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RABiD BUNNY FEVER
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Results from my first high-load scalable system
Putting the cloud on a scale so it’s not so heavy

I’ve wanted to create and test a large-scale application for a very long time but have never really had the chance until recently. The Vintage Experience project I did earlier this year finally gave me the opportunity. As one of many parts of the project, I was tasked to create a voting system that could handle 1 million votes via a web page in a 30 second time span. The final system was deployed successfully without any problems for Gala Artis 2013 (a French Canadian artist/TV awards show). The following are the results of my implementation and testing.

The main front-end was done via a static HTML page (smart-phone optimized) that was hosted by Amazon S3, where handling 33k requests/second is a drop in the bucket. All voting requests were done via AJAX from this web page to backend servers hosted by Amazon EC2.

The backend was programmed in GoLang as a simple web server, optimized for memory and speed, which spawned a new goroutine for each incoming request. The request returned a message to the user stating either the error message, or success if the vote was added to the database. Each server held a single persistent MySQL connection to an Amazon RDS “Large DB Instance” with the minimum IOPS (1000). Votes from a server were sent to the database in batches once a second, or earlier if 10,000 votes had been received.

The servers were Amazon “M1 Standard Extra Large” (m1.xlarge) instances running Linux, of which there were 6 total, handling vote requests delegated by a round-robin DNS on Amazon’s Route 53. During stress testing, each server was found to be able to handle 6800 requests/second, and load was staying under 3, so there were was probably another bottle neck. Running the same tests using php(sapi)+apache(fork), only 4500 requests/second could be executed, and there was a 16+ load.

On the servers, I found it necessary to set the following sysctl setting to increase performance “net.core.somaxconn=1024”. The following commands need to be run to execute this:

sysctl 'net.core.somaxconn=1024' #Store for the current computer session
echo 'net.core.somaxconn=1024' >> /etc/sysctl.conf #Set after a reboot

Stress test client instances were also run on Amazon as m1.xlarge instances, and were found to be able to push 5000-6000 requests/second. The GoLang test clients spawned 200 requests at a time and waited for them to finish before sending the next batch. The client system needed the following sysctl settings for optimal performance:

net.ipv4.tcp_tw_recycle=1
net.ipv4.tcp_tw_reuse=1
net.ipv4.tcp_fin_timeout=30
net.ipv4.ip_local_port_range="15000 65534"
Installing PSLib for PHP
I was setting up a brand new server yesterday running Cent OS 6.4 and had the need to install PSLib (PostScript) for PHP.
The initial setup commands all worked as expected:
cd /src #A good directory to install stuff in. You may need to create it first

#Install intltool (required for pslib)
yum install intltool

#Install pslib
wget http://sourceforge.net/projects/pslib/files/latest/download?source=files
tar -xzvf pslib-*.tar.gz
cd pslib-*
./configure
make
make install
cd ..

#Install pslib wrapper for php
pecl download ps
tar -xzvf ps-*.tgz
cd ps-*
phpize
./configure
make

At this point, the make failed with
/src/ps-1.3.6/ps.c:58: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘ps_functions’

After a little bit of browsing the code and a really lucky first guess, I found that changing the following fixed the problem:
In ps.c change: “function_entry ps_functions[] = {” to “zend_function_entry ps_functions[] = {

Then to finish the install, just run:
make
make install
and you’re done!
Using Twitter API v1.1

Twitter recently turned off their v1.0 API which broke a multitude of applications, many of which are still broken today. I had the need to immediately update at least one website to the new Twitter v1.1 API, but I could not find a simple bare bones example on the internet. Pretty much all the code/libraries out there I could find for the new API version were hundreds to thousands of lines long, or didn’t work >.<; . So anywho, here is the simple PHP code I put together to make API calls.

This code requires certain consumer/authentication keys and secrets. You can find how to generate them elsewhere online.

