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  • How to handle failure to release a resource which is contained in a smart pointer?

    - by cj
    How should an error during resource deallocation be handled, when the object representing the resource is contained in a shared pointer? Smart pointers are a useful tool to manage resources safely. Examples of such resources are memory, disk files, database connections, or network connections. // open a connection to the local HTTP port boost::shared_ptr<Socket> socket = Socket::connect("localhost:80"); In a typical scenario, the class encapsulating the resource should be noncopyable and polymorphic. A good way to support this is to provide a factory method returning a shared pointer, and declare all constructors non-public. The shared pointers can now be copied from and assigned to freely. The object is automatically destroyed when no reference to it remains, and the destructor then releases the resource. /** A TCP/IP connection. */ class Socket { public: static boost::shared_ptr<Socket> connect(const std::string& address); virtual ~Socket(); protected: Socket(const std::string& address); private: // not implemented Socket(const Socket&); Socket& operator=(const Socket&); }; But there is a problem with this approach. The destructor must not throw, so a failure to release the resource will remain undetected. A common way out of this problem is to add a public method to release the resource. class Socket { public: virtual void close(); // may throw // ... }; Unfortunately, this approach introduces another problem: Our objects may now contain resources which have already been released. This complicates the implementation of the resource class. Even worse, it makes it possible for clients of the class to use it incorrectly. The following example may seem far-fetched, but it is a common pitfall in multi-threaded code. socket->close(); // ... size_t nread = socket->read(&buffer[0], buffer.size()); // wrong use! Either we ensure that the resource is not released before the object is destroyed, thereby losing any way to deal with a failed resource deallocation. Or we provide a way to release the resource explicitly during the object's lifetime, thereby making it possible to use the resource class incorrectly. There is a way out of this dilemma. But the solution involves using a modified shared pointer class. These modifications are likely to be controversial. Typical shared pointer implementations, such as boost::shared_ptr, require that no exception be thrown when their object's destructor is called. Generally, no destructor should ever throw, so this is a reasonable requirement. These implementations also allow a custom deleter function to be specified, which is called in lieu of the destructor when no reference to the object remains. The no-throw requirement is extended to this custom deleter function. The rationale for this requirement is clear: The shared pointer's destructor must not throw. If the deleter function does not throw, nor will the shared pointer's destructor. However, the same holds for other member functions of the shared pointer which lead to resource deallocation, e.g. reset(): If resource deallocation fails, no exception can be thrown. The solution proposed here is to allow custom deleter functions to throw. This means that the modified shared pointer's destructor must catch exceptions thrown by the deleter function. On the other hand, member functions other than the destructor, e.g. reset(), shall not catch exceptions of the deleter function (and their implementation becomes somewhat more complicated). Here is the original example, using a throwing deleter function: /** A TCP/IP connection. */ class Socket { public: static SharedPtr<Socket> connect(const std::string& address); protected: Socket(const std::string& address); virtual Socket() { } private: struct Deleter; // not implemented Socket(const Socket&); Socket& operator=(const Socket&); }; struct Socket::Deleter { void operator()(Socket* socket) { // Close the connection. If an error occurs, delete the socket // and throw an exception. delete socket; } }; SharedPtr<Socket> Socket::connect(const std::string& address) { return SharedPtr<Socket>(new Socket(address), Deleter()); } We can now use reset() to free the resource explicitly. If there is still a reference to the resource in another thread or another part of the program, calling reset() will only decrement the reference count. If this is the last reference to the resource, the resource is released. If resource deallocation fails, an exception is thrown. SharedPtr<Socket> socket = Socket::connect("localhost:80"); // ... socket.reset();

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  • Storing database settings outside app.config

    - by Piers
    I've been writing a c# exe that will be running on a live web server, but I want to be able to test it on our staging server. Since the staging server has different database settings (in the app.config) from my localhost, is there any way I can store the connection string outside the app.config so that I can easily get to it? Also, is it possible to store the database connection string, then access it via the app.config? This might sound odd, but I'm using a dll from a CMS that uses the value in the .config file.

