parallel and CoreFoundation on OSX about httpuv

[jcheng5]

It looks to me like a combination of how parallel is implemented (fork without exec), and something that libuv is using in CoreServices. I don't know what libuv actually uses but I know it wouldn't build on Mac until I linked in the CoreServices framework.

This explains the general problem: http://objectivistc.tumblr.com/post/16187948939/you-must-exec-a-core-foundation-fork-safety-tale

Sooner or later (probably within 2 months?) I am going to add a daemonize option to httpuv, it is needed for gigvis.

[jeroen]

Interesting. Thanks.

[jeroen]

What I don't understand is why it also happens when httpuv is only loaded in the forked child process, not in the parent process. So in this case, the CF process is not forked.

Also the error only appears when used in Rstudio. When running the above code snippet in a regular R session in the console on the same machine, I don't get to see this warning.

[jcheng5]

The problem seems to occur whenever CF has been loaded in the parent process (whether by httpuv or anything else). So the Mac R GUI also triggers this problem; the reason it doesn't occur at the command line must be because no CF code is being loaded (which would not be very surprising).

Another link (the referenced Apple docs are instructive):
http://stackoverflow.com/questions/2707572/fork-within-cocoa-application

If you could exec the child process then it would be fine.

[jeroen]

Hmm alright. I asked @s-u for his 2ct, hope he can have a look.

[s-u]

gdb is your friend:

#0  0x00007fff842a84f4 in __THE_PROCESS_HAS_FORKED_AND_YOU_CANNOT_USE_THIS_COREFOUNDATION_FUNCTIONALITY___YOU_MUST_EXEC__ ()
#1  0x00007fff841f46f5 in CFRunLoopSourceCreate ()
#2  0x0000000103d85b61 in uv__platform_loop_init (loop=0x103dae2c0, default_loop=0) at darwin.c:69
#3  0x0000000103d7b5da in uv__loop_init (loop=0x103dae2c0, default_loop=0) at loop.c:62
#4  0x0000000103d78c51 in uv_default_loop () at core.c:222
#5  0x0000000103d62c2c in makeServer (host=@0x7fff5fbf7908, port=1606383360, onHeaders=@0x0, onBodyData=@0x0, onRequest=@0x0, onWSOpen=@0x7fff5fbf7930, onWSMessage=@0x7fff5fbf7920, onWSClose=@0x7fff5fbf7910) at httpuv.cpp:327

as you can see httpuv is trying to run the CF event loop despite R_isForkedChild being set. Ideally, it should not be running the event loop itself but add a hook into the R event loop -- that would work, because R suspends the event loop when unsafe (e.g. while forked).