[ruby-core:39659] [Ruby 1.9 - Bug #5343] Unexpected blocking behavior when interrupt Socket#accept

Issue #5343 has been updated by Tomoyuki Chikanaga.


Koichi Sasada wrote:
>  Could you commit it?  Maybe 1.9.3 also needs this patch.  But I'm not
>  sure how to commit frozen 1.9.3 branch.
I'd be happy to commit it. I'll check in it to trunk and create a backport request ticket.

BTW, let me summarize the reason why this patch works fine. If I misunderstand, please point out.
When interrupt other thread (cf. by Thread#kill, Thread#raise) in blocking region, unblocking function (ubf) is called to interrupt blocking system call like select/ppoll etc... The default ubf (ubf_select) call pthread_kill() to send SIGVTALRM to interrupted thread.
But There's race condition. If interrupted thread was just released GVL and received SIGVTALRM before entering blocking systemcall, signal was lost.
To cover this race condition, ubf_select() also call add_signal_thread_list() to register "signal thread list". Timer thread periodically send SIGVTALRM to threads in signal thread list. Recently timer thread is suspended when there's no more than one runnable thread. So when interrupt other thread and register to signal thread list, you should activate timer thread to polling-mode.

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Bug #5343: Unexpected blocking behavior when interrupt Socket#accept
http://redmine.ruby-lang.org/issues/5343

Author: Tomoyuki Chikanaga
Status: Assigned
Priority: High
Assignee: Koichi Sasada
Category: ext
Target version: 1.9.3
ruby -v: -


In CentOS release 5.6 (Kernel: 2.6.18-238.12.1.el5, glibc 2.5),
the following sample script rarely (about once every 1000) blocks at Thread#join with 1.9.3-head.

require "socket"
require "thread"

queue = Queue.new

th = Thread.start {
  s = TCPServer.new(10000)
  queue.push(nil)
  cli = s.accept
}

queue.pop
th.kill.join

Backtrace:
thread-1:
#0  0x0000003a3500aee9 in pthread_cond_wait@@GLIBC_2.3.2 ()
   from /lib64/libpthread.so.0
#1  0x000000000052d81b in native_cond_wait (th=0x19551550, timeout_tv=0x0)
    at ../ruby-1.9.3/thread_pthread.c:307
#2  native_sleep (th=0x19551550, timeout_tv=0x0)
    at ../ruby-1.9.3/thread_pthread.c:908
#3  0x000000000052f9ab in sleep_forever (th=0x19551550, deadlockable=1)
    at ../ruby-1.9.3/thread.c:855
#4  0x000000000052fa4d in thread_join_sleep (arg=140733838958496)
    at ../ruby-1.9.3/thread.c:688
#5  0x0000000000417abb in rb_ensure (b_proc=0x52fa00 <thread_join_sleep>,
    data1=140733838958496, e_proc=0x5288e0 <remove_from_join_list>,
    data2=140733838958496) at ../ruby-1.9.3/eval.c:736
#6  0x000000000052a78e in thread_join (argc=<value optimized out>,
    argv=<value optimized out>, self=<value optimized out>)
    at ../ruby-1.9.3/thread.c:721
#7  thread_join_m (argc=<value optimized out>, argv=<value optimized out>,
    self=<value optimized out>) at ../ruby-1.9.3/thread.c:802
#8  0x0000000000524b0d in vm_call_cfunc (th=0x19551550, cfp=0x2b38cc37df08,
    num=<value optimized out>, blockptr=<value optimized out>,
    flag=<value optimized out>, id=<value optimized out>, me=0x196663c0,
    recv=427644560) at ../ruby-1.9.3/vm_insnhelper.c:404
#9  vm_call_method (th=0x19551550, cfp=0x2b38cc37df08,
    num=<value optimized out>, blockptr=<value optimized out>,
    flag=<value optimized out>, id=<value optimized out>, me=0x196663c0,
    recv=427644560) at ../ruby-1.9.3/vm_insnhelper.c:530
#10 0x000000000051908d in vm_exec_core (th=0x19551550,
    initial=<value optimized out>) at ../ruby-1.9.3/insns.def:1015
#11 0x000000000051ed7e in vm_exec (th=0x19551550) at ../ruby-1.9.3/vm.c:1220
#12 0x0000000000525f9f in rb_iseq_eval_main (iseqval=427473840)
    at ../ruby-1.9.3/vm.c:1461
#13 0x0000000000414c22 in ruby_exec_internal (n=0x197abbb0)
    at ../ruby-1.9.3/eval.c:204
#14 0x00000000004172d4 in ruby_exec_node (n=<value optimized out>)
    at ../ruby-1.9.3/eval.c:251
#15 ruby_run_node (n=<value optimized out>) at ../ruby-1.9.3/eval.c:244
#16 0x0000000000414689 in main (argc=2, argv=0x7fff267aa588)
    at ../ruby-1.9.3/main.c:38