//OAuth Request parameters
$ConsumerKey='FILL ME IN';
$ConsumerSecret='FILL ME IN';
$AccessToken='FILL ME IN';
$AccessTokenSecret='FILL ME IN';

function EncodeParam($input) { return strtr(rawurlencode($input), Array('+'=>' ', '%7E'=>'~')); }
function SendTwitterRequest($RequestURL, $Params=Array())
{
	//Compile the OAuth parameters
	global $ConsumerKey, $ConsumerSecret, $AccessToken, $AccessTokenSecret;
	$Params=array_merge(
		$Params,
		Array('oauth_version'=>'1.0', 'oauth_nonce'=>mt_rand(), 'oauth_timestamp'=>time(), 'oauth_consumer_key'=>$ConsumerKey, 'oauth_signature_method'=>'HMAC-SHA1'),
		isset($AccessToken) ? Array('oauth_token'=>$AccessToken) : Array()
	);
	uksort($Params, 'strcmp'); //Must be sorted to determine the signature
	foreach($Params as $Key => &$Val) //Create the url encoded parameter list
		$Val=EncodeParam($Key).'='.EncodeParam($Val);
	$Params=implode('&', $Params); //Combine the parameter list
	$Params.='&oauth_signature='.EncodeParam(base64_encode(hash_hmac('sha1', 'GET&'.EncodeParam($RequestURL).'&'.EncodeParam($Params), EncodeParam($ConsumerSecret).'&'.EncodeParam($AccessTokenSecret), TRUE)));

	//Do the OAuth request
	$CurlObj=curl_init();
	foreach(Array(CURLOPT_URL=>"$RequestURL?$Params", CURLOPT_SSL_VERIFYHOST=>0, CURLOPT_SSL_VERIFYPEER=>0, CURLOPT_RETURNTRANSFER=>1) as $Key => $CurlVal)
		curl_setopt($CurlObj, $Key, $CurlVal);
	$Result=curl_exec($CurlObj);
	curl_close($CurlObj);
	return $Result;
}

If you don’t have an AccessToken and AccessSecret yet, you can get them through the following code:
$OAuthResult=SendTwitterRequest('https://twitter.com/oauth/request_token');
parse_str($OAuthResult, $OauthRet);
if(!isset($OauthRet['oauth_token']))
	throw new Exception("OAuth error: $OAuthResult");
$AccessToken=$OauthRet['oauth_token'];
$AccessSecret=$OauthRet['oauth_token_secret'];

Here is an example to pull the last 4 tweets from a user:
$UserName='TheUserName';
$Result=json_decode(SendTwitterRequest('https://api.twitter.com/1.1/statuses/user_timeline.json', Array('screen_name'=>$UserName, 'count'=>4)));
if(isset($Result->{'errors'}))
	throw new Exception($Result->{'errors'}[0]->{'message'});
$Tweets=Array();
foreach($Result as $Tweet)
	$Tweets[]=$Tweet->text;

print implode('<br>', $Tweets);
JavaScript Cookies Functions

Just throwing these up here for reference. Simple JavaScript scripts to get and set cookies. Not particularly foolproof, robust, or fully featured.

function SetCookie(Name, Value, SecondsToExpire) { document.cookie=Name+"="+escape(Value)+"; expires="+new Date(new Date().getTime()+SecondsToExpire*1000).toUTCString(); }
function GetCookie(Name)
{
	var Match=document.cookie.match(new RegExp('(?:^|; ?)'+Name+'=(.*?)(?:;|$)'));
	return Match ? unescape(Match[1]) : null;
}
Converting Videos to HTML5 Formats

The following is a Linux script I threw together to convert an mpeg4 (.mp4, .mpv, .mpeg4, .mpg) file into ogg vorbis (.ogg, .ogv) and flash video (.flv) maintaining the same bit rate. It also doesn’t hurt to have a .webm format for some older devices. This assumes you already have the appropriate packages installed, including ffmpeg. The script also wasn’t made to be foolproof, and might not be able to read the bitrate on some videos. The script takes a list of mpeg4 files to convert.

