Thread Programming

Thread Programming :
--------------------------------
  I faced Threading problems.

I developed the thread for reading from Network :

 int ThreadProc() 
 {
  while(bRun)
  {
   ReadFromNetwork();
  }
  return 0;
  
 }

 if I put the above code, I am getting CPU time as almost 100%.
CPU doesnt execute other processes. I put a Sleep(100), So that the OS executes the other processes during the sleep of that  program.
Sleep(0) also gives timeslice to execute other process.
 

 

 while(1){ } or While(bRun) {}  is called as Busy loop technically.

 Technically they call it as Busy waiting or Spinning.

busy waiting or spinning is a technique in which a process repeatedly checks to see if a condition is true,
such as waiting for keyboard input or waiting for a lock to become available. It can also be used to delay execution for some
amount of time; this was necessary on old computers that had no method of waiting a specific length of time other than
by repeating a useless loop a specific number of times, but on modern computers with clocks and different processor speeds,
this form of time delay is often inaccurate and a sign of a naïve attempt at programming.

Alternatives to busy waiting:
-----------------------------------------
 Most operating systems and threading libraries provide a wide set of system calls which will block the process
on an event, such as lock acquisitions, timers, I/O availability, or signals. This is often the simplest, most efficient, fair, and
race-free way. A single call checks, informs the scheduler of the event it is waiting for, inserts a memory barrier where applicable,
and may perform a requested I/O operation before returning. Other processes can use the CPU while the caller is blocked.
The scheduler is given the information needed to implement priority inheritance or other mechanisms to avoid starvation.

 Busy waiting itself can be made much less wasteful by using a "delay" function found on most operating systems.
This puts a thread to sleep for a specified time, during which the thread will waste no CPU time.
 If the loop is checking something simple then it will spend most of its time asleep and will not waste a large proportion
of the available CPU time. It will still consume some CPU time though.

When busy waits are appropriate :
------------------------------------------------
 In low-level hardware driver programming, sometimes busy waits are actually desirable.
It is not practical to implement hardware interrupt-based signalling for every hardware device, particularly for devices
 that are seldom accessed. Sometimes it is necessary to write some sort of control data to a hardware device and
then read back some sort of status data, which is not valid until several, perhaps even tens of clock cycles later.
The programmer could call an operating system delay function, but more time would be spent simply performing the
 function call (let alone switching to an interim thread) than is required by the hardware. In such cases, it is common to
implement a busy wait that keeps reading the status data until it is valid. Calling a delay function in this case would actually
waste CPU time due to the comparatively large overhead involved in the function call and thread switching.

 For Some important Operations, we can set the ThreadPriority to Highest.This will improves the execution speed.

For Windows programming, we can do the following:

ThreadProc()
{
 While(true)
 {
  DWORD dwWait = WaitForSingleObject(m_hThreadStopEvent,5);
  if (dwWait == WAIT_OBJECT_0)  //ThreadStopEvent occurred
  {
   break;
  }

  ReadFromNetwork();
 }
  return 0;

} 

The Description for the above code is as follows:
 it will waits for 5 milliseconds for ThreadStop Event. if this event occurs, the control comes out of the while loop.
other wise control will be in loop and will reads data from the network.
 whenever we want to comes out of the ThreadProc() fn just rise the ThreadStopEvent.