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  • How to retrieve all errors and messages from a query using ADO

    - by Johan Levin
    When a SQL batch returns more than one message from e.g. print statements, then I can only retrieve the first one using the ADO connection's Errors collection. How do I get the rest of the messages? If I run this script: Option Explicit Dim conn Set conn = CreateObject("ADODB.Connection") conn.Provider = "SQLOLEDB" conn.ConnectionString = "Data Source=(local);Integrated Security=SSPI;Initial Catalog=Master" conn.Open conn.Execute("print 'Foo'" & vbCrLf & "print 'Bar'" & vbCrLf & "raiserror ('xyz', 10, 127)") Dim error For Each error in conn.Errors MsgBox error.Description Next Then I only get "Foo" back, never "Bar" or "xyz". Is there a way to get the remaining messages?

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  • "SQL Server does not exist or access denied." upon VB.Net Deployment

    - by JasonMHirst
    Have built a small VB.Net app in VS2010. The connection string to the SQL Server is as follows: <connectionStrings> <add name="IWSR_DataDownloadWizard.My.MySettings.sqlConnection" connectionString="Provider=SQLOLEDB.1;Data Source=SQLServer;Integrated Security=SSPI;Initial Catalog=IWSROL" providerName="System.Data.OleDb" /> </connectionStrings> Within the VS2010 environment AND on my machine, the connection works perfectly, however when I deploy to clients I get an error message of: [DBNETLIB][ConnectionOpen (Connect()).]SQL Server does not exist or access denied. I've tried to search the net for solutions, have seen a few instances of people saying to NOT use the Server Name but the IP Address instead (this doesn't work) and some saying to remove the "Provider=SQLOLEDB.1", again this doesn't work. Can anyone suggest a solution please? Further information: Development System is Windows7 using VS2010 Deployment systems are a combination of Windows XP, Windows 2000 and Windows 7 SQL Server is SQL2000 (soon to be SQL2005). TIA

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  • Connecting Ingres from C

    - by avesus
    I need to connect to an Ingres supplied demodb through OpenAPI, both Ingres and C application running on windows. What i have done: Created a "node" in the Ingres Network Utility named "usernode". created user accounts in the Ingres installation (named "user" password "user") and in the Windows user management (the same creds.) Granted necessary privileges to the user in the database. In C code i have called IIapi_connect() function with an IIAPI_CONNPARM structure. Used members: co_target = "usernode::demodb", co_username = "user", co_password = "user" But IIapi_connect() call returns an error: "User provided a vnode as part of the database name (vnode::dbname), but connection information for that vnode is missing. Enter connection information for the vnode using NETUTIL." Anybody knows something that is a weird concept "node"? What are the minimum steps (in the database administration and the function parameters passing) necessary for the successful connect?

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  • Offline mode app in a (HTML5) browser possible?

    - by Horace Ho
    Is it possible to build an application inside in browser? An application means: 1 Where there is connection (online mode) between the browser and an remote application server: the application runs in typical web-based mode the application stores necessary data in offline storage, to be used in offline mode (2) the application sync/push data (captured during offline mode) back to the server when it is resumed from offline mode back to online mode 2 Where there is no connection (offline mode) between the browser and an remote application server: the application will still run (javascript?) the application will present data (which is stored offline) to user the application can accept input from user (and store/append in offline storage) Is this possible? If the answer is a yes, is there any (Ruby/Python/PHP) framework being built? Thanks

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  • How do I write sql data into a textbox after a submit type event

