Pthread barrier的简单使用示例：

C++代码如下：

// ThreadingLoadImages.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <pthread.h>
#include <opencv2/opencv.hpp>

#define THREADS 3

// Barrier variable
pthread_barrier_t barr;


struct Param
{
	cv::Mat img;
	int index;
	char* file_path;
} params[THREADS];

void* entry_point(void* arg)
{
	Param* p = (Param*)arg;
	
	int index = p->index;
	char* file_path = p->file_path;

	p->img = cv::imread(file_path);

	printf("The %d thread is doing job! \n", index);

	// Synchronization point
	int rc = pthread_barrier_wait(&barr);
	if (rc != 0 && rc != PTHREAD_BARRIER_SERIAL_THREAD)
	{
		printf("Could not wait on barrier\n");
		exit(-1);
	}
}


int main()
{
	pthread_t thr[THREADS];
	//pthread_mutex_init(&g_mtx, NULL);

	// Barrier initialization
	if (pthread_barrier_init(&barr, NULL, THREADS))
	{
		printf("Could not create a barrier\n");
		return -1;
	}

	//int t[THREADS];
	params[0].file_path = "../micky.png";
	params[1].file_path = "../umbrella.png";
	params[2].file_path = "../beard.jpg";

	for (int i = 0; i < THREADS; ++i)
	{
		//t[i] = i;
		params[i].index = i;
	
		if (pthread_create(&thr[i], NULL, &entry_point, (void *)&params[i]))
		{
			printf("Could not create thread %d\n", i);
			return -1;
		}
	}

	for (int i = 0; i < THREADS; ++i)
	{
		if (pthread_join(thr[i], NULL))
		{
			printf("Could not join thread %d\n", i);
			return -1;
		}
	}
	printf("All threads finish jobs! \n");

	for(int i=0; i<THREADS; i++)
		cv::imshow(params[i].file_path, params[i].img);
	cv::waitKey(0);

    return 0;
}

相关资料：pthread线程使用小结 

多线程本地图片加载示例【OpenCV】【Pthread】