Search Results

Search found 24293 results on 972 pages for 'static ip'.

facebook twitter digg google delicious technorati stumbleupon myspace wordpress linkedin gmail igoogle windows live tumblr viadeo yahoo buzz yahoo mail yahoo bookmarks favorites email print

Page 153/972 | < Previous Page | 149 150 151 152 153 154 155 156 157 158 159 160  | Next Page >

  • What does this error mean (Can't create TCP/IP socket (24))?

    - by user105196
    I have web server with OS RHEL 6.2 and Mysql 5.5.23 on another server and the web server can read from Mysql server without problem, but some time I got this error: [Sun Sep 23 06:13:07 2012] [error] [client XXXXX] DBI connect('XXXX:192.168.1.2:3306','XXX',...) failed: Can't create TCP/IP socket (24) at /var/www/html/file.pm line 199. my question : What does this error mean (Can't create TCP/IP socket (24))? is it OS error or Mysql error ? perl -v This is perl, v5.10.1 (*) built for x86_64-linux-thread-multi mysql -V mysql Ver 14.14 Distrib 5.5.23, for Linux (x86_64) using readline 5.1 su - mysql -s /bin/bash -c 'ulimit -a' core file size (blocks, -c) 0 data seg size (kbytes, -d) unlimited scheduling priority (-e) 0 file size (blocks, -f) unlimited pending signals (-i) 127220 max locked memory (kbytes, -l) 64 max memory size (kbytes, -m) unlimited open files (-n) 1024 pipe size (512 bytes, -p) 8 POSIX message queues (bytes, -q) 819200 real-time priority (-r) 0 stack size (kbytes, -s) 10240 cpu time (seconds, -t) unlimited max user processes (-u) 1024 virtual memory (kbytes, -v) unlimited file locks (-x) unlimited

    Read the article

  • How do I prevent lighttpd from caching static files, even when modified on disk?

    - by Pixelastic
    I am using lighttpd to serve static files. I have a bunch of images in a dir that I regularly update. This will change the file content (and filesize) as well as the modification date, but not their filename. When I access the files through http, the updates are not taken into account and lighty serves the old file. I can manually rename the file to something different, then lighttpd will return a 404 error, and if I rename my file back, I will get the correct updated version. Seems like lightty is using some kind of cache mechanism of its own (which is fine) to return static files. Unfortunatly, it seems that this mechanism doesn't update itself when files are modified. I checked through Wireshark, and my browser is really doing a request to the file, this is not a browser caching issue. It returns a 200 OK when requesting it from an empty cache, and a 304 Not Modified otherwise, as expected. But the file is returned with a wrong Last-Modified header that do not reflect the real last modification date. Maybe there is some config directive that I am not aware of ? I would like the files returned by lighty to reflect the changes made on disk directly, or at least being able to invalidate its cache.

    Read the article

  • Access logs show someone "GET"ing a random ip, why does this return 200?

    - by Wilduck
    I have a small linux box set up with Apache as a way to teach myself Apache. I've set up port forwarding on my router so it's accessible from the outside world, and I've gotten a few strange requests for pages that don't exist from an ip address in China. Looking at my access_log shows that most of these return 404 errors, which I'm guessing is a good thing. However, there is one request that looks like this: 58.218.204.110 - - [25/Dec/2010:19:05:25 -600] "GET http://173.201.161.57/ HTTP/1.1" 200 3895 I'm curious what this request means... That ip address is unconnected to my server as far as I know, and visiting it simply tells me information about my uid. So, my questions are: How is it that this request is showing up in my access_log, why is it returning 200, and is this a bad thing (do I need to set up more security)?

    Read the article

  • Recommended Free DNS hosting for my webserve on a dynamic IP? [closed]

    - by JSchwartz
    I have finished a webserver project (for school) and the professor wants to be able to "test it" from home whenever he is free - this means I need to provide his with the URL to my webserver (which is fine). The only issue is that my IP-Address is dynamic (changes almost everyday) and I would rather not have to email him everytime - nor do I want him to try when it isn't working ... So I was looking into alternative solutions like DNS hosting (I hope that is the right terminology), so I could provide something static for him to connect to ... problem is I have never done this before... Are there any recommeneded free ones? Does Google or someone provide something good? I found http://www.no-ip.com/ which seems like it does what I want... Any feedback would be appreciated. Thanks,

    Read the article

  • Printer on different network(IP range), can i print to it?

    - by John
    Heres my situation, client PC is on the same network as the printer to start with: 192.168.1.X Thats fine and printing is fine, however our clients are required to connect to the VPN using the installed cisco client - this creates a virtual adapter and now the PC is connected to a 10.0.0.X IP range and can no longer see the printer, thus my problem! If I do an IPCONFIG/ALL the PC still has the 192.168.1.X address but it I can't ping anything on it. Is it possible to use both IP ranges at the same time?

