单线程排序

           【快速排序，使用STL sort函数】

#include <stdio.h>
#include <stdlib.h>

#include <pthread.h>
#include <sys/time.h>

#include <algorithm>
using namespace std;

#define NUMNUM 8000000L
long nums[NUMNUM];  //待排序数组

bool compare(long a, long b)
{
    return a < b;
}

int main()
{
    freopen("back.txt","w",stdout);

    unsigned long   i;
    struct timeval  start, end;
    long long       startusec, endusec;
    double          elapsed;

    srandom(time(NULL));
    for (i = 0; i < NUMNUM; i++)
        nums[i] = random();

    //计时开始
    gettimeofday(&start,NULL);
    sort(nums,nums+NUMNUM,compare); //单线程排序,快速排序
    gettimeofday(&end,NULL);

    //计算用时
    startusec = start.tv_sec * 1000000 + start.tv_usec;
    endusec = end.tv_sec * 1000000 + end.tv_usec;
    elapsed = (double)(endusec - startusec) / 1000000.0;
    printf("sort took %.4f seconds\n", elapsed);

    //查看是否已经排好序
    for (i = 0; i < NUMNUM; i++)
        printf("%ld\n", nums[i]);

    exit(0);
}

耗时:

1、单核，单线程

          sort took 2.2911 seconds

2、双核，四线程

           sort took 3.1645 seconds

           sort took 3.1613 seconds

多线程排序

#include <stdio.h>
#include <stdlib.h>
#include <limits.h>

#include <pthread.h>
#include <sys/time.h>

#include <algorithm>
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 */

long nums[NUMNUM];
long snums[NUMNUM];

pthread_barrier_t b;    //屏障

bool compare(long a, long b)
{
    return a < b;
}

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

    sort(&nums[idx],&nums[idx+TNUM],compare);
    pthread_barrier_wait(&b);

    pthread_exit(NULL);
}

/*
 * 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()
{
    freopen("back.txt","w",stdout);
    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(time(NULL));
    for (i = 0; i < NUMNUM; i++)
        nums[i] = random();

    /*
     * 创建八个线程分别对数组的八个段进行排序
     */
    gettimeofday(&start, NULL);
    pthread_barrier_init(&b, NULL, NTHR+1);
    for (i = 0; i < NTHR; i++)
    {
        err = pthread_create(&tid, NULL,workThread, (void *)(i * TNUM));
        if (err != 0)
        {
            perror("pthread_create");
            return -1;
        }
    }
    pthread_barrier_wait(&b);
    merge();
    gettimeofday(&end, NULL);

    //计算用时
    startusec = start.tv_sec * 1000000 + start.tv_usec;
    endusec = end.tv_sec * 1000000 + end.tv_usec;
    elapsed = (double)(endusec - startusec) / 1000000.0;
    printf("sort took %.4f seconds\n", elapsed);

    for (i = 0; i < NUMNUM; i++)
        printf("%ld\n", snums[i]);
    exit(0);
}

附：Makefile源码

CC = g++
CPPFLAGS = -Wall -g -pthread

BIN = main
SOURCES = $(wildcard *.cpp)
OBJECTS = $(SOURCES:.cpp=.o)

.PHONY: clean all

all: $(BIN)
$(BIN): $(OBJECTS)
    $(CC) $(CPPFLAGS) -o $@ $<

%.o: %.cpp
    $(CC) $(CPPFLAGS) -o $@ -c $<

clean:
    -rm -rf $(BIN) $(OBJECTS)

单线程与多线程排序对比