Posts categorized “.NET”


August 4, 2014
  A Handy C# Async Utility Method

In the course of writing C# code utilizing the new (for 4.5.1) Task-based asynchronous programming, I’ve run across a couple of places where the await keyword either is not allowed (a catch block or a property accessor) or the async keyword greatly complicates the syntax (lambda expressions). I’ve found myself writing this method for two different projects, and so I thought I would drop this Q&D, more-comments-than-code utility method here for others to use if you see the need.

(UPDATE: This works well in console applications; it can cause deadlocks in desktop and web apps. Test before you rely on it.)

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/// <summary>
/// Get the result of a task in contexts where the "await" keyword may be prohibited
/// </summary>
/// <typeparam name="T">The return type for the task</typeparam>
/// <param name="task">The task to be awaited</param>
/// <returns>The result of the task</returns>
public static T TaskResult<T>(Task<T> task)
{
Task.WaitAll(task);
return task.Result;
}

And, in places where you can’t do something like this…

ExampleClass.cs
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/// <summary>
/// A horribly contrived example class
/// </summary>
/// <remarks>Don't ever structure your POCOs this way, unless EF is handling the navigation properties</remarks>
public class ExampleClass
{
/// <summary>
/// A contrived ID to a dependent entity
/// </summary>
public int ForeignKeyID { get; set; }
/// <summary>
/// The contrived dependent entity
/// </summary>
public DependentEntity DependentEntity
{
get
{
// Does not compile; can't use await without async, can't mark a property as async
return await Data.DependentEntities
.FirstOrDefaultAsync(entity => entity.ID == ForeignKeyID);
}
}
}

…you can instead do this in that “DependentEntity” property…

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/// <summary>
/// The contrived dependent entity
/// </summary>
public DependentEntity DependentEntity
{
get
{
return UtilClass.TaskResult<DependentEntity>(Data.DependentEntities
.FirstOrDefaultAsync(entity => entity.ID == ForeignKeyID));
}
}
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October 22, 2011
  Database Abstraction v0.8

When we began developing C# web applications, we found ourselves in the position of determining what the best way of accessing the database is. We evaluated several technologies…

  • NHibernate - May be very good, but it was overkill for what we were trying to do.
  • LINQ to SQL - This brings C#’s LINQ (Language-Integrated Query) to SQL databases. You create database-aware classes and use LINQ to select from collections, which LINQ to SQL converts to database access. This is a good abstraction, but it relies on SQL Server; as we typically deploy to PostgreSQL, this didn’t work. (We also couldn’t get DBLinq, a database-agnostic implementation, to work.)
  • ADO.NET - This is the tried-and-true database access methodology, released as part of the initial release of the .NET framework. The downside to this is that it encourages SQL in the code at the point of data retrieval; it does not provide a clean separation of data access from data processing.
  • EF Code First - This didn’t exist; it’s also very SQL Server-centric. Not faulting Microsoft for that, especially since they release a free version now; but, as we deploy on Linux, until they release a Linux version, SQL Server is not an option.

With our PHP applications, we had written a database service that read queries from XML files. Then, queries were accessed by name, with parameters passed via arrays. The one thing that ADO.NET has that was useful was the fact that it is based on interfaces. This means that if we wrote something that exposed, manipulated, and depended on IDataConnection (instead of SqlConnection, the SQL Server implementation of that interface), we could support any implementation of database. The SqlDataReader implements IDataReader as well. Our solution was becoming apparent.

Over time, we developed what is now the Database Abstraction project hosted on CodePlex (UPDATE: migrated project to GitHub). On Thursday, we released the first public release (although the DLLs are in the repository, and are usually current at every commit). If you are looking for a way to separate your data access from the rest of your code, or want a solution that’s database-agnostic, check it out. It supports SQL Server, MySQL, PostgreSQL, SQLite, and ODBC connections , using the data provider name to derive the proper connection to implement. There is also a Mock implementation to support unit tests; this mock can provide data, providing a useful way to test methods. Finally, there is a membership and role provider based on Database Abstraction; simply configure the connection string, create the database tables, and away you go! *

A pre-release version is already in production use in our PrayerTracker application, and others are being built around it. If this sounds like something that could help your project, certainly feel free to check it out!

* Oracle is omitted from this list, as their DLL had redistribution restrictions; this meant that the source code repository, upon check-out, would have build errors. There may be an Oracle implementation in the future (it would be trivial), but there is not one now.

** The membership and role providers are untested; they will be tested and tweaked by version 0.9.

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August 24, 2011
  Tech Blog 3.0 (aka "You win, PHP...")