    Read the article

  • I can't get an IP address from a VirtualBox VM on OSX from some routers (ie Internet cafes)

    - by ezrock
    On OSX 10.7.3, VirtualBox, using bridged adapter. Everything on the networking side works perfectly as expected in some networking environments, like my home router and some cafes. In others, I can't get an IP address over DHCP, and I don't know why. I suspect there is some setting on the router that is preventing me, or I have some issue with my MAC adress. When it's not working, in syslog, I'll see a few DHCPDISCOVER messages as my VM tries to find a DHCP server, and after a while, "No DHCPOFFERS received" And when I go to a "good" router, a simple "service network restart" is all I need to get an IP. Any ideas?

    Read the article

  • Class Loading Deadlocks

    - by tomas.nilsson
    Mattis follows up on his previous post with one more expose on Class Loading Deadlocks As I wrote in a previous post, the class loading mechanism in Java is very powerful. There are many advanced techniques you can use, and when used wrongly you can get into all sorts of trouble. But one of the sneakiest deadlocks you can run into when it comes to class loading doesn't require any home made class loaders or anything. All you need is classes depending on each other, and some bad luck. First of all, here are some basic facts about class loading: 1) If a thread needs to use a class that is not yet loaded, it will try to load that class 2) If another thread is already loading the class, the first thread will wait for the other thread to finish the loading 3) During the loading of a class, one thing that happens is that the <clinit method of a class is being run 4) The <clinit method initializes all static fields, and runs any static blocks in the class. Take the following class for example: class Foo { static Bar bar = new Bar(); static { System.out.println("Loading Foo"); } } The first time a thread needs to use the Foo class, the class will be initialized. The <clinit method will run, creating a new Bar object and printing "Loading Foo" But what happens if the Bar object has never been used before either? Well, then we will need to load that class as well, calling the Bar <clinit method as we go. Can you start to see the potential problem here? A hint is in fact #2 above. What if another thread is currently loading class Bar? The thread loading class Foo will have to wait for that thread to finish loading. But what happens if the <clinit method of class Bar tries to initialize a Foo object? That thread will have to wait for the first thread, and there we have the deadlock. Thread one is waiting for thread two to initialize class Bar, thread two is waiting for thread one to initialize class Foo. All that is needed for a class loading deadlock is static cross dependencies between two classes (and a multi threaded environment): class Foo { static Bar b = new Bar(); } class Bar { static Foo f = new Foo(); } If two threads cause these classes to be loaded at exactly the same time, we will have a deadlock. So, how do you avoid this? Well, one way is of course to not have these circular (static) dependencies. On the other hand, it can be very hard to detect these, and sometimes your design may depend on it. What you can do in that case is to make sure that the classes are first loaded single threadedly, for example during an initialization phase of your application. The following program shows this kind of deadlock. To help bad luck on the way, I added a one second sleep in the static block of the classes to trigger the unlucky timing. Notice that if you uncomment the "//Foo f = new Foo();" line in the main method, the class will be loaded single threadedly, and the program will terminate as it should. public class ClassLoadingDeadlock { // Start two threads. The first will instansiate a Foo object, // the second one will instansiate a Bar object. public static void main(String[] arg) { // Uncomment next line to stop the deadlock // Foo f = new Foo(); new Thread(new FooUser()).start(); new Thread(new BarUser()).start(); } } class FooUser implements Runnable { public void run() { System.out.println("FooUser causing class Foo to be loaded"); Foo f = new Foo(); System.out.println("FooUser done"); } } class BarUser implements Runnable { public void run() { System.out.println("BarUser causing class Bar to be loaded"); Bar b = new Bar(); System.out.println("BarUser done"); } } class Foo { static { // We are deadlock prone even without this sleep... // The sleep just makes us more deterministic try { Thread.sleep(1000); } catch(InterruptedException e) {} } static Bar b = new Bar(); } class Bar { static { try { Thread.sleep(1000); } catch(InterruptedException e) {} } static Foo f = new Foo(); }

    Read the article

  • Is the IP from the source or target in this System.Net.Sockets.SocketException?

    - by Jeremy Mullin
    I'm making an outbound connection using a DNS name to a server other than the localhost, and I get this exception: System.Net.WebException: Unable to connect to the remote server --- System.Net.Sockets.SocketException: No connection could be made because the target machine actively refused it 127.0.0.1:5555 The text implies that the TARGET machine refused the connection, but the IP address and port are from the localhost, which is kind of confusing. So is that IP address really the outgoing IP and port, even though the exception was caused by the target refusing the connection? Or is the exception from the local firewall blocking the outgoing connection?

