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Thread-safety of static initializers in C#

Everyone says static initializers are thread-safe, but I'm worried about a particular detail.
Let's say I have
static class MyStaticClass
{
public static readonly object myField = MyOtherClass.GetNewObject();
}
static class MyOtherClass
{
public static object GetNewObject()
{ /* arbitrary code that returns a new object */ }
}
Which of the following does C# guarantee, when MyStaticClass.myField is not yet initialized?
If threads 1 and 2 try to access myField together (in that order), GetNewObject will have started executing before thread 2 reads myField.
If threads 1 and 2 try to access myField together (in that order), GetNewObject will have finished executing before thread 2 reads myField.
How about the CLR in general: if its guarantees differ from C#'s, in what ways do they differ?
Has the behavior changed in more recent versions of the .NET framework?
Note:
It's a tricky question, and I think a complete answer would probably mention the difference between a static constructor and a static initializer, and how they interact with beforefieldinit to produce the claimed result.

Case 2 will be honoured. A class field, property, or method cannot be dereferenced until the type has been initialized, and the type will not be initialized until the static constructor is completed. The static constructor is, to the best of my knowledge, therefore a blocking call.
http://msdn.microsoft.com/en-us/library/aa645612(v=vs.71).aspx
"The static constructor for a class executes at most once in a given application domain."
See this reply from Eric Lippert: https://stackoverflow.com/a/9399027/2420979 and note that "cctor" is IL for static constructor.
No cctors call MyMethod, directly or indirectly! Now is it ever possible for a static method like MyMethod to be called before the cctor of MyClass completes?
No.
Is that still true even if there are multiple threads involved?
Yes. The cctor will finish on one thread before the static method can be called on any thread.
Can the cctor be called more than once? Suppose two threads both cause the cctor to be run.
The cctor is guaranteed to be called at most once, no matter how many threads are involved. If two threads call MyMethod "at the same time" then they race. One of them loses the race and blocks until the MyClass cctor completes on the winning thread.

Taken from MSDN:
Static members are initialized before the static member is accessed for the first time and before the static constructor, if there is one, is called.
If you second method is run in two different threads but never use the static class, it will never be built. However, if there is a reference to it, it will be initialized before any of the two thread access it.

Static members and instance methods for multiple requests at the same time

If I define an object like a logger object as static in a class, then call a method like the following:
public class Manager
{
private static ClientLogManager log = new ClientLogManager();
public void Log(string Message)
{
log.Debug(string Message);
}
}
This is defined in a class library project.
My understanding is that the static variable is shared between all requests for this application, so the log object is shared. However the method Debug itself is not static, but the object is static, so there will be only one instance of this method. Is that correct?
If a lot of users are calling this code at the same time, if 2 requests are calling the log.Debug method at the same time, can the message of the 2nd request overwrite the message of the 1st request?
Also, is it better to replace this with a Singleton? wouldn't it be one Singleton object per request?
Here is the ClientLogManager code
public class ClientLogManager
{
#region Member Variables
private static readonly ILog _log = LogManager.GetLogger(typeof(ClientLogManager));
#endregion
#region Constructors
public ClientLogManager()
{
}
#endregion
#region Public Methods
public void Debug(string message)
{
_log.Debug(message);
}
#endregion
}

If a lot of users are calling this code at the same time, if 2 requests are calling the log.Debug method at the same time, can the message of the 2nd request overwrite the message of the 1st request?
Yes, unless the logger is specifically written to support this. Most loggers are designed to support this, so unless you rolled your own from scratch chances are it will synchronize all writes internally (so that you don't have to). If you are unsure you should check the documentation for the specific logger you are using to see if it will support or break when written to simultaneously.

"My understanding is that the static variable is shared between all requests for this application, so the log object is shared."
Correct, there exists only 1 instance of a static member per AppDomain.
"However the method Debug itself is not static, but the object is static, so there will be only one instance of this method. Is that correct?"
The statement in itself is correct, but...
What it boils down to is this:
Both static and instance methods "exist" only once in memory, the difference is that
a static method does not need an instance of the class it's declared on in order to
be executed, whereas an instance method does.
If multiple requests can be handled concurrently, they have to be executed on different
threads. Each thread has its own call stack, and if you use a thread to perform a method
call on, the arguments passed to that method are placed on the call stack of that thread.
This means that, as long as the argument is either a valuetype (such as an int) or an
immutable type (such as in this case, a string) it cannot be modified by another thread
(because it is either not visible from another thread, or not modifyable).
Hence, you don't have to worry that the messages get mixed up inside your Manager.Log() or ClientLogManager.Debug() method.
So, both your current Manager and ClientLogManager implementations are thread-safe (at least, if the _log instance is thread-safe).
Once you start declaring non-static member variables in your Manager class, and
you're going to use them in Manager.Log(), then it is no longer thread-safe:
The same Manager instance could then be accessed by multiple threads, and once they
all start writing in the same member variable, you're in trouble...
I hope this clarifies things a bit.

