Multithreading Part I: Multithreading and Multitasking

In this and a series of articles that would follow, we would learn about threads and how to write multi-threaded programs in C#. 

In this article we would learn what threads are and why they are needed. In part2 we would learn about threading with respect to the .NET framework. At the end of this article series you would have learnt how to create and manage threads, set thread priorities, determine thread states, thread pooling and thread synchronization.

Introduction

When the computers were first invented, they were capable of executing one program at a time. Thus once one program was completely executed, they then picked the second one to execute and so on. With time, the concept of timesharing was developed whereby each program was given a specific amount of processor time and when its time got over the second program standing in queue was called upon (this is called Multitasking, and we would learn more about it soon). Each running program (called the process) had its own memory space, its own stack, heap and its own set of variables. One process could spawn another process, but once that occurred the two behaved independent of each other. Then the next big thing happened. The programs wanted to do more than one thing at the same time (this is called Multithreading, and we would learn what it is soon). A browser, for example, might want to download one file in one window, while it is trying to upload another and print some other file. This ability of a program to do multiple things simultaneously is implemented through threads (detailed description on threads follows soon).

Multitasking vs. Multithreading

As explained above, Multitasking is the ability of an operating system to execute more than one program simultaneously. Though we say so but in reality no two programs on a single processor machine can be executed at the same time. The CPU switches from one program to the next so quickly that appears as if all of the programs are executing at the same time. Multithreading is the ability of an operating system to execute the different parts of the program, called threads, simultaneously. The program has to be designed well so that the different threads do not interfere with each other. This concept helps to create scalable applications because you can add threads as and when needed. Individual programs are all isolated from each other in terms of their memory and data, but individual threads are not as they all share the same memory and data variables. Hence, implementing multitasking is relatively easier in an operating system than implementing multithreading.

Hey, wait!!! all that’s fine but I still do not understand fully what threads are!!!

Understanding Threading in .NET Framework

Summary

Thread basics using followings:

• How to Create thread; use System.Thread() class and create an instance

• How to Join thread; use object.Join() to join threads.

• How to Suspend thread; use object.Sleep(<No of seconds>) to Suspend thread

• How to Kill thread; use object.Abort() to Suspend thread

• Using Interlocked class which uses Increment and decrement method to increment and decrement values.

Thread Synchronization using followings:

• Using Locks: allows to mark a lock on the critical section of the code(program), provides synchronization to an object and then to execute the lock is in effect.

• Using Monitor: allows to decide when to enter and exit the synchronization, and it lets us wait for another area of code to become free. Monitor acts as a smart lock on a resource. When the we need synchronization, we can call the enter() method of the monitor passing the object we want to monitor. We can explicitly choose to wait () method of the monitor to control thread ordering. In case of using wait () waiting threads will be allowed to notified of a chance to run again if the active thread calls Pulse (). This signals the CLR that there has been a chance in the state that might free a thread that is waiting. The CLR tracks of the fact that the earlier thread asked to wait, and the thread will be guaranteed access in the order in which the wait where requested. Exit () can be called once when the thread is finished with the monitor.

Understanding Low-Lock Techniques in Multithreaded Apps

Understand the Impact of Low-Lock Techniques in Multithreaded Apps

Introduction to Multithreading in C#

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Introduction to Multithreading in C#

In working in New York and talking to programmers all over Wall Street, I’ve noticed a common thread of knowledge expected in most real time programming applications.  That knowledge is known as multithreading.  As I have migrated around the programming world, and performed interviews on potential programming candidates, it never ceases to amaze me how little is known about multithreading or why or how threading is applied.  In a series of excellent articles written by Vance Morrison, MSDN has tried to address this problem:  (See the August Issue of MSDN, What every Developer Must Know about Multithreaded Apps,  and the October issue Understand the Impact of Low-Lock Techniques in Multithreaded Apps. Also there are many articles here on C# Corner on threading such as Understanding Threading in the .NET Framework by Chandrakant Parmar or the four part series by Manisha Mehta: Multithreading Part 1: Multithreading and Multitasking,    Multithreading Part 2: Understanding the System.Threading.Thread Class,  Multithreading Part 3: Thread Synchronization, and Multithreading Part 4: The ThreadPool, Timer Classes and Asynchronous Programming Discussed.

In this article I will attempt to give an introductory discussion on threading, why it is used, and how you use it in .NET.  I hope to once and for all unveil the mystery behind multithreading, and in explaining it, help avert potential threading disasters in your code.

