我编写了一个 C 程序来接收 UDP 多播数据包，并且它可以工作。然而，当程序运行几秒钟时，丢包的情况经常发生。当我按Ctrl + C终止程序并重新启动它时，它会收到大部分数据包，但几秒钟后就会发生数据包丢失。这很奇怪，到底是什么问题呢？这是我的 C 代码。
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <android/log.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/resource.h>
#define BUF_SIZE 4
int mjpeg_main(){
int sockfd;
struct sockaddr_in localSock;
struct ip_mreq group;
char buf[BUF_SIZE];
int len = sizeof(localSock);
/* Create a datagram socket on which to receive. */
if((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) == -1)
{
perror("Can't create socket!");
exit(1);
}
/* Enable SO_REUSEADDR to allow multiple instances of this */
/* application to receive copies of the multicast datagrams. */
int reuse = 1;
if(setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, (char *)&reuse, sizeof(reuse)) < 0)
{
perror("Setting SO_REUSEADDR error");
close(sockfd);
exit(1);
}
int n = 1024 * 1024;
if (setsockopt(sockfd,SOL_SOCKET,SO_RCVBUFFORCE,(const char*)&n, sizeof(int)) == -1)
{
// deal with failure, or ignore if you can live with the default size
}
/* Bind to the proper port number with the IP address */
/* specified as INADDR_ANY. */
memset((char *) &localSock, 0, sizeof(localSock));
localSock.sin_family = AF_INET;
localSock.sin_port = htons(2068);
localSock.sin_addr.s_addr = INADDR_ANY;
if(bind(sockfd, (struct sockaddr*)&localSock, sizeof(localSock)))
{
perror("Binding datagram socket error");
close(sockfd);
exit(1);
}
/* Join the multicast group 239.100.15.101 on the local 203.106.93.94 */
/* interface. Note that this IP_ADD_MEMBERSHIP option must be */
/* called for each local interface over which the multicast */
/* datagrams are to be received. */
group.imr_multiaddr.s_addr = inet_addr("239.100.15.101");
group.imr_interface.s_addr = inet_addr("10.100.15.115");
if(setsockopt(sockfd, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char *)&group, sizeof(group)) < 0)
{
perror("Adding multicast group error");
close(sockfd);
exit(1);
}
printf("Start to receive!n");
__android_log_print(ANDROID_LOG_INFO,"mjpeg","mjpeg start !!");
//Wait for connect
while(1)
{
memset(buf, 0, sizeof(buf));
int z = recvfrom(sockfd, // Socket
buf, // Receiving buffer
sizeof buf, // Max recv buf size
0, // Flags: no options
(struct sockaddr *)&localSock,// Addr
&len); // Addr len, in & out
if ( z < 0 )
{
perror("recv");
exit(1);
}
printf("Frame: %02X:%02X, Sequence: %02X:%02X\n", buf[0], buf[1], buf[2], buf[3]);
}
close(sockfd);
return 0;
}
而且，这就是结果。发送端是一个硬件，一个帧包含很多序列。序列号将依次增加。