    - by Matt
    Finishing up some homework and Im having trouble with figuring out how to take information generated in sql column(a primary key set up to assign a record number to a customer example 1046) at submit and writing it to my redirected recipt page. I call it recipt.aspx. Any takers Professor says to use a datareader...but things go bad after that. public partial class _Default : System.Web.UI.Page { String cnStr = "EDITED FOR THE PURPOSE OF NOT DISPLAYED SQL SERVERta Source=111.11.111.11; uid=xxxxxxx; password=xxxx; database=xxxxxx; "; String insertStr; SqlDataReader reader; SqlConnection myConnection = new SqlConnection(); protected void submitbutton_Click(object sender, EventArgs e) { myConnection.ConnectionString = cnStr; try { //more magic happens as myConnection opens myConnection.Open(); insertStr = "insert into connectAssignment values ('" + TextBox2.Text + "','" + TextBox3.Text + "','" + TextBox4.Text + "','" + TextBox5.Text + "','" + bigtextthing.Text + "','" + DropDownList1.SelectedItem.Value + "')"; //magic happens as Connection string is assigned to connection object and passes in the SQL statment //associate the command to the the myConnection connection object SqlCommand cmd = new SqlCommand(insertStr, myConnection); cmd.ExecuteNonQuery(); Session["passmyvalue1"] = TextBox2.Text; Session["passmyvalue2"] = TextBox3.Text; Session["passmyvalue3"] = TextBox4.Text; Session["passmyvalue4"] = TextBox5.Text; Session["passmyvalue5"] = bigtextthing.Text; Session["I NEED SOME HELP RIGHT HERE"] =Textbox6.Text; Response.Redirect("receipt.aspx"); } catch { bigtextthing.Text = "Error submitting" + "Possible casues: Internet is down,server is down, check your settings!"; } finally { myConnection.Close(); TextBox2.Text = ""; TextBox3.Text = ""; TextBox4.Text = ""; TextBox5.Text = ""; bigtextthing.Text = ""; } //reset validators? } The recipt page public partial class _Default : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { if(Session["passmyvalue1"] != null) { TextBox1.Text = (string)Session["passmyvalue1"]; TextBox2.Text = (string)Session["passmyvalue2"]; TextBox3.Text = (string)Session["passmyvalue3"]; TextBox4.Text = (string)Session["passmyvalue4"]; TextBox5.Text = (string)Session["passmyvalue5"]; TextBox6.Text = I don't know ; } } } THanks for the help

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  • Abnormally disconnected TCP sockets and write timeout

    - by James
    Hello I will try to explain the problem in shortest possible words. I am using c++ builder 2010. I am using TIdTCPServer and sending voice packets to a list of connected clients. Everything works ok untill any client is disconnected abnormally, For example power failure etc. I can reproduce similar disconnect by cutting the ethernet connection of a connected client. So now we have a disconnected socket but as you know it is not yet detected at server side so server will continue to try to send data to that client too. But when server try to write data to that disconnected client ...... Write() or WriteLn() HANGS there in trying to write, It is like it is wating for somekind of Write timeout. This hangs the hole packet distribution process as a result creating a lag in data transmission to all other clients. After few seconds "Socket Connection Closed" Exception is raised and data flow continues. Here is the code try { EnterCriticalSection(&SlotListenersCriticalSection); for(int i=0;i<SlotListeners->Count;i++) { try { //Here the process will HANG for several seconds on a disconnected socket ((TIdContext*) SlotListeners->Objects[i])->Connection->IOHandler->WriteLn("Some DATA"); }catch(Exception &e) { SlotListeners->Delete(i); } } }__finally { LeaveCriticalSection(&SlotListenersCriticalSection); } Ok i already have a keep alive mechanism which disconnect the socket after n seconds of inactivity. But as you can imagine, still this mechnism cant sync exactly with this braodcasting loop because this braodcasting loop is running almost all the time. So is there any Write timeouts i can specify may be through iohandler or something ? I have seen many many threads about "Detecting disconnected tcp socket" but my problem is little different, i need to avoid that hangup for few seconds during the write attempt. So is there any solution ? Or should i consider using some different mechanism for such data broadcasting for example the broadcasting loop put the data packet in some kind of FIFO buffer and client threads continuously check for available data and pick and deliver it to themselves ? This way if one thread hangs it will not stop/delay the over all distribution thread. Any ideas please ? Thanks for your time and help. Regards Jams

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  • OracleDataAdapter returns no rows, but the query string works in SQLDeveloper

    - by belzebu
    visual studion 2008 oracle db 11.1.0.7 oracle client for .NET I have a relatively simple query, that selects the rows from across multiple tables (up to 4) using joins. OracleDataAdapter returns no rows for the only dataset's table, but if I copy and paste that query in SQLDeveloper then I get the desired results. I can get the data from other tables using the adapter with no problem, but it seems like it struggles with the bit longer selection query (string length is ~ 300 (not that much at all)) Connection string for the connection is 100% correct. Any ideas? thank you...

