Summary:
This can cause a deadlock if `func()` calls `create_callsite`.

Usually it's rare. But (Python) signal handler makes it realistic.

Example backtrace:

  Traceback (most recent call first):
    File "/opt/fb/mercurial/edenscm/tracing.py", line 337, in event
    File "/opt/fb/mercurial/edenscm/mercurial/ui.py", line 1275, in debug
      tracing.debug(msg.rstrip("\n"), depth=1)
    File "/opt/fb/mercurial/edenscm/mercurial/commandserver.py", line 608, in _reapworkers
      self.ui.debug("worker process exited (pid=%d)\n" % pid)
    File "/opt/fb/mercurial/edenscm/mercurial/commandserver.py", line 591, in _sigchldhandler
      self._reapworkers(os.WNOHANG)
    File "/opt/fb/mercurial/edenscm/tracing.py", line 337, in event
    File "/opt/fb/mercurial/edenscm/mercurial/ui.py", line 1275, in debug
      tracing.debug(msg.rstrip("\n"), depth=1)
    File "/opt/fb/mercurial/edenscm/mercurial/commandserver.py", line 608, in _reapworkers
      self.ui.debug("worker process exited (pid=%d)\n" % pid)
    File "/opt/fb/mercurial/edenscm/mercurial/commandserver.py", line 591, in _sigchldhandler
      self._reapworkers(os.WNOHANG)

  #0  syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
  #1  0x000055d0d65ba339 in <parking_lot::raw_rwlock::RawRwLock>::lock_upgradable_slow ()
  #2  0x000055d0d55b5814 in tracing_runtime_callsite::create_callsite::<tracing_runtime_callsite::callsite_info::EventKindType, pytracing::new_callsite<tracing_runtime_callsite::callsite_info::EventKindType>::{closure#2}> ()
  #3  0x000055d0d5584cb9 in <pytracing::EventCallsite>::__new__ ()
  #4  0x000055d0d55a3eaa in std::panicking::try::<*mut python3_sys::object::PyObject, cpython::function::handle_callback<<pytracing::EventCallsite>::create_instance::TYPE_OBJECT::wrap_newfunc::{closure#0}, pytracing::EventCallsite, cpython::function::PyObjectCallbackConverter>::{closure#0}> ()
  #5  0x000055d0d5589365 in cpython::function::handle_callback::<<pytracing::EventCallsite>::create_instance::TYPE_OBJECT::wrap_newfunc::{closure#0}, pytracing::EventCallsite, cpython::function::PyObjectCallbackConverter> ()
  #6  0x000055d0d55856e1 in <pytracing::EventCallsite>::create_instance::TYPE_OBJECT::wrap_newfunc ()
  #7  0x00007ff88d576230 in type_call (
      kwds={'obj': Frame 0x7ff87c1f8c40, for file /opt/fb/mercurial/edenscm/mercurial/commandserver.py, line 608, in _reapworkers (self=<unixforkingservice(ui=<ui(_buffers=[], _bufferstates=[], _bufferapplylabels=None, _outputui=None, callhooks=True, insecureconnections=False, _colormode=None, _styles={}, _terminaloutput=None, cmdname=None, _uiconfig=<uiconfig(quiet=False, verbose=False, debugflag=False, tracebackflag=False, logmeasuredtimes=False, _rcfg=<localrcfg(_rcfg=<bindings.configparser.config at remote 0x7ff87d7325d0>) at remote 0x7ff87eb73e80>, _unserializable={}, _pinnedconfigs=set(), _knownconfig={'alias': <itemregister(_generics={<configitem(section='alias', name='.*', default=None, alias=[], generic=True, priority=0, _re=<re.Pattern at remote 0x7ff87d69bed0>) at remote 0x7ff87d690a60>}) at remote 0x7ff87dbfde50>, 'annotate': <itemregister(_generics=set()) at remote 0x7ff87d6ad9f0>, 'auth': <itemregister(_generics=set()) at remote 0x7ff87dc037c0>, 'blackbox': <itemregister(_generics=set()) at remote 0x7ff87d...(truncated), args=(),
