Feature request: continuous mode

[trombonehero]

I'd love it if Ninja could continuously monitor my source files and re-build things whenever they change.

[evmar]

I use inotifywatch in my own projects for this sometimes.

brevity due to phone
On Oct 23, 2014 9:22 AM, "Jonathan Anderson" notifications@github.com
wrote:

I'd love it if Ninja could continuously monitor my source files and
re-build things whenever they change.

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#833.

[nico]

pcc has an experimental branch that adds support for this, see https://groups.google.com/forum/#!topic/ninja-build/94xqWwgbFD8 (I did a mac port of that branch at https://github.com/nico/ninja/commits/mac)

I'm not fully convinced that this should be a ninja core feature. It can be done external to ninja with inotifywatch or Facebook's watchman. Supporting this in ninja core would require different code on Linux, Mac OS, and Windows, and it requires quite a bit of code on each platform too. The Mac implementation I currently have needs one fd per watched file and each parent directory, and for large projects I'd expect ninja to run out of fds (though I haven't tried it yet). From what I understand, there's a different method of implementing this that might fewer fds, but that requires changing ninja's main loop to not call pselect() on OS X. So the feature feels like high-cost/low-benefit to me at the moment. (On the other hand, trying the feature motivated me to make compiling ninja itself about twice as fast and make the tests completely silent, so the feature does set some good incentives.)

[eli-schwartz]

Also requested at mesonbuild/meson#13143

[evmar]

Would be at least nice to add to the docs a suggested way to invoke watchman/inotifywait.

It feels like you could add some glue to make watchman integration smarter too: ask ninja for which files it would inspect to build a given target, then set up a watchman watch for just those files so that it doesn't needlessly rebuild. (On the other hand it should be relatively cheap to invoke ninja more often than you need so maybe it doesn't matter?)