for filename in "$@"
do
  extension="${filename##*.}"
  filename="${filename%.*}"

  export BITRATE=`ffmpeg -i $filename.$extension 2>&1 | grep -oP 'Video.*\d+ kb/s' | grep -oP '\d+ kb/s' | grep -oP '\d+'`
  ffmpeg2theora -V $BITRATE -o $filename.ogv $filename.$extension
  ffmpeg -i $filename.$extension -ar 44100 -b ${BITRATE}k -f flv $filename.flv #Add an optional "-threads #" to make this faster
done
Font size hack for Mac Web Browsers

Mac renders fonts differently than windows, which is a problem when trying to make cross-system compatible web pages. I've read in many places that using "em" instead of pixels fixes this problem, but sometimes using pixel based measurements is required for a project.

I found when testing a recent project's web page out on Apple's OSX that no matter what browser I used, the fonts were always 2px bigger than on windows, which threw off my layouts. So I used the simple JavaScript solution below (jQuery required). Note that this assumes all font sizes are in pixels. It might not hurt to add a check for that if you mix font size types.

$(document).ready(function() {
	if(/Macintosh/.test(navigator.userAgent))
		$.each(document.styleSheets, function(Indx, SS) {
			var rules=SS.cssRules || SS.rules;
			for(var i=0;i<rules.length;i++)
				if(rules[i].style && rules[i].style.fontSize!='')
					rules[i].style.fontSize=(parseInt(rules[i].style.fontSize, 10)-2)+'px';
});
Progress on Windows Logon Background Hacking
AND THEN I HOOKED THE MIGHTY OPCODE, AND SMOTE IT TO RUIN WITH INTERRUPTS AND NOTS!
Since my last post, I’ve made some progress in my spare time on working out how the windows logon screen displays the background. I’ve gotten to try out a lot of new tools, since I haven’t done anything like this in over 10 years, and quite frankly, I’m mostly disappointed. All the tools I already had seem to do the job better than anything new I could find (though, granted, I need to learn WinDBG more). So at this point I can debug the dll, while it’s running live in Windows, via the following process:
  1. Run the Windows Terminal Services hack (WinXP version explanation) so you can have multiple desktops running at once on the virtual machine, which makes things a little easier, but is not necessary.
  2. Make a backup of C:\Windows\System32\LogonUI.exe and made it editable (see previous post for risks and further info).
  3. Add an INT3 interrupt breakpoint near the beginning of LogonUI.exe. I just changed the first conditional jump in the dll startup code that is supposed to fail to an INT3, padded with NOPs.
  4. Set OllyDbg as the JIT debugger, so whenever LoginUI.exe is run and hits the interrupt, it automatically spawns OllyDbg and is attached.
  5. Tell windows to lock itself (Start>Shut Down>Lock [if available] or Win+L).
  6. As soon as OllyDbg is spawned with LoginUI.exe attached, also attach winlogon.exe in another debugger and keep it paused so it doesn’t keep trying to respawn LoginUI.exe when your attached copy doesn’t respond.

It would be nice if I could find an [easy] way to make a spawned process automatically go into my debugger without the need to add an interrupt, especially to a remote debugger, but oh well.

So my plan of action after this is to:
  1. Get the handle or memory location of where the image is stored by monitoring the GDI calls made after the text reference to C:\Windows\System32\oobe\info\backgrounds\backgroundDefault.jpg .
  2. Put a hardware breakpoint on that memory location/handle and find where it is used to draw to the screen background.
  3. At that point, the GDI call could be manipulated to not shrink the image to the primary monitor (easy), or multiple GDI calls could be made to each monitor for all the images (much harder).
The image might actually be shrunk before it is stored in memory too, though from what I’ve gleamed from the disassembly so far, I do not believe this to be the case.

