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  • Python XMLRPC with concurrent requests

    - by MattB
    I'm looking for a way to prevent multiple hosts from issuing simultaneous commands to a Python XMLRPC listener. The listener is responsible for running scripts to perform tasks on that system that would fail if multiple users tried to issue these commands at the same time. Is there a way I can block all incoming requests until the single instance has completed?

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  • Implementing a robust async stream reader for a console

    - by Jon
    I recently provided an answer to this question: C# - Realtime console output redirection. As often happens, explaining stuff (here "stuff" was how I tackled a similar problem) leads you to greater understanding and/or, as is the case here, "oops" moments. I realized that my solution, as implemented, has a bug. The bug has little practical importance, but it has an extremely large importance to me as a developer: I can't rest easy knowing that my code has the potential to blow up. Squashing the bug is the purpose of this question. I apologize for the long intro, so let's get dirty. I wanted to build a class that allows me to receive input from a Stream in an event-based manner. The stream, in my scenario, is guaranteed to be a FileStream and there is also an associated StreamReader already present to leverage. The public interface of the class is this: public class MyStreamManager { public event EventHandler<ConsoleOutputReadEventArgs> StandardOutputRead; public void StartSendingEvents(); public void StopSendingEvents(); } Obviously this specific scenario has to do with a console's standard output. StartSendingEvents and StopSendingEvents do what they advertise; for the purposes of this discussion, we can assume that events are always being sent without loss of generality. The class uses these two fields internally: protected readonly StringBuilder inputAccumulator = new StringBuilder(); protected readonly byte[] buffer = new byte[256]; The functionality of the class is implemented in the methods below. To get the ball rolling: public void StartSendingEvents(); { this.stopAutomation = false; this.BeginReadAsync(); } To read data out of the Stream without blocking, and also without requiring a carriage return char, BeginRead is called: protected void BeginReadAsync() { if (!this.stopAutomation) { this.StandardOutput.BaseStream.BeginRead( this.buffer, 0, this.buffer.Length, this.ReadHappened, null); } } The challenging part: BeginRead requires using a buffer. This means that when reading from the stream, it is possible that the bytes available to read ("incoming chunk") are larger than the buffer. Since we are only handing off data from the stream to a consumer, and that consumer may well have inside knowledge about the size and/or format of these chunks, I want to call event subscribers exactly once for each chunk. Otherwise the abstraction breaks down and the subscribers have to buffer the incoming data and reconstruct the chunks themselves using said knowledge. This is much less convenient to the calling code, and detracts from the usefulness of my class. Edit: There are comments below correctly stating that since the data is coming from a stream, there is absolutely nothing that the receiver can infer about the structure of the data unless it is fully prepared to parse it. What I am trying to do here is leverage the "flush the output" "structure" that the owner of the console imparts while writing on it. I am prepared to assume (better: allow my caller to have the option to assume) that the OS will pass me the data written between two flushes of the stream in exactly one piece. To this end, if the buffer is full after EndRead, we don't send its contents to subscribers immediately but instead append them to a StringBuilder. The contents of the StringBuilder are only sent back whenever there is no more to read from the stream (thus preserving the chunks). private void ReadHappened(IAsyncResult asyncResult) { var bytesRead = this.StandardOutput.BaseStream.EndRead(asyncResult); if (bytesRead == 0) { this.OnAutomationStopped(); return; } var input = this.StandardOutput.CurrentEncoding.GetString( this.buffer, 0, bytesRead); this.inputAccumulator.Append(input); if (bytesRead < this.buffer.Length) { this.OnInputRead(); // only send back if we 're sure we got it all } this.BeginReadAsync(); // continue "looping" with BeginRead } After any read which is not enough to fill the buffer, all accumulated data is sent to the subscribers: private void OnInputRead() { var handler = this.StandardOutputRead; if (handler == null) { return; } handler(this, new ConsoleOutputReadEventArgs(this.inputAccumulator.ToString())); this.inputAccumulator.Clear(); } (I know that as long as there are no subscribers the data gets accumulated forever. This is a deliberate decision). The good This scheme works almost perfectly: Async functionality without spawning any threads Very convenient to the calling code (just subscribe to an event) Maintains the "chunkiness" of the data; this allows the calling code to use inside knowledge of the data without doing any extra work Is almost agnostic to the buffer size (it will work correctly with any size buffer irrespective of the data being read) The bad That last almost is a very big one. Consider what happens when there is an incoming chunk with length exactly equal to the size of the buffer. The chunk will be read and buffered, but the event will not be triggered. This will be followed up by a BeginRead that expects to find more data belonging to the current chunk in order to send it back all in one piece, but... there will be no more data in the stream. In fact, as long as data is put into the stream in chunks with length exactly equal to the buffer size, the data will be buffered and the event will never be triggered. This scenario may be highly unlikely to occur in practice, especially since we can pick any number for the buffer size, but the problem is there. Solution? Unfortunately, after checking the available methods on FileStream and StreamReader, I can't find anything which lets me peek into the stream while also allowing async methods to be used on it. One "solution" would be to have a thread wait on a ManualResetEvent after the "buffer filled" condition is detected. If the event is not signaled (by the async callback) in a small amount of time, then more data from the stream will not be forthcoming and the data accumulated so far should be sent to subscribers. However, this introduces the need for another thread, requires thread synchronization, and is plain inelegant. Specifying a timeout for BeginRead would also suffice (call back into my code every now and then so I can check if there's data to be sent back; most of the time there will not be anything to do, so I expect the performance hit to be negligible). But it looks like timeouts are not supported in FileStream. Since I imagine that async calls with timeouts are an option in bare Win32, another approach might be to PInvoke the hell out of the problem. But this is also undesirable as it will introduce complexity and simply be a pain to code. Is there an elegant way to get around the problem? Thanks for being patient enough to read all of this.