thread-2:
#0  0x0000003a344cb696 in poll () from /lib64/libc.so.6
#1  0x00000000005301ba in ppoll (fd=<value optimized out>,
    events=<value optimized out>, tv=0x0) at ../ruby-1.9.3/thread.c:2820
#2  rb_wait_for_single_fd (fd=<value optimized out>,
    events=<value optimized out>, tv=0x0) at ../ruby-1.9.3/thread.c:2849
#3  0x000000000053052c in rb_thread_wait_fd_rw (fd=5)
    at ../ruby-1.9.3/thread.c:2686
#4  rb_thread_wait_fd (fd=5) at ../ruby-1.9.3/thread.c:2699
#5  0x00002aaaab0b7b6f in rsock_s_accept (klass=427743720, fd=5,
    sockaddr=<value optimized out>, len=0x40473a3c)
    at ../../../ruby-1.9.3/ext/socket/init.c:499
#6  0x00002aaaab0c3310 in tcp_accept (sock=<value optimized out>)
    at ../../../ruby-1.9.3/ext/socket/tcpserver.c:55
#7  0x0000000000524b0d in vm_call_cfunc (th=0x197ffe90, cfp=0x2aaaab3d3f08,
    num=<value optimized out>, blockptr=<value optimized out>,
    flag=<value optimized out>, id=<value optimized out>, me=0x1980ba70,
    recv=427644480) at ../ruby-1.9.3/vm_insnhelper.c:404
#8  vm_call_method (th=0x197ffe90, cfp=0x2aaaab3d3f08,
    num=<value optimized out>, blockptr=<value optimized out>,
    flag=<value optimized out>, id=<value optimized out>, me=0x1980ba70,
    recv=427644480) at ../ruby-1.9.3/vm_insnhelper.c:530
#9  0x000000000051908d in vm_exec_core (th=0x197ffe90,
    initial=<value optimized out>) at ../ruby-1.9.3/insns.def:1015
#10 0x000000000051ed7e in vm_exec (th=0x197ffe90) at ../ruby-1.9.3/vm.c:1220
#11 0x000000000051fad5 in invoke_block_from_c (th=0x197ffe90,
    block=<value optimized out>, self=<value optimized out>, argc=0,
    argv=<value optimized out>, blockptr=<value optimized out>, cref=0x0)
    at ../ruby-1.9.3/vm.c:624
#12 0x000000000052026f in rb_vm_invoke_proc (th=0x197ffe90, proc=0x196d72a0,
    self=425420560, argc=0, argv=0x197d56c8, blockptr=0x0)
    at ../ruby-1.9.3/vm.c:670
#13 0x000000000052f5c1 in thread_start_func_2 (th=0x197ffe90,
    stack_start=<value optimized out>) at ../ruby-1.9.3/thread.c:453
#14 0x000000000052f75e in thread_start_func_1 (th_ptr=0x197ffe90)
    at ../ruby-1.9.3/thread_pthread.c:656
#15 0x0000003a3500673d in start_thread () from /lib64/libpthread.so.0
#16 0x0000003a344d44bd in clone () from /lib64/libc.so.6



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