      type=0x55d0d8ea5b40 <_RNvNvMs1R_CsgCrAUYYhx1D_9pytracingNtB8_13EventCallsite15create_instance11TYPE_OBJECT.llvm.4665269759137401160>) at Objects/typeobject.c:974
  #8  _PyObject_MakeTpCall (callable=<type at remote 0x55d0d8ea5b40>, args=<optimized out>,
      nargs=<optimized out>, keywords=<optimized out>) at Objects/call.c:159
  #9  0x00007ff88d56dc81 in _PyObject_Vectorcall (
      kwnames=('obj', 'name', 'target', 'level', 'fieldnames'), nargsf=<optimized out>,
      args=<optimized out>, callable=<type at remote 0x55d0d8ea5b40>) at ./Include/cpython/abstract.h:125
  #10 _PyObject_Vectorcall (kwnames=('obj', 'name', 'target', 'level', 'fieldnames'),
      nargsf=<optimized out>, args=<optimized out>, callable=<type at remote 0x55d0d8ea5b40>)
      at ./Include/cpython/abstract.h:115
  #11 call_function (kwnames=('obj', 'name', 'target', 'level', 'fieldnames'), oparg=<optimized out>,
      pp_stack=<synthetic pointer>, tstate=<optimized out>) at Python/ceval.c:4963
  #12 _PyEval_EvalFrameDefault (f=<optimized out>, throwflag=<optimized out>) at Python/ceval.c:3515
  #13 0x00007ff88d566268 in PyEval_EvalFrameEx (throwflag=0,
      f=Frame 0x7ff87cced010, for file /opt/fb/mercurial/edenscm/tracing.py, line 337, in event (message='worker process exited (pid=3953080)', name=None, target=None, level=1, depth=1, meta={}, frame=Frame 0x7ff87c1f8c40, for file /opt/fb/mercurial/edenscm/mercurial/commandserver.py, line 608, in _reapworkers (self=<unixforkingservice(ui=<ui(_buffers=[], _bufferstates=[], _bufferapplylabels=None, _outputui=None, callhooks=True, insecureconnections=False, _colormode=None, _styles={}, _terminaloutput=None, cmdname=None, _uiconfig=<uiconfig(quiet=False, verbose=False, debugflag=False, tracebackflag=False, logmeasuredtimes=False, _rcfg=<localrcfg(_rcfg=<bindings.configparser.config at remote 0x7ff87d7325d0>) at remote 0x7ff87eb73e80>, _unserializable={}, _pinnedconfigs=set(), _knownconfig={'alias': <itemregister(_generics={<configitem(section='alias', name='.*', default=None, alias=[], generic=True, priority=0, _re=<re.Pattern at remote 0x7ff87d69bed0>) at remote 0x7ff87d690a60>}) at remote 0x7ff87dbfde50>, 'annotate': ...(truncated))
      at Python/ceval.c:741
  #14 _PyEval_EvalCodeWithName (_co=<optimized out>, globals=<optimized out>, locals=<optimized out>,
      args=<optimized out>, argcount=<optimized out>, kwnames=<optimized out>, kwargs=0x7ff87c0fdc78,
      kwcount=<optimized out>, kwstep=1, defs=0x7ff87d572558, defcount=4, kwdefs=0x0, closure=0x0,
      name='event', qualname='event') at Python/ceval.c:4298
  #15 0x00007ff88d57fdce in _PyFunction_Vectorcall (func=<optimized out>, stack=0x7ff87c0fdc70,
      nargsf=<optimized out>, kwnames=<optimized out>) at Objects/call.c:435
  #16 0x00007ff88d57574f in _PyObject_FastCallDict (callable=<function at remote 0x7ff87d5741f0>,
      args=0x7ff87eb63838, nargsf=<optimized out>, kwargs=<optimized out>) at Objects/call.c:104
  #17 0x00007ff88d66d1ab in partial_fastcall (kwargs={'level': 1, 'depth': 1}, nargs=<optimized out>,
      args=<optimized out>, pto=0x7ff87d572630) at ./Modules/_functoolsmodule.c:169
  #18 partial_call (pto=0x7ff87d572630, args=<optimized out>, kwargs=<optimized out>)
      at ./Modules/_functoolsmodule.c:224
  #19 0x00007ff88d576331 in _PyObject_MakeTpCall (callable=<functools.partial at remote 0x7ff87d572630>,
      args=<optimized out>, nargs=<optimized out>, keywords=<optimized out>) at Objects/object.c:2207