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  • Mysterious constraints problem with SQL Server 2000

    - by Ramon
    Hi all I'm getting the following error from a VB NET web application written in VS 2003, on framework 1.1. The web app is running on Windows Server 2000, IIS 5, and is reading from a SQL server 2000 database running on the same machine. System.Data.ConstraintException: Failed to enable constraints. One or more rows contain values violating non-null, unique, or foreign-key constraints. at System.Data.DataSet.FailedEnableConstraints() at System.Data.DataSet.EnableConstraints() at System.Data.DataSet.set_EnforceConstraints(Boolean value) at System.Data.DataTable.EndLoadData() at System.Data.Common.DbDataAdapter.FillFromReader(Object data, String srcTable, IDataReader dataReader, Int32 startRecord, Int32 maxRecords, DataColumn parentChapterColumn, Object parentChapterValue) at System.Data.Common.DbDataAdapter.Fill(DataSet dataSet, String srcTable, IDataReader dataReader, Int32 startRecord, Int32 maxRecords) at System.Data.Common.DbDataAdapter.FillFromCommand(Object data, Int32 startRecord, Int32 maxRecords, String srcTable, IDbCommand command, CommandBehavior behavior) at System.Data.Common.DbDataAdapter.Fill(DataSet dataSet, Int32 startRecord, Int32 maxRecords, String srcTable, IDbCommand command, CommandBehavior behavior) at System.Data.Common.DbDataAdapter.Fill(DataSet dataSet) The problem appears when the web app is under a high load. The system runs fine when volume is low, but when the number of requests becomes high, the system starts rejecting incoming requests with the above exception message. Once the problem appears, very few requests actually make it through and get processed normally, about 2 in every 30. The vast majority of requests fail, until a SQL Server restart or IIS reset is performed. The system then start processing requests normally, and after some time it starts throwing the same error. The error occurs when a data adapter runs the Fill() method against a SELECT statement, to populate a strongly-typed dataset. It appears that the dataset does not like the data it is given and throws this exception. This error occurs on various SELECT statements, acting on different tables. I have regenerated the dataset and checked the relevant constraints, as well as the table from which the data is read. Both the dataset definition and the data in the table are fine. Admittedly, the hardware running both the web app and SQL Server 2000 is seriously outdated, considering the numbers of incoming requests it currently receives. The amount of RAM consumed by SQL Server is dynamically allocated, and at peak times SQL Server can consume up to 2.8 GB out of a total of 3.5 GB on the server. At first I suspected some sort of index or database corruption, but after running DBCC CHECKDB, no errors were found in the database. So now I'm wondering whether this error is a result of the hardware limitations of the system. Is it possible for SQL Server to somehow mess up the data it's supposed to pass to the dataset, resulting in constraint violation due to, say, data type/length mismatch? I tried accessing the RowError messages of the data rows in the retrieved dataset tables but I kept getting empty strings. I know that HasErrors = true for the datatables in question. I have not set the EnableConstraints = false, and I don't want to do that. Thanks in advance. Ray

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  • Android: how to detect a private number programmatically

    - by Bao Le
    I use BroadcastReceiver to intercept incoming call on Android phone as below tm = (TelephonyManager) context.getSystemService(Context.TELEPHONY_SERVICE); Bundle bundle = intent.getExtras(); String number = bundle.getString(TelephonyManager.EXTRA_INCOMING_NUMBER); In the "private number" case, I tested on two devices, it shows the number as -1 on HTC Wildfire and -2 on Galaxy S. I checked the android.telephony.PhoneNumberUtils but it could't help me. Is there a function or a generic way to detect a private number on Android phone? Thanks

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  • Is it possible to parse a URL into it's composite components?