    Read the article

  • "LNK2001: unresolved external symbol" when trying to build my program

    - by random
    I get the following error(s) on my program that captures the mouse and then draws a line. Errors: 1>------ Build started: Project: Capture_Mouse_Line, Configuration: Debug Win32 ------ 1> main.cpp 1>main.obj : error LNK2001: unresolved external symbol "public: static long * Line::yc2" (?yc2@Line@@2PAJA) 1>main.obj : error LNK2001: unresolved external symbol "public: static long * Line::xc2" (?xc2@Line@@2PAJA) 1>main.obj : error LNK2001: unresolved external symbol "public: static long * Line::yc1" (?yc1@Line@@2PAJA) 1>main.obj : error LNK2001: unresolved external symbol "public: static long * Line::xc1" (?xc1@Line@@2PAJA) 1>MSVCRTD.lib(crtexe.obj) : error LNK2019: unresolved external symbol _main referenced in function ___tmainCRTStartup 1>D:\Visual C++ Projects\Capture_Mouse_Line\Debug\Capture_Mouse_Line.exe : fatal error LNK1120: 5 unresolved externals ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ========== Here is my code: #include<allegro5\allegro.h> #include<allegro5\allegro_native_dialog.h> #include<allegro5\allegro_primitives.h> #include<Windows.h> #include<allegro5\allegro_windows.h> #ifndef WIDTH #define WIDTH 1440 #endif #ifndef HEIGHT #define HEIGHT 900 #endif class Line { public: static void ErasePreviousLine(); static void DrawLine(long* x, long* y,long* x2,long* y2); static bool Erasable(); static long* xc1; static long* yc1; static long* xc2; static long* yc2; }; void Line::ErasePreviousLine() { delete xc1; xc1 = NULL; delete yc1; yc1 = NULL; delete xc2; xc2 = NULL; delete yc2; yc2 = NULL; } bool Line::Erasable() { if(xc1 && yc1 && xc2 && yc2 == NULL) { return false; } else { return true; } } void Line::DrawLine(long* x,long* y,long* x2,long* y2) { if(!al_init_primitives_addon()) { al_show_native_message_box(NULL,NULL,NULL,"failed to initialize allegro", NULL,NULL); } xc1 = x; yc1 = y; xc2 = x2; yc2 = y2; al_draw_line((float)*xc1, (float)*yc1, (float)*xc2, (float)*yc2,al_map_rgb(255,0,255), 1); delete x; delete y; delete x2; delete y2; } LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam); int WINAPI WinMain(HINSTANCE hInstance,HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow) { MSG msg; ALLEGRO_DISPLAY* display = NULL; if(!al_init()) { al_show_native_message_box(NULL,NULL,NULL,"failed to initialize allegro", NULL,NULL); return -1; } display = al_create_display(WIDTH,HEIGHT); if(!display) { al_show_native_message_box(NULL,NULL,NULL,"failed to initialize display", NULL,NULL); return -1; } HWND hwnd = al_get_win_window_handle(display); if(hwnd == NULL) { MessageBox(NULL, "Window Creation Failed!", "Error!", MB_ICONEXCLAMATION | MB_OK); return 0; } ShowWindow(hwnd, nCmdShow); UpdateWindow(hwnd); while(GetMessage(&msg, NULL, 0, 0) > 0) { TranslateMessage(&msg); DispatchMessage(&msg); } return msg.wParam; } LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) { static bool bIsCaptured; static POINTS ptsBegin; static POINTS ptsEnd; switch(msg) { case WM_LBUTTONDOWN: SetCapture(hwnd); bIsCaptured = true; ptsBegin = MAKEPOINTS(lParam); return 0; case WM_MOUSEMOVE: if(wParam & MK_LBUTTON) { if(!Line::Erasable()) { return 0; } Line::ErasePreviousLine(); ptsEnd = MAKEPOINTS(lParam); Line::DrawLine(new long(ptsBegin.x),new long(ptsBegin.y),new long(ptsEnd.x),new long(ptsEnd.y)); } break; case WM_LBUTTONUP: bIsCaptured = false; ReleaseCapture(); break; case WM_ACTIVATEAPP: { if(wParam == TRUE) { if(bIsCaptured){ SetCapture(hwnd);} } } break; } return 0; }

    Read the article

  • Which database engines support IP addresses as a native type?

