Confusion About Node.js Internal Asynchronous I/O Mechanism

I have learned that node.js use libeio internally to perform async file I/O, with thread pool, on *nix platform, am I right? What about async network I/O? Is it done by libev?

Solution 1:

1. First of all, libuv has removed the libeio from it. But it does perform async file I/O with a thread pool like libeio just as you mentioned.

2. libuv also removes libev. It does the async network I/O based on the async I/O interfaces in different platforms, such as epoll, kqueue and IOCP, without a thread pool. There is a event loop which runs on the main thread of uv which polls the I/O events and processes them.

3. The thread pool inside libuv is a fixed size thread pool (4 in uinx like system). It performs a task queue role and avoids the exhaustion of the system resources by generating threads indefinitely when the requests increase.

Solution 2:

Uptil version 0.6 node used libev to run event-loop and libeio for asynchronous I/O, (Unix backend sits heavily on these two libraries). But libuv has started replacing libev and libeio in version 0.8. It performs, mantains and manages all the io and events in the event pool. libuv is the choice in cross-platform asynchronous IO libraries.

1. Yes, upto node 0.6, deprecated in 0.8 and uses thread pool

2. Yes, but libev does not use thread pool. See here

   Clarification : According to the link in the question I posted, libeio does support all POSIX functions dealing with I/O (which includes socket). But node author decided to use it for async file I/O only, and uses libev for network I/O. I dont know where you heard it from but you can use epoll on regular files.

3. libev uses event loop so no problems here.

4. Yes IOCP handles async I/O in windows, kernel does use thread pools.
5. New linux kernel has epoll, kqueue in new BSD kernel. libev and libeio were for linux environment and provides event loop/async IO for all kernel (supports select, poll, epoll, kqueue).

Update questions:

1. dont know much about libuv
2. maybe enough (dont know)

3. Here are my findings on Windows 8, checked it via Process Explorer. Showed 4 threads, 1 DLL, 1 File and 1 Section (total 7 entries) for a node application process.

4. ps -eLf does show all threads and processes, maybe you are over-filtering it, just look for the node process pid like ps -eLf | grep x where x is pid for node process.