1
我试图创建一个应用程序，允许我通过局域网使用特定的多播地址多播网络摄像头馈送，并使用sendto（）发送帧缓冲区。我试图构建的应用程序与本网站上的应用程序几乎相同 http://nashruddin.com/Streaming_OpenCV_Videos_Over_the_Network 并且使用相同的体系结构。 而不是我使用SOCK_DGRAM的TCP套接字。问题是，当我从不同的线程使用sendto（）函数时，它往往会失败，即它返回-1并且errno被设置为90（EMSGSIZE），这基本上意味着形成的数据包太大而无法通过网络。 但即使我尝试发送一个简单的字符串（如“hello”）到相同的多播地址，也会发生这种情况。这似乎工作正常，如果应用程序是一个单线程。也就是说我只是捕捉图像并将它全部在同一个线程中多播。这是代码：通过来自不同线程的UDP进行多播
#include <netinet/in.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
#include "cv.h"
#include "highgui.h"
#define PORT 12345
#define GROUP "225.0.0.37"
CvCapture* capture;
IplImage* img0;
IplImage* img1;
int is_data_ready = 0;
int serversock, clientsock;
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
void* streamServer(void* arg);
void quit(char* msg, int retval);
int main(int argc, char** argv)
{
pthread_t thread_s;
int key;
if (argc == 2) {
capture = cvCaptureFromFile(argv[1]);
} else {
capture = cvCaptureFromCAM(0);
}
if (!capture) {
quit("cvCapture failed", 1);
}
img0 = cvQueryFrame(capture);
img1 = cvCreateImage(cvGetSize(img0), IPL_DEPTH_8U, 1);
cvZero(img1);
cvNamedWindow("stream_server", CV_WINDOW_AUTOSIZE);
/* print the width and height of the frame, needed by the client */
fprintf(stdout, "width: %d\nheight: %d\n\n", img0->width, img0->height);
fprintf(stdout, "Press 'q' to quit.\n\n");
/* run the streaming server as a separate thread */
if (pthread_create(&thread_s, NULL, streamServer, NULL)) {
quit("pthread_create failed.", 1);
}
while(key != 'q') {
/* get a frame from camera */
img0 = cvQueryFrame(capture);
if (!img0) break;
img0->origin = 0;
cvFlip(img0, img0, -1);
/**
* convert to grayscale
* note that the grayscaled image is the image to be sent to the client
* so we enclose it with pthread_mutex_lock to make it thread safe
*/
pthread_mutex_lock(&mutex);
cvCvtColor(img0, img1, CV_BGR2GRAY);
is_data_ready = 1;
pthread_mutex_unlock(&mutex);
/* also display the video here on server */
cvShowImage("stream_server", img0);
key = cvWaitKey(30);
}
/* user has pressed 'q', terminate the streaming server */
if (pthread_cancel(thread_s)) {
quit("pthread_cancel failed.", 1);
}
/* free memory */
cvDestroyWindow("stream_server");
quit(NULL, 0);
}
/**
* This is the streaming server, run as a separate thread
* This function waits for a client to connect, and send the grayscaled images
*/
void* streamServer(void* arg)
{
struct sockaddr_in server;
/* make this thread cancellable using pthread_cancel() */
pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);
pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL);
/* open socket */
if ((serversock = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
quit("socket() failed", 1);
}
memset(&server,0,sizeof(server));
server.sin_family = AF_INET;
server.sin_port = htons(PORT);
server.sin_addr.s_addr = inet_addr(GROUP);
int opt = 1;
//if(setsockopt(serversock,SOL_SOCKET,SO_BROADCAST,&opt,sizeof(int))==-1){
// quit("setsockopt failed",0);
//}
// /* setup server's IP and port */
// memset(&server, 0, sizeof(server));
// server.sin_family = AF_INET;
// server.sin_port = htons(PORT);
// server.sin_addr.s_addr = INADDR_ANY;
//
// /* bind the socket */
// if (bind(serversock, (const void*)&server, sizeof(server)) == -1) {
// quit("bind() failed", 1);
// }
//
// /* wait for connection */
// if (listen(serversock, 10) == -1) {
// quit("listen() failed.", 1);
// }
//
// /* accept a client */
// if ((clientsock = accept(serversock, NULL, NULL)) == -1) {
// quit("accept() failed", 1);
// }
/* the size of the data to be sent */
int imgsize = img1->imageSize;
int bytes=0, i;
/* start sending images */
while(1)
{
/* send the grayscaled frame, thread safe */
pthread_mutex_lock(&mutex);
if (is_data_ready) {
// bytes = send(clientsock, img1->imageData, imgsize, 0);
is_data_ready = 0;
if((bytes = sendto(serversock,img1->imageData,imgsize,0,(struct sockaddr*)&server,sizeof(server)))==-1){
quit("sendto FAILED",1);
}
}
pthread_mutex_unlock(&mutex);
// /* if something went wrong, restart the connection */
// if (bytes != imgsize) {
// fprintf(stderr, "Connection closed.\n");
// close(clientsock);
//
// if ((clientsock = accept(serversock, NULL, NULL)) == -1) {
// quit("accept() failed", 1);
// }
// }
/* have we terminated yet? */
pthread_testcancel();
/* no, take a rest for a while */
usleep(1000);
}
}
/**
* this function provides a way to exit nicely from the system
*/
void quit(char* msg, int retval)
{
if (retval == 0) {
fprintf(stdout, (msg == NULL ? "" : msg));
fprintf(stdout, "\n");
} else {
fprintf(stderr, (msg == NULL ? "" : msg));
fprintf(stderr, "\n");
}
if (clientsock) close(clientsock);
if (serversock) close(serversock);
if (capture) cvReleaseCapture(&capture);
if (img1) cvReleaseImage(&img1);
pthread_mutex_destroy(&mutex);
exit(retval);
}
我敢肯定这是不是因为UDP的硬限制，因为当我使用单线程方法，这已经奏效。当我尝试在代码的那部分代替图像传递一个简单的字符串（比如“hello”）时，对'sendto'的调用甚至失败。 – 2012-01-11 04:37:36