Frame: 09:1F, Sequence: 00:00 Frame: 09:1F, Sequence: 00:01 Frame: 09:1F, Sequence: 00:02 Frame: 09:1F, Sequence: 00:03 Frame: 09:1F, Sequence: 00:04 Frame: 09:1F, Sequence: 00:05 Frame: 09:1F, Sequence: 00:06 Frame: 09:1F, Sequence: 00:07 Frame: 09:1F, Sequence: 00:08 Frame: 09:1F, Sequence: 00:09 Frame: 09:1F, Sequence: 00:0A Frame: 09:1F, Sequence: 00:0B Frame: 09:1F, Sequence: 00:0C Frame: 09:1F, Sequence: 00:0D Frame: 09:1F, Sequence: 00:0E Frame: 09:1F, Sequence: 00:0F Frame: 09:1F, Sequence: 00:10 Frame: 09:1F, Sequence: 00:11 Frame: 09:1F, Sequence: 00:12 Frame: 09:1F, Sequence: 00:13 Frame: 09:1F, Sequence: 00:14 Frame: 09:1F, Sequence: 00:15 Frame: 09:1F, Sequence: 00:16 Frame: 09:1F, Sequence: 00:17 Frame: 09:1F, Sequence: 00:18 Frame: 09:1F, Sequence: 00:19 Frame: 09:1F, Sequence: 00:1A Frame: 09:1F, Sequence: 00:1B Frame: 09:1F, Sequence: 00:1C Frame: 09:1F, Sequence: 00:1D Frame: 09:1F, Sequence: 00:1E Frame: 09:1F, Sequence: 00:1F Frame: 09:1F, Sequence: 00:20 Frame: 09:1F, Sequence: 00:21 Frame: 09:1F, Sequence: 00:22 Frame: 09:1F, Sequence: 00:23 Frame: 09:1F, Sequence: 00:24 Frame: 09:1F, Sequence: 00:25 Frame: 09:1F, Sequence: 00:26 Frame: 09:1F, Sequence: 00:27 Frame: 09:1F, Sequence: 00:28 Frame: 09:1F, Sequence: 00:29 Frame: 09:1F, Sequence: 00:2A Frame: 09:1F, Sequence: 00:2B Frame: 09:1F, Sequence: 00:2C Frame: 09:1F, Sequence: 00:2D Frame: 09:1F, Sequence: 00:2E Frame: 09:1F, Sequence: 00:2F Frame: 09:1F, Sequence: 00:30 Frame: 09:1F, Sequence: 00:31 Frame: 09:1F, Sequence: 00:32 Frame: 09:1F, Sequence: 00:33 Frame: 09:1F, Sequence: 00:34 Frame: 09:1F, Sequence: 00:35 Frame: 09:1F, Sequence: 00:36 Frame: 09:1F, Sequence: 00:37 Frame: 09:1F, Sequence: 00:38 Frame: 09:1F, Sequence: 00:39 Frame: 09:1F, Sequence: 00:3A Frame: 09:1F, Sequence: 00:3B Frame: 09:1F, Sequence: 00:3C Frame: 09:1F, Sequence: 00:3D Frame: 09:1F, Sequence: 00:3E Frame: 09:1F, Sequence: 00:3F Frame: 09:1F, Sequence: 00:40 Frame: 09:1F, Sequence: 00:41 Frame: 09:1F, Sequence: 00:42 Frame: 09:1F, Sequence: 00:43 Frame: 09:1F, Sequence: 00:44 Frame: 09:1F, Sequence: 00:45 Frame: 09:1F, Sequence: 00:46 Frame: 09:1F, Sequence: 00:47 Frame: 09:1F, Sequence: 00:48 Frame: 09:1F, Sequence: 00:49 Frame: 09:1F, Sequence: 00:4A Frame: 09:1F, Sequence: 00:4B Frame: 09:1F, Sequence: 00:4C Frame: 09:1F, Sequence: 00:4D Frame: 09:1F, Sequence: 80:4E Frame: 09:20, Sequence: 00:00 Frame: 09:20, Sequence: 00:01 Frame: 09:20, Sequence: 00:02 Frame: 09:20, Sequence: 00:03 Frame: 09:20, Sequence: 00:04 Frame: 09:20, Sequence: 00:05 Frame: 09:20, Sequence: 00:06 Frame: 09:20, Sequence: 00:07 Frame: 09:20, Sequence: 00:08 Frame: 09:20, Sequence: 00:09 Frame: 09:20, Sequence: 00:0A Frame: 09:20, Sequence: 00:0B Frame: 09:20, Sequence: 00:0C Frame: 09:20, Sequence: 00:0D Frame: 09:20, Sequence: 00:0E Frame: 09:20, Sequence: 00:0F Frame: 09:20, Sequence: 00:10 Frame: 09:20, Sequence: 