Self-Signed Certificates on IIS 7 – the Easy Way and the Most Effective Way | Demystifying The Code

Self-Signed Certificates on IIS 7 – the Easy Way and the Most Effective Way

Decrypting SSL traffic using Wireshark – Tom Decaluwé

Decrypting SSL traffic using Wireshark

Decrypting SSL traffic using Wireshark – Tom Decaluwé

Decrypting SSL traffic using Wireshark

Self-Signed Certificates on IIS 7 – the Easy Way and the Most Effective Way | Demystifying The Code

Self-Signed Certificates on IIS 7 – the Easy Way and the Most Effective Way

Supporting multiple sites with a single SSL Certificate « Binarymist

Using the appcmd utility

We now add the https binding and host information to our sites that need to share the wild card certificate.

Run a command prompt as administrator and

 

cd to %WINDIR%\system32\inetsrv

 

The format of the command looks like the following:

 

appcmd set site /site.name:"<your website name>" /+bindings.[protocol='https',bindingInformation='*:443:<your ssl domain>']

 

For our above three sites we wanted to use the same certificate,
mysane.site.com, myinsane.site.com, mycrazy.site.com
They may be named respectively:
mysane, myinsane, mycrazy
So for example,
we’d run the following commands:

 

appcmd set site /site.name:"mysane" /+bindings.[protocol='https',bindingInformation='*:443:mysane.site.com']

 

You should get feedback similar to the following:

 

SITE object "mysane.site.com" changed

 

if all goes well

 

appcmd set site /site.name:"myinsane" /+bindings.[protocol='https',bindingInformation='*:443:myinsane.site.com']

 

You should get feedback similar to the following:

 

SITE object "myinsane.site.com" changed

 

if all goes well

 

appcmd set site /site.name:"mycrazy" /+bindings.[protocol='https',bindingInformation='*:443:mycrazy.site.com']

 

You should get feedback similar to the following:

 

SITE object "mycrazy.site.com" changed

 

if all goes well

Although I normally keep it simple and name my sites the same as the URL (your ssl domain) I want to use.

IIS 6

Now this is a bit more work than with IIS 7.

If it’s not already installed, you’ll need the SelfSSL tool.
You can get this from the SSL Diagnostics Kit or the IIS 6.0 Resource Kit which contains lots of other stuff.
Once installed, run IIS.

Create the self signed wildcard certificate

You’ll need to generate the certificate for one existing IIS site.
For the first site take note of the site idendifier.
You can see this in the right pane when you select Web Sites from the server node in the IIS manager.
Open a command prompt, you’ll need to run the SelfSSL app.
Actually I think the easiest way to run this is Start menu -> All Programs -> IIS Resources -> SelfSSL -> SelfSSL.
The command string looks like this:

 

selfssl /n:cn=<your wild card domain> /s:<first website identifier> /P:<port you want to use> /v:<number of days to expiration>

 

So for example, we’d run the following command:

 

selfssl /n:cn=*.site.com /s:1 /P:443 /v:365

 

Options for SelfSSL

 

selfssl /?

 

some of them are:

/N: – This specifies the common name of the certificate. The computer name is used if there is no common name specified.
/K: – This specifies the key length of the certificate. The default is length 1024.
/V: – This specifies the amount of time the certificate will be valid for, calculated in days. The default setting is seven days.
/S: – This specifies the Identifier of the site, which we obtained earlier. The default will always be 1, which is the Default Web Site in IIS.

Assign the certificate to the sites that need it

Have a look at the site properties in IIS Manager -> Directory Security tab -> Server Certificate button.
This will start the IIS wizard.
Click Next -> Assign an existing certificate -> Next.
You should see the wild card certificate you created.
Select it, click next, and make sure you assign it the same port that was assigned to the first site.

Configure the SecureBindings

In order for IIS to use the host headers with SSL and secure the certificate as we did with appcmd,
you’ll need to run the following command for each of the sites that require it.
My adsutil is found in C:\Inetpub\AdminScripts\
It’s probably not in your path, so you’ll have to run it from location.

cscript adsutil.vbs set /w3svc/<website identifier>/SecureBindings ":443:<your ssl domain>"

 

So for example, we’d run the following command:

cscript adsutil.vbs set /w3svc/1/SecureBindings ":443:mysane.site.com"

 

That should be it.

Now if you need to remove a certificate from your store

Run mmc.exe

File menu -> Add/Remove Snap-in… -> Add… -> select Certificates -> Add -> select Computer account -> Next -> select Local computer -> Close -> Ok.
Select the Certificates node, expand Personal, Certificates.
Now in the right window pane, you can manage the certificates.
Delete, Renew etc.