多線程對800萬個數據進行排序

分8個線程對800萬個數據分別排序，等全部線程排完序以後，進行簡單的多路歸併。這和外排的多路歸併是同樣的，也可使用優化的勝者樹算法。

#include <iostream>
#include <stdlib.h>
#include <pthread.h>
#include <limits.h>
#include <sys/time.h>
using namespace std;
#define NTHR   8				/* number of threads */
#define NUMNUM 8000000L			/* number of numbers to sort */
#define TNUM   (NUMNUM/NTHR)	/* number to sort per thread */

int nums[NUMNUM];
int snums[NUMNUM];

pthread_barrier_t b;

void HeapAdjust(int *a, int i, int size)
{
	int lchild = 2*i;
	int rchild = 2*i + 1;
	int max = i;
	if(i <=size/2)
	{
		if(lchild <=size && a[lchild] > a[max] )
		{
			max = lchild;
		}
		if(rchild <=size && a[rchild] > a[max])
		{
			max = rchild;
		}
		if(max != i)
		{
			swap(a[i], a[max]);
			HeapAdjust(a, max, size);
		}
	}
}

void BuildHeap(int *a, int size)
{
	int i;
	for(i = size/2; i >= 1; i--)
	{
		HeapAdjust(a, i, size);
	}
}

void HeapSort(int *a, int size)
{
	int i;
	BuildHeap(a, size);
	for(i=size;i>=1;i--)
	{
		swap(a[1], a[i]);
		HeapAdjust(a, 1, i-1);
	}
}

/*
 * Worker thread to sort a portion of the set of numbers.
 */
void * thr_fn(void *arg)
{
	long idx = (long)arg;

	HeapSort(&nums[idx], TNUM);
	pthread_barrier_wait(&b);

	/*
	 * Go off and perform more work ...
	 */
	return((void *)0);
}

/*
 * Merge the results of the individual sorted ranges.
 */
void merge()
{
	long	idx[NTHR];
	long	i, minidx, sidx, num;

	for (i = 0; i < NTHR; i++)
		idx[i] = i * TNUM;
	for (sidx = 0; sidx < NUMNUM; sidx++) {
		num = LONG_MAX;
		for (i = 0; i < NTHR; i++) {
			if ((idx[i] < (i+1)*TNUM) && (nums[idx[i]] < num)) {
				num = nums[idx[i]];
				minidx = i;
			}
		}
		snums[sidx] = nums[idx[minidx]];
		idx[minidx]++;
	}
}

int
main()
{
	unsigned long	i;
	struct timeval	start, end;
	long long		startusec, endusec;
	double			elapsed;
	int				err;
	pthread_t		tid;

	/*
	 * Create the initial set of numbers to sort.
	 */
	srandom(1);
	for (i = 0; i < NUMNUM; i++)
		nums[i] = random();

	/*
	 * Create 8 threads to sort the numbers.
	 */
	gettimeofday(&start, NULL);
	pthread_barrier_init(&b, NULL, NTHR+1);
	for (i = 0; i < NTHR; i++) {
		err = pthread_create(&tid, NULL, thr_fn, (void *)(i * TNUM));
		if (err != 0)
			cout<<"can't create thread";
	}
	pthread_barrier_wait(&b);
	merge();
	gettimeofday(&end, NULL);

	/*
	 * Print the sorted list.
	 */
	startusec = start.tv_sec * 1000000 + start.tv_usec;
	endusec = end.tv_sec * 1000000 + end.tv_usec;
	elapsed = (double)(endusec - startusec) / 1000000.0;
	for (i = 0; i < NUMNUM; i++)
		cout<<snums[i]<<"\n";
	cout<<"sort took seconds"<<elapsed;
	exit(0);
}

##Reference## [1].編程珠璣. P5

[2].http://blog.chinaunix.net/uid-25324849-id-2182916.html