  #20 0x00007ff88d56dc81 in _PyObject_Vectorcall (kwnames=('depth',), nargsf=<optimized out>,
      args=<optimized out>, callable=<functools.partial at remote 0x7ff87d572630>)
      at ./Include/cpython/abstract.h:125
  #21 _PyObject_Vectorcall (kwnames=('depth',), nargsf=<optimized out>, args=<optimized out>,
      callable=<functools.partial at remote 0x7ff87d572630>) at ./Include/cpython/abstract.h:115
  #22 call_function (kwnames=('depth',), oparg=<optimized out>, pp_stack=<synthetic pointer>,
      tstate=<optimized out>) at Python/ceval.c:4963
  #23 _PyEval_EvalFrameDefault (f=<optimized out>, throwflag=<optimized out>) at Python/ceval.c:3515
  #24 0x00007ff88d566268 in PyEval_EvalFrameEx (throwflag=0,
      f=Frame 0x7ff87c0e43c0, for file /opt/fb/mercurial/edenscm/mercurial/ui.py, line 1275, in debug (self=<ui(_buffers=[], _bufferstates=[], _bufferapplylabels=None, _outputui=None, callhooks=True, insecureconnections=False, _colormode=None, _styles={}, _terminaloutput=None, cmdname=None, _uiconfig=<uiconfig(quiet=False, verbose=False, debugflag=False, tracebackflag=False, logmeasuredtimes=False, _rcfg=<localrcfg(_rcfg=<bindings.configparser.config at remote 0x7ff87d7325d0>) at remote 0x7ff87eb73e80>, _unserializable={}, _pinnedconfigs=set(), _knownconfig={'alias': <itemregister(_generics={<configitem(section='alias', name='.*', default=None, alias=[], generic=True, priority=0, _re=<re.Pattern at remote 0x7ff87d69bed0>) at remote 0x7ff87d690a60>}) at remote 0x7ff87dbfde50>, 'annotate': <itemregister(_generics=set()) at remote 0x7ff87d6ad9f0>, 'auth': <itemregister(_generics=set()) at remote 0x7ff87dc037c0>, 'blackbox': <itemregister(_generics=set()) at remote 0x7ff87dc039a0>, 'bookmarks': <itemregister(_generics=se...(truncated))
      at Python/ceval.c:741
  #25 _PyEval_EvalCodeWithName (_co=<optimized out>, globals=<optimized out>, locals=<optimized out>,
      args=<optimized out>, argcount=<optimized out>, kwnames=<optimized out>, kwargs=0x7ff87c1f8de8,
      kwcount=<optimized out>, kwstep=1, defs=0x0, defcount=0, kwdefs=0x0, closure=0x0, name='debug',
      qualname='ui.debug') at Python/ceval.c:4298
  #26 0x00007ff88d57fdce in _PyFunction_Vectorcall (func=<optimized out>, stack=0x7ff87c1f8dd8,
      nargsf=<optimized out>, kwnames=<optimized out>) at Objects/call.c:435
  #27 0x00007ff88d56821a in _PyObject_Vectorcall (kwnames=0x0, nargsf=<optimized out>,
      args=0x7ff87c1f8dd8, callable=<function at remote 0x7ff87d57e9d0>)
      at ./Include/cpython/abstract.h:127
  #28 call_function (kwnames=0x0, oparg=<optimized out>, pp_stack=<synthetic pointer>,
      tstate=0x7ff88ca08780) at Python/ceval.c:4963
  #29 _PyEval_EvalFrameDefault (f=<optimized out>, throwflag=<optimized out>) at Python/ceval.c:3486
  #30 0x00007ff88d57fd38 in PyEval_EvalFrameEx (throwflag=0,
