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  • What is the point/purpose of Ruby EventMachine, Python Twisted, or JavaScript Node.js?

    - by CCw
    I don't understand what problem these frameworks solve. Are they replacements for a HTTP server like Apache HTTPD, Tomcat, Mongrel, etc? Or are they more? Why might I use them... some real world examples? I've seen endless examples of chat rooms and broadcast services, but don't see how this is any different than, for instance, setting up a Java program to open sockets and dispatch a thread for each request. I think I understand the non-blocking I/O, but I don't understand how that is any different than a multi-threaded web server.

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  • MongoDB: What's the point of using MapReduce without parallelism?

    - by netvope
    Quoting http://www.mongodb.org/display/DOCS/MapReduce#MapReduce-Parallelism As of right now, MapReduce jobs on a single mongod process are single threaded Without parallelism, what are the benefits of MapReduce compared to simpler or more traditional methods for queries and data aggregation? To avoid confusion: the question is NOT "what are the benefits of document-oriented DB over traditional relational DB"

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  • How to printf a time_t variable as a floating point number?

    - by soneangel
    Hi guys, I'm using a time_t variable in C (openMP enviroment) to keep cpu execution time...I define a float value sum_tot_time to sum time for all cpu's...I mean sum_tot_time is the sum of cpu's time_t values. The problem is that printing the value sum_tot_time it appear as an integer or long, by the way without its decimal part! I tried in these ways: to printf sum_tot_time as a double being a double value to printf sum_tot_time as float being a float value to printf sum_tot_time as double being a time_t value to printf sum_tot_time as float being a time_t value Please help me!!

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  • Ruby implementation of conversion between Latitude/Longitude and OS National Grid Reference point?

    - by Harry Wood
    For converting between Latitude/Longitude and UK's Ordnance Survey National Grid eastings and northings, this seems to be the most popular explanation and reference implementation in JavaScript: http://www.movable-type.co.uk/scripts/latlong-gridref.html The web is littered with other implementations in different languages. Making the conversion via PostGIS queries is another alternative. ...but did anyone implement this maths in ruby? OSGridToLatLong is the direction I'm looking for just at this moment, but I would have thought a library for converting in both directions must surely be available in a gem somewhere. I'm just not searching for the right thing.

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  • how to use iterator in c++?

    - by tsubasa
    I'm trying to calculate distance between 2 points. The 2 points I stored in a vector in c++: (0,0) and (1,1). I'm supposed to get results as 0 1.4 1.4 0 but the actual result that I got is 0 1 -1 0 I think there's something wrong with the way I use iterator in vector. Could somebody help? I posted the code below. typedef struct point { float x; float y; } point; float distance(point *p1, point *p2) { return sqrt((p1->x - p2->x)*(p1->x - p2->x) + (p1->y - p2->y)*(p1->y - p2->y)); } int main() { vector <point> po; point p1; p1.x=0; p1.y=0; point p2; p2.x=1; p2.y=1; po.push_back(p1); po.push_back(p2); vector <point>::iterator ii; vector <point>::iterator jj; for (ii=po.begin(); ii!=po.end(); ii++) { for (jj=po.begin(); jj!=po.end(); jj++) { cout<<distance(ii,jj)<<" "; } } return 0; }

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  • Is this a good starting point for iptables in Linux?

    - by sbrattla
    Hi, I'm new to iptables, and i've been trying to put together a firewall which purpose is to protect a web server. The below rules are the ones i've put together so far, and i would like to hear if the rules makes sense - and wether i've left out anything essential? In addition to port 80, i also need to have port 3306 (mysql) and 22 (ssh) open for external connections. Any feedback is highly appreciated! #!/bin/sh # Clear all existing rules. iptables -F # ACCEPT connections for loopback network connection, 127.0.0.1. iptables -A INPUT -i lo -j ACCEPT # ALLOW established traffic iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT # DROP packets that are NEW but does not have the SYN but set. iptables -A INPUT -p tcp ! --syn -m state --state NEW -j DROP # DROP fragmented packets, as there is no way to tell the source and destination ports of such a packet. iptables -A INPUT -f -j DROP # DROP packets with all tcp flags set (XMAS packets). iptables -A INPUT -p tcp --tcp-flags ALL ALL -j DROP # DROP packets with no tcp flags set (NULL packets). iptables -A INPUT -p tcp --tcp-flags ALL NONE -j DROP # ALLOW ssh traffic (and prevent against DoS attacks) iptables -A INPUT -p tcp --dport ssh -m limit --limit 1/s -j ACCEPT # ALLOW http traffic (and prevent against DoS attacks) iptables -A INPUT -p tcp --dport http -m limit --limit 5/s -j ACCEPT # ALLOW mysql traffic (and prevent against DoS attacks) iptables -A INPUT -p tcp --dport mysql -m limit --limit 25/s -j ACCEPT # DROP any other traffic. iptables -A INPUT -j DROP

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  • I'm having a problem identifying a floating point exception.