More to come if and when I make progress.
Encoding & decoding HTML in JavaScript with jQuery

Here are a few functions I’ve been finding a lot of use for lately. They are basically the JavaScript equivalent for PHP’s htmlentities and html_entity_decode. These functions are useful for inserting HTML dynamically, and getting values of contentEditable fields. These functions do replace line breaks appropriately, and HTML2Text removes a trailing line break.


var TextTransformer=$('<div></div>');
function Text2HTML(T) { return TextTransformer.text(T).html().replace(/\r?\n/g, '<br>'); }
function HTML2Text(T) { return TextTransformer.html(ReplaceBreaks(T, "\x01br\x01")).text().replace(/\x01br\x01/g, "\n").replace(/\n$/, ''); }
function ReplaceBreaks(TheHTML, ReplaceText) { return TheHTML.replace(/<\s*br\s*\/?\s*>/g, ReplaceText || ' - '); }
Overcoming the 250KB Windows Login Background Cap

I had the need this year to upgrade to a 6+1 monitor setup for some of the work I’ve been doing.

Home Office 1

Home Office 2

It took me a bit to get everything how I wanted, using Display Fusion for multi monitor control, and a customized version of Window Manager for organizing window positioning. I am very happy with the final result.

However, there was one minor annoyance I decided to tackle as a fun get-back-into-reverse-engineering project (it’s been years since I’ve done any real fun programming, which saddens me greatly). When in the lock/logon screen for Windows 7, only one monitor can show a background, and that background must be limited to a filesize of 250KB, which can greatly reduce the quality of the image.

The C:\Windows\System32\authui.dll controls the lock screen behavior, so it is to this file I looked to for the solutions. Before I go on, there are 2 very important notes I should make:

  1. It can be very dangerous to modify system DLLs. This could crash your operating system, or even make it not able to load! Always backup the files you are modifying first, and make sure you are comfortable with restoring them somehow (most likely using a separate operating system like a Linux Boot CD).
  2. You need to make sure you are actually editing the right file when you open it up. While the file you want will always be in c:\Windows\System32, on 64-bit windows machines there is also a directory at c:\Windows\SysWOW64 that contains a 32-bit version of the file. (Brilliant naming scheme Microsoft! 32 bit files in the “64” directory and vice versa). Depending on the software you are using, sometimes when you try to access the authui.dll in the System32 directory (~1.84MB), it actually modifies the file in SysWOW64 (~1.71MB) using obfuscated Windows magic.

After a little bit of playing, so far I’ve solved the 250KB size limitation, and I plan on continuing to tinker with it a bit more until the other is solved too. To start, you will need to give yourself file system access to modify the c:\Windows\System32\authui.dll file. To do so, go into the file’s property page, change the owner to yourself, and then give appropriate user permissions so you can modify it as you see fit.

Open the authui.dll in your favorite hex editor and replace:
41 B9 00 E8 03 00
with
41 B9 FF FF FF 00
this essentially changes the size cap to ~16MB. However, I haven’t tested anything larger than 280KB yet. There is possibly a size limitation somewhere that may be dangerous to breech, but from what I gleam from the code; I do not think this is the case.

What this change actually does is update the 256,000 value to (2^24)-1 in the following code:
jmp __imp_GetFileSize
41 B9 00 E8 03 00mov r9d, 3E800h
41 3B C1cmp eax, r9d
jnb short loc_xxx

It’s been a bit tedious working on the assembly code of the authui.dll, as my favorite disassembler/debugger (ollydbg) does not work with 64-bit files, and I am not very comfortable with other dissasemblers I have tried. :-\ Alas. Hopefully more coming soon on this topic.

Transferring an Excel Spreadsheet to MySQL [Again]
Data manipulation primer

Sigh, I just realized after writing this post that I had already covered this topic... oh well, this version has some new information the other one is missing.


