Attempt to make libuv fork safe.

[yacobucci]

If threadpool is initialized try and make libuv fork safe. As a library
it's hard to predict what an application may do and a programmer not
realizing libuv may spawn threads may fork without an exec call. If this
occurs and threadpool is initialized the child will abort in shutdown as
the threads no longer exist and pthread_join fails.

This checkin doesn't work at the moment - the threadpool is now fork
safe, but on BSD kqueue is not and any loop will have an invalid kqueue

More info here: https://groups.google.com/forum/#!topic/libuv/jJcVpdflSIU
in the child.

[Nodejs-Jenkins]

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Commit yacobucci/libuv@7ffe3a0 has the following error(s):

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• Matthew Yacobucci

You can fix all these things without opening another issue.

Please see CONTRIBUTING.md for more information

[txdv]

General whitespace issue, you should go through the code and check for whitespaces.

Every worker is now going through a lock and unlock. I don't know how much of a performance drain that would is. Can you create a libuv test where you do a simple while loop of N times where in one you do nothing and in the other a lock and unlock subsequently?

In general I wonder why we would want to make libuv fork safe. As you said in the forum kqueue is not forkable, I doubt the others are and even if they are, you don't want to

[saghul]

@txdv this cannot land in its current form, it's Unix specific and the threadpool is shared now.

[txdv]

I wonder why he wants it all.

He said fork-exec is the only reason why you would want to fork and IMO that have basically the the same functionality as uv_spawn.

Could this performance wise be faster?

[brimworks]

FWIW, I ran into this when trying to write a program that "daemonize's" (fork, setsid, fork):

http://www.microhowto.info/howto/cause_a_process_to_become_a_daemon_in_c.html

...I know this is out-of-date advice since most Linux flavors use upstart, supervisord, or other process managers, but I was trying to write my daemon in a way that would work with SysV.

Thanks,
-Brian