTable->new->table }; die "Alarm rang for $$!\n"; }; foreach ( 0 .. $ARGV[1] ) { print "."; print "\n" unless $count++ % 50; my $pid = $pm->start and next; local $SIG{ALRM} = $alarm_sub; eval { alarm( 2 ); system "$^X -le '<STDIN>'"; # this will hang alarm( 0 ); }; $pm->finish; } If you want to run out of processes, take out the kill. I thought that setting a process group would work so I could kill everything together, but that blocks: my $alarm_sub = sub { kill 9, -$$; # blocks here die "Alarm rang for $$!\n"; }; foreach ( 0 .. $ARGV[1] ) { print "."; print "\n" unless $count++ % 50; my $pid = $pm->start and next; setpgrp(0, 0); local $SIG{ALRM} = $alarm_sub; eval { alarm( 2 ); system "$^X -le '<STDIN>'"; # this will hang alarm( 0 ); }; $pm->finish; } The same thing with POSIX's setsid didn't work either, and I think that actually broke things in a different way since I'm not really daemonizing this. Curiously, Parallel::ForkManager's run_on_finish happens too late for the same clean-up code: the grandchildren are apparently already disassociated from the child processes at that point.

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• Object hierarchy returned by WCF Service is different than expected

  - by robalot

  Good Day Everyone... My understanding may be wrong, but I thought once you applied the correct attributes the DataContractSerializer would render fully-qualified instances back to the caller. The code runs and the objects return. But oddly enough, once I look at the returned objects I noticed the namespacing disappeared and the object-hierarchy being exposed through the (web applications) service reference seems to become "flat" (somehow). Now, I expect this from a web-service…but not through WFC. Of course, my understanding of what WFC can do may be wrong. ...please keep in mind I'm still experimenting with all this. So my questions are… Q: Can I do something within the WFC Service to force the namespacing to render through the (service reference) data client proxy? Q: Or perhaps, am I (merely) consuming the service incorrectly? Q: Is this even possible? The service code looks like… [ServiceBehavior(InstanceContextMode = InstanceContextMode.PerSession)] public class DataService : IFishData { public C1FE GetC1FE(Int32 key) { //… more stuff here … } public Project GetProject(Int32 key) { //… more stuff here … } } [ServiceContract] [ServiceKnownType(typeof(wcfFISH.StateManagement.C1FE.New))] [ServiceKnownType(typeof(wcfFISH.StateManagement.Project.New))] public interface IFishData { [OperationContract] C1FE GetC1FE(Int32 key); [OperationContract] Project GetProject(Int32 key); } [DataContract] [KnownType(typeof(wcfFISH.StateManagement.ObjectState))] public class Project { [DataMember] public wcfFISH.StateManagement.ObjectState ObjectState { get; set; } //… more stuff here … } [DataContract] KnownType(typeof(wcfFISH.StateManagement.ObjectState))] public class C1FE { [DataMember] public wcfFISH.StateManagement.ObjectState ObjectState { get; set; } //… more stuff here … } [DataContract(Namespace = "wcfFISH.StateManagement")] [KnownType(typeof(wcfFISH.StateManagement.C1FE.New))] [KnownType(typeof(wcfFISH.StateManagement.Project.New))] public abstract class ObjectState { //… more stuff here … } [DataContract(Namespace = "wcfFISH.StateManagement.C1FE", Name="New")] [KnownType(typeof(wcfFISH.StateManagement.ObjectState))] public class New : ObjectState { //… more stuff here … } [DataContract(Namespace = "wcfFISH.StateManagement.Project", Name = "New")] [KnownType(typeof(wcfFISH.StateManagement.ObjectState))] public class New : ObjectState { //… more stuff here … } The web application code looks like… public partial class Fish_Invite : BaseForm { protected void btnTest_Click(object sender, EventArgs e) { Project project = new Project(); project.Get(base.ProjectKey, base.AsOf); mappers.Project mapProject = new mappers.Project(); srFish.Project fishProject = new srFish.Project(); srFish.FishDataClient fishService = new srFish.FishDataClient(); mapProject.MapTo(project, fishProject); fishProject = fishService.AddProject(fishProject, IUser.UserName); project = null; } } In case I’m not being clear… The issue arises as there is a difference in (the name spacing) that I expect to see (returned) is different from what is actually returned. fishProject.ObjectState should look like... srFish.StateManagement.Project.New fishC1FE.ObjectState should look like... srFish.StateManagement.C1FE.New fishProject.ObjectState looks like... srFish.New1 fishC1FE.ObjectState looks like... srFish.New …“Help me Obi-Wan Kenobi, you’re my only hope!”

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• Which option do you like the most?

  - by spderosso

  I need to show a list of movies ordered by the date they were registered in the system and the amount of comments users have made about them. E.g: Title | Register Date | # of comments Gladiator | 02-01-2010 | 30 Matrix | 01-02-2010 | 20 It is a web application that follows MVC. So, I have the object "Movie", there is a MovieManager interface that is used for retrieving/persisting data to the database and a servlet RecentlyAddedMovies.java that forwards to a .jsp to render the list. I will explain my problem by showing an example of how I am doing another similar task: Showing top ranked movies. Regarding the MovieManager: /** * Returns a collection of the x best-ranked movies * @param x the amount of movies to return * @return A collection of movies * @throws SQLException */ public Collection<Movie> getTopX(int x) throws SQLException; The servlet: public class Top5 extends HttpServlet{ @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { MovieManager movManager = JDBCMovieManager.getInstance(); try { req.setAttribute("movies", movManager.getTopX(5)); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } req.getRequestDispatcher("listMovies.jsp").forward(req, resp); } } And the listMovies.jsp has is some place something like: <c:forEach var="movie" items="${movies}"> ... <c:out value="${movie.title}"/> ... </c:forEach> The difference between the top5 problem and the problem I am trying to solve is that with the top5 thing all the data I needed to show in the view where part of the "Movie" object, so the MovieManager simply returned a Collection of Movies. Now, the MovieManager must retrieve an ordered list of (Movie, # of comments). The Movie object has a collection of Comment associated but of course, it lacks an instance variable with the length of that collection. The following things came into my mind: a) Create a MovieView object or something like that, that is only used by the "View" and "Controller" layer of the MVC which is not part of the "Model" in the sense that is used only for easy retrieval and display of information. This MovieView object will have a title, registerDate and # of Comments so the thing would look something like this: /** * Returns a collection of the x most recently added movies * @param x the amount of movies to return * @return A collection of movies * @throws SQLException */ public Collection<Movie2> getXRecentlyAddedMovies(int x) throws SQLException; The .jsp: <c:forEach var="movie2" items="${movies2}"> ... <c:out value="${movie2.title}"/> <c:out value="${movie2.registerDate}"/> <c:out value="${movie2.noOfComments}"/> ... </c:forEach> b) Add to the Collection the movie has, empty Comments (there is no actual need to retrieve all the comment data from the database) so that the comment's collection.size() will show the number of comments that movie has. (This sounds horrible to me) c) Add to the "Movie" object an instance field noOfComments with the setter and getter that will help with this type of cases even if, looking only from the object point of view, it is a redundant field since it already has a Collection that is ".size()"able . d) Make the MovieManager retrieve some structure like a Map or a Collection of a two component array or something like that that will contain both a Movie object and the associated number of comments and with JSLT iterate over it and show it accordingly.