After a little over a year running on Tech Blog 2.0, you are now viewing version 3.0. For this version, we’ve returned to WordPress from BlogEngine. There are several issues that colluded to drive this change, most of which surrounded PHP and its crazy behavior. (Geeky details follow - skip to the paragraph starting with “Bottom line:” if you don’t want the geek stuff. I bolded it so it would be easy to spot.)

PHP’s recommended configuration is to run under Apache using the pre-fork multi-processing module (MPM). The advantage to this is that Apache does not have to spin off another process to handle each request; it handles it in the same thread. However, this means that each instance of the server must have all enabled modules loaded. This means that each instance of the server (AKA “thread”) is very large, so the number of threads run is lower (typically 5-15 in a server the size we’re on). Also, this means that each thread can only handle one request at a time; if you have 7 threads configured, each serving one of 7 requests, and an 8th request comes it, it has to wait for one to finish. If the requests are served quickly, this may not be a problem; however, the avalanche of request that follow the typical front-page mention on mega-blogs can easily overwhelm it.

To fix this problem, there is another MPM, this one called worker. In this scenario, there are spare thread waiting to fill requests, and these can spawn other threads to do further work if required. So, the Apache threads would realize that a request needs to be handled by PHP, and pass it off to that process to be completed. The Apache memory footprint is much smaller; it serves the images, scripts, and other static files, and passes off the requests that require heavy lifting. PHP, then, has a (FastCGI) process where it receives these requests, processes them, and returns the response to the caller. Because each of these threads only has to load the PHP requirements, they are smaller too, so you can have more threads processing at the same time; you just might survive that front-page mention! (This is the same technique applied by LightTPD and Nginx, two other servers I tried at various times.)

It is in this scenario where PHP fails to live up to its expectations. These PHP processes would simply stop responding, but the controller thinks they’re still there. The end result to the user is a site that just sits and waits for output that will never come. Eventually, they may receive a Gateway Timeout or Bad Gateway error. The problem is worse on slower sites, but even popular sites seemed to fall victim to this from time to time. This was also a problem whether PHP controlled its threads, or Apache controlled them.

The one thing that really perturbs me is instability. If something is broken, I can fix it; if it works, I can fix it ‘til it’s broke. :) But something that works sometimes, and other times doesn’t, simply won’t fly. I was able to introduce some stability by restarting the server 4 times a day, but that’s a band-aid, not a long term solution. I was tired of fighting.

Bottom line: the configuration required for a stable server is in opposition to a lean-and-mean configuration. So, I installed the required Apache modules, and will continue to run my PHP-serving server at a configuration twice as large as it needs to be. I’ll eventually move the Mono (.NET) processes to another machine, where the fast configuration won’t cause stability problems.

But, PHP isn’t all. While I would still heartily recommend BlogEngine.NET to someone who was going to serve the blog from a Windows machine, but I had some issues getting upgrades to go smoothly under Mono. It also is optimized for fast serving, at the expense of RAM. At this point, that’s not the tradeoff we need.

Finally, with this update, the blog has received its first new theme. It’s a clean, clear theme that should serve the content well. Plus, the social media icons up in the corner are just too cool, IMO. I’ve also applied tags to all posts except the “My Linux Adventure” series, and this theme displays them. (Comments are not here now, but will be migrated shortly.)

So, there you have it. Enjoy!

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September 3, 2010
  Mono / FastCGI Startup Script

We’ve begun running Mono on some Bit Badger Solutions servers to enable us to support the .NET environment, in addition to the PHP environment most of our other applications use. While Ubuntu has nice packages (and Badgerports even brings brought them up to the latest release), one thing that we were missing was a “conf.d”-type of configuration; my “/applications=” clause of the command was getting really, really long. We decided to see if we could create something similar to Apache / Nginx’s sites-available/sites-enabled paradigm, and we have succeeded!

To begin, you’ll need to create the directories /etc/mono/fcgi/apps-available and /etc/mono/fcgi/apps-enabled. These directories will hold files that will be used define applications. The intent of these directories is to put the actual files in apps-available, then symlink the ones that are enabled from apps-enabled. These files have no name restrictions, but do not put an extra newline character in them. The script will concatenate the contents of that file to create the MONO_FCGI_APPLICATIONS environment variable, which tells the server what applications exist. (The syntax is the same as that for the “/applications=” clause - [domain]:[URL path]:[filesystem path].) Here’s how the site you’re reading now is configured (from the file djs-consulting.com.techblog.conf)…

djs-consulting.com.techblog.conf
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techblog.djs-consulting.com:/:/path/to/install/base/for/this/site

Finally, what brings it all together is a shell script. This should be named “monoserve” and placed in /etc/init.d. (This borrows heavily from this script a script we found online, which we used until we wrote this one.) Note the group of variables surrounded by the “make changes here” notes - these are the values that are used in starting the server. They are at the top so that you can easily modify this for your own needs.