      f=Frame 0x7ff87c1f8c40, for file /opt/fb/mercurial/edenscm/mercurial/commandserver.py, line 608, in _reapworkers (self=<unixforkingservice(ui=<ui(_buffers=[], _bufferstates=[], _bufferapplylabels=None, _outputui=None, callhooks=True, insecureconnections=False, _colormode=None, _styles={}, _terminaloutput=None, cmdname=None, _uiconfig=<uiconfig(quiet=False, verbose=False, debugflag=False, tracebackflag=False, logmeasuredtimes=False, _rcfg=<localrcfg(_rcfg=<bindings.configparser.config at remote 0x7ff87d7325d0>) at remote 0x7ff87eb73e80>, _unserializable={}, _pinnedconfigs=set(), _knownconfig={'alias': <itemregister(_generics={<configitem(section='alias', name='.*', default=None, alias=[], generic=True, priority=0, _re=<re.Pattern at remote 0x7ff87d69bed0>) at remote 0x7ff87d690a60>}) at remote 0x7ff87dbfde50>, 'annotate': <itemregister(_generics=set()) at remote 0x7ff87d6ad9f0>, 'auth': <itemregister(_generics=set()) at remote 0x7ff87dc037c0>, 'blackbox': <itemregister(_generics=set()) at remote 0x7ff87dc039a0>,...(truncated))
      at Python/ceval.c:738
  #31 function_code_fastcall (globals=<optimized out>, nargs=2, args=<optimized out>, co=<optimized out>)
      at Objects/call.c:283
  #32 _PyFunction_Vectorcall (func=<optimized out>, stack=<optimized out>, nargsf=<optimized out>,
      kwnames=<optimized out>) at Objects/call.c:410
  #33 0x00007ff88d56821a in _PyObject_Vectorcall (kwnames=0x0, nargsf=<optimized out>,
      args=0x7ff87c0f26d8, callable=<function at remote 0x7ff87d73b310>)
      at ./Include/cpython/abstract.h:127
  #34 call_function (kwnames=0x0, oparg=<optimized out>, pp_stack=<synthetic pointer>,
      tstate=0x7ff88ca08780) at Python/ceval.c:4963
  #35 _PyEval_EvalFrameDefault (f=<optimized out>, throwflag=<optimized out>) at Python/ceval.c:3486
  #36 0x00007ff88d57fd38 in PyEval_EvalFrameEx (throwflag=0,
      f=Frame 0x7ff87c0f2550, for file /opt/fb/mercurial/edenscm/mercurial/commandserver.py, line 591, in _sigchldhandler (self=<unixforkingservice(ui=<ui(_buffers=[], _bufferstates=[], _bufferapplylabels=None, _outputui=None, callhooks=True, insecureconnections=False, _colormode=None, _styles={}, _terminaloutput=None, cmdname=None, _uiconfig=<uiconfig(quiet=False, verbose=False, debugflag=False, tracebackflag=False, logmeasuredtimes=False, _rcfg=<localrcfg(_rcfg=<bindings.configparser.config at remote 0x7ff87d7325d0>) at remote 0x7ff87eb73e80>, _unserializable={}, _pinnedconfigs=set(), _knownconfig={'alias': <itemregister(_generics={<configitem(section='alias', name='.*', default=None, alias=[], generic=True, priority=0, _re=<re.Pattern at remote 0x7ff87d69bed0>) at remote 0x7ff87d690a60>}) at remote 0x7ff87dbfde50>, 'annotate': <itemreg
  ister(_generics=set()) at remote 0x7ff87d6ad9f0>, 'auth': <itemregister(_generics=set()) at remote 0x7ff87dc037c0>, 'blackbox': <itemregister(_generics=set()) at remote 0x7ff87dc039a...(truncated))
      at Python/ceval.c:738
  #37 function_code_fastcall (globals=<optimized out>, nargs=3, args=<optimized out>, co=<optimized out>)
      at Objects/call.c:283
  #38 _PyFunction_Vectorcall (func=<optimized out>, stack=<optimized out>, nargsf=<optimized out>,
      kwnames=<optimized out>) at Objects/call.c:410
  #39 0x00007ff88d592153 in _PyObject_Vectorcall (kwnames=<optimized out>, nargsf=<optimized out>,
      args=<optimized out>, callable=<optimized out>) at ./Include/cpython/abstract.h:115
  #40 method_vectorcall (method=<optimized out>, args=<optimized out>, nargsf=<optimized out>,
      kwnames=<optimized out>) at Objects/classobject.c:67
  #41 0x00007ff88d5963fb in PyVectorcall_Call (kwargs=0x0, tuple=<optimized out>,
      callable=<method at remote 0x7ff87c70d5c0>) at Objects/dictobject.c:1802
  #42 PyObject_Call (callable=<method at remote 0x7ff87c70d5c0>, args=<optimized out>, kwargs=0x0)
      at Objects/call.c:227