I find people very often asking me to move data from an Excel spreadsheet to a MySQL database, so I thought I’d write up the procedure I follow when doing so. This assumes no multi-line cells or tabs in the excel spreadsheet data.

  1. You need a good text editor with regular expression support. I highly recommend EditPad Pro (a free version is available too), and will be assuming you are using it for the steps below.
  2. Make sure all data in the Excel spreadsheet is formatted for SQL insertion, for example:
    To convert a date “mm/dd/yyyy” to SQL:
    1. Copy the entire row to your text editor
    2. Run the following regular expression replace:
      Find TextReplace Text
      ^(\d+)/(\d+)/(\d+)$$3-$1-$2
    3. Copy the text back to the spreadsheet row
  3. Copy all the data into the text editor, and run the following regular expressions:
    Find TextReplace TextExplanation
    \\\\\\Escape backslash
    '\\'Escape single quotation mark
    \t','Change separators so that all values are encased as strings
    ^('Line prefix to insert a row and stringify the first value
    $'),Line suffix to insert a row and stringify the last value
  4. Change the very last character on the last line from a comma to a semi colon to end the query
  5. Add the following to the top of the file:
    SET NAMES 'utf8' COLLATE 'utf8_general_ci';
    SET CHARACTER SET 'utf8';
    TRUNCATE TABLE TABLE_NAME;
    INSERT INTO TABLE_NAME (Field1, Field2, ...) VALUES
    		
  6. Make sure the file is saved as UTF8: Menu -> Convert -> Text Encoding -> (Encode the data with another character set ...) AND (Unicode, UTF-8)
  7. Make sure the file is saved with Unix line breaks: Menu -> Convert -> To Unix (LF Only)
  8. Save the file and run the following in your MySQL command line prompt to import it:
    \u DATABASE_NAME
    \. FILE_NAME
    		

There are of course easier solutions, but they can often be buggy, and I figured this is a good primer on regular expressions and simple data manipulation :-)

My MySQL Replication Ring Configuration

As of 2010, if you wanted to set up a MySQL replication configuration with multiple servers which could all update and send the updates to the other servers, a replication ring was the only solution (in which every server has a master and a slave in a ring configuration). While there are new (probably better) solutions as of late including using MariaDB’s multi-source replication, and tungsten-replicator (which I was referred to in late April and have not yet tried), I still find a replication ring to be an easy to use solution in some circumstances. However, there are some major disadvantages including:

  • If one node in the ring goes down, the entire ring stops replicating at that point until the node is brought back up
  • If a node goes down in the ring and has corrupted or incomplete data, say, from a power outdate, the entire ring may have to be painstakingly synced and rebuilt.
Anywho, the following is my basic MySQL configurations for setting up a replication ring, which needs to be put on every server node in the ring: (See MySQL docs for more information on each configuration)
[mysqld]
#---GENERAL REPLICATION VARIABLES--- (These should never change)
log_bin=mysql-bin.log                           #Turn on the binary log, which is used to hold queries that are propagated to other machines
slave-skip-errors               = 1062          #Do not stop replication if a duplicate key is found (which shouldn’t happen anyways). You may want to turn this off to verify integrity, but then your replication ring will stop if a duplicate key is found
#master-connect-retry           = 5             #How often to keep trying to reconnect to the master node of the current machine after a connection is lost. This has been removed as of MySQL 5.5, and needs to instead be included in the “CHANGE MASTER” command
sync_binlog                     = 100           #After how many queries, sync to the binlog
slave_net_timeout               = 120           #The number of seconds to wait for more data from a master/slave before restarting the connection
max_binlog_size                 = 1000M         #The maximum size the binlog can get before creating a new binlog
log-slave-updates                               #Log slave updates to the binary log. If there are only 2 nodes in the ring, this is not required
slave_exec_mode                 = IDEMPOTENT    #Suppression of duplicate-key and no-key-found errors
replicate-same-server-id        = 0             #Skip running SQL commands received via replication that were generated by the current server node

