Page 320 - DCAP404 _Object Oriented Programming

Unit 14: Advanced Concept in C++

Thread Notes

A thread is a sequence of instructions to be executed within a program. Each thread has its own
set of resources such as instruction pointer, set of registers and stack memory. The virtual
address space is common to all threads within a process. This enables all the threads to access
data on the heap.
Normal processes consist of a single thread of execution that starts in a single method (main() in
UNIX). Each line of the code is executed exactly one line at a time. Earlier the normal way to
achieve concurrency in a program was to use the fork() and exec() system calls (or equivalent
system calls in other operating systems) to create several processes. Each of these processes used
to e executed as a single thread of execution.

Since there are a lot of similarities between a process and a thread, a thread is often referred to
as lightweight process.
Threads can be created as instances of the Thread class. It has attributes and methods that create
and control a thread, set its priority, and get its status. The namespace of the Thread class is
System.Threading assembled in mscorlib.dll. Given below is its syntax.

[ComVisibleAttribute(true)]
[ClassInterfaceAttribute(ClassInterfaceType::None)]
public ref class Thread sealed : public CriticalFinalizerObject, _Thread
A single process can create as many threads as required to execute different portions of the code.
The program code to be executed by a thread is specified using ThreadStart delegate or the
ParameterizedThreadStart delegate. The ParameterizedThreadStart delegate allows one to pass
data to the thread procedure.
The following program demonstrates simple threading functionality offered by C++. The code
must be compiled using /clr option.
using namespace System;
using namespace System::Threading;
public ref class ExampleThread

{
public:
// The ThreadProc method is called when the thread starts. It loops five
times, writing to
// the console and yielding the rest of its time slice each time, and then
ends.
static void ThreadProc()
{
for ( int i = 0; i < 5; i++ )
{
Console::Write( “Thread Procedure: “ );

Console::WriteLine( i );
Thread::Sleep(0);
}

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