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• boost::serialization with mutable members

  - by redmoskito

  Using boost::serialization, what's the "best" way to serialize an object that contains cached, derived values in mutable members, such that cached members aren't serialized, but on deserialization, they are initialized the their appropriate default. A definition of "best" follows later, but first an example: class Example { public: Example(float n) : num(n), sqrt_num(-1.0) {} float get_num() const { return num; } // compute and cache sqrt on first read float get_sqrt() const { if(sqrt_num < 0) sqrt_num = sqrt(num); return sqrt_num; } template <class Archive> void serialize(Archive& ar, unsigned int version) { ... } private: float num; mutable float sqrt_num; }; On serialization, only the "num" member should be saved. On deserialization, the sqrt_num member must be initialized to its sentinel value indicating it needs to be computed. What is the most elegant way to implement this? In my mind, an elegant solution would avoid splitting serialize() into separate save() and load() methods (which introduces maintenance problems). One possible implementation of serialize: template <class Archive> void serialize(Archive& ar, unsigned int version) { ar & num; sqrt_num = -1.0; } This handles the deserialization case, but in the serialization case, the cached value is killed and must be recomputed. Also, I've never seen an example of boost::serialize that explicitly sets members inside of serialize(), so I wonder if this is generally not recommended. Some might suggest that the default constructor handles this, for example: int main() { Example e; { std::ifstream ifs("filename"); boost::archive::text_iarchive ia(ifs); ia >> e; } cout << e.get_sqrt() << endl; return 0; } which works in this case, but I think fails if the object receiving the deserialized data has already been initialized, as in the example below: int main() { Example ex1(4); Example ex2(9); cout << ex1.get_sqrt() << endl; // outputs 2; cout << ex2.get_sqrt() << endl; // outputs 3; // the following two blocks should implement ex2 = ex1; // save ex1 to archive { std::ofstream ofs("filename"); boost::archive::text_oarchive oa(ofs); oa << ex1; } // read it back into ex2 { std::ifstream ifs("filename"); boost::archive::text_iarchive ia(ifs); ia >> ex2; } // these should be equal now, but aren't, // since Example::serialize() doesn't modify num_sqrt cout << ex1.get_sqrt() << endl; // outputs 2; cout << ex2.get_sqrt() << endl; // outputs 3; return 0; } I'm sure this issue has come up with others, but I have struggled to find any documentation on this particular scenario. Thanks!

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• certain Smarty tags don't work in OpenX templates

  - by mikez302

  I am on a team that is developing an OpenX plugin, and I am responsible for the UI. I noticed that if I use certain Smarty tags in my template, the app doesn't work and I see an error message, similar to this: Plugin by name 'Html_select_date' was not found in the registry; used paths: default_views_helpers_: /openx/www/admin/plugins/myApp/application/modules/default/views/helpers/ OX_OXP_UI_View_Helper_: /openx/www/admin/plugins/myApp/application/../library/OX/OXP/UI/View/Helper/ OX_UI_View_Helper_: /openx/www/admin/plugins/myApp/application/../library/OX/UI/View/Helper/ Zend_View_Helper_: Zend/View/Helper/ (stack trace) The stack trace looks like this: #0 /openx/www/admin/plugins/myApp/library/Zend/View/Abstract.php(1117): Zend_Loader_PluginLoader-load('Html_select_dat...') #1 /openx/www/admin/plugins/myApp/library/Zend/View/Abstract.php(568): Zend_View_Abstract-_getPlugin('helper', 'html_select_dat...') #2 /openx/www/admin/plugins/myApp/library/OX/UI/Smarty/SmartyWithViewHelper.php(25): Zend_View_Abstract-getHelper('html_select_dat...') #3 /openx/var/templates_compiled/%2Fdefault%2Fviews%2Fscripts%2Findex%2Fview-reports.html^%%E8^E80^E80B56F2%%view-reports.html.php(38): OX_UI_Smarty_SmartyWithViewHelper-callViewHelper('html_select_dat...', Array) #4 /openx/lib/smarty/Smarty.class.php(1274): include('/openx...') #5 /openx/www/admin/plugins/myApp/library/OX/UI/View/SmartyView.php(103): Smarty-fetch('/openx...') #6 /openx/www/admin/plugins/myApp/library/Zend/View/Abstract.php(832): OX_UI_View_SmartyView-_run('/openx...') #7 /openx/www/admin/plugins/myApp/library/OX/UI/View/SmartyView.php(151): Zend_View_Abstract-render('index/view-repo...') #8 /openx/www/admin/plugins/myApp/library/OX/UI/View/Helper/WithViewScript.php(23): OX_UI_View_SmartyView-render('index/view-repo...') #9 /openx/www/admin/plugins/myApp/application/modules/default/views/helpers/ViewReports.php(5): OX_UI_View_Helper_WithViewScript::renderViewScript('index/view-repo...', Array) #10 /openx/www/admin/plugins/myApp/application/modules/default/controllers/IndexController.php(98): Default_Views_Helpers_ViewReports-renderPage() #11 /openx/www/admin/plugins/myApp/library/Zend/Controller/Action.php(512): IndexController-viewReportsAction() #12 /openx/www/admin/plugins/myApp/library/Zend/Controller/Dispatcher/Standard.php(288): Zend_Controller_Action-dispatch('viewReportsActi...') #13 /openx/www/admin/plugins/myApp/library/Zend/Controller/Front.php(945): Zend_Controller_Dispatcher_Standard-dispatch(Object(Zend_Controller_Request_Http), Object(Zend_Controller_Response_Http)) #14 /openx/www/admin/plugins/myApp/application/bootstrap.php(117): Zend_Controller_Front-dispatch() #15 /openx/www/admin/plugins/myApp/public/index.php(7): require('/openx...') #16 {main} This does not happen with all Smarty tags. For example, I can use {if}, {foreach}, or {assign} tags without any problems. But whenever I try to use {html_select_date}, {html_image}, or {html_table}, I get the errors. In case this matters, the programmer who is designing the plugin copied the openXWorkflow plugin and made some changes. I noticed that the openXWorkflow plugin has a file (openx/plugins_repo/openXWorkflow/www/admin/plugins/openXWorkflow/library/OX/UI/Smarty/SmartyCompilerWithViewHelper.php) with a class that overrides the default Smarty compiler, supposedly with the ability to compile shorthands for calling ZF view helpers. That file has a list of Smarty functions, but the list is incomplete. If I add the functions to the list, or simply delete the file, my template works fine, but I don't like to change library files. It may make the app hard to maintain, and I don't know if it will mess up something else. The file has the comment "There is no easy access to the list of Smarty's built-in functions so we need to list them here. HTML-specific functions are not included as we cover HTML generation separately.", so it seems like certain Smarty functions may be disabled on purpose for some reason. Will anything bad happen if I try to use them? If, for example, I want to use the {html_select_date} tag in my template, how would I go about doing that? Keep in mind that much of this stuff is new and unfamiliar to me. This is my first time ever using OpenX or Smarty, and I only have a little bit of experience with the Zend framework. Please let me know if we are using the wrong approach.