Why should the Main() method be static?

I tried to create public void Main() in C#; it says no static void Main found.
What exactly does it mean for Main to be static? I know the code works fine for public static void Main().
But why does Main have to be static?

You need an entry point into your program. Static means that you can call the function without having to instantiate an object/instance of a class. It's a bit "chicken and egg"... you can't instantiate an object before you're inside the program.
A static method can be called without instantiating an object. Therefore main() needs to be static in order to allow it to be the entry to your program.
As David says, you can just add the keyword static to the function definition to change it. It's worth looking into static (class) methods vs instance methods, and knowing the difference can be useful at times.

Only the static main method can do the job because there is a convention that defines this behavior. There is not another reason.
Take a look at the C# language specification:
Application startup occurs when the execution environment calls a
designated method, which is referred to as the application's entry
point. This entry point method is always named Main, and shall have
one of the following signatures:
static void Main() {…}
static void Main(string[] args) {…}
static int Main() {…}
static int Main(string[] args) {…}
As shown, the entry point can optionally
return an int value. This return value is used in application
termination (§10.2).
Note: The above is quoted from the 4th edition, now labeled "historical". The current edition is worded differently.
In addition to that, the name Main can be changed to something else. In this case a compiler option must be added telling the C# compiler to mark a different method as the entry point of the program.

There are two types of method within a class:
Non-static method
Static method
// Example of static and non-static methods and how to call
namespace TestStaticVoidMain
{
class Program
{
Static Void Main(string[] args)
{
// Instantiate or create object of the non-static method:
Exam ob = new Exam();
// Call the instance:
ob.Test1();
// Directly the call the static method by its class:
Exam.Test2();
Console.ReadKey();
}
}
class Exam
{
public void Test1()
{
Console.WriteLine("This is a non-static method");
}
public static void Test2()
{
Console.WriteLine("This is a static method");
}
}
}
1. Static method:
To call a static method (function), we don't need to instantiate or create an object of that method. We can't use new keyword because, when the class is loaded and compiled, the static keyword by default instantiates or creates an object of that class method, so that is why we directly call a static method.
In reference to static void Main(string[] args), we already discussed static. The remainder is void Main(string[] args). void is a data type which returns nothing. Main() is the standard entry point to execution of a C# program. The optional argument string[] args receives the optional "command line" parameters that the program was run with.
2. Non-static sethod:
To call a non-static method, we have to instantiate or create an object of the class method to call the method (function) of the class using the keyword new.
If a class named Test has a non-static method named show(), then how it would call an instance:
// to call non-static method
Test ob=new Test();
ob.show();

Conceptually, it would be possible for a framework to specify that rather than using a particular static method to run a program, it will instead construct a default instance of some particular class and run some particular method thereon. If one had a framework which implemented static methods by having them be instance members of a compiler-initialized singleton instance, such an approach might be entirely reasonable, since the framework would have to generate a new object instance before calling the main function in any case.
If calling a static method is "easier" than constructing a new object instance and calling a method thereon, however, there isn't really much benefit to requiring that a framework use the more expensive course of action. Any code which wants to use the latter approach would be perfectly free to use:
public static void Main( [[params]] )
{
var mainObject = new MainObject();
mainObject.Main( [[params]] );
}
There could be some potential benefits to having the system include its own static method which looked something like:
public static void SysMain( [[params]] )
{
using (Application app = new UserApp( [[params]] )) // UserApp derives from Application
{
app.Start(); // Virtual method
app.AllowNext(); // Base method--see text
app.Run(); // Abstract method
}
}
where app.AllowNext() was a method to coordinate with other application instances launched at essentially the same time, to ensure that repeated attempts to launch an application in background would have their Start calls processed strictly sequentially. Absent such a coordination scheme, however, there's not really much benefit to requiring that the framework construct an application object before running it. The cost wouldn't be huge, but without any potential identifiable benefit there's not much point in accepting even a trivial cost.

During app startup, when no objects of the class have been created, the Main method must be called to begin program execution. Main is sometimes called the app’s entry point. Declaring Main as static allows the execution environment to invoke Main without creating an instance of the class. Method Main is typically declared with the header:
static void Main(){..}
but also can be declared with the header:
static void Main(string[] args){..}
You can declare Main with return type int (instead of void)—this can be useful if an app is executed by another app and needs to return an indication of success or failure to that other app.