monoserve
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#/bin/bash
### BEGIN INIT INFO
# Provides: monoserve.sh
# Required-Start: $local_fs $syslog $remote_fs
# Required-Stop: $local_fs $syslog $remote_fs
# Default-Start: 2 3 4 5
# Default-Stop: 0 1 6
# Short-Description: Start FastCGI Mono server with hosts
### END INIT INFO
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
DAEMON=/usr/bin/mono
NAME=monoserver
DESC=monoserver
## Begin -- MAKE CHANGES HERE --
PROGRAM=fastcgi-mono-server2 # The program which will be started
ADDRESS=127.0.0.1 # The address on which the server will listen
PORT=9001 # The port on which the server will listen
USER=www-data # The user under which the process will run
GROUP=$USER # The group under which the process will run
## End -- MAKE CHANGES HERE --
# Determine the environment
MONOSERVER=$(which $PROGRAM)
MONOSERVER_PID=""
FCGI_CONFIG_DIR=/etc/mono/fcgi/apps-enabled
# Start up the Mono server
start_up() {
get_pid
if [ -z "$MONOSERVER_PID" ]; then
echo "Configured Applications"
echo "-----------------------"
# Construct the application list if the configuration directory exists
if [ -d $FCGI_CONFIG_DIR ]; then
MONO_FCGI_APPLICATIONS=""
for file in $( ls $FCGI_CONFIG_DIR ); do
if [ "$MONO_FCGI_APPLICATIONS" != "" ]; then
MONO_FCGI_APPLICATIONS=$MONO_FCGI_APPLICATIONS,
fi
MONO_FCGI_APPLICATIONS=$MONO_FCGI_APPLICATIONS`cat $FCGI_CONFIG_DIR/$file`
done
export MONO_FCGI_APPLICATIONS
echo -e ${MONO_FCGI_APPLICATIONS//,/"\n"}
else
echo "None (config directory $FCGI_CONFIG_DIR not found)"
fi
echo
# Start the server
start-stop-daemon -S -c $USER:$GROUP -x $MONOSERVER -- /socket=tcp:$ADDRESS:$PORT &
echo "Mono FastCGI Server $PROGRAM started as $USER on $ADDRESS:$PORT"
else
echo "Mono FastCGI Server is already running - PID $MONOSERVER_PID"
fi
}
# Shut down the Mono server
shut_down() {
get_pid
if [ -n "$MONOSERVER_PID" ]; then
kill $MONOSERVER_PID
echo "Mono FastCGI Server stopped"
else
echo "Mono FastCGI Server is not running"
fi
}
# Refresh the PID
get_pid() {
MONOSERVER_PID=$(ps auxf | grep $PROGRAM.exe | grep -v grep | awk '{print $2}')
}
case "$1" in
start)
start_up
;;
stop)
shut_down
;;
restart|force-reload)
shut_down
start_up
;;
status)
get_pid
if [ -z "$MONOSERVER_PID" ]; then
echo "Mono FastCGI Server is not running"
else
echo "Mono FastCGI Server is running - PID $MONOSERVER_PID"
fi
;;
*)
echo "Usage: monoserve (start|stop|restart|force-reload|status)"
;;
esac
exit 0

This needs to be owned by root and be executable (chmod +x monoserve). You can use update-rc.d monoserve defaults to set this to start at boot.

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August 5, 2010
  Tech Blog 2.0

After three years on WordPress, The Bit Badger Blog has moved to BlogEngine.NET. There are several reasons for this change, some technical and some not.

  • PHP’s Fast CGI processor has a problem where, if all of the processes are busy, the server will simply time out. While this hasn’t afflicted my server as much as others, it has caused problems; when this problem occurred, none of the PHP sites were accessible.
  • Through experience with a very heavily-used site, I became less enamored of WordPress’s “read from the database every time” way of doing business. I also found that various caching plug-ins for WordPress, on this particular site, did very little to ease the load.
  • Since I first looked at Mono (Linux’s implementation of the .NET framework), it has matured significantly. It supports most of C# 4.0 already, which was released earlier this year.
  • BlogEngine.NET is a rapidly-maturing blog platform, and the project has a stated goal of 100% compatibility with Mono. This is good, because you can mention Mono problems to the team, and you’re not dismissed because you’re running Linux.

As part of the move, the URL has changed; the new link is https://blog.bitbadger.solutions. I have implemented redirection for each post, the category and category feed links, and the main blog feed and home page from the old URL, so you may not have even realized that you’re looking at the new site. The Bit Badger Solutions Software Repository remains at https://hosted.djs-consulting.com/software/.

I’m looking forward to this new setup!

(NOTE: The next-to-last paragraph was updated with correct links as of February 2017.)

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