    - by Matt McClellan
    I'm trying to find databases with support for IP addresses as a native type (as opposed to storing as a string, or an unsigned integer, which at least one commenter has already pointed out won't work for IPv6). The primary reason I'm looking for this is ease of development. For example, sorting on a "native" IP address column would be correct (as opposed to when it's stored as a string). I would assume support for such a type would also include useful operations such as determining if an IP address is inside a specified network for use in WHERE clauses. The only one I'm aware of so far is PostgreSQL with its inet class. Does anyone have any others?

    Read the article

  • Interview Questions that can be asked on TCP/IP, UDP, Socket Programming ?

    - by Shantanu Gupta
    I am going for an interview day after tomorrow where i will be asked vaious questions related to TCP/IP and UDP. As of now i have prepared theoritical knowledge about it. But now I am looking up for gaining some practicle knowledge related to how it works in a network. What all is going in vaious .NET classes. I want to create a very small application like a chat or something that can make me all these concepts very much clear. Could you please suggest some questions related to TCP/IP that you generally ask or that you might have faced. How communication is going from server to client. Right now I am studying TcpClient, TcpListener and UdpClient Class but I want to implement all of them so as to get aware about its working. Is Chat application a Tcp/IP application ? I would appreciate your help.

    Read the article

  • Play 2.0 javaToDo tutorial doesn't compile

    - by chsn
    I'm trying to follow the Play2.0 JavaToDO tutorial and for some reason it just doesn't want to work. Have looked through stackoverflow and other online resources, but haven't find an answer to this and it's driving me crazy. Attached code of the Application.java package controllers; import models.Task; import play.data.Form; import play.mvc.Controller; import play.mvc.Result; public class Application extends Controller { static Form<Task> taskForm = form(Task.class); public static Result index() { return redirect(routes.Application.tasks()); } public static Result tasks() { return ok( views.html.index.render(Task.all(), taskForm)); } public static Result newTask() { return TODO; } public static Result deleteTask(Long id) { return TODO; } } Attached code of the Task java package models; import java.util.List; import javax.persistence.Entity; import play.data.Form; import play.data.validation.Constraints.Required; import play.db.ebean.Model.Finder; import play.mvc.Result; import controllers.routes; @Entity public class Task { public Long id; @Required public String label; // search public static Finder<Long,Task> find = new Finder( Long.class, Task.class); // display tasks public static List<Task> all() { return find.all(); } // create task public static void create(Task task) { task.create(task); } // delete task public static void delete(Long id) { find.ref(id).delete(id); // find.ref(id).delete(); } // create new task public static Result newTask() { Form<Task> filledForm = taskForm.bindFromRequest(); if(filledForm.hasErrors()) { return badRequest( views.html.index.render(Task.all(), filledForm) ); } else { Task.create(filledForm.get()); return redirect(routes.Application.tasks()); } } } I get a compile error on Task.java on the line static Form<Task> taskForm = form(Task.class); As I'm working on eclipse (the project is eclipsified before import), it's telling me that taskForm cannot be resolved and it also underlines every play 2 command e.g. "render(), redirect(), bindFromRequest()" asking me to create a method for it. Any ideas how to solve the compilations error and also how to get Eclipse to recognize the play2 commands? EDIT: updated Application.java package controllers; import models.Task; import play.data.Form; import play.mvc.Controller; import play.mvc.Result; public class Application extends Controller { // create new task public static Result newTask() { Form<Task> filledForm = form(Task.class).bindFromRequest(); if(filledForm.hasErrors()) { return badRequest( views.html.index.render(Task.all(), filledForm) ); } else { Task.newTask(filledForm.get()); return redirect(routes.Application.tasks()); } } public static Result index() { return redirect(routes.Application.tasks()); } public static Result tasks() { return ok( views.html.index.render(Task.all(), taskForm)); } public static Result deleteTask(Long id) { return TODO; } } Updated task.java package models; import java.util.List; import javax.persistence.Entity; import play.data.Form; import play.data.validation.Constraints.Required; import play.db.ebean.Model; import play.db.ebean.Model.Finder; import play.mvc.Result; import controllers.routes; @Entity public class Task extends Model { public Long id; @Required public String label; // Define a taskForm static Form<Task> taskForm = form(Task.class); // search public static Finder<Long,Task> find = new Finder( Long.class, Task.class); // display tasks public static List<Task> all() { return find.all(); } // create new task public static Result newTask(Task newTask) { save(task); } // delete task public static void delete(Long id) { find.ref(id).delete(id); // find.ref(id).delete(); } }