    - by Paul Alexander
    I'd like to parse an incoming URL into it's component parts for some pre-processing before passing it into the standard MVC routing logic. For example given your standard route {controller}/{action}/{id} and the URL /user/show/10 Is there a way to have the Routing system return a dictionary containing controller, action and id keys with their corresponding values?

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  • Having issues with setting up Inbound Email in SP2010

    - by Bill Daugherty
    I am having issues with setting up the Inbound Email with SP 2010. I have enabled the settings in Central Admin for Inbound Email, set up an MX record, added the IP to my Exchange Server, then created a new doc-lib in SP and i am still not seeing the "Incoming e-mail settings" option under communications in the doc-lib setup screen. Can someone let me know what I may be doing wrong, or missing?

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  • Wampserver Error

    - by Ryan
    Ok http://localhost/ won't load now. Recently I installed skype and am aware of the skype port conflict error. I have removed 'use port 80 and 443 as alternatives for incoming connections' from options and still no luck. I have also uninstalled skype, reinstalled it and restarted my machine several times to no avail. Also, I just tried to run my torrent client and I am getting an error for the first time. Any ideas? many thanks

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  • WCF port routing

    - by C james
    I have NAT which received incoming WCF requests and changes port number before it hands off to the host however, this is causing problem is there anyway to turn this off or fix? ex) wcf.service.com:80 - NAT - wcf.service.2522 !error Thank you.

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  • WCF Endpoint rounting

    - by Dmitriy Sosunov
    Hi, Guys, how to route inbound message between different endpoints. I need to expose the single endpoint that could accept different credentials. I guess, solve this by intercept the incoming message and based on message header then do forward message to appropriate endpoint. Thanks.

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  • Call into a website and use php to recognize caller ID

    - by Phil
    I have this idea where I want to allow someone to call a phone number from their cell phone, and then a website would display their caller ID. I want to do this in php, but I'm really not sure how. I'm pretty good with PHP and I'm assuming you need some kind of GSM modem attached to the web server to accept the incoming phone calls, but that's really as far as I can get. If anyone can point me in the right direction that would be great. Thanks!

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  • How to Join N live MP3 streams into one using FFMPEG?

    - by Ole Jak
    How to Join N live MP3 streams (radio streams like such live KCDX mp3 stream http://mp3.kcdx.com:8000/stream ) into 1 using FFMPEG? (I have N incoming live mp3 streams I want to join them and stream out 1 live mp3 stream) I mean I want to mix sounds like thay N speakers speak at the same time (btw N stereo to 1 mono), please help. BTW: My problem is mainly how to make FFMPEG read from stream not from file... Would you mind giving some code examples, please.

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  • Where to get pure C++ Lame MP3 encoder - PCM to MP3 example?

    - by Ole Jak
    So all I need is a simple function that sets it up (eating incoming PCM RATE (for example: rate near to 44100) It's channels (for example: 2) and -bits (for example: 16) and desirable 128 kb\s rate) and another one that takes PCM data and encodes it into pure MP3 frames. I know it looks like a silly homework task but I assure you - it is not. I hope it will be of help to all C++ developers starting with MP3s. So can anybody please help me with that?

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  • Django: What's the correct way to get the requesting IP address?

    - by swisstony
    I'm trying to develop an app using Django 1.1 on Webfaction. I'd like to get the IP address of the incoming request, but when I use request.META['REMOTE_ADDR'] it returns 127.0.0.1. There seems to be a number of different ways of getting the address, such as using HTTP_X_FORWARDED_FOR or plugging in some middleware called SetRemoteAddrFromForwardedFor. Just wondering what the best approach was?

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  • SOAP logging axis2

    - by salcin
    Using axis1 it is possible to log incoming/outgoing soap messages by adding logging on HTTPSender in log4j.properties. After migrating to axis2 (version 1.4.1) I have a hard time figuring out how to accomplish the same kind of logging. I have tried to add logging on the axis2 package and org.apache.commons.httpclient but no logging is provided. Any ideas? TIA

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