  #43 0x00007ff88d6405ea in _PyErr_CheckSignals () at ./Modules/signalmodule.c:1689
  #44 0x00007ff88d5a41a1 in _PyErr_CheckSignals () at Objects/object.c:577
  #45 PyErr_CheckSignals () at ./Modules/signalmodule.c:1649
  #46 PyObject_Str (v='_reapworkers') at Objects/object.c:561
  #47 0x000055d0d557c821 in pytracing::tostr_opt ()
  #48 0x000055d0d55b5a7d in tracing_runtime_callsite::create_callsite::<tracing_runtime_callsite::callsite_info::EventKindType, pytracing::new_callsite<tracing_runtime_callsite::callsite_info::EventKindType>::{closure#2}> ()
  #49 0x000055d0d5584cb9 in <pytracing::EventCallsite>::__new__ ()
  #50 0x000055d0d55a3eaa in std::panicking::try::<*mut python3_sys::object::PyObject, cpython::function::handle_callback<<pytracing::EventCallsite>::create_instance::TYPE_OBJECT::wrap_newfunc::{closure#0}, pytracing::EventCallsite, cpython::function::PyObjectCallbackConverter>::{closure#0}> ()
  #51 0x000055d0d5589365 in cpython::function::handle_callback::<<pytracing::EventCallsite>::create_instance::TYPE_OBJECT::wrap_newfunc::{closure#0}, pytracing::EventCallsite, cpython::function::PyObjectCallbackConverter> ()
  #52 0x000055d0d55856e1 in <pytracing::EventCallsite>::create_instance::TYPE_OBJECT::wrap_newfunc ()
  #53 0x00007ff88d576230 in type_call (
      kwds={'obj': Frame 0x7ff87c1f8440, for file /opt/fb/mercurial/edenscm/mercurial/commandserver.py, line 608, in _reapworkers (self=<unixforkingservice(ui=<ui(_buffers=[], _bufferstates=[], _bufferapplylabels=None, _outputui=None, callhooks=True, insecureconnections=False, _colormode=None, _styles={}, _terminaloutput=None, cmdname=None, _uiconfig=<uiconfig(quiet=False, verbose=False, debugflag=False, tracebackflag=False, logmeasuredtimes=False, _rcfg=<localrcfg(_rcfg=<bindings.configparser.config at remote 0x7ff87d7325d0>) at remote 0x7ff87eb73e80>, _unserializable={}, _pinnedconfigs=set(), _knownconfig={'alias': <itemregister(_generics={<configitem(section='alias', name='.*', default=None, alias=[], generic=True, priority=0, _re=<re.Pattern at remote 0x7ff87d69bed0>) at remote 0x7ff87d690a60>}) at remote 0x7ff87dbfde50>, 'annotate': <itemregister(_generics=set()) at remote 0x7ff87d6ad9f0>, 'auth': <itemregister(_generics=set()) at remote 0x7ff87dc037c0>, 'blackbox': <itemregister(_generics=set()) at remote 0x7ff87d...(truncated), args=(),
      type=0x55d0d8ea5b40 <_RNvNvMs1R_CsgCrAUYYhx1D_9pytracingNtB8_13EventCallsite15create_instance11TYPE_OBJECT.llvm.4665269759137401160>) at Objects/typeobject.c:974
  #54 _PyObject_MakeTpCall (callable=<type at remote 0x55d0d8ea5b40>, args=<optimized out>,
      nargs=<optimized out>, keywords=<optimized out>) at Objects/call.c:159
  #55 0x00007ff88d56dc81 in _PyObject_Vectorcall (
      kwnames=('obj', 'name', 'target', 'level', 'fieldnames'), nargsf=<optimized out>,
      args=<optimized out>, callable=<type at remote 0x55d0d8ea5b40>) at ./Include/cpython/abstract.h:125
  #56 _PyObject_Vectorcall (kwnames=('obj', 'name', 'target', 'level', 'fieldnames'),
      nargsf=<optimized out>, args=<optimized out>, callable=<type at remote 0x55d0d8ea5b40>)
      at ./Include/cpython/abstract.h:115
  #57 call_function (kwnames=('obj', 'name', 'target', 'level', 'fieldnames'), oparg=<optimized out>,
      pp_stack=<synthetic pointer>, tstate=<optimized out>) at Python/ceval.c:4963