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• rm on a directory with millions of files

  - by BMDan

  Background: physical server, about two years old, 7200-RPM SATA drives connected to a 3Ware RAID card, ext3 FS mounted noatime and data=ordered, not under crazy load, kernel 2.6.18-92.1.22.el5, uptime 545 days. Directory doesn't contain any subdirectories, just millions of small (~100 byte) files, with some larger (a few KB) ones. We have a server that has gone a bit cuckoo over the course of the last few months, but we only noticed it the other day when it started being unable to write to a directory due to it containing too many files. Specifically, it started throwing this error in /var/log/messages: ext3_dx_add_entry: Directory index full! The disk in question has plenty of inodes remaining: Filesystem Inodes IUsed IFree IUse% Mounted on /dev/sda3 60719104 3465660 57253444 6% / So I'm guessing that means we hit the limit of how many entries can be in the directory file itself. No idea how many files that would be, but it can't be more, as you can see, than three million or so. Not that that's good, mind you! But that's part one of my question: exactly what is that upper limit? Is it tunable? Before I get yelled at--I want to tune it down; this enormous directory caused all sorts of issues. Anyway, we tracked down the issue in the code that was generating all of those files, and we've corrected it. Now I'm stuck with deleting the directory. A few options here: rm -rf (dir)I tried this first. I gave up and killed it after it had run for a day and a half without any discernible impact. unlink(2) on the directory: Definitely worth consideration, but the question is whether it'd be faster to delete the files inside the directory via fsck than to delete via unlink(2). That is, one way or another, I've got to mark those inodes as unused. This assumes, of course, that I can tell fsck not to drop entries to the files in /lost+found; otherwise, I've just moved my problem. In addition to all the other concerns, after reading about this a bit more, it turns out I'd probably have to call some internal FS functions, as none of the unlink(2) variants I can find would allow me to just blithely delete a directory with entries in it. Pooh. while [ true ]; do ls -Uf | head -n 10000 | xargs rm -f 2/dev/null; done ) This is actually the shortened version; the real one I'm running, which just adds some progress-reporting and a clean stop when we run out of files to delete, is: export i=0; time ( while [ true ]; do ls -Uf | head -n 3 | grep -qF '.png' || break; ls -Uf | head -n 10000 | xargs rm -f 2/dev/null; export i=$(($i+10000)); echo "$i..."; done ) This seems to be working rather well. As I write this, it's deleted 260,000 files in the past thirty minutes or so. Now, for the questions: As mentioned above, is the per-directory entry limit tunable? Why did it take "real 7m9.561s / user 0m0.001s / sys 0m0.001s" to delete a single file which was the first one in the list returned by "ls -U", and it took perhaps ten minutes to delete the first 10,000 entries with the command in #3, but now it's hauling along quite happily? For that matter, it deleted 260,000 in about thirty minutes, but it's now taken another fifteen minutes to delete 60,000 more. Why the huge swings in speed? Is there a better way to do this sort of thing? Not store millions of files in a directory; I know that's silly, and it wouldn't have happened on my watch. Googling the problem and looking through SF and SO offers a lot of variations on "find" that obviously have the wrong idea; it's not going to be faster than my approach for several self-evident reasons. But does the delete-via-fsck idea have any legs? Or something else entirely? I'm eager to hear out-of-the-box (or inside-the-not-well-known-box) thinking. Thanks for reading the small novel; feel free to ask questions and I'll be sure to respond. I'll also update the question with the final number of files and how long the delete script ran once I have that. Final script output!: 2970000... 2980000... 2990000... 3000000... 3010000... real 253m59.331s user 0m6.061s sys 5m4.019s So, three million files deleted in a bit over four hours.

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• java - BigDecimal

  - by Mk12

  I was trying to make my own class for currencies using longs, but Apparently I should use BigDecimal (and then whenever I print it just add the $ sign before it). Could someone please get me started? What would be the best way to use BigDecimals for Dollar currencies, like making it at least but no more than 2 decimal places for the cents, etc. The api for BigDecimal is huge, and I don't know which methods to use. Also, BigDecimal has better precision, but isn't that all lost if it passes through a double? if I do new BigDecimal(24.99), how will it be different than using a double? Or should I use the constructor that uses a String instead? EDIT: I decided to use BigDecimals, and then use: private static final java.text.NumberFormat moneyt = java.text.NumberFormat.getCurrencyInstance(); { money.setRoundingMode(RoundingMode.HALF_EVEN); } and then whenever I display the BigDecimals, to use money.format(theBigDecimal). Is this alright? Should I have the BigDecimal rounding it too? Because then it doesn't get rounded before it does another operation.. if so, could you show me how? And how should I create the BigDecimals? new BigDecimal("24.99") ? Well, after many comments to Vineet Reynolds (thanks for keeping coming back and answering), this is what I have decided. I use BigDecimals and a NumberFormat. Here is where I create the NumberFormat instance. private static final NumberFormat money; static { money = NumberFormat.getCurrencyInstance(Locale.CANADA); money.setRoundingMode(RoundingMode.HALF_EVEN); } Here is my BigDecimal: private final BigDecimal price; Whenever I want to display the price, or another BigDecimal that I got through calculations of price, I use: money.format(price) to get the String. Whenever I want to store the price, or a calculation from price, in a database or in a field or anywhere, I use (for a field): myCalculatedResult = price.add(new BigDecimal("34.58")).setScale(2, RoundingMode.HALF_EVEN); .. but I'm thinking now maybe I should not have the NumberFormat round, but when I want to display do this: System.out.print(money.format(price.setScale(2, RoundingMode.HALF_EVEN); That way to ensure the model and things displayed in the view are the same. I don't do: price = price.setScale(2, RoundingMode.HALF_EVEN); Because then it would always round to 2 decimal places and wouldn't be as precise in calculations. So its all solved now, I guess. But is there any shortcut to typing calculatedResult.setScale(2, RoundingMode.HALF_EVEN) all the time? All I can think of is static importing HALF_EVEN... EDIT: I've changed my mind a bit, I think if I store a value, I won't round it unless I have no more operations to do with it, e.g. if it was the final total that will be charged to someone. I will only round things at the end, or whenever necessary, and I will still use NumberFormat for the currency formatting, but since I always want rounding for display, I made a static method for display: public static String moneyFormat(BigDecimal price) { return money.format(price.setScale(2, RoundingMode.HALF_EVEN)); } So values stored in variables won't be rounded, and I'll use that method to display prices.

