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本版专家分：2255结帖率 99.24% -
Level-Triggered and Edge-Triggered
The epoll event distribution interface is able to behave both as edge-triggered (ET) and as level-triggered (LT). The difference between the two mechanisms can be described
as follows. Suppose that this scenario happens:
1. The file descriptor that represents the read side of a pipe (rfd) is registered on the epoll instance.
2. A pipe writer writes 2 kB of data on the write side of the pipe.
3. A call to epoll_wait(2) is done that will return rfd as a ready file descriptor.
4. The pipe reader reads 1 kB of data from rfd.
5. A call to epoll_wait(2) is done.
If the rfd file descriptor has been added to the epoll interface using the EPOLLET (edge-triggered) flag, the call to epoll_wait(2) done in step 5 will probably hang despite the available data still present in the file input buffer; meanwhile the remote peer might be expecting a response based on the data it already sent. The reason for this is that edge-triggered mode only delivers events when changes occur on the monitored file descriptor. So, in step 5 the caller might end up waiting for some data that is already present inside the input buffer. In the above example, an event on rfd will be generated because of the write done in 2 and the event is consumed in 3. Since the read operation done in 4 does not consume the whole buffer data, the call to epoll_wait(2) done in step 5 might block indefinitely.
最后一句 ：
Since the read operation done in 4 does not consume the whole buffer data, the call to epoll_wait(2) done in step 5 might block indefinitely.(2) done in step 5 might block indefinitely.
是不是如果上一次数据没有接收完全，即便是客户端再次发送数据，epoll_wait也一直是 阻塞的，不会触发！？
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本版专家分：2255
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好吧，测试了下，客户端不断发送数据，每秒一次，1次100bytes左右，服务器每次只接收数据头大小的字节。
static const int __head_size = 12;
unsigned long __usable_size = 0;
int __packet_length = 0;
int __log_level = 0;
int __frame_number = 0;
int __head = 0;
unsigned int __guid = 0;
unsigned char __packet_head[__head_size] = {};
int __recv_size = 0;
{
{
_get_usable(__fd,__usable_size);
printf("__usable_size1 = %ld\n",__usable_size);
{
__recv_size = Event_Handle_Srv::read(__fd,(char*)&__packet_head,__head_size);
printf("__recv_size = %d\n",__recv_size);
if(__head_size != __recv_size)
{
printf("error: __recv_size = %d",__recv_size);
return ;
}
}
}
}
结果：
hostname: localhost.localdomain
address list:
127.0.0.1
on_connected __fd = 5
__usable_size1 = 178
__recv_size = 12
__usable_size1 = 230
__recv_size = 12
__usable_size1 = 340
__recv_size = 12
__usable_size1 = 419
__recv_size = 12
__usable_size1 = 483
__recv_size = 12
__usable_size1 = 543
__recv_size = 12
__usable_size1 = 595
__recv_size = 12
__usable_size1 = 655
__recv_size = 12
__usable_size1 = 760
__recv_size = 12
__usable_size1 = 825
__recv_size = 12
__usable_size1 = 877
__recv_size = 12
__usable_size1 = 929
__recv_size = 12
__usable_size1 = 1036
__recv_size = 12
__usable_size1 = 1122
__recv_size = 12
__usable_size1 = 1232
__recv_size = 12
__usable_size1 = 1322
__recv_size = 12
__usable_size1 = 1382
__recv_size = 12
__usable_size1 = 1442
__recv_size = 12
__usable_size1 = 1552
__recv_size = 12
__usable_size1 = 1627
__recv_size = 12
__usable_size1 = 1684
__recv_size = 12
__usable_size1 = 1774
__recv_size = 12
__usable_size1 = 1831
__recv_size = 12
__usable_size1 = 1895
__recv_size = 12
__usable_size1 = 1952
__recv_size = 12
__usable_size1 = 2004
__recv_size = 12
__usable_size1 = 2114
__recv_size = 12
__usable_size1 = 2204
__recv_size = 12
__usable_size1 = 2264
__recv_size = 12
__usable_size1 = 2430
__recv_size = 12
还是可以继续受到的，而且数据好像是没有丢的，累积到下一次了，所以，下次接收的时候，数据应该是完整的！
备注一下，不知道理解是不是有错！