In order not to block the reactor I would like to read files asynchronously, but I've found no obvious way of doing it using EventMachine. I've tried a few different approaches, but none of them feels right:
- Just read the file, it'll block the reactor, but what the hell, it's not that slow (unless it's a big file, and then it definitely is).
- Open the file for reading and read a chunk on each tick (but how much to read? too much and it'll block the reactor, too little and reading will get slower than necessary).
EM.popen('cat some/file', FileReader)feels really weird, but works better than the alternatives above. In combination with theLineAndTextProtocolit reads lines pretty swiftly.EM.attach, but I haven't found any examples of how to use it, and the only thing I've found on the mailing list is that it's deprecated in favour of…EM.watch, which I've found no examples of how to use for reading files.
How do you read files within a EventMachine reactor loop?
EM.attach/watch cannot be used on files, as select/epoll on a disk-based file descriptor will always return readable.
Ultimately, it depends on what you're trying to do. If it's a small file, just File.read it. If it is larger, you can read small chunks over time. For example, EM::FileStreamer does this to send large file over the network.
Another common use-case is to tail a file and read in new contents when it changes. This can be achieved using EM.watch_file: http://github.com/jordansissel/eventmachine-tail
来源：https://stackoverflow.com/questions/2749503/what-is-the-best-way-to-read-files-in-an-eventmachine-based-app