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Tarsnap / libcperciva

BSD-licensed C99/POSIX library code shared between tarsnap, scrypt, kivaloo, spiped, and bsdiff.
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Add & use ipc_sync.h #514

Closed gperciva closed 6 months ago

gperciva commented 8 months ago

Don't know if you'll like this; I found it helpful for quickly adding blocking to https://github.com/Tarsnap/spiped/pull/399. And it makes daemonize.c easier to understand.

This basically implements a semaphore with pipes (as you did in daemonize.c). Ideally, we'd be able to use sem_init() etc., but that's part of the REALTIME option of POSIX, and it isn't supported by macOS. :(

This version has everything in the ipc_sync.h file; I have another version which puts the implementation in ipc_sync.c.

cperciva commented 7 months ago

I like it, but

  1. I don't know why you're putting everything into the .h file as inline functions; why not just use a .c file normally?

  2. Needs more usage documentation, in particular "you have to call _init before forking, then _wait+_done in one process and _signal+_done in the other".

  3. For that matter, is there any reason for _done to be a separate function?

gperciva commented 7 months ago

  1. I submitted the .h version because I wanted to keep the wait and signal functionality as unchanged as possible -- if that code ended up in a different .o file, would it receive the same optimization that it did previously?

    I do prefer the .c version, so I'll put that up.

  2. will do.

  3. _done could be called by signal and wait, but it includes close(), which might be slow. (Especially when we switch to noeintr_close.) So I figured that the signal & wait should be kept as fast as possible (e.g., inside timed code), while _done could be deferred until the caller wanted it.