    Read the article

  • nginx problem accessing virtual hosts

    - by Sc0rian
    I am setting up nginx as a reverse proxy. The server runs on directadmin and lamp stack. I have nginx running on port 81. I can access all my sites (including virtual ips) on the port 81. However when I forward the traffic from port 80 to 81, the virtual ips have a message saying "Apache is running normally". Server IPs are fine, and I can still access virtual IP's on 81. [root@~]# netstat -an | grep LISTEN | egrep ":80|:81" tcp 0 0 <virtual ip>:81 0.0.0.0:* LISTEN tcp 0 0 <virtual ip>:81 0.0.0.0:* LISTEN tcp 0 0 <serverip>:81 0.0.0.0:* LISTEN tcp 0 0 :::80 :::* LISTEN apache 24090 0.6 1.3 29252 13612 ? S 18:34 0:00 /usr/sbin/httpd -k start -DSSL apache 24092 0.9 2.1 39584 22056 ? S 18:34 0:00 /usr/sbin/httpd -k start -DSSL apache 24096 0.2 1.9 35892 20256 ? S 18:34 0:00 /usr/sbin/httpd -k start -DSSL apache 24120 0.3 1.7 35752 17840 ? S 18:34 0:00 /usr/sbin/httpd -k start -DSSL apache 24495 0.0 1.4 30892 14756 ? S 18:35 0:00 /usr/sbin/httpd -k start -DSSL apache 24496 1.0 2.1 39892 22164 ? S 18:35 0:00 /usr/sbin/httpd -k start -DSSL apache 24516 1.5 3.6 55496 38040 ? S 18:35 0:00 /usr/sbin/httpd -k start -DSSL apache 24519 0.1 1.2 28996 13224 ? S 18:35 0:00 /usr/sbin/httpd -k start -DSSL apache 24521 2.7 4.0 58244 41984 ? S 18:35 0:00 /usr/sbin/httpd -k start -DSSL apache 24522 0.0 1.2 29124 12672 ? S 18:35 0:00 /usr/sbin/httpd -k start -DSSL apache 24524 0.0 1.1 28740 12364 ? S 18:35 0:00 /usr/sbin/httpd -k start -DSSL apache 24535 1.1 1.7 36008 17876 ? S 18:35 0:00 /usr/sbin/httpd -k start -DSSL apache 24536 0.0 1.1 28592 12084 ? S 18:35 0:00 /usr/sbin/httpd -k start -DSSL apache 24537 0.0 1.1 28592 12112 ? S 18:35 0:00 /usr/sbin/httpd -k start -DSSL apache 24539 0.0 0.0 0 0 ? Z 18:35 0:00 [httpd] <defunct> apache 24540 0.0 1.1 28592 11540 ? S 18:35 0:00 /usr/sbin/httpd -k start -DSSL apache 24541 0.0 1.1 28592 11548 ? S 18:35 0:00 /usr/sbin/httpd -k start -DSSL root 24548 0.0 0.0 4132 752 pts/0 R+ 18:35 0:00 egrep apache|nginx root 28238 0.0 0.0 19576 284 ? Ss May29 0:00 nginx: master process /usr/local/nginx/sbin/nginx -c /usr/local/nginx/conf/nginx.conf apache 28239 0.0 0.0 19888 804 ? S May29 0:00 nginx: worker process apache 28240 0.0 0.0 19888 548 ? S May29 0:00 nginx: worker process apache 28241 0.0 0.0 19736 484 ? S May29 0:00 nginx: cache manager process here is my nginx conf: cat /usr/local/nginx/conf/nginx.conf user apache apache; worker_processes 2; # Set it according to what your CPU have. 4 Cores = 4 worker_rlimit_nofile 8192; pid /var/run/nginx.pid; events { worker_connections 1024; } http { include mime.types; default_type application/octet-stream; log_format main '$remote_addr - $remote_user [$time_local] ' '"$request" $status $body_bytes_sent "$http_referer" ' '"$http_user_agent" "$http_x_forwarded_for"'; server_tokens off; access_log /var/log/nginx_access.log main; error_log /var/log/nginx_error.log debug; server_names_hash_bucket_size 64; sendfile on; tcp_nopush on; tcp_nodelay off; keepalive_timeout 30; gzip on; gzip_comp_level 9; gzip_proxied any; proxy_buffering on; proxy_cache_path /usr/local/nginx/proxy_temp levels=1:2 keys_zone=one:15m inactive=7d max_size=1000m; proxy_buffer_size 16k; proxy_buffers 100 8k; proxy_connect_timeout 60; proxy_send_timeout 60; proxy_read_timeout 60; server { listen <server ip>:81 default rcvbuf=8192 sndbuf=16384 backlog=32000; # Real IP here server_name <server host name> _; # "_" is for handle all hosts that are not described by server_name charset off; access_log /var/log/nginx_host_general.access.log main; location / { proxy_set_header Host $host; proxy_set_header X-Real-IP $remote_addr; proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; proxy_pass http://<server ip>; # Real IP here client_max_body_size 16m; client_body_buffer_size 128k; proxy_buffering on; proxy_connect_timeout 90; proxy_send_timeout 90; proxy_read_timeout 120; proxy_buffer_size 16k; proxy_buffers 32 32k; proxy_busy_buffers_size 64k; proxy_temp_file_write_size 64k; } location /nginx_status { stub_status on; access_log off; allow 127.0.0.1; deny all; } } include /usr/local/nginx/vhosts/*.conf; } here is my vhost conf: # cat /usr/local/nginx/vhosts/1.conf server { listen <virt ip>:81 default rcvbuf=8192 sndbuf=16384 backlog=32000; # Real IP here server_name <virt domain name>.com ; # "_" is for handle all hosts that are not described by server_name charset off; access_log /var/log/nginx_host_general.access.log main; location / { proxy_set_header Host $host; proxy_set_header X-Real-IP $remote_addr; proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; proxy_pass http://<virt ip>; # Real IP here client_max_body_size 16m; client_body_buffer_size 128k; proxy_buffering on; proxy_connect_timeout 90; proxy_send_timeout 90; proxy_read_timeout 120; proxy_buffer_size 16k; proxy_buffers 32 32k; proxy_busy_buffers_size 64k; proxy_temp_file_write_size 64k; } }