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• Disable antialiasing for a specific GDI device context

  - by Jacob Stanley

  I'm using a third party library to render an image to a GDI DC and I need to ensure that any text is rendered without any smoothing/antialiasing so that I can convert the image to a predefined palette with indexed colors. The third party library i'm using for rendering doesn't support this and just renders text as per the current windows settings for font rendering. They've also said that it's unlikely they'll add the ability to switch anti-aliasing off any time soon. The best work around I've found so far is to call the third party library in this way (error handling and prior settings checks ommitted for brevity): private static void SetFontSmoothing(bool enabled) { int pv = 0; SystemParametersInfo(Spi.SetFontSmoothing, enabled ? 1 : 0, ref pv, Spif.None); } // snip Graphics graphics = Graphics.FromImage(bitmap) IntPtr deviceContext = graphics.GetHdc(); SetFontSmoothing(false); thirdPartyComponent.Render(deviceContext); SetFontSmoothing(true); This obviously has a horrible effect on the operating system, other applications flicker from cleartype enabled to disabled and back every time I render the image. So the question is, does anyone know how I can alter the font rendering settings for a specific DC? Even if I could just make the changes process or thread specific instead of affecting the whole operating system, that would be a big step forward! (That would give me the option of farming this rendering out to a separate process- the results are written to disk after rendering anyway) EDIT: I'd like to add that I don't mind if the solution is more complex than just a few API calls. I'd even be happy with a solution that involved hooking system dlls if it was only about a days work. EDIT: Background Information The third-party library renders using a palette of about 70 colors. After the image (which is actually a map tile) is rendered to the DC, I convert each pixel from it's 32-bit color back to it's palette index and store the result as an 8bpp greyscale image. This is uploaded to the video card as a texture. During rendering, I re-apply the palette (also stored as a texture) with a pixel shader executing on the video card. This allows me to switch and fade between different palettes instantaneously instead of needing to regenerate all the required tiles. It takes between 10-60 seconds to generate and upload all the tiles for a typical view of the world. EDIT: Renamed GraphicsDevice to Graphics The class GraphicsDevice in the previous version of this question is actually System.Drawing.Graphics. I had renamed it (using GraphicsDevice = ...) because the code in question is in the namespace MyCompany.Graphics and the compiler wasn't able resolve it properly. EDIT: Success! I even managed to port the PatchIat function below to C# with the help of Marshal.GetFunctionPointerForDelegate. The .NET interop team really did a fantastic job! I'm now using the following syntax, where Patch is an extension method on System.Diagnostics.ProcessModule: module.Patch( "Gdi32.dll", "CreateFontIndirectA", (CreateFontIndirectA original) => font => { font->lfQuality = NONANTIALIASED_QUALITY; return original(font); }); private unsafe delegate IntPtr CreateFontIndirectA(LOGFONTA* lplf); private const int NONANTIALIASED_QUALITY = 3; [StructLayout(LayoutKind.Sequential)] private struct LOGFONTA { public int lfHeight; public int lfWidth; public int lfEscapement; public int lfOrientation; public int lfWeight; public byte lfItalic; public byte lfUnderline; public byte lfStrikeOut; public byte lfCharSet; public byte lfOutPrecision; public byte lfClipPrecision; public byte lfQuality; public byte lfPitchAndFamily; public unsafe fixed sbyte lfFaceName [32]; }

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• OpenID and Iframes

  - by Phood

  hey guys, I'm having a little bit of trouble making OpenID work from within an iframe. basically I have some heavy handed content loaded on the main page and I want to build a log in system where the page doesn't need to be reloaded (and thus reload all of that content again). I fell in love with OpenID from using stack exchange websites, and have intergrated it relatively well into other projects. I feel to do what I want to do I would like to try and use an iframe (because new windows make me cry), however I have stumbled at some form of hurdle somewhere near the middle and for the life of me can't work out whats going on... basically I have a form in a jQuery generated DIV and openID form that seems to work to dynamically load an iframe. something along these lines: <script type="text/javascript"> contentboxs = 0; function contentbox() { if (contentboxs == 0){ $('#mainpage').append("<div id='contentbox'><div style='clear:both;' id='oritext'></div><div id='f_content'><iframe src ='' name='framedcontent' width='580' height='600' scrolling='false'></iframe></div></div>"); $('#f_content').hide(); contentboxs++; } else { $('#contentbox-wipe').remove(); $('#contentbox').remove(); contentboxs--; } } function loginpanel(){ contentbox(); if (contentboxs == 1){ $('#oritext').append("<form method='post' action='login.php' name='oidform' target='framedcontent'>Please Select your OpenID Provider: <br/><input type='text' name=\"id\" id='openidbox' /><br /><input type='submit' name='submit' value='Log In' onclick='loginsubmit();' ></form>"); } } function loginsubmit() { $('#oritext').html(''); $('#contentbox').animate({'height':'600px', 'width':'700px', 'margin-top' : '-300px', 'margin-left' : '-350px'},500, 'linear', function() { $('#f_content').show(); }); } </script> <a href='javascript:loginpanel();'>login</a> and as far as I can tell this all works fine. my problem comes in my re-direction to the openID remote sites (again doing it with JS along these lines:) echo("<div><p><center>Redirecting...</center></div>"); echo "<script type='text/javascript'> function delayer() { this.location = '".$url."' } setTimeout('delayer()', 3000) </script>"; sorry this is a bit long winded, but here is my problem (finally): this works fine for some of the OID sites that I have tried, but some are giving me problems: Google won't load at all, Yahoo and mySpace open fine in the iframe then instantly redirect the full window to the home page and the OID page respectively, and wordpress returns an error. I'm assuming that this is a counter measure put in place to stop me stealing login details (thats not what i'm trying to achieve btw, hence the preamble), and thats fair enough, but still bloody aggravating. is there any thing here that i'm doing retardedly, is there some way round this, and if neither of the above, is my only other options to create new windows or build my own login/registration. If you have got this far thank you very much for your time, and I hope you didn't mind too much the spelling mistakes.

