Advisory lock on an open file using flock not working

[kjpou1]

Using flock does not seem to work.

The API is implemented and it's used by some of emscripten internal tooling (https://github.com/emscripten-core/emscripten/blob/master/tools/filelock.py#L363).

In the tests there are tests for fnctl that reference struct flock: https://github.com/emscripten-core/emscripten/blob/master/tests/fcntl/test_fcntl.c#L57

But there do not seem to be any tests that use flock.

[sbc100]

The python locking implemented in tools/filelock.py is part of the compiler driver and nothing to do with the runtime.

It looks like flock is linux/bsd and not part of POSIX, which is probably why we have not gotten around to implementing it yet. I don't think anyone would object if somebody wanted to add it. It looks like we have a stub right here that can be filled in:

emscripten/src/library.js

Line 112 in c5cc009

flock: function(fd, operation) {

[kjpou1]

@sbc100 thank you for the information.

Are you saying that POSIX record locks (fcntl) is implemented and should work?

[sbc100]

I looks from the test you linked to at hat least the F_GETLK and F_SETLK fcntls return errno 0.

It looks like they mostly stubbed out:

emscripten/src/library_syscall.js

Line 1160 in 126fa66

__sys_fcntl64__deps: ['$setErrNo'],

Remember that emscripten is not multi-process and the filesystem is basically local the running module, so the actually locking functionality I don't think make much sense.

What you are hoping to lock against in your application exactly?

[kjpou1]

@sbc100 thank you for the information. We will need to discuss the locking and whether or not it makes sense as you have mentioned.

[stale]

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