[Experimental] Pitchfork::Info.close_all_fds!

[casperisfine]

Ensuring that an application is fork safe can be complex, and in case of mistake, one of the error condition is shared file descriptors, causing one worker to read packets from another which could have dire consequences.

Rather than to track down all the file descriptors that need reopening, close_all_fds! allows to automatically close all file descriptors that aren't explicitly marked as needing to be kept.

And in case of mistake, the error condition is that trying to read or write into that file descriptor will fail, which is much less critical than to read packets from another worker.

[casperisfine]

And in case of mistake, the error condition is that trying to read or write into that file descriptor will fail, which is much less critical than to read packets from another worker.

Correction here. FDs are fairly heavily recycled, so if we close the FD of some native code without its knowledge, while it's very likely it will just crash, it could end up reading or writing in a random file or socket, so it could potentially be worse.

In the end I think this approach make sense, but should be limited to Ruby level IOs via ObjectSpace.each_object(IO, &:close) given that Ruby IOs automatically keep track of them being closed and won't attempt to read/write the FD anymore.

That should take care of any potential fork safety issue in pure Ruby gems, but doesn't solve potential issues in native gems.

One downside is that ObjectSpace.each_object is quite slow on large heaps.