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  • MySQL parameter resource error

    - by Derek
    Here is my error: Warning: mysql_query() expects parameter 2 to be resource, null given... This refers to line 23 of my code which is: $result = mysql_query($sql, $connection) My entire query code looks like this: $query = "SELECT * from users WHERE userid='".intval( $_SESSION['SESS_USERID'] )."'"; $result = mysql_query($query, $connection) or die ("Couldn't perform query $query <br />".mysql_error()); $row = mysql_fetch_array($result); I don't have a clue what has happpened here. All I wanted to do was to have the value of the users 'fullname' displayed in the header section of my web page. So I am outputting this code immediately after to try and achieve this: echo 'Hello '; echo $row['fullname']; Before this change, I had it working perfectly, where the session variable of fullname was echoed $_SESSION['SESS_NAME']. However, because my user can update their information (including their name), I wanted the name displayed in the header to be updated accordingly, and not displaying the session value.

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  • Active Directory on local server and intranet on external server.

    - by cvack
    I have a local Active Directory server and a external web server where my intranet is located. $ad = ldap_connect("ldap://ip-address") or die("Couldn't connect to AD!"); ldap_set_option($ad, LDAP_OPT_PROTOCOL_VERSION, 3); $bd = ldap_bind( $ad, "user@domain", "password") or die("Can't bind to server."); When I run this on a local web server it succesfully binds the connection. If I run the same code on the external server its unable to bind the ldap connection. Both port 389 and 636 is open on the AD server. I've tried google for an answer, but all the tutorials is for Active Directory and webserver on the same server. Is this even possible?

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  • Proper abstraction of the database tier in a 3 tier system?

    - by Earlz
    Hello, I am creating a 3 tier application. Basically it goes Client - (through optional server to be a thin-client) - Business Logic - Database Layer And basically making it so that there is never any skipping around. As such, I want for all of the SQL queries and such to be in the Database Layer. Well, now I'm a bit confused. I made a few static classes to start off the database tier but what should I do for the database connections? Should I just create a new database connection anytime I enter the Database Layer or would that be wasteful? Does Connection.Open() take time whenever you have a ConnectionPool? To me, it just feels wrong for the Business tier to have to pass in a IdbConnection object to the Database tier. It seems like the Database tier should handle all of that DB-specific code. What do you think? How can I do it the proper way while staying practical?

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  • PHP and MySQLi close()

    - by Theopile
    Hello all. I am new to mysql and php, but am attempting to make my own cms to help make managing my websites easier. Can someone explain the mysqli's close() function. 1)Is it nesseccary? 2)What exactly does it do? 3)I heard that after php runs its script that it closes the connection, is that true? 4)Lastly, is there a security issue when not closing your connection to the database? Thanks

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  • UITableView Reload Data

    - by william-hu
    Hi, i used UITableView to show the info which was get for server. - (void)viewWillAppear:(BOOL)animated { //Create connection } Then i put the received data into array : NSSArray *dataFromServer: Then i want to show the data on each cell (some NSString object). As the connection was release, i call [self.tableView reloadData] , but cant work. So i'd like to know, how to make this? It means cellForRowAtIndexPath: has nothing at beginning, but after few seconds, shows something. Thank you so much!

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  • How to show / debug PEAR::DB errors in webpage?

    - by Markus Ossi
    I am connecting to MySQL database on my webpage and have this copy-pasted code for errors: if(DB::isError($db)) die($db->getMessage()); I have the connection code in an outside file called connection.inc that I include at the beginning of my page before the DOCTYPE and html tags. For debugging purposes, how can I print the database errors on my webpage? I thought I could do something like this: echo 'Could not connect to database. The error was:' . $db->getMessage(); but this returns: Fatal error: Call to undefined method DB_mysql::getMessage()

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  • how to use Thread in java ?