#---INDEPENDENT REPLICATION VARIABLES--- (These should change per setup)
binlog-do-db                   = DATABASE_NAME  #Only add statements from this database to the binlog. You can have multiple of these configurations
replicate-do-db                = DATABASE_NAME  #Only read statements from this database during replication. You can have multiple of these configurations
auto_increment_increment        = 2             #After ever auto-increment, add this to its number. Set this to the number of nodes. This helps assures no duplicate IDs

#---SERVER CONFIGURATION--- (These numbers should match)
server-id                       = 1             #The current node number in the ring. Every node needs to have its own incremental server number starting at 1
auto_increment_offset           = 1             #What to start auto-increment numbers at for this server. Set this to the server-id. This helps assures no duplicate IDs
Cygwin SIGINT fix for golang

Cygwin has had a long time problem that, depending on your configuration, may cause you to be unable to send a SIGINT (interrupt signal via Ctrl+C) to a native Windows command line executables. As a matter of fact, trying to do so may completely freeze up the console, requiring a process kill of the actual console, bash, and the executable you ran. This problem can crop up for many reasons including the version of Cygwin you are running and your terminal emulator. I specifically installed mintty as my default Cygwin console to get rid of this problem a long time ago (among many other features it had), and now it even has this problem.

While my normal solution is to try and steer clear of native Windows command line executables in Cygwin, this is not always an option. Golang was also causing me this problem every time I ran a network server, which was especially problematic as I would have to ALSO manually kill the server process or it would continue to hold the network port so another test of the code could not use it. An example piece of code is as follows:

package main
import ( "net/http"; "fmt" )
func main() {
	var HR HandleRequest
	if err := http.ListenAndServe("127.0.0.1:81", HR); err!=nil {
		fmt.Println("Error starting server") }
}

//Handle a server request
type HandleRequest struct{}
func (HR HandleRequest) ServeHTTP(w http.ResponseWriter, req *http.Request) {
	fmt.Printf("Received connection from: %s\n", req.RemoteAddr)
}
---
go run example.go

The first solution I found to this problem, which is by far the best solution, was to build the executable and then run it, instead of just running it straight from go.
go build example.go && example.exe
However, as of this post, it seems to no longer work! The last time I tested it and confirmed it was working was about 3 months ago, so who knows what has changed since then.

The second solution is to just build in some method of killing the process that uses “os.Exit”. For example, the following will exit if the user types “exit”
func ListenForExitCommand() {
	for s:=""; s!="exit"; { //Listen for the user to type exit
		if _, err:=fmt.Scanln(&s); err!=nil {
			if err.Error()!="unexpected newline" {
				fmt.Println(err) }
		} else if s=="flush" || s=="exit" {
			//Clean up everything here
		}
	}
	fmt.Println("Exit received, closing process")
	os.Exit(1)
}
and then add the following at the top of the main function:
go ListenForExitCommand() //Listen for "exit" command
HTML5 Video in Chrome for Android
It never ends when programming for browsers

Due to the facts of life and economic demand, a majority of the work I’ve been doing over the past 10 years has been web work (PHP, JavaScript, SQL, HTML, CSS). When I first started in this field, browser incompatibilities were a MAJOR problem, but nowadays, it’s incredibly rare for me to write a piece of code in one browser that doesn’t automatically work in all the others without bugs. Maybe it’s just the fact I’ve been doing this for so long that I know what to avoid, but I’d like to think it’s mostly because the browser makers have gotten their acts together and subscribe to making everything compatible by following [W3C] guidelines.

Browser incompatibilities still creep up from time to time though, and I’ll be writing up about a few of them in some of my upcoming posts. The majority and biggest problems I seem to run into nowadays revolve around mobiles.


So in Google Chrome for Android, when trying to include an HTML5 video, the “autoplay” HTML5 attribute seems to be ignored. The obvious less-than-optimal hack would be to just include a “.play()” call in JavaScript, but this seems to only work if the action is triggered by the user (like when trying to create a popup window). So as far as I can see right now, there is no way to autoplay a video in Google Chrome for Android.

