//***************************************************************
// illustrates two processes cooperating in a producer/consumer relationship
// The producer/consumer relationship is managed by two semaphores
// EMPTY and FULL, When EMPTY the producer can produce into empty buffer,
// when FULL the consumer can consume buffer.
// the buffer is passed through shared memory using the file mapping mechanism
// This code demonstrates the consumer side
// AUTHOR: Chris Wild
// DATE: September 10, 1997
//***************************************************************


#include <windows.h>
#include <iostream.h>
#include <stdlib.h>

const int NBUFFERS = 3;	// allow 3 buffers for bounded buffer
typedef struct{
	int bufID;	// buffer number
	int bufValue;	// monotonically increasing number
} Buffer;


void main(int argc, char *argv[])
{
	HANDLE empty, full;	// control bounded buffer access
	HANDLE mapFileHandle;	// used to access the shared 
	Buffer* commonBuffers; // pointer into memory mapped file to array of buffer structures
	
	
	cout << "Entered consumer: v2\n";
    empty = OpenSemaphore(SEMAPHORE_ALL_ACCESS,FALSE, "NTcourse.semaphore.empty");
	if(empty == NULL) {
		cout << "Error opening empty: " 
			<< GetLastError() << endl;
		ExitProcess(1);
	}
	
	full = OpenSemaphore(SEMAPHORE_ALL_ACCESS, FALSE, "NTcourse.semaphore.full");
	if(full == NULL) {
		cout << "Error opening full: " 
			<< GetLastError() << endl;
		ExitProcess(1);
	}
	
	mapFileHandle = OpenFileMapping(PAGE_READWRITE,
		FALSE,	// child cannot inherit
		"commonBuffer");
	if(mapFileHandle == NULL) {
		cout << "Error opening commonBuffer: " 
			<< GetLastError() << endl;
		ExitProcess(1);
	}
	commonBuffers = (Buffer*) MapViewOfFile(mapFileHandle,
		FILE_MAP_READ,
		0,	// High offset
		0,	// Low offest
		0);	// 0 for mapping entire file
	if(commonBuffers == NULL) {
		cout << "Error mapping file: " 
			<< GetLastError() << endl;
		ExitProcess(1);
	}
	
	
	
	// enter a loops consuming some things
	int bufN = 0;
	DWORD returnValue;
	while(true) {
		// First wait for buffer to be produced
		cout << "CONSUMER: waiting for full buffer\n";
		returnValue = WaitForSingleObject(full, 10000); // wait 10 seconds
		if( returnValue == WAIT_TIMEOUT) {
			cout << "Waited too long for producer - assumed died\n";
			break;
		}
		// Have full buffer - consume it
		cout << "CONSUMER: emptied buffer: " << 
			commonBuffers[bufN].bufID <<
			" with value: " << commonBuffers[bufN].bufValue << endl;
		bufN = (bufN+1) % NBUFFERS;
		ReleaseSemaphore(empty,1,0);	// signals empty
	}
	CloseHandle(empty);
	CloseHandle(full);
	CloseHandle(mapFileHandle);
	
}