    - by tiendv
    Hi all i have code use googleseach API I want to use Thread to improve speed of my program. But i have a problem here is code import java.io.BufferedReader; import java.io.DataInputStream; import java.io.DataOutputStream; import java.io.InputStreamReader; import java.net.URL; import java.net.URLConnection; import java.net.URLEncoder; import java.util.ArrayList; import java.util.Enumeration; import java.util.Hashtable; import java.util.List; import org.json.JSONArray; import org.json.JSONObject; import com.yahoo.search.WebSearchResult; /** * Simple Search using Google ajax Web Services * * @author Daniel Jones Copyright 2006 Daniel Jones Licensed under BSD open * source license http://www.opensource.org/licenses/bsd-license.php */ public class GoogleSearchEngine extends Thread { private String queryString; private int maxResult; private ArrayList<String> resultGoogleArrayList = null; public ArrayList<String> getResultGoogleArrayList() { return resultGoogleArrayList; } public void setResultGoogleArrayList(ArrayList<String> resultGoogleArrayList) { this.resultGoogleArrayList = resultGoogleArrayList; } public String getQueryString() { return queryString; } public void setQueryString(String queryString) { this.queryString = queryString; } public int getMaxResult() { return maxResult; } public void setMaxResult(int maxResult) { this.maxResult = maxResult; } // Put your website here public final static String HTTP_REFERER = "http://www.example.com/"; public static ArrayList<String> makeQuery(String query, int maxResult) { ArrayList<String> finalArray = new ArrayList<String>(); ArrayList<String> returnArray = new ArrayList<String>(); try { query = URLEncoder.encode(query, "UTF-8"); int i = 0; String line = ""; StringBuilder builder = new StringBuilder(); while (true) { // Call GoogleAjaxAPI to submit the query URL url = new URL("http://ajax.googleapis.com/ajax/services/search/web?start=" + i + "&rsz=large&v=1.0&q=" + query); URLConnection connection = url.openConnection(); if (connection == null) { break; } // Value i to stop while or Max result if (i >= maxResult) { break; } connection.addRequestProperty("Referer", HTTP_REFERER); BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream(),"utf-8")); while ((line = reader.readLine()) != null) { builder.append(line); } String response = builder.toString(); JSONObject json = new JSONObject(response); JSONArray ja = json.getJSONObject("responseData").getJSONArray("results"); for (int j = 0; j < ja.length(); j++) { try { JSONObject k = ja.getJSONObject(j); // Break string into 2 parts: URL and Title by <br> returnArray.add(k.getString("url") + "<br>" + k.getString("titleNoFormatting")); } catch (Exception e) { e.printStackTrace(); } } i += 8; } // Remove objects that is over the max number result required if (returnArray.size() > maxResult) { for (int k=0; k<maxResult; k++){ finalArray.add(returnArray.get(k)); } } else return returnArray; return finalArray; } catch (Exception e) { e.printStackTrace(); } return null; } @Override public void run() { // TODO Auto-generated method stub //super.run(); this.resultGoogleArrayList = GoogleSearchEngine.makeQuery(queryString, maxResult); System.out.println("Code run here "); } public static void main(String[] args) { Thread test = new GoogleSearchEngine(); ((GoogleSearchEngine) test).setQueryString("data "); ((GoogleSearchEngine) test).setMaxResult(10); test.start(); ArrayList<String> returnGoogleArrayList = null; returnGoogleArrayList = ((GoogleSearchEngine) test).getResultGoogleArrayList(); System.out.print("contents of al:" + returnGoogleArrayList); } } when i run it, it can run into run method but it don't excute make query methor and return null array. when i do't use Thread it can nomal . Can you give me the reason why ? or give a sulution Thanks

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  • Which collation should I use to store these country names in MySQL?

    - by morpheous
    I am trying to store a list of countries in a mySQL database. I am having problems storing (non English) names like these: São Tomé and Príncipe República de El Salvador They are stored with strange characters in the db, (and therefore output strangely in my HTML pages). I have tried using different combinations of collations for the database and the MySQL connection collation: The "obvious" setting was to use utf8_unicode_ci for both the databse and the connection information. To my utter surprise, that did not solve the problem. Does anyone know how to resolve this issue?

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  • Is it possible to dynamically set a static string during *class* Initialisation?

