//================================================= file = semaphore1,c =====
//=  A simple bare-bones example of Windows semaphores and threads          =
//===========================================================================
//=  Notes:                                                                 =
//=    1) This program demonstrates how a semaphore can be used to make a   =
//=       thread wait for work.  Work is generated in the main program.     =
//=    2) Ignore two compile-time warnings on unreachable code and unused   =
//=       parameter                                                         =
//=-------------------------------------------------------------------------=
//= Example execution:                                                      =
//=                                                                         =
//=     Count = 6 --- 6 5 4 3 2 1                                           =
//=     Count = 0 ---                                                       =
//=     Count = 2 --- 2 1                                                   =
//=     Count = 0 ---                                                       =
//=     Count = 6 --- 6 5 4 3 2 1                                           =
//=     Count = 7 --- 7 6 5 4 3 2 1                                         =
//=     Count = 5 --- 5 4 3 2 1                                             =
//=     Count = 5 --- 5 4 3 2 1                                             =
//=     Count = 8 --- 8 7 6 5 4 3 2 1                                       =
//=-------------------------------------------------------------------------=
//=  Build: bcc32 -WM semaphore1.c                                          =
//=-------------------------------------------------------------------------=
//=  Execute: semaphore1                                                    =
//=-------------------------------------------------------------------------=
//=  Author: Ken Christensen                                                =
//=          University of South Florida                                    =
//=          WWW: http://www.csee.usf.edu/~christen                         =
//=          Email: christen@csee.usf.edu                                   =
//=-------------------------------------------------------------------------=
//=  History: KJC (07/04/07) - Genesis (from MSDN examples)                 =
//=           KJC (02/28/11) - Renamed semaphore.c to semaphore1.c          =
//===========================================================================
//----- Include files -------------------------------------------------------
#include <stdio.h>                // Needed for printf()
#include <stdlib.h>               // Needed for rand() and exit()
#include <windows.h>              // Needed for windows stuff

//----- Globals -------------------------------------------------------------
HANDLE ghSemaphore;               // Windows semaphore
int    Count;                     // Global counter variable

//----- Function prototypes -------------------------------------------------
DWORD WINAPI ThreadProc(LPVOID);  // Thread function

//===========================================================================
//=  Main program                                                           =
//===========================================================================
int main(void)
{
  HANDLE aThread;      // Thread handle
  DWORD ThreadID;      // Thread ID
  int i;               // Loop counter

  // Create a semaphore with initial and max counts of 1
  ghSemaphore = CreateSemaphore(NULL, 1, 1, NULL);
  if (ghSemaphore == NULL)
  {
    printf("*** ERROR - CreateSemaphore() failed \n");
    exit(1);
  }

  // Create a thread
  aThread = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE) ThreadProc, NULL, 0, &ThreadID);
  if(aThread == NULL)
  {
    printf("*** ERROR - CreateThread() failed \n");
    exit(1);
  }

  // Main loop
  Count = 0;
  while(1)
  {
    // Create some work for the thread
    Count = Count + (rand() % 10);
    printf("\n  Count = %d --- ", Count);

    // Release the semaphore to kick-off the thread
    ReleaseSemaphore(ghSemaphore, 1, NULL);

    // Sleep for 1 second
    Sleep(1000);
  }

  // Wait for thread to terminate
  WaitForMultipleObjects(1, aThread, TRUE, INFINITE);

  // Close thread handle
  CloseHandle(aThread);

  // Close semaphone handle
  CloseHandle(ghSemaphore);

  // Return
  return(0);
}

//===========================================================================
//=  This is is the thread function                                         =
//=   - Wait for semaphore release to begin work                            =
//===========================================================================
DWORD WINAPI ThreadProc(LPVOID lpParam)
{
  // Loop forever
  while(1)
  {
    // Wait for main program to release the semaphore
    WaitForSingleObject(ghSemaphore, INFINITE);

    // Do some work
    while(Count > 0)
    {
      printf("%d ", Count);
      Count--;
    }
  }
}