Linux,C.以下问题仅通过使用epoll((发生。如果我在服务器套接字上使用select((,则不会丢失数据。
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更新:我在read((中收到errno=11(重试(。我需要继续还是打破while循环?
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我有客户端,10次发送1280K数据(每次发送128K数据(;
我有服务器端,使用epoll((来监视传入的数据。
收到通知后,我使用以下代码读取数据:
nbytes = Nread(current_fd, buffer, bytes_to_be_read);
int Nread(int fd, char *buffer, size_t count)
{
ssize_t r;
size_t left = count;
printf("===>n");
while (left > 0){
r = read(fd, buffer, left);
printf("data: %ldn", r);
if (r < 1) {
printf("errno: %dn", errno);
break; //I do received 2 errors of Try Again. How to try again?
}
left -= r;
buffer += r;
}
printf("=> done, %ldn", total - left);
return count - left;
}
在Nread中,我期望读取bytes_to_be_read(65536(字节并返回。
但是,当运行该工具时,我发现服务器端只收到这样的东西。在某些情况下,我似乎没有从缓冲区读取所有数据。为什么?
1===>
data: 65536
=> done, 65536
2===>
data: 65536
=> done, 65536
3===>
data: 60734
data: 4802
=> done, 65536
4===>
data: 55934
data: -1
errno: 11
=> done, 55934 //data is not enough. the missing part should come soon. but why I am not notified?
5===>
data: 60736
data: 4800
=> done, 65536
6===>
data: 65536
=> done, 65536
7===>
data: 65536
=> done, 65536
8===>
data: 65536
=> done, 65536
9===>
data: 65536
=> done, 65536
10===>
data: 65536
=> done, 65536
11===>
data: 65536
=> done, 65536
12===>
data: 65536
=> done, 65536
13===>
data: 65536
=> done, 65536
14===>
data: 65536
=> done, 65536
15===>
data: 65536
=> done, 65536
16===>
data: 65536
=> done, 65536
17===>
data: 65536
=> done, 65536
18===>
data: 65536
=> done, 65536
19===>
data: 65536
=> done, 65536
================
更新:
如果使用此代码读取所有数据,则不会丢失字节。但性能很差:
36 int read_all(int fd, char *buffer)
37 {
38 ssize_t count = 0, bytes = 0;
39
40 while(1){
41 bytes = read(fd, buffer, sizeof(buffer));
42 if (bytes < 1)
43 break;
44 count += bytes;
45 }
46 return count;
47 }
====================================
EPOLL((
efd = epoll_create1 (0);
event.data.fd = listener_fd;
event.events = EPOLLIN | EPOLLET;
epoll_ctl(efd, EPOLL_CTL_ADD, listener_fd, &event);
while (1){
n_fds = epoll_wait (efd, events, MAX_EPOLL_EVENTS, -1);
for (i = 0; i < n_fds; i++){
...........
if (islistener) {
.....
//handle new connections
}
else{
bzero(buffer, recv_buf_size);
if ((n= Nread(fd, buffer, recv_buf_size)) <= 0) {
//error
}
else
{
//add bytes to total:
__sync_fetch_and_add(&(mythreads->total_bytes_transferred), n) ;
}
}
break; //I do received 2 errors of Try Again. How to try again?
回到你的epoll循环。
data: 60734 //??? why I am not able to read all 65536 bytes?
因为他们还没有收到。
我想您可能会错过关于如何使用epoll
进行非阻塞I/O的总体介绍。
epoll
告诉你什么时候有数据- 那时你尽可能多地读书
- 返回步骤1
event.events = EPOLLIN | EPOLLET;
您正在执行边缘触发轮询。这意味着你的最后一次阅读可能没有阅读所有可用的数据。即使有更多可用数据,它也会在读取64k数据后停止。但由于边缘触发,轮询将不会再次触发。建议删除EPOLLET
。