    - by Peter Stewart
    I'm using c++ in visual studio express to generate random expression trees for use in a genetic algorithm type of program. Because they are random, the trees often generate (I'll call them exceptions, I'm not sure what they are) Thanks to a suggestion by George, I turned the mask _MCW_EM on so that hardware interrupts are turned off. (the default) So, the program runs uninterrupted, but some of the values returned are: -1.#INF, -1.#NAN, -1.#INV. I don't know how to identify these so that I can throw an exeption: if ( variable == -1.#INF) ?? DigitalRoss in this post seemed to have the solution, but as I understood it I couldn't make it work. I've been looking all over the place for this simple bit of code, that I assumed would be used all the time, but have had no luck. thanks

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  • Fastest way to clamp a real (fixed/floating point) value?

    - by Niklas
    Hi, Is there a more efficient way to clamp real numbers than using if statements or ternary operators? I want to do this both for doubles and for a 32-bit fixpoint implementation (16.16). I'm not asking for code that can handle both cases; they will be handled in separate functions. Obviously, I can do something like: double clampedA; double a = calculate(); clampedA = a > MY_MAX ? MY_MAX : a; clampedA = a < MY_MIN ? MY_MIN : a; or double a = calculate(); double clampedA = a; if(clampedA > MY_MAX) clampedA = MY_MAX; else if(clampedA < MY_MIN) clampedA = MY_MIN; The fixpoint version would use functions/macros for comparisons. This is done in a performance-critical part of the code, so I'm looking for an as efficient way to do it as possible (which I suspect would involve bit-manipulation) EDIT: It has to be standard/portable C, platform-specific functionality is not of any interest here. Also, MY_MIN and MY_MAX are the same type as the value I want clamped (doubles in the examples above).

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  • Cannot use String.Empty as a default value for an optional parameter in C# - then what's the point?

    - by Mikeyg36
    I am reading Effective C# by Bill Wagner. In Item 14 - Minimize Duplicate Initialization Logic, he shows the following example of using the new optional parameters feature in a constructor: public MyClass(int initialCount = 0, string name = "") Notice that he used "" instead of string.Empty. He comments: You'll note [in an example above] that the second constructor specified "" for the default value on the name parameter, rather than the more customary string.Empty. That's because string.Empty is not a compile-time constant. It is a static property defined in the string class. Because it is not a compile constant, you cannot use it for the default value for a parameter. If we cannot use the string.Empty static in all situations, then doesn't that defeat the purpose of it? I thought that we would use it to be sure that we have a system-independent means of referring to the empty string. Is my understanding wrong? Thanks.

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  • Android - Get Notified when a new access point is added?

    - by Donal Rafferty
    I was wondering is it possible to get a notification of when a new configured network is added to the WifiManager in Android? I know you can get the current list of configured networks getConfiguredNetworks But is it possible to get notification of when a new one is added? I dont see anything in the WifiManager that would be helpful. Has anyone any other ideas? Or insight into how this could be achieved?

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  • Path with no slash after drive letter and colon - what does it point to?

    - by ya23
    I have mistyped a path and instead of c:\foo.txt wrote c:foo.txt. I expected it to either fail or to resolve to c:\foo.txt, but instead it seems to be resolved to foo.txt in a current user's home folder. Powershell returns: PS C:\> [System.IO.Path]::GetFullPath("c:\foo.txt") c:\foo.txt PS C:\> [System.IO.Path]::GetFullPath("c:foo.txt") C:\Users\Administrator\foo.txt PS C:\> [System.IO.Path]::GetFullPath("g:foo.txt") G:\foo.txt Running explorer.exe from commandline and passing it any of the above results in C:\Users\Administrator\Documents to be opened. I haven't found any documentation of that and I'm utterly confused, please explain the behaviour.

