C# 0 The Complete Reference

out

 parameters.

Friend Assemblies

It is possible to make one assembly the 

friend

 of another. A friend has access to the private 

members of the assembly of which it is a friend. This feature makes it possible to share 

members between selected assemblies without making those members public.

To declare a friend assembly, you must specify the friend assembly’s name and its 

public key token in an 

InternalsVisibleTo

 attribute.

Miscellaneous Keywords

To conclude Part I, the few remaining keywords defined by C# that have not been described 

elsewhere are briefly discussed.

lock

The

lock

 keyword is used when creating multithreaded programs. It is examined in detail 

in Chapter 23, where multithreaded programming is discussed. A brief description is given 

here for the sake of completeness.

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P a r t   I :  

T h e   C #   L a n g u a g e

In C#, a program can contain more than one 

thread of execution.

 When this is the case, the 

program is said to be 

multithreaded,

 and pieces of the program are executed concurrently. Thus, 

pieces of the program execute independently and simultaneously. This raises the prospect 

of a special type of problem: What if two threads try to use a resource that can be used by 

only one thread at a time? To solve this problem, you can create a 

critical code section

 that 

will be executed by one and only one thread at a time. This is accomplished by 

lock

. Its 

general form is shown here:

lock(

obj

) {

   // 

critical section

}

Here, 

obj

 is the object on which the lock is synchronized. If one thread has already entered 

the critical section, then a second thread will wait until the first thread exits the critical 

section. When the first thread leaves the critical section, the lock is released and the second 

thread can be granted the lock, at which point the second thread can execute the critical 

section.