    Read the article

  • A ToDynamic() Extension Method For Fluent Reflection

    - by Dixin
    Recently I needed to demonstrate some code with reflection, but I felt it inconvenient and tedious. To simplify the reflection coding, I created a ToDynamic() extension method. The source code can be downloaded from here. Problem One example for complex reflection is in LINQ to SQL. The DataContext class has a property Privider, and this Provider has an Execute() method, which executes the query expression and returns the result. Assume this Execute() needs to be invoked to query SQL Server database, then the following code will be expected: using (NorthwindDataContext database = new NorthwindDataContext()) { // Constructs the query. IQueryable<Product> query = database.Products.Where(product => product.ProductID > 0) .OrderBy(product => product.ProductName) .Take(2); // Executes the query. Here reflection is required, // because Provider, Execute(), and ReturnValue are not public members. IEnumerable<Product> results = database.Provider.Execute(query.Expression).ReturnValue; // Processes the results. foreach (Product product in results) { Console.WriteLine("{0}, {1}", product.ProductID, product.ProductName); } } Of course, this code cannot compile. And, no one wants to write code like this. Again, this is just an example of complex reflection. using (NorthwindDataContext database = new NorthwindDataContext()) { // Constructs the query. IQueryable<Product> query = database.Products.Where(product => product.ProductID > 0) .OrderBy(product => product.ProductName) .Take(2); // database.Provider PropertyInfo providerProperty = database.GetType().GetProperty( "Provider", BindingFlags.NonPublic | BindingFlags.GetProperty | BindingFlags.Instance); object provider = providerProperty.GetValue(database, null); // database.Provider.Execute(query.Expression) // Here GetMethod() cannot be directly used, // because Execute() is a explicitly implemented interface method. Assembly assembly = Assembly.Load("System.Data.Linq"); Type providerType = assembly.GetTypes().SingleOrDefault( type => type.FullName == "System.Data.Linq.Provider.IProvider"); InterfaceMapping mapping = provider.GetType().GetInterfaceMap(providerType); MethodInfo executeMethod = mapping.InterfaceMethods.Single(method => method.Name == "Execute"); IExecuteResult executeResult = executeMethod.Invoke(provider, new object[] { query.Expression }) as IExecuteResult; // database.Provider.Execute(query.Expression).ReturnValue IEnumerable<Product> results = executeResult.ReturnValue as IEnumerable<Product>; // Processes the results. foreach (Product product in results) { Console.WriteLine("{0}, {1}", product.ProductID, product.ProductName); } } This may be not straight forward enough. So here a solution will implement fluent reflection with a ToDynamic() extension method: IEnumerable<Product> results = database.ToDynamic() // Starts fluent reflection. .Provider.Execute(query.Expression).ReturnValue; C# 4.0 dynamic In this kind of scenarios, it is easy to have dynamic in mind, which enables developer to write whatever code after a dot: using (NorthwindDataContext database = new NorthwindDataContext()) { // Constructs the query. IQueryable<Product> query = database.Products.Where(product => product.ProductID > 0) .OrderBy(product => product.ProductName) .Take(2); // database.Provider dynamic dynamicDatabase = database; dynamic results = dynamicDatabase.Provider.Execute(query).ReturnValue; } This throws a RuntimeBinderException at runtime: 'System.Data.Linq.DataContext.Provider' is inaccessible due to its protection level. Here dynamic is able find the specified member. So the next thing is just writing some custom code to access the found member. .NET 4.0 DynamicObject, and DynamicWrapper<T> Where to put the custom code for dynamic? The answer is DynamicObject’s derived class. I first heard of DynamicObject from Anders Hejlsberg's video in PDC2008. It is very powerful, providing useful virtual methods to be overridden, like: TryGetMember() TrySetMember() TryInvokeMember() etc.  (In 2008 they are called GetMember, SetMember, etc., with different signature.) For example, if dynamicDatabase is a DynamicObject, then the following code: dynamicDatabase.Provider will invoke dynamicDatabase.TryGetMember() to do the actual work, where custom code can be put into. Now create a type to inherit DynamicObject: public class DynamicWrapper<T> : DynamicObject { private readonly bool _isValueType; private readonly Type _type; private T _value; // Not readonly, for value type scenarios. public DynamicWrapper(ref T value) // Uses ref in case of value type. { if (value == null) { throw new ArgumentNullException("value"); } this._value = value; this._type = value.GetType(); this._isValueType = this._type.IsValueType; } public override bool TryGetMember(GetMemberBinder binder, out object result) { // Searches in current type's public and non-public properties. PropertyInfo property = this._type.GetTypeProperty(binder.Name); if (property != null) { result = property.GetValue(this._value, null).ToDynamic(); return true; } // Searches in explicitly implemented properties for interface. MethodInfo method = this._type.GetInterfaceMethod(string.Concat("get_", binder.Name), null); if (method != null) { result = method.Invoke(this._value, null).ToDynamic(); return true; } // Searches in current type's public and non-public fields. FieldInfo field = this._type.GetTypeField(binder.Name); if (field != null) { result = field.GetValue(this._value).ToDynamic(); return true; } // Searches in base type's public and non-public properties. property = this._type.GetBaseProperty(binder.Name); if (property != null) { result = property.GetValue(this._value, null).ToDynamic(); return true; } // Searches in base type's public and non-public fields. field = this._type.GetBaseField(binder.Name); if (field != null) { result = field.GetValue(this._value).ToDynamic(); return true; } // The specified member is not found. result = null; return false; } // Other overridden methods are not listed. } In the above code, GetTypeProperty(), GetInterfaceMethod(), GetTypeField(), GetBaseProperty(), and GetBaseField() are extension methods for Type class. For example: internal static class TypeExtensions { internal static FieldInfo GetBaseField(this Type type, string name) { Type @base = type.BaseType; if (@base == null) { return null; } return @base.GetTypeField(name) ?? @base.GetBaseField(name); } internal static PropertyInfo GetBaseProperty(this Type type, string name) { Type @base = type.BaseType; if (@base == null) { return null; } return @base.GetTypeProperty(name) ?? @base.GetBaseProperty(name); } internal static MethodInfo GetInterfaceMethod(this Type type, string name, params object[] args) { return type.GetInterfaces().Select(type.GetInterfaceMap).SelectMany(mapping => mapping.TargetMethods) .FirstOrDefault( method => method.Name.Split('.').Last().Equals(name, StringComparison.Ordinal) && method.GetParameters().Count() == args.Length && method.GetParameters().Select( (parameter, index) => parameter.ParameterType.IsAssignableFrom(args[index].GetType())).Aggregate( true, (a, b) => a && b)); } internal static FieldInfo GetTypeField(this Type type, string name) { return type.GetFields( BindingFlags.GetField | BindingFlags.Instance | BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic).FirstOrDefault( field => field.Name.Equals(name, StringComparison.Ordinal)); } internal static PropertyInfo GetTypeProperty(this Type type, string name) { return type.GetProperties( BindingFlags.GetProperty | BindingFlags.Instance | BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic).FirstOrDefault( property => property.Name.Equals(name, StringComparison.Ordinal)); } // Other extension methods are not listed. } So now, when invoked, TryGetMember() searches the specified member and invoke it. The code can be written like this: dynamic dynamicDatabase = new DynamicWrapper<NorthwindDataContext>(ref database); dynamic dynamicReturnValue = dynamicDatabase.Provider.Execute(query.Expression).ReturnValue; This greatly simplified reflection. ToDynamic() and fluent reflection To make it even more straight forward, A ToDynamic() method is provided: public static class DynamicWrapperExtensions { public static dynamic ToDynamic<T>(this T value) { return new DynamicWrapper<T>(ref value); } } and a ToStatic() method is provided to unwrap the value: public class DynamicWrapper<T> : DynamicObject { public T ToStatic() { return this._value; } } In the above TryGetMember() method, please notice it does not output the member’s value, but output a wrapped member value (that is, memberValue.ToDynamic()). This is very important to make the reflection fluent. Now the code becomes: IEnumerable<Product> results = database.ToDynamic() // Here starts fluent reflection. .Provider.Execute(query.Expression).ReturnValue .ToStatic(); // Unwraps to get the static value. With the help of TryConvert(): public class DynamicWrapper<T> : DynamicObject { public override bool TryConvert(ConvertBinder binder, out object result) { result = this._value; return true; } } ToStatic() can be omitted: IEnumerable<Product> results = database.ToDynamic() .Provider.Execute(query.Expression).ReturnValue; // Automatically converts to expected static value. Take a look at the reflection code at the beginning of this post again. Now it