  #58 _PyEval_EvalFrameDefault (f=<optimized out>, throwflag=<optimized out>) at Python/ceval.c:3515
  #59 0x00007ff88d566268 in PyEval_EvalFrameEx (throwflag=0,
      f=Frame 0x7ff87ccec890, for file /opt/fb/mercurial/edenscm/tracing.py, line 337, in event (message='worker process exited (pid=3953122)', name=None, target=None, level=1, depth=1, meta={}, frame=Frame 0x7ff87c1f8440, for file /opt/fb/mercurial/edenscm/mercurial/commandserver.py, line 608, in _reapworkers (self=<unixforkingservice(ui=<ui(_buffers=[], _bufferstates=[], _bufferapplylabels=None, _outputui=None, callhooks=True, insecureconnections=False, _colormode=None, _styles={}, _terminaloutput=None, cmdname=None, _uiconfig=<uiconfig(quiet=False, verbose=False, debugflag=False, tracebackflag=False, logmeasuredtimes=False, _rcfg=<localrcfg(_rcfg=<bindings.configparser.config at remote 0x7ff87d7325d0>) at remote 0x7ff87eb73e80>, _u
  nserializable={}, _pinnedconfigs=set(), _knownconfig={'alias': <itemregister(_generics={<configitem(section='alias', name='.*', default=None, alias=[], generic=True, priority=0, _re=<re.Pattern at remote 0x7ff87d69bed0>) at remote 0x7ff87d690a60>}) at remote 0x7ff87dbfde50>, 'annotate': ...(truncated))
      at Python/ceval.c:741
  #60 _PyEval_EvalCodeWithName (_co=<optimized out>, globals=<optimized out>, locals=<optimized out>,
      args=<optimized out>, argcount=<optimized out>, kwnames=<optimized out>, kwargs=0x7ff87c0fdd78,
      kwcount=<optimized out>, kwstep=1, defs=0x7ff87d572558, defcount=4, kwdefs=0x0, closure=0x0,
      name='event', qualname='event') at Python/ceval.c:4298
  #61 0x00007ff88d57fdce in _PyFunction_Vectorcall (func=<optimized out>, stack=0x7ff87c0fdd70,
      nargsf=<optimized out>, kwnames=<optimized out>) at Objects/call.c:435
  #62 0x00007ff88d57574f in _PyObject_FastCallDict (callable=<function at remote 0x7ff87d5741f0>,
      args=0x7ff87eb59d18, nargsf=<optimized out>, kwargs=<optimized out>) at Objects/call.c:104
  #63 0x00007ff88d66d1ab in partial_fastcall (kwargs={'level': 1, 'depth': 1}, nargs=<optimized out>,
      args=<optimized out>, pto=0x7ff87d572630) at ./Modules/_functoolsmodule.c:169
  #64 partial_call (pto=0x7ff87d572630, args=<optimized out>, kwargs=<optimized out>)
      at ./Modules/_functoolsmodule.c:224
  #65 0x00007ff88d576331 in _PyObject_MakeTpCall (callable=<functools.partial at remote 0x7ff87d572630>,
      args=<optimized out>, nargs=<optimized out>, keywords=<optimized out>) at Objects/object.c:2207
  #66 0x00007ff88d56dc81 in _PyObject_Vectorcall (kwnames=('depth',), nargsf=<optimized out>,
      args=<optimized out>, callable=<functools.partial at remote 0x7ff87d572630>)
      at ./Include/cpython/abstract.h:125
  #67 _PyObject_Vectorcall (kwnames=('depth',), nargsf=<optimized out>, args=<optimized out>,
      callable=<functools.partial at remote 0x7ff87d572630>) at ./Include/cpython/abstract.h:115
  #68 call_function (kwnames=('depth',), oparg=<optimized out>, pp_stack=<synthetic pointer>,
      tstate=<optimized out>) at Python/ceval.c:4963
  #69 _PyEval_EvalFrameDefault (f=<optimized out>, throwflag=<optimized out>) at Python/ceval.c:3515
  #70 0x00007ff88d566268 in PyEval_EvalFrameEx (throwflag=0,