00:11 Frame: 09:20, Sequence: 00:12 Frame: 09:20, Sequence: 00:13 Frame: 09:20, Sequence: 00:14 Frame: 09:20, Sequence: 00:15 Frame: 09:20, Sequence: 00:16 Frame: 09:20, Sequence: 00:17 Frame: 09:20, Sequence: 00:18 Frame: 09:20, Sequence: 00:19 Frame: 09:20, Sequence: 00:1A Frame: 09:20, Sequence: 00:1B Frame: 09:20, Sequence: 00:1C Frame: 09:20, Sequence: 00:1D Frame: 09:20, Sequence: 00:1E Frame: 09:20, Sequence: 00:1F Frame: 09:20, Sequence: 00:20 Frame: 09:20, Sequence: 00:21 Frame: 09:20, Sequence: 00:22 Frame: 09:20, Sequence: 00:23 Frame: 09:20, Sequence: 00:24 Frame: 09:20, Sequence: 00:25 Frame: 09:20, Sequence: 00:26 Frame: 09:20, Sequence: 00:27 Frame: 09:20, Sequence: 00:28 Frame: 09:20, Sequence: 00:29 Frame: 09:20, Sequence: 00:2E Frame: 09:20, Sequence: 00:31 Frame: 09:20, Sequence: 00:37 Frame: 09:20, Sequence: 00:3B Frame: 09:20, Sequence: 00:3D Frame: 09:20, Sequence: 00:3F Frame: 09:20, Sequence: 00:41 Frame: 09:20, Sequence: 00:42 Frame: 09:20, Sequence: 00:44 Frame: 09:20, Sequence: 00:46 Frame: 09:20, Sequence: 00:4B Frame: 09:20, Sequence: 80:4E Frame: 09:21, Sequence: 00:00 Frame: 09:21, Sequence: 00:01 start packet lost... Frame: 09:21, Sequence: 00:06 Frame: 09:21, Sequence: 00:10 Frame: 09:21, Sequence: 00:1C Frame: 09:21, Sequence: 00:25 Frame: 09:21, Sequence: 00:2F Frame: 09:21, Sequence: 00:35 Frame: 09:21, Sequence: 00:3B Frame: 09:21, Sequence: 00:3C Frame: 09:21, Sequence: 00:3E Frame: 09:21, Sequence: 00:40 Frame: 09:21, Sequence: 00:42 Frame: 09:21, Sequence: 00:43 Frame: 09:21, Sequence: 00:45 Frame: 09:21, Sequence: 00:47 Frame: 09:21, Sequence: 00:4D Frame: 09:22, Sequence: 00:01 Frame: 09:22, Sequence: 00:05 Frame: 09:22, Sequence: 00:0D Frame: 09:22, Sequence: 00:1B Frame: 09:22, Sequence: 00:23 Frame: 09:22, Sequence: 00:2F Frame: 09:22, Sequence: 00:34 Frame: 09:22, Sequence: 00:3A Frame: 09:22, Sequence: 00:3C Frame: 09:22, Sequence: 00:3E Frame: 09:22, Sequence: 00:40 Frame: 09:22, Sequence: 00:41 Frame: 09:22, Sequence: 00:43 Frame: 09:22, Sequence: 00:45 Frame: 09:22, Sequence: 00:47 Frame: 09:22, Sequence: 00:4D Frame: 09:23, Sequence: 00:01 Frame: 09:23, Sequence: 00:04 Frame: 09:23, Sequence: 00:0A Frame: 09:23, Sequence: 00:19 Frame: 09:23, Sequence: 00:20 Frame: 09:23, Sequence: 00:2E Frame: 09:23, Sequence: 00:32 Frame: 09:23, Sequence: 00:39 Frame: 09:23, Sequence: 00:3C Frame: 09:23, Sequence: 00:3E Frame: 09:23, Sequence: 00:3F Frame: 09:23, Sequence: 00:41 Frame: 09:23, Sequence: 00:43 Frame: 09:23, Sequence: 00:45 Frame: 09:23, Sequence: 00:46 Frame: 09:23, Sequence: 00:4D
最佳答案
问题已经解决了。原因是我们的PHY使用的是外部晶振，内核时钟配置不正确。
关于C UDP组播接收包丢失，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/28081907/