Suppose I have a file that I initialise with n bytes of data (eg “hello world!”). I set up a process which opens the file via an in_channel, and repeatedly reads n bytes from the beginning of the file. Whenever the bytes change, the process should print out the new bytes. I now start a second proce…

[image] thomas_ridge: Is this intended behaviour? and if so, is there a way to force the in_channel to read from the underlying file descriptor? alternatively, should I be using standard Unix IO instead? I tend to think this is expected given the buffering behaviour of in_channel. If you don’…

Do you have any alternative semantics in mind? Cheers, Nicolas

I think unbuffered IO would be a reasonable default, since you can build buffered IO on top, but not vice-versa. I also think that the behavior of in_channel is a bit strange, particularly since there isn’t a way to reset the buffer.

[image] jfeser: I think unbuffered IO would be a reasonable default, since you can build buffered IO on top, but not vice-versa. I’m not sure I agree here. Unbuffered IO is an easy way to kill the performance of your program, and buffered is the right default in most use-cases. If you need un…

I don’t mind the buffering, but a general rule of buffering is that if the underlying data changes, the buffer should detect this and reset itself accordingly. I realise this is difficult to do in this situation (because there is no reliable way to detect that the underlying data has changed short o…

Also, at the risk of pushing my luck and annoying even more people… Can I repeat my oft-made request to have pread and pwrite included in the Unix library? Given that multicore is just round the corner, pread and pwrite have substantial advantages over seek+(read/write), in that the user doesn’t hav…

[image] thomas_ridge: Can I repeat my oft-made request to have pread and pwrite included in the Unix library? Probably worth opening an issue for this Issues · ocaml/ocaml · GitHub . And PRs are always welcome… :slight_smile: Cheers, Nicolas

[image] thomas_ridge: if this is really the semantics we should be upfront about it. A note to this effect in the documentation seems like a good idea. You can open an issue at Issues · ocaml/ocaml · GitHub or, better yet, propose a PR in this direction directly. Cheers, Nicolas

[image] nojb: A note to this effect in the documentation seems like a good idea. It is interesting, but is it really a good idea? Off the top of my head I cannot recall coming across languages which provide a buffered file abstraction for input (whether called channels, streams, ports or wha…

Maybe default is the wrong word. I agree that most programs should use buffered IO. But, Unix isn’t portable and channels are (I think?). It would be better to have a portable api that can do buffered and unbuffered IO.

Semantics of in_channel, out_channel, when two processes operate on the same file

Learning

thomas_ridge December 6, 2021, 8:57pm 3

Ok, but I still think this is a bit strange!

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Semantics of in_channel, out_channel, when two processes operate on the same file

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