UTF8 fix for iOS mail
Thanks apple</sarcasm>

Nowadays, it just makes sense to do everything in utf8 from the start. Most everything of consequence now supports it, it keeps byte count down for most anyone using an alphabet that is primarily latin, it is compatible with a old of older software, and can help lead to some useful shortcuts in programming. A very good number of libraries and languages even assume it as the default character encoding now.

It’s especially nice for html and web pages, so content can just be pasted in as-is, except of course for single and double quotes (which I always replace with ’ “ ” anyways) and < > &. However, I was recently thrown for a loop when my utf8 encoding was not being read correctly in Apple’s iOS mail client. After lots of testing and research, I came to the conclusion that it just plain doesn’t support utf-8 by default! I think I read somewhere you have to install foreign language packs to make it available, but that doesn’t help our normal latin-based-alphabet users.


The simple solution for diacritic (and other html encodable) characters is to just encode them as html: (only supported for php>=5.3.4)
function EncodeForIOS($String) //This assumes the following characters are already encoded (line 2): & < >
{
	$MailHTMLConvertArray=get_html_translation_table(HTML_ENTITIES, ENT_NOQUOTES, 'UTF-8');
	unset($MailHTMLConvertArray['&'], $MailHTMLConvertArray['<'], $MailHTMLConvertArray['>']);
	return strtr($String, $MailHTMLConvertArray);
}
Windows “ln” (symbolic linking) support for Cygwin
Cygwin requires lots of tweaks to really be usable
The “ln -s” command in Cygwin creates a fake symbolic link only supported in Cygwin. I whipped up the following script to create a true windows symbolic link that is supported in both Windows and Cygwin (it shows up as a symlink in Cygwin).
TARGET=`echo $1 | perl -pe 's/\\//\\\\/g'`; #Determine the target from the first parameter (where we are linking to). Change forward slashes to back slashes
LINK=`echo $2 | perl -pe 's/\\//\\\\/g'` #Determine the link name from the second parameter (where the symlink is made). Change forward slashes to back slashes
cmd /c mklink $3 $4 $5 $6 "$LINK" "$TARGET" #Perform the windows mklink command with optional extra parameters
Note that for the link name, you have to include the full filename, not just specify a directory.
See here for information on mklink and its switches. Specifically:
  • /d : directory symlink (more hard)
  • /j : directory junction (more soft)
This handles the problem a little more directly than my other post on the topic ("Symlinks in a Windows programming environment").

[Edit on 2016-01-12 @ 12:34am]
And once again, I have a new version of the code. This version has the following advantages:
  • No longer limited to just 4 extra parameters (dynamic instead of static)
  • Can now just specify your directory as the link location, and the filename will be automatically filled in
  • Handles spaces better
Do note, if you want to link directly to a hard drive letter, you must use "c:/" instead of "/cygdrive/c/"

#Get the target and link
TARGET="$1"
shift
LINK="$1"
shift

#If the link is already a directory, append the filename to the end of it
if [ -d "$LINK" ]; then
    #Get the file/directory name without the rest of the path
    ELEMENT_NAME=`echo "$TARGET" | perl -pe 's/^.*?\/([^\/]+)\/?$/$1/'`

    #Append the file name to the target, making sure there is only 1 separating "/"
    LINK=`echo "$LINK" | perl -pe 's/^(.*?)\/?$/$1/'`
    LINK="$LINK"/"$ELEMENT_NAME"
fi

#Replace forward slashes with back slashes
TARGET=`echo $TARGET | perl -pe 's/\\//\\\\/g'`
LINK=`echo $LINK | perl -pe 's/\\//\\\\/g'`

#Perform the windows mklink command with optional extra parameters
cmd /c mklink "$@" "$LINK" "$TARGET"
Thread synchronization in C#
Building the wheel that should have already existed

