Visual Basic.NET How to Program (PDF)

628 Multithreading Chapter 14
Fig. 14.16 Producer and consumer threads accessing a circular buffer (part 4 of 4).
In Fig. 14.16, the outputs include the current occupiedBufferCount, the contents
of the buffers and the current writeLocation and readLocation. In the output, the
letters W and R represent the current writeLocation and readLocation, respectively.
Notice that, after the third value is placed in the third element of the buffer, the fourth value
is inserted at the beginning of the array. This produces the circular buffer effect.
SUMMARY
Computers can perform operations concurrently, such as compiling programs, printing files and
receiving electronic mail messages over a network.
Programming languages generally provide only a simple set of control structures that enable programmers
to perform one action at a time, proceeding to the next action only after the previous one
finishes.
Historically, the type of concurrency that computers perform generally has been implemented as
operating system “primitives” available only to highly experienced “systems programmers.”
The .NET Framework Class Library makes concurrency primitives available to the applications
programmer. The programmer can specify that an application contains threads of execution, where
each thread designates a portion of a program that might execute concurrently with other threads—
this capability is called multithreading.
A thread that was just created is in the Unstarted state. A thread is initialized using the Thread
class’s constructor, which receives a ThreadStart delegate. This delegate specifies the method
that contains the tasks that a thread will perform.
A thread remains in the Unstarted state until the thread’s Start method is called; this causes the
thread to enter the Started state (also known as the Ready, or Runnable, state).
A thread in the Started state enters the Running state when the system assigns a processor to the
thread. The system assigns the processor to the highest-priority Started thread.
A thread enters the Stopped (or Dead) state when its ThreadStart delegate completes or terminates.
A thread is forced into the Stopped state when its Abort method is called (by itself or
by another thread).