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• Temporary "Backup" of SharePoint Content During Feature and Solution Deployment

  - by ccomet

  I need to decide on a method for storing a subset of the content in a SharePoint site, so that when I delete and recreate certain lists as part of a feature activation, I can re-insert all of this content back where it should belong. I have an idea myself, but I don't know if it's the only method and more importantly, the right method. My client has me creating a SharePoint system for them to communicate with their clients. The business process has maybe 5 stages in it (maybe it's more, I don't even know because they don't tell me everything), and the current system I've written over the past months is maybe 2 stages through. This meets our deadline of completing those systems by Monday next week... but at that point my client is planning on making the site live from that point. In effect, their work with their clients will be running parallel with my work for them. As I complete my own work on a separate test server, I'll push each following stage of the process onto the live server. Scheduled downtimes during non-business times (like a weekend) will be available for me to perform these pushes. Keeping pace so that my development is faster than the actual business process is my own problem and off-topic... so let's get back to the problem I stated at the start of this post. In this system, we have sets of features which will create lists for their associated content types and field types when activated, and delete these lists when the feature is deactivated. Most updates don't need to deactivate and reactivate these features, such as workflow changes, custom actions, custom forms, and similar ilk. But there are some parts which do require this. On my test server, it's okay for me to obliterate lists, but once the site is live and there's real correspondence data, it's absolutely unacceptable to do this. So when I need to implement a new change in functionality, I need to be able to store the currently present data in several lists, deactivate the feature, reactivate the feature, and restore all of this data. Perhaps I have hoist myself by my own petard with the feature system I implemented. Unfortunately, the necessity to later on make several of these "project sites" meant I had to do a lot of my code with the concept of "Can be deployed repeatedly" in mind. My current plan is to run through lists and libraries which will be affected by the particular feature that is to be reset. Files and all of their versions will be saved in a directory on the server. Then, a set of text files will be used to store all of the important field values for the items. This includes a lot of cross-list reference lookups that will need to be maintained, but that's simple enough. Then, I deactivate the feature, deploy the new solution, and reactivate the feature. We upload all of the files in the order specified by their versions and update them with the stored fields for those versions, so that we retain the version structure. As each one is first uploaded, the new ID is picked out, and all relevant lookups in the rest of the files are updated (in some manner that I make sure I don't re-update it later with an incorrect value, of course). After that, we run through all the rest of the items in the order most conducive to keeping the relational data correct. This roughly summarizes what my current plan is. To my advantage, there are no long running workflows in the system that will be affected by this, so there's nothing I will have to worry about making sure nothing is "still running" when I do this stuff. I don't really know all the cons of this approach... I can imagine they're quite hefty. But I'm unsure what other choices I even have, and my searches haven't turned up anything. Is there anyone who can think of a better idea? Or will anyone just tell me that I really have no other choice? Thanks in advance!

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• Domain Validation in a CQRS architecture

  - by Jupaol

  Basically I want to know if there is a better way to validate my domain entities. This is how I am planning to do it but I would like your opinion The first approach I considered was: class Customer : EntityBase<Customer> { public void ChangeEmail(string email) { if(string.IsNullOrWhitespace(email)) throw new DomainException(“...”); if(!email.IsEmail()) throw new DomainException(); if(email.Contains(“@mailinator.com”)) throw new DomainException(); } } I actually do not like this validation because even when I am encapsulating the validation logic in the correct entity, this is violating the Open/Close principle (Open for extension but Close for modification) and I have found that violating this principle, code maintenance becomes a real pain when the application grows up in complexity. Why? Because domain rules change more often than we would like to admit, and if the rules are hidden and embedded in an entity like this, they are hard to test, hard to read, hard to maintain but the real reason why I do not like this approach is: if the validation rules change, I have to come and edit my domain entity. This has been a really simple example but in RL the validation could be more complex So following the philosophy of Udi Dahan, making roles explicit, and the recommendation from Eric Evans in the blue book, the next try was to implement the specification pattern, something like this class EmailDomainIsAllowedSpecification : IDomainSpecification<Customer> { private INotAllowedEmailDomainsResolver invalidEmailDomainsResolver; public bool IsSatisfiedBy(Customer customer) { return !this.invalidEmailDomainsResolver.GetInvalidEmailDomains().Contains(customer.Email); } } But then I realize that in order to follow this approach I had to mutate my entities first in order to pass the value being valdiated, in this case the email, but mutating them would cause my domain events being fired which I wouldn’t like to happen until the new email is valid So after considering these approaches, I came out with this one, since I am going to implement a CQRS architecture: class EmailDomainIsAllowedValidator : IDomainInvariantValidator<Customer, ChangeEmailCommand> { public void IsValid(Customer entity, ChangeEmailCommand command) { if(!command.Email.HasValidDomain()) throw new DomainException(“...”); } } Well that’s the main idea, the entity is passed to the validator in case we need some value from the entity to perform the validation, the command contains the data coming from the user and since the validators are considered injectable objects they could have external dependencies injected if the validation requires it. Now the dilemma, I am happy with a design like this because my validation is encapsulated in individual objects which brings many advantages: easy unit test, easy to maintain, domain invariants are explicitly expressed using the Ubiquitous Language, easy to extend, validation logic is centralized and validators can be used together to enforce complex domain rules. And even when I know I am placing the validation of my entities outside of them (You could argue a code smell - Anemic Domain) but I think the trade-off is acceptable But there is one thing that I have not figured out how to implement it in a clean way. How should I use this components... Since they will be injected, they won’t fit naturally inside my domain entities, so basically I see two options: Pass the validators to each method of my entity Validate my objects externally (from the command handler) I am not happy with the option 1 so I would explain how I would do it with the option 2 class ChangeEmailCommandHandler : ICommandHandler<ChangeEmailCommand> { public void Execute(ChangeEmailCommand command) { private IEnumerable<IDomainInvariantValidator> validators; // here I would get the validators required for this command injected, and in here I would validate them, something like this using (var t = this.unitOfWork.BeginTransaction()) { var customer = this.unitOfWork.Get<Customer>(command.CustomerId); this.validators.ForEach(x =. x.IsValid(customer, command)); // here I know the command is valid // the call to ChangeEmail will fire domain events as needed customer.ChangeEmail(command.Email); t.Commit(); } } } Well this is it. Can you give me your thoughts about this or share your experiences with Domain entities validation EDIT I think it is not clear from my question, but the real problem is: Hiding the domain rules has serious implications in the future maintainability of the application, and also domain rules change often during the life-cycle of the app. Hence implementing them with this in mind would let us extend them easily. Now imagine in the future a rules engine is implemented, if the rules are encapsulated outside of the domain entities, this change would be easier to implement