is much much simplified! Special scenarios In 90% of the scenarios ToDynamic() is enough. But there are some special scenarios. Access static members Using extension method ToDynamic() for accessing static members does not make sense. Instead, DynamicWrapper<T> has a parameterless constructor to handle these scenarios: public class DynamicWrapper<T> : DynamicObject { public DynamicWrapper() // For static. { this._type = typeof(T); this._isValueType = this._type.IsValueType; } } The reflection code should be like this: dynamic wrapper = new DynamicWrapper<StaticClass>(); int value = wrapper._value; int result = wrapper.PrivateMethod(); So accessing static member is also simple, and fluent of course. Change instances of value types Value type is much more complex. The main problem is, value type is copied when passing to a method as a parameter. This is why ref keyword is used for the constructor. That is, if a value type instance is passed to DynamicWrapper<T>, the instance itself will be stored in this._value of DynamicWrapper<T>. Without the ref keyword, when this._value is changed, the value type instance itself does not change. Consider FieldInfo.SetValue(). In the value type scenarios, invoking FieldInfo.SetValue(this._value, value) does not change this._value, because it changes the copy of this._value. I searched the Web and found a solution for setting the value of field: internal static class FieldInfoExtensions { internal static void SetValue<T>(this FieldInfo field, ref T obj, object value) { if (typeof(T).IsValueType) { field.SetValueDirect(__makeref(obj), value); // For value type. } else { field.SetValue(obj, value); // For reference type. } } } Here __makeref is a undocumented keyword of C#. But method invocation has problem. This is the source code of TryInvokeMember(): public override bool TryInvokeMember(InvokeMemberBinder binder, object[] args, out object result) { if (binder == null) { throw new ArgumentNullException("binder"); } MethodInfo method = this._type.GetTypeMethod(binder.Name, args) ?? this._type.GetInterfaceMethod(binder.Name, args) ?? this._type.GetBaseMethod(binder.Name, args); if (method != null) { // Oops! // If the returnValue is a struct, it is copied to heap. object resultValue = method.Invoke(this._value, args); // And result is a wrapper of that copied struct. result = new DynamicWrapper<object>(ref resultValue); return true; } result = null; return false; } If the returned value is of value type, it will definitely copied, because MethodInfo.Invoke() does return object. If changing the value of the result, the copied struct is changed instead of the original struct. And so is the property and index accessing. They are both actually method invocation. For less confusion, setting property and index are not allowed on struct. Conclusions The DynamicWrapper<T> provides a simplified solution for reflection programming. It works for normal classes (reference types), accessing both instance and static members. In most of the scenarios, just remember to invoke ToDynamic() method, and access whatever you want: StaticType result = someValue.ToDynamic()._field.Method().Property[index]; In some special scenarios which requires changing the value of a struct (value type), this DynamicWrapper<T> does not work perfectly. Only changing struct’s field value is supported. The source code can be downloaded from here, including a few unit test code.

    Read the article

  • Using static vs. member find method on a STL set?

    - by B Johnson
    I am using a set because, i want to use the quick look up property of a sorted container such as a set. I am wondering if I have to use the find member method to get the benefit of a sorted container, or can I also use the static find method in the STL algorithms? My hunch is that using the static version will use a linear search instead of a binary search like I want.

    Read the article

  • Why attached property Set and Get static methods are not called in XAML?

    - by JD
    Hi, I have set break points on my attached properties SetXXX and GetXXX static methods. In Xaml, I have assigned values to the attached property. However, I was expecting the Set or Get static methods to be called but they are not. The attached property works as expected and if I call SetXXX and GetXXX methods in code, then it works are expected. Why are the methods not called when set from Xaml? JD.

    Read the article

facebook twitter digg google delicious technorati stumbleupon myspace wordpress linkedin gmail igoogle windows live tumblr viadeo yahoo buzz yahoo mail yahoo bookmarks favorites email print

< Previous Page | 149 150 151 152 153 154 155 156 157 158 159 160  | Next Page >