The main should be static that it loads first and become your entry point to your program so it's crucial for the main to be static.

C# static garbage collector?

I have a simple class which has a static constructor and a instance constructor. Now when i initialized the class , both static and instance constructor are called. Only static is referred once in a application domain . Can i again call the same class initialization and static constructor initialize again? I have tried but it didn't happen? Is there any way we can call static constructor again in main() method after using garbage collection on the class.
Here is the code:
public class Employee
{
public Employee()
{
Console.WriteLine("Instance constructor called");
}
static Employee()
{
Console.WriteLine("Static constructor called");
}
~Employee()
{
//Dispose();
}
}
Now in main method call:
static void Main(string[] args)
{
Employee emp = new Employee();
Employee emp = new Employee();
}
Output:
Static constructor called
Instance constructor called
Instance constructor called
Now the static didn't called again. Because it is called once in application domain. But is their any way we could call it again without unloading application domain. Can we use GC class over here?
Thanks.
Pal

Unless you prod it with reflection, the static constructor (or more generally, the type initializer) is only executed once per concrete class, per AppDomain.
Note that for generics, using different type arguments you'll get different concrete classes:
public class Foo<T>
{
Foo()
{
Console.WriteLine("T={0}", typeof(T));
}
public static void DummyMethod() {}
}
...
Foo<int>.DummyMethod(); // Executes static constructor first
Foo<string>.DummyMethod(); // Executes static constructor first
Foo<string>.DummyMethod(); // Type is already initialized; no more output

Not possible. The CLR keeps an internal status bit that tracks whether the type initializer was started. It cannot run again. That status bit is indeed stored in the loader heap as part of the AppDomain state. The workaround is simple, just add a static method to the class.

The point of a constructor is to put things into a desired initial valid state.
An instance constructor puts an instance into an initial valid state.
An instance constructor that takes arguments puts an instance into a initial valid state that reflects its arguments.
A static constructor puts the type into an initial valid state. E.g. initialising static members used by the class' static methods or shared by all instances.
Ideally all methods will leave the object and the type in a valid state, but constructors differ in being responsible for getting it into one in the first place.
Any attempt to call a constructor twice is therefore a mistake, since "put it into an initial valid state again" isn't something you can logically do twice ("initial" and "again" don't work well in the same clause). We are helped by the compiler (in it refusing to compile) and the language (in there being no way to express this) from doing such a thing.
And, being a logical impossibility it isn't something you can actually want to do (well, I can want to draw a triangle with more than 3 sides, but only to say that I did). This suggests that you are using your constructor to do something other than setting up an initial valid state.
Doing anything other than establishing such a valid state in a constructor is (as is failing to do so) at best an optimisation, quite often a serious design flaw and quite possibly (worse of all because it goes unfixed longer) an attempted optimisation that is really a serious design flaw.
One sign that your attempt at an optimisation is really a design flaw is a desire to call a static constructor more than once, or to call an instance constructor more than once on the same object.
Identify the desired repeatable behaviour, move it into a separate method, and have it called as needed from both the constructor and elsewhere. Then double check your design's logic, as this is quite a serious mistake to find in a class design and suggests you've got deeper problems.

Static method and threads

I have put one question on MSDN forum but got two opposite answers. In general I am intersted how threading works with static classes. If my code calls this(below) static method from 10 threads at the same time, is it thread safe? I mean, how the code flows behind the scenes? Does every thread executes the code within itself (like I think it does with non-static classes) or it is different with static method and, because its static, all threads try to reach the code and collide? Thanks!
public static class A
{
static void Method(object parameter)
{
SqlCeConnection = .....
}
}
Link to MSDN question: Here
PS: I am sorry due to IE page errors I cannot click on "Add comment" or "Answer", Jon Skeet answer is good (as usually :)

It's exactly the same as with non-static classes. Being static doesn't affect anything really - except that static methods are generally expected to be thread-safe. They're not automatically thread-safe, but you should make sure that you implement them in a thread-safe manner.
If the code doesn't use any shared state, it should be fine. And yes, without any locking, all the threads can be executing the same method concurrently.

A nice example can be singleton pattern.In this all you need is a single instance for a given class and that can be made sure by making the constructor private and giving a static method or property to access the instance.Following code snippets highlight the same :-
class MyClass
{
private MyClass()
{
}
public static MyClass Instance
{
get
{
lock(typeof(MyClass))
{
if(__instance == null)
__instance = new MyClass();
}
return __instance;
}
}
}
Since the "Instance" method is marked static(thread consistent access) , but in multi threaded envoirnment you need to manully take care of it(using lock).