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• VFS: file-max limit 1231582 reached

  - by Rick Koshi

  I'm running a Linux 2.6.36 kernel, and I'm seeing some random errors. Things like ls: error while loading shared libraries: libpthread.so.0: cannot open shared object file: Error 23 Yes, my system can't consistently run an 'ls' command. :( I note several errors in my dmesg output: # dmesg | tail [2808967.543203] EXT4-fs (sda3): re-mounted. Opts: (null) [2837776.220605] xv[14450] general protection ip:7f20c20c6ac6 sp:7fff3641b368 error:0 in libpng14.so.14.4.0[7f20c20a9000+29000] [4931344.685302] EXT4-fs (md16): re-mounted. Opts: (null) [4982666.631444] VFS: file-max limit 1231582 reached [4982666.764240] VFS: file-max limit 1231582 reached [4982767.360574] VFS: file-max limit 1231582 reached [4982901.904628] VFS: file-max limit 1231582 reached [4982964.930556] VFS: file-max limit 1231582 reached [4982966.352170] VFS: file-max limit 1231582 reached [4982966.649195] top[31095]: segfault at 14 ip 00007fd6ace42700 sp 00007fff20746530 error 6 in libproc-3.2.8.so[7fd6ace3b000+e000] Obviously, the file-max errors look suspicious, being clustered together and recent. # cat /proc/sys/fs/file-max 1231582 # cat /proc/sys/fs/file-nr 1231712 0 1231582 That also looks a bit odd to me, but the thing is, there's no way I have 1.2 million files open on this system. I'm the only one using it, and it's not visible to anyone outside the local network. # lsof | wc 16046 148253 1882901 # ps -ef | wc 574 6104 44260 I saw some documentation saying: file-max & file-nr: The kernel allocates file handles dynamically, but as yet it doesn't free them again. The value in file-max denotes the maximum number of file- handles that the Linux kernel will allocate. When you get lots of error messages about running out of file handles, you might want to increase this limit. Historically, the three values in file-nr denoted the number of allocated file handles, the number of allocated but unused file handles, and the maximum number of file handles. Linux 2.6 always reports 0 as the number of free file handles -- this is not an error, it just means that the number of allocated file handles exactly matches the number of used file handles. Attempts to allocate more file descriptors than file-max are reported with printk, look for "VFS: file-max limit reached". My first reading of this is that the kernel basically has a built-in file descriptor leak, but I find that very hard to believe. It would imply that any system in active use needs to be rebooted every so often to free up the file descriptors. As I said, I can't believe this would be true, since it's normal to me to have Linux systems stay up for months (even years) at a time. On the other hand, I also can't believe that my nearly-idle system is holding over a million files open. Does anyone have any ideas, either for fixes or further diagnosis? I could, of course, just reboot the system, but I don't want this to be a recurring problem every few weeks. As a stopgap measure, I've quit Firefox, which was accounting for almost 2000 lines of lsof output (!) even though I only had one window open, and now I can run 'ls' again, but I doubt that will fix the problem for long. (edit: Oops, spoke too soon. By the time I finished typing out this question, the symptom was/is back) Thanks in advance for any help. And another update: My system was basically unusable, so I decided I had no option but to reboot. But before I did, I carefully quit one process at a time, checking /proc/sys/fs/file-nr after each termination. I found that, predictably, the number of open files gradually went down as I closed things down. Unfortunately, it wasn't a large effect. Yes, I was able to clear up 5000-10000 open files, but there were still over 1.2 million left. I shut down just about everything. All interactive shells, except for the one ssh I left open to finish closing down, httpd, even nfs service. Basically everything in the process table that wasn't a kernel process, and there were still an appalling number of files apparently left open. After the reboot, I found that /proc/sys/fs/file-nr showed about 2000 files open, which is much more reasonable. Starting up 2 Xvnc sessions as usual, along with the dozen or so monitoring windows I like to keep open, brought the total up to about 4000 files. I can see nothing wrong with that, of course, but I've obviously failed to identify the root cause. I'm still looking for ideas, since I definitely expect it to happen again. And another update, the next day: I watched the system carefully, and discovered that /proc/sys/fs/file-nr showed a growth of about 900 open files per hour. I shut down the system's only NFS client for the night, and the growth stopped. Mind you, it didn't free up the resources, but it did at least stop consuming more. Is this a known bug with NFS? I'll be bringing the NFS client back online today, and I'll narrow it down further. If anyone is familiar with this behavior, feel free to jump in with "Yeah, NFS4 has this problem, go back to NFS3" or something like that.

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• Bug in CF9: values for unique struct keys referenced and overwritten by other keys.

  - by Gin Doe

  We've run into a serious issue with CF9 wherein values for certain struct keys can be referenced by other keys, despite those other keys never being set. See the following examples: Edit: Looks like it isn't just something our servers ate. This is Adobe bug-track ticket 81884: http://cfbugs.adobe.com/cfbugreport/flexbugui/cfbugtracker/main.html#bugId=81884. <cfset a = { AO = "foo" } /> <cfset b = { AO = "foo", B0 = "bar" } /> <cfoutput> The following should throw an error. Instead both keys refer to the same value. <br />Struct a: <cfdump var="#a#" /> <br />a.AO: #a.AO# <br />a.B0: #a.B0# <hr /> The following should show a struct with 2 distinct keys and values. Instead it contains a single key, "AO", with a value of "bar". <br />Struct b: <cfdump var="#b#" /> This is obviously a complete show-stopper for us. I'd be curious to know if anyone has encountered this or can reproduce this in their environment. For us, it happens 100% of the time on Apache/CF9 running on Linux, both RH4 and RH5. We're using the default JRun install on Java 1.6.0_14. To see the extent of the problem, we ran a quick loop to find other naming sequences that are affected and found hundreds of matches for 2 letter key names. A similar loop found more conflicts in 3 letter names. <cfoutput>Testing a range of affected key combinations. This found hundreds of cases on our platform. Aborting after 50 here.</cfoutput> <cfscript> teststring = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"; stringlen = len(teststring); matchesfound = 0; matches = ""; for (i1 = 1; i1 <= stringlen; i1++) { symbol1 = mid(teststring, i1, 1); for (i2 = 1; i2 <= stringlen; i2++) { teststruct = structnew(); symbol2 = mid(teststring, i2, 1); symbolwhole = symbol1 & symbol2; teststruct[ symbolwhole ] = "a string"; for (q1 = 1; q1 <= stringlen; q1++) { innersymbol1 = mid(teststring, q1, 1); for (q2 = 1; q2 <= stringlen; q2++) { innersymbol2 = mid(teststring, q2, 1); innersymbolwhole = innersymbol1 & innersymbol2; if ((i1 != q1 || i2 != q2) && structkeyexists(teststruct, innersymbolwhole)) { // another affected pair of keys! writeoutput ("<br />#symbolwhole# = #innersymbolwhole#"); if (matchesfound++ > 50) { // we've seen enough abort; } } } } } } </cfscript> And edit again: This doesn't just affect struct keys but names in the variables scope as well. At least the variables scope has the presence of mind to throw an error, "can't load a null": <cfset test_b0 = "foo" /> <cfset test_ao = "bar" /> <cfoutput> test_b0: #test_b0# <br />test_ao: #test_ao# </cfoutput>