      f=Frame 0x7ff87c0e4200, for file /opt/fb/mercurial/edenscm/mercurial/ui.py, line 1275, in debug (self=<ui(_buffers=[], _bufferstates=[], _bufferapplylabels=None, _outputui=None, callhooks=True, insecureconnections=False, _colormode=None, _styles={}, _terminaloutput=None, cmdname=None, _uiconfig=<uiconfig(quiet=False, verbose=False, debugflag=False, tracebackflag=False, logmeasuredtimes=False, _rcfg=<localrcfg(_rcfg=<bindings.configparser.config at remote 0x7ff87d7325d0>) at remote 0x7ff87eb73e80>, _unserializable={}, _pinnedconfigs=set(), _knownconfig={'alias': <itemregister(_generics={<configitem(section='alias', name='.*', default=None, alias=[], generic=True, priority=0, _re=<re.Pattern at remote 0x7ff87d69bed0>) at remote 0x7ff87d690a60>}) at remote 0x7ff87dbfde50>, 'annotate': <itemregister(_generics=set()) at remote 0x7ff87d6ad9f0>, 'auth': <itemregister(_generics=set()) at remote 0x7ff87dc037c0>, 'blackbox': <itemregister(_generics=set()) at remote 0x7ff87dc039a0>, 'bookmarks': <itemregister(_generics=se...(truncated))
      at Python/ceval.c:741
  #71 _PyEval_EvalCodeWithName (_co=<optimized out>, globals=<optimized out>, locals=<optimized out>,
      args=<optimized out>, argcount=<optimized out>, kwnames=<optimized out>, kwargs=0x7ff87c1f85e8,
      kwcount=<optimized out>, kwstep=1, defs=0x0, defcount=0, kwdefs=0x0, closure=0x0, name='debug',
      qualname='ui.debug') at Python/ceval.c:4298
  #72 0x00007ff88d57fdce in _PyFunction_Vectorcall (func=<optimized out>, stack=0x7ff87c1f85d8,
      nargsf=<optimized out>, kwnames=<optimized out>) at Objects/call.c:435
  #73 0x00007ff88d56821a in _PyObject_Vectorcall (kwnames=0x0, nargsf=<optimized out>,
      args=0x7ff87c1f85d8, callable=<function at remote 0x7ff87d57e9d0>)
      at ./Include/cpython/abstract.h:127
  #74 call_function (kwnames=0x0, oparg=<optimized out>, pp_stack=<synthetic pointer>,
      tstate=0x7ff88ca08780) at Python/ceval.c:4963
  #75 _PyEval_EvalFrameDefault (f=<optimized out>, throwflag=<optimized out>) at Python/ceval.c:3486
  #76 0x00007ff88d57fd38 in PyEval_EvalFrameEx (throwflag=0,
      f=Frame 0x7ff87c1f8440, for file /opt/fb/mercurial/edenscm/mercurial/commandserver.py, line 608, in _reapworkers (self=<unixforkingservice(ui=<ui(_buffers=[], _bufferstates=[], _bufferapplylabels=None, _outputui=None, callhooks=True, insecureconnections=False, _colormode=None, _styles={}, _terminaloutput=None, cmdname=None, _uiconfig=<uiconfig(quiet=False, verbose=False, debugflag=False, tracebackflag=False, logmeasuredtimes=False, _rcfg=<localrcfg(_rcfg=<bindings.configparser.config at remote 0x7ff87d7325d0>) at remote 0x7ff87eb73e80>, _unserializable={}, _pinnedconfigs=set(), _knownconfig={'alias': <itemregister(_generics={<configitem(section='alias', name='.*', default=None, alias=[], generic=True, priority=0, _re=<re.Pattern at remote 0x7ff87d69bed0>) at remote 0x7ff87d690a60>}) at remote 0x7ff87dbfde50>, 'annotate': <itemregister(_generics=set()) at remote 0x7ff87d6ad9f0>, 'auth': <itemregister(_generics=set()) at remote 0x7ff87dc037c0>, 'blackbox': <itemregister(_generics=set()) at remote 0x7ff87dc039a0>,...(truncated))
      at Python/ceval.c:738
  #77 function_code_fastcall (globals=<optimized out>, nargs=2, args=<optimized out>, co=<optimized out>)
  {<configitem(section='alias', name='.*', default=None, alias=[], generic=True, priority=0, _re=<re.Pattern at remote 0x7ff87d69bed0>) at remote 0x7ff87d690a60>}) at remote 0x7ff87dbfde50>, 'annotate': <itemregister(_generics=set()) at remote 0x7ff87d6ad9f0>, 'auth': <itemregister(_generics=set()) at remote 0x7ff87dc037c0>, 'blackbox': <itemregister(_generics=set()) at remote 0x7ff87dc039a0>,...(truncated))
