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Bug #17677
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Ractor crashes fork when blocking
Description
Background¶
If you create a Ractor which blocks (e.g. receive), then fork the process, the fork will segfault upon completion.
How to reproduce¶
r2 = Ractor.new do
Ractor.receive
end
sleep(1)
puts "Forking..."
fork do
sleep(1)
puts "End fork."
end
loop do
puts "Main thread."
sleep(1)
end
Expectation and result¶
Application prints “Main thread” from main process every second, while fork prints “End fork.” then produces a segfault. Main process continues to run.
Expected fork to not raise a segfault.
<internal:ractor>:267: warning: Ractor is experimental, and the behavior may change in future versions of Ruby! Also there are many implementation issues.
Forking...
Main thread.
Main thread.
End fork.
app/sandbox.rb:80: [BUG]: Device or resource busy (EBUSY)
ruby 3.0.0p0 (2020-12-25 revision 95aff21468) [x86_64-linux]
-- Control frame information -----------------------------------------------
c:0003 p:---- s:0011 e:000010 CFUNC :fork
c:0002 p:0048 s:0007 E:001b48 EVAL app/sandbox.rb:80 [FINISH]
c:0001 p:0000 s:0003 E:002590 (none) [FINISH]
-- Ruby level backtrace information ----------------------------------------
app/sandbox.rb:80:in `<main>'
app/sandbox.rb:80:in `fork'
-- C level backtrace information -------------------------------------------
/usr/local/lib/libruby.so.3.0(rb_print_backtrace+0x11) [0x7f9848528cfb] vm_dump.c:758
/usr/local/lib/libruby.so.3.0(rb_vm_bugreport) vm_dump.c:998
/usr/local/lib/libruby.so.3.0(bug_report_end+0x0) [0x7f9848354808] error.c:763
/usr/local/lib/libruby.so.3.0(rb_bug_without_die) error.c:763
/usr/local/lib/libruby.so.3.0(die+0x0) [0x7f98482c6902] error.c:771
/usr/local/lib/libruby.so.3.0(rb_bug) error.c:773
/usr/local/lib/libruby.so.3.0(rb_bug_errno+0x3c) [0x7f9848354a1c] error.c:802
/usr/local/lib/libruby.so.3.0(rb_native_mutex_destroy+0x20) [0x7f98484ce380] thread_pthread.c:444
/usr/local/lib/libruby.so.3.0(rb_native_cond_initialize) (null):0
/usr/local/lib/libruby.so.3.0(ractor_free+0xd) [0x7f984844487d] ractor.c:229
/usr/local/lib/libruby.so.3.0(run_final+0xb) [0x7f9848371c66] gc.c:3670
/usr/local/lib/libruby.so.3.0(finalize_list) gc.c:3689
/usr/local/lib/libruby.so.3.0(rb_objspace_call_finalizer+0x33d) [0x7f984837cc5d] gc.c:3852
/usr/local/lib/libruby.so.3.0(rb_ec_cleanup+0x311) [0x7f984835f0b1] eval.c:184
/usr/local/lib/libruby.so.3.0(ruby_stop+0x9) [0x7f984835f339] eval.c:329
/usr/local/lib/libruby.so.3.0(rb_f_fork+0x1f) [0x7f98484402f8] process.c:4348
/usr/local/lib/libruby.so.3.0(rb_f_fork) process.c:4338
/usr/local/lib/libruby.so.3.0(vm_call_cfunc_with_frame+0x11b) [0x7f984850672b] vm_insnhelper.c:2898
/usr/local/lib/libruby.so.3.0(vm_call_method_each_type+0xf9) [0x7f98485192c9] vm_insnhelper.c:3388
/usr/local/lib/libruby.so.3.0(vm_call_method+0xb4) [0x7f9848519b24] vm_insnhelper.c:3506
/usr/local/lib/libruby.so.3.0(vm_sendish+0xb3) [0x7f984850a3d3] vm_insnhelper.c:4499
/usr/local/lib/libruby.so.3.0(vm_exec_core+0x140) [0x7f98485123e0] insns.def:770
/usr/local/lib/libruby.so.3.0(rb_vm_exec+0x176) [0x7f9848517b26] vm.c:2163
/usr/local/lib/libruby.so.3.0(rb_ec_exec_node+0xd9) [0x7f9848359719] eval.c:317
/usr/local/lib/libruby.so.3.0(ruby_run_node+0x55) [0x7f984835f395] eval.c:375
/usr/local/bin/ruby(main+0x5b) [0x565147e5410b] ./main.c:50
...
Main thread.
Main thread.
Main thread.
Additional notes¶
This does not happen if a blocking operation does not occur in the Ractor. E.g.
r2 = Ractor.new do
loop { puts "[#{Process.pid}] Ractor"; sleep(1) }
end
Segfault can also be prevented by invoking close_incoming prior to forking, although this raises another error internally.
It also does not crash on MacOS 10.15.7: ruby 3.0.0p0 (2020-12-25 revision 95aff21468) [x86_64-darwin19].
Suggested solutions¶
(None)
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