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• Windows XP periodically disconnects, reconnects; Windows 7 doesn't

  - by einpoklum

  My setup: I have a PC with a Gigabyte GA-MA78S2H motherboard (Realtek Gigabit wired Ethernet on-board). I have the latest drivers (at least the latest driver for the NIC. I'm connecting via an Edimax BR-6216Mg (again, wired connection). For some reason I experience short periodic disconnects and reconnects. Specifically, Skype disconnects, tries to connect, succeeds after a short while; incoming SFTP sessions get dropped; using a browser, I sometime get stuck in the DNS lookup or connection to the website and a page won't load. A couple of seconds later, a reload works. All this happens with Windows XP SP3. With Windows 7, it doesn't happen. The connection is smooth (OS is sluggish though, but never mind that). Like I said, I updated the NIC driver. I tried reducing the MTU (used something called Dr. TCP), thinking maybe that would help, but it didn't. (I'm a bit but not super-knowledgeable about TCP parameters.) I'm guessing it's either a problem with the driver or some settings which are different between the two OSes. ipconfig for my adapter: Ethernet adapter Local Area Connection: Connection-specific DNS Suffix . : Description . . . . . . . . . . . : Realtek PCIe GBE Family Controller Physical Address. . . . . . . . . : 00-1D-7D-E9-72-9E Dhcp Enabled. . . . . . . . . . . : Yes Autoconfiguration Enabled . . . . : Yes IP Address. . . . . . . . . . . . : 192.168.0.2 Subnet Mask . . . . . . . . . . . : 255.255.255.0 Default Gateway . . . . . . . . . : 192.168.0.254 DHCP Server . . . . . . . . . . . : 192.168.0.254 DNS Servers . . . . . . . . . . . : 192.117.235.235 62.219.186.7 Lease Obtained. . . . . . . . . . : Saturday, March 10, 2012 8:28:20 AM Lease Expires . . . . . . . . . . : Friday, January 26, 1906 2:00:04 AM

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• Making a non-trivial Image and Video Gallery with a really nice interface

  - by Cawas

  Short part: I'm starting to build an Image and Video Gallery for our intranet. It's pretty much like an image gallery with video thumbnails that play on click. It's just good to keep that in mind because caching and streaming happen in very different ways there. It will serve to browse our reference database, which will also contain searching, tagging and voting. There are 3 features that I need to begin with: Quick preview of thumbnails from each Gallery Fast zoom in / out Animated scrolling Now to the long part, since I can't seem to reduce this: I hope this question belongs here. Maybe people can read this through and identify with it, specially since I expect answers to be pretty specific. The first plan was getting Apple's mobile me gallery as base, because it just so happens to have all those 3 features. If you've never seem it, you should check it out. Move the mouse over each collection and you'll get a nice preview "per pixel". Carousel got a really good scrolling, not just because of the pretty effect. I like it much more than cooliris, but it would be nice to have it in several rows, maybe without the magnifying effect... Then it could be all in the same place with the zoom. The more the features blend-in together, the better. Zooming out with the mouse, scrolling by dragging, once the zoom is really out it becomes a browsing through galleries, with the quick-show preview of each, all properly cached and fast. That'd be perfect. A very compelling interface will be important in this project. Well, my point here is just describing what I need and hope to hear from people with more experience in all that stuff of what's already done and what I'd have to do myself. And how (i.e. which framework to use) to do it. To begin with, I've found a gallery demo and its source code (I think it was from here, but the link seems broken now). I guess it was made in SproutCore, which is what mobileme was based upon. Definitely with JQuery (which already seems a little slow). But I'm still missing two features there: the carousel and the fast zoom (it's just not as slow as the zoom in this demo with cappuccino). Then I've found a supposedly better one with a pretty good and similar zoom, that I'm not sure if it's using any framework and is already in php. Right now it'd be better having just the HTML, no server-side, since I'm building interface first. So, can anyone point directions? There are way too many options! Should I look for another solution closer to what I need, or try and tweak this one? I'm not familiar with any framework at all. Sorry for bringing this question that I will have to answer myself anyway sooner or later and sorry that I couldn't make this smaller. Thanks.

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• Python: Memory usage and optimization when modifying lists