      at Python/ceval.c:738
  #77 function_code_fastcall (globals=<optimized out>, nargs=2, args=<optimized out>, co=<optimized out>)
  --Type <RET> for more, q to quit, c to continue without paging--
      at Objects/call.c:283
  #78 _PyFunction_Vectorcall (func=<optimized out>, stack=<optimized out>, nargsf=<optimized out>,
      kwnames=<optimized out>) at Objects/call.c:410
  #79 0x00007ff88d56821a in _PyObject_Vectorcall (kwnames=0x0, nargsf=<optimized out>,
      args=0x7ff87c0f2528, callable=<function at remote 0x7ff87d73b310>)
      at ./Include/cpython/abstract.h:127
  #80 call_function (kwnames=0x0, oparg=<optimized out>, pp_stack=<synthetic pointer>,
      tstate=0x7ff88ca08780) at Python/ceval.c:4963
  #81 _PyEval_EvalFrameDefault (f=<optimized out>, throwflag=<optimized out>) at Python/ceval.c:3486
  #82 0x00007ff88d57fd38 in PyEval_EvalFrameEx (throwflag=0,
      f=Frame 0x7ff87c0f23a0, for file /opt/fb/mercurial/edenscm/mercurial/commandserver.py, line 591, in _sigchldhandler (self=<unixforkingservice(ui=<ui(_buffers=[], _bufferstates=[], _bufferapplylabels=None, _outputui=None, callhooks=True, insecureconnections=False, _colormode=None, _styles={}, _terminaloutput=None, cmdname=None, _uiconfig=<uiconfig(quiet=False, verbose=False, debugflag=False, tracebackflag=False, logmeasuredtimes=False, _rcfg=<localrcfg(_rcfg=<bindings.configparser.config at remote 0x7ff87d7325d0>) at remote 0x7ff87eb73e80>, _unserializable={}, _pinnedconfigs=set(), _knownconfig={'alias': <itemregister(_generics={<configitem(section='alias', name='.*', default=None, alias=[], generic=True, priority=0, _re=<re.Pattern at remote 0x7ff87d69bed0>) at remote 0x7ff87d690a60>}) at remote 0x7ff87dbfde50>, 'annotate': <itemregister(_generics=set()) at remote 0x7ff87d6ad9f0>, 'auth': <itemregister(_generics=set()) at remote 0x7ff87dc037c0>, 'blackbox': <itemregister(_generics=set()) at remote 0x7ff87dc039a...(truncated))
      at Python/ceval.c:738
  #83 function_code_fastcall (globals=<optimized out>, nargs=3, args=<optimized out>, co=<optimized out>)
      at Objects/call.c:283
  #84 _PyFunction_Vectorcall (func=<optimized out>, stack=<optimized out>, nargsf=<optimized out>,
      kwnames=<optimized out>) at Objects/call.c:410
  #85 0x00007ff88d592153 in _PyObject_Vectorcall (kwnames=<optimized out>, nargsf=<optimized out>,
      args=<optimized out>, callable=<optimized out>) at ./Include/cpython/abstract.h:115
  #86 method_vectorcall (method=<optimized out>, args=<optimized out>, nargsf=<optimized out>,
      kwnames=<optimized out>) at Objects/classobject.c:67
  #87 0x00007ff88d5963fb in PyVectorcall_Call (kwargs=0x0, tuple=<optimized out>,
      callable=<method at remote 0x7ff87c70d5c0>) at Objects/dictobject.c:1802
  #88 PyObject_Call (callable=<method at remote 0x7ff87c70d5c0>, args=<optimized out>, kwargs=0x0)
      at Objects/call.c:227
  #89 0x00007ff88d6405ea in _PyErr_CheckSignals () at ./Modules/signalmodule.c:1689
  #90 0x00007ff88d59b7fd in _PyErr_CheckSignals () at ./Modules/signalmodule.c:1660
  #91 PyErr_CheckSignals () at ./Modules/signalmodule.c:1649
  ....

Reviewed By: DurhamG

Differential Revision: D27111187

fbshipit-source-id: 1aa29ab24088b57b98de3741eb81c0a7be01237d