Hi Wankai,

The following design document explains the rationale behind the new epoll
implementation. Polling island was added as a part of this change.
https://github.com/grpc/grpc/blob/master/doc/epoll-polling-engine.md
(see section 4).

Here is some high level summary:
- Polling island represents the underlying epoll set containing the file
descriptors (which is why it contains the epoll-fd)
- The main idea in having them is to prevent a file descriptor from being
in multiple epoll sets. This means that whenever we add a file descriptor
(that already belongs to an epoll set) to another epoll set,  we merge the
underlying polling islands and old polling island's merged_to field points
to the new polling island..

the document's section 4 explains it all

thanks,
Sree

On Tue, Oct 18, 2016 at 8:38 AM, Wankai Zhang <wankaizhan...@gmail.com>
wrote:

>
> Hello, all:
> I am using c/c++.
> I am confused of polling_island data structure. Why it contains a field
> "merged_to" ?
> Could anyone help me?
>
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