  - by xApple

  The problem My concern is the following: I am storing a relativity large dataset in a classical python list and in order to process the data I must iterate over the list several times, perform some operations on the elements, and often pop an item out of the list. It seems that deleting one item out of a Python list costs O(N) since Python has to copy all the items above the element at hand down one place. Furthermore, since the number of items to delete is approximately proportional to the number of elements in the list this results in an O(N^2) algorithm. I am hoping to find a solution that is cost effective (time and memory-wise). I have studied what I could find on the internet and have summarized my different options below. Which one is the best candidate ? Keeping a local index: while processingdata: index = 0 while index < len(somelist): item = somelist[index] dosomestuff(item) if somecondition(item): del somelist[index] else: index += 1 This is the original solution I came up with. Not only is this not very elegant, but I am hoping there is better way to do it that remains time and memory efficient. Walking the list backwards: while processingdata: for i in xrange(len(somelist) - 1, -1, -1): dosomestuff(item) if somecondition(somelist, i): somelist.pop(i) This avoids incrementing an index variable but ultimately has the same cost as the original version. It also breaks the logic of dosomestuff(item) that wishes to process them in the same order as they appear in the original list. Making a new list: while processingdata: for i, item in enumerate(somelist): dosomestuff(item) newlist = [] for item in somelist: if somecondition(item): newlist.append(item) somelist = newlist gc.collect() This is a very naive strategy for eliminating elements from a list and requires lots of memory since an almost full copy of the list must be made. Using list comprehensions: while processingdata: for i, item in enumerate(somelist): dosomestuff(item) somelist[:] = [x for x in somelist if somecondition(x)] This is very elegant but under-the-cover it walks the whole list one more time and must copy most of the elements in it. My intuition is that this operation probably costs more than the original del statement at least memory wise. Keep in mind that somelist can be huge and that any solution that will iterate through it only once per run will probably always win. Using the filter function: while processingdata: for i, item in enumerate(somelist): dosomestuff(item) somelist = filter(lambda x: not subtle_condition(x), somelist) This also creates a new list occupying lots of RAM. Using the itertools' filter function: from itertools import ifilterfalse while processingdata: for item in itertools.ifilterfalse(somecondtion, somelist): dosomestuff(item) This version of the filter call does not create a new list but will not call dosomestuff on every item breaking the logic of the algorithm. I am including this example only for the purpose of creating an exhaustive list. Moving items up the list while walking while processingdata: index = 0 for item in somelist: dosomestuff(item) if not somecondition(item): somelist[index] = item index += 1 del somelist[index:] This is a subtle method that seems cost effective. I think it will move each item (or the pointer to each item ?) exactly once resulting in an O(N) algorithm. Finally, I hope Python will be intelligent enough to resize the list at the end without allocating memory for a new copy of the list. Not sure though. Abandoning Python lists: class Doubly_Linked_List: def __init__(self): self.first = None self.last = None self.n = 0 def __len__(self): return self.n def __iter__(self): return DLLIter(self) def iterator(self): return self.__iter__() def append(self, x): x = DLLElement(x) x.next = None if self.last is None: x.prev = None self.last = x self.first = x self.n = 1 else: x.prev = self.last x.prev.next = x self.last = x self.n += 1 class DLLElement: def __init__(self, x): self.next = None self.data = x self.prev = None class DLLIter: etc... This type of object resembles a python list in a limited way. However, deletion of an element is guaranteed O(1). I would not like to go here since this would require massive amounts of code refactoring almost everywhere.

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• Template problems: No matching function for call

  - by Nick Sweet

  I'm trying to create a template class, and when I define a non-member template function, I get the "No matching function for call to randvec()" error. I have a template class defined as: template <class T> class Vector { T x, y, z; public: //constructors Vector(); Vector(const T& x, const T& y, const T& z); Vector(const Vector& u); //accessors T getx() const; T gety() const; T getz() const; //mutators void setx(const T& x); void sety(const T& y); void setz(const T& z); //operations void operator-(); Vector plus(const Vector& v); Vector minus(const Vector& v); Vector cross(const Vector& v); T dot(const Vector& v); void times(const T& s); T length() const; //Vector<T>& randvec(); //operators Vector& operator=(const Vector& rhs); friend std::ostream& operator<< <T>(std::ostream&, const Vector<T>&); }; and the function in question, which I've defined after all those functions above, is: //random Vector template <class T> Vector<double>& randvec() { const int min=-10, max=10; Vector<double>* r = new Vector<double>; int randx, randy, randz, temp; const int bucket_size = RAND_MAX/(max-min +1); temp = rand(); //voodoo hackery do randx = (rand()/bucket_size)+min; while (randx < min || randx > max); r->setx(randx); do randy = (rand()/bucket_size)+min; while (randy < min || randy > max); r->sety(randy); do randz = (rand()/bucket_size)+min; while (randz < min || randz > max); r->setz(randz); return *r; } Yet, every time I call it in my main function using a line like: Vector<double> a(randvec()); I get that error. However, if I remove the template and define it using 'double' instead of 'T', the call to randvec() works perfectly. Why doesn't it recognize randvec()? P.S. Don't mind the bit labeled voodoo hackery - this is just a cheap hack so that I can get around another problem I encountered.

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• Can a conforming C implementation #define NULL to be something wacky

  - by janks

  I'm asking because of the discussion that's been provoked in this thread: http://stackoverflow.com/questions/2597142/when-was-the-null-macro-not-0/2597232 Trying to have a serious back-and-forth discussion using comments under other people's replies is not easy or fun. So I'd like to hear what our C experts think without being restricted to 500 characters at a time. The C standard has precious few words to say about NULL and null pointer constants. There's only two relevant sections that I can find. First: 3.2.2.3 Pointers An integral constant expression with the value 0, or such an expression cast to type void * , is called a null pointer constant. If a null pointer constant is assigned to or compared for equality to a pointer, the constant is converted to a pointer of that type. Such a pointer, called a null pointer, is guaranteed to compare unequal to a pointer to any object or function. and second: 4.1.5 Common definitions <stddef.h> The macros are NULL which expands to an implementation-defined null pointer constant; The question is, can NULL expand to an implementation-defined null pointer constant that is different from the ones enumerated in 3.2.2.3? In particular, could it be defined as: #define NULL __builtin_magic_null_pointer Or even: #define NULL ((void*)-1) My reading of 3.2.2.3 is that it specifies that an integral constant expression of 0, and an integral constant expression of 0 cast to type void* must be among the forms of null pointer constant that the implementation recognizes, but that it isn't meant to be an exhaustive list. I believe that the implementation is free to recognize other source constructs as null pointer constants, so long as no other rules are broken. So for example, it is provable that #define NULL (-1) is not a legal definition, because in if (NULL) do_stuff(); do_stuff() must not be called, whereas with if (-1) do_stuff(); do_stuff() must be called; since they are equivalent, this cannot be a legal definition of NULL. But the standard says that integer-to-pointer conversions (and vice-versa) are implementation-defined, therefore it could define the conversion of -1 to a pointer as a conversion that produces a null pointer. In which case if ((void*)-1) would evaluate to false, and all would be well. So what do other people think? I'd ask for everybody to especially keep in mind the "as-if" rule described in 2.1.2.3 Program execution. It's huge and somewhat roundabout, so I won't paste it here, but it essentially says that an implementation merely has to produce the same observable side-effects as are required of the abstract machine described by the standard. It says that any optimizations, transformations, or whatever else the compiler wants to do to your program are perfectly legal so long as the observable side-effects of the program aren't changed by them. So if you are looking to prove that a particular definition of NULL cannot be legal, you'll need to come up with a program that can prove it. Either one like mine that blatantly breaks other clauses in the standard, or one that can legally detect whatever magic the compiler has to do to make the strange NULL definition work. Steve Jessop found an example of way for a program to detect that NULL isn't defined to be one of the two forms of null pointer constants in 3.2.2.3, which is to stringize the constant: #define stringize_helper(x) #x #define stringize(x) stringize_helper(x) Using this macro, one could puts(stringize(NULL)); and "detect" that NULL does not expand to one of the forms in 3.2.2.3. Is that enough to render other definitions illegal? I just don't know. Thanks!

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