//
// A thread demo in C++ using the thread facility defined in the C++-11
// standard.  The layout is much like pthreads, but the interface is much
// cleaner.  As the other thread examples, the main declares a certain amount of
// "resources" (just an integer number) then starts two threads which
// "work through" the resources (mostly by printing that they did).  
//
#include <cstdlib>
#include <iostream>
#include <string>
#include <thread>
#include <mutex>

// This is for the Unix gitpid() used for randomization.  It has nothing to do
// with the C++-11 threading.
#include <unistd.h>

using std::string;
using std::cout;
using std::endl;

/* Shared data.  */
int depot;

/* Used tosynchronize access to the resource depot. */
std::mutex depot_sync;

/* Thread function.  Takes a string to print and range for the random number
   generator for the number of resources used. */
void thbod(string topr, int low, int high)
{
	while(1)
	{
		/* Choose a random number in range. */
		int amt = rand() % (high - low + 1) + low;

		/* Acquire the lock and obtain needed resource. */
		depot_sync.lock();
		if(depot < amt) amt = depot;
		depot -= amt;
		depot_sync.unlock();

		/* When the resource is exhausted, we're done. */
		if(amt == 0) return;

		/* Do that much "work." */
		while(amt--) { 
			cout << "[" << topr << "]"; 
			cout.flush();
		}
		cout << endl;
	}
}

/* Main starts two threads and waits for them to end. */
main()
{
	/* Seed the random number generator to vary behavior. */
	srand(time(0) ^ 387*getpid());

	/* Create the threads. Both start running thbod, and finish when
	   the function returns.  The depot provides resources for the
	   the threads to run. */
	depot = 3000;

	/* Two thread objects.  These declarations both create the objects and
	   call the indicated function (thbod in both cases) in a new thread
	   of control. */
	std::thread th1(thbod, "Z", 14, 18);
	std::thread th2(thbod, "EE", 8, 12);

	/* Wait for each of them to be done. */
	th1.join();
	cout << "First Done" << endl;
	th2.join();
	cout << "Second Done" << endl;
}