I have been working heavily in C# CE (Compact Edition) v2.0 for the last 2 years for clients, and one of the very many things that I was never really happy with (in at least that version of the language, though it looks like it might plague all versions of C#) is the available thread synchronization tools. I’ve come to love the lock/wait/notify model (in Java it’s synchronized/wait/notify and in Perl it’s lock/cond_wait/cond_signal), but I have found nothing as intuitive and safe to use in C#. To alleviate this, I went ahead and wrote my own ThreadLockAndWait class that achieves this functionality.


This works the same as the POSIX lock, unlock, cond_wait, cond_signal, and cond_timedwait functions, except:
  • Lock is not required before CondSignal (it does its own inner lock and unlock)
  • If ReacquireLockAfterWait is false, in which case CondWait will not lock again after signaled and just continue immediately
  • Only 1 thread can be CondWaiting at a time (If one is CondWaiting and is signaled but not reacquired the lock, its ok for another to start CondWaiting)

public class ThreadLockAndWait
{
	private Mutex TheLock=new Mutex(), CondWaitLock=new Mutex(); //CondWaitLock makes sure 1 thread stops waiting before the next one starts waiting
	private ManualResetEvent WaitTimer=new ManualResetEvent(false);
	private string OwnersThreadName=null;
	private int OwnerLockCount=0;

	public void Lock()
	{
		TheLock.WaitOne();
		if(OwnerLockCount++==0)
			OwnersThreadName=Thread.CurrentThread.Name;
	}
	public void UnLock()
	{
		TheLock.WaitOne();
		if(OwnerLockCount==0)
		{
			TheLock.ReleaseMutex();
			throw new Exception("Cannot unlock if not locked");
		}
		TheLock.ReleaseMutex();
		if(--OwnerLockCount==0)
			OwnersThreadName=null;
		TheLock.ReleaseMutex();
	}
	public void CondWait() { RealCondWait(-1, true); }
	public void CondWait(bool ReacquireLockAfterWait) { RealCondWait(-1, ReacquireLockAfterWait); }
	public void CondTimedWait(int TimeToWait) { RealCondWait(Math.Max(0, TimeToWait), true); }
	public void CondTimedWait(int TimeToWait, bool ReacquireLockAfterWait) { RealCondWait(Math.Max(0, TimeToWait), ReacquireLockAfterWait); }
	private void RealCondWait(int TimeToWait, bool ReacquireLockAfterWait)
	{
		//Prepare to wait
		TheLock.WaitOne();
		if(OwnerLockCount==0)
		{
			TheLock.ReleaseMutex();
			throw new Exception("Cannot wait if not locked");
		}
		CondWaitLock.WaitOne(); //Release this wait before the next one starts
		WaitTimer.Reset();
		TheLock.ReleaseMutex();

		//Release all locks
		int PreviousLockCount=OwnerLockCount;
		OwnersThreadName=null;
		OwnerLockCount=0;
		if(PreviousLockCount!=1)
			System.Diagnostics.Debug.Print("Warning, mutex has multiple locks from thread!");
		for(int i=0;i<PreviousLockCount;i++)
			TheLock.ReleaseMutex();

		//Wait
		if(TimeToWait>0)
			WaitTimer.WaitOne(TimeToWait, false);
		else if(TimeToWait!=0)
			WaitTimer.WaitOne();
		CondWaitLock.ReleaseMutex();

		//Reacquire lock
		if(!ReacquireLockAfterWait)
			return;
		for(int i=0;i<PreviousLockCount;i++)
			TheLock.WaitOne();
		OwnerLockCount=PreviousLockCount;
		OwnersThreadName=Thread.CurrentThread.Name;
	}

	public void CondSignal()
	{
		TheLock.WaitOne();
		WaitTimer.Set();
		TheLock.ReleaseMutex();
	}
}