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  • Should we point to an NSManagedObject entity with weak instead of strong pointer?

    - by Jim Thio
    I think because NSManagedObject is managed by the managedObject context the pointer should be weak. Yet it often goes back to 0 in my cases. for (CategoryNearby * CN in sorted) { //[arrayOfItems addObject:[NSString stringWithFormat:@"%@ - %d",CN.name,[CN.order intValue]]]; NearbyShortcutTVC * tvc=[[NearbyShortcutTVC alloc]init]; tvc.categoryNearby =CN; // tvc.titleString=[NSString stringWithFormat:@"%@",CN.name]; // tvc.displayed=CN.displayed; [arrayOfItemsLocal addObject:tvc]; //CN PO(tvc); PO(tvc.categoryNearby); while (false); } self.arrayOfItems = arrayOfItemsLocal; PO(self.categoriesNearbyInArrayOfItems); [self.tableViewa reloadData]; ... Yet somewhere down the line: tvc.categoryNearby becomes nil. I do not know how or when or where it become nil. How do I debug this? Or should the reference be strong instead? This is the interface of NearbyShortcutTVC by the way @interface NearbyShortcutTVC : BGBaseTableViewCell{ } @property (weak, nonatomic) CategoryNearby * categoryNearby; @end To make sure that we're talking about the same object I print all the memory addresses of the NSArray They're both the exact same object. But somehow the categoryNearby property of the object is magically set to null somewhere. self.categoriesNearbyInArrayOfItems: ( 0x883bfe0, 0x8b6d420, 0x8b6f9f0, 0x8b71de0, 0xb073f90, 0xb061a10, 0xb06a880, 0x8b74940, 0x8b77110, 0x8b794e0, 0x8b7bf40, 0x8b7cef0, 0x8b7f4b0, 0x8b81a30, 0x88622d0, 0x8864e60, 0xb05c9a0 ) self.categoriesNearbyInArrayOfItems: ( 0x883bfe0, 0x8b6d420, 0x8b6f9f0, 0x8b71de0, 0xb073f90, 0xb061a10, 0xb06a880, 0x8b74940, 0x8b77110, 0x8b794e0, 0x8b7bf40, 0x8b7cef0, 0x8b7f4b0, 0x8b81a30, 0x88622d0, 0x8864e60, 0xb05c9a0 )

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  • How do I dynamically point an interface to a specific class at runtime?

    - by Jon
    As a simple example, I have an xml file with a list of names of classes which actually carry out the work and all implement interface IDoWork with a method Process(). I loop through the items in the xml file. How do I actually dynamically assign the class to the interface from a string name? e.g. var IDoWork = new "DoWorkType1"(); IDoWork.Process(); <work> <item id="DoWorkType1"> </item> <item id="DoWorkType2"> </item> </work> I want to achieve a plugin type architecture, except the plugin isn't at an assembly level only a class level within my program.

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  • How do you calculate div and mod of floating point numbers?

    - by boost
    In Perl, the % operator seems to assume integers. For instance: sub foo { my $n1 = shift; my $n2 = shift; print "perl's mod=" . $n1 % $n2, "\n"; my $res = $n1 / $n2; my $t = int($res); print "my div=$t", "\n"; $res = $res - $t; $res = $res * $n2; print "my mod=" . $res . "\n\n"; } foo( 3044.952963, 7.1 ); foo( 3044.952963, -7.1 ); foo( -3044.952963, 7.1 ); foo( -3044.952963, -7.1 ); gives perl's mod=6 my div=428 my mod=6.15296300000033 perl's mod=-1 my div=-428 my mod=6.15296300000033 perl's mod=1 my div=-428 my mod=-6.15296300000033 perl's mod=-6 my div=428 my mod=-6.15296300000033 Now as you can see, I've come up with a "solution" already for calculating div and mod. However, what I don't understand is what effect the sign of each argument should have on the result. Wouldn't the div always be positive, being the number of times n2 fits into n1? How's the arithmetic supposed to work in this situation?

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  • Classes. Whats the point?

    - by Ben Shelock
    I'm fairly new to OOP in PHP, I've made a couple of basic scripts but nothing impressive. All I've really taken from it is that it would probably be easier just make a collection of functions and include them. The structure of classes seems to just confuse what was otherwise a simple process. And in collating everything into a class it doesn't really add any functionality. So I'm clearly missing something. Could someone explain what functionality is added by creating classes

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