    - by LonnieBest
    I'm trying to dynamically create a connection string during compile time: public static string ConnectionString { get { string connectionString = @"Data Source=" + myLibrary.common.GetExeDir() + @"\Database\db.sdf;"; return connectionString; } } I keep running into type initialisation errors. I was trying to avoid having to set the connection string for all applications that user my code library. The location of the database is different for each project that uses the library. I have code that can determine the correction string, but was wanting run it during compile time. Is this even possible?

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  • Regular expression and newline

    - by Ockonal
    Hello guys, I have such text: <[email protected]> If you do so, please include this problem report. <[email protected]> You can delete your own text from the attached returned message. The mail system <[email protected]>: connect to *.net[82.*.86.*]: Connection timed out I have to parse email from it. Could you help me with this job? upd There could be another email addresses in <%here%. There should be connection between 'The mail system' text. I need in email which goes after that text.

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  • J2ME's extra annoying HTTP permission prompt

    - by Hans Malherbe
    Some phones only prompt the user for permission the first time a connection is made. Others pop up the permission prompt whenever the MIDlet attempts to make a HTTP connection! What are the options if we want to suppress the prompt? Can we sign the JAR using only one CA (Certificate Authority) and have it work on all devices? Do we have to pay for a signature on every release? Is it an option to create our own CA certificate and tell our customers to install it on there device? Alternatively, it seems that plain socket connections do not suffer so. Is there a free implementation of HTTP on top of TCP for J2ME?

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  • http authenitcation in xcode

    - by user313100
    I am trying to make twitter work in my app and everything works fine except the code does not seem to recognize an error from twitter. If the username/password are not valid, I get an error message through this function: - (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data { NSString* strData = [[[NSString alloc] initWithBytes:[data bytes] length:[data length] encoding:NSASCIIStringEncoding] autorelease]; NSLog(@"Received data: %@", strData ) ; return ; } It prints: Received data: Could not authenticate you. . However, the app continues to the post a tweet view I have and ignores the error. Obviously, I do not have something setup right to detect such an error from twitter so my question is how do I get xcode to recognize an error like this? This uses basic http auth btw and don't mention anything about OAuth...just trying to get this to work for now.

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  • Check if server exists

    - by buhtla
    Here is the problem. User can enter server name and connection string for database. If server is not accessible (wrong address, firewalls or any other issue), I want to be aware of this as quickly as possible. If I'm using sqlConnection and try to connect to a non-accessible server this takes very long (I think more than 1 minute!). This has nothing to do with connection timeout btw so setting this property won't help. My idea is to first try to ping server and if I get response (which means server is accessible from the point of application), than proceed with sqlConnection. If there is no response from ping, operation is aborted and user is properly notified. Is there any better way of doing this? Any idea would be welcome.

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  • Oracle data provider hangs IIS worker process when web site is stopped

    - by Greg
    We're experiencing a nasty issue in Oracle 11g Release 2 where the w3wp process takes over and entire processor core, and debugging shows that the Oracle data provider is throwing ThreadAbortExceptions infinitely. A developer found this issue by doing the following: 1) Browse a web site that uses Oracle data connections locally (http://localhost/OracleWebSite) - we use IIS, not the ASP.NET dev server, for all of our sites. This ensures that the w3wp process is running and that an active Oracle pool of connections exists in the app pool. 2) Stop the web site (or perform a Rebuild All operation in Visual Studio on the web site in question). Our Oracle connection handling in the affected applications (all Oracle web apps) is well-established and robust. This issue does not occur if we disable connection pooling. This issue does not occur in Oracle 11g Release 1.

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  • Python, implementing proxy support for a socket based application (not urllib2)

    - by Terry Felkrow
    Hey guys, I am little stumped: I have a simple messenger client program (pure python, sockets), and I wanted to add proxy support (http/s, socks), however I am a little confused on how to go about it. I am assuming that the connection on the socket level will be done to the proxy server, at which point the headers should contain a CONNECT + destination IP (of the chat server) and authentication, (if proxy requires so), however the rest is a little beyond me. How is the subsequent connection handled, specifically the reading/writing, etc... Are there any guides on proxy support implementation for socket based (tcp) programming in Python? Thank you

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