Multi-threading causes `hchebyshevcenter` to trigger a segmentation fault

[ferrolho]

I have been trying this with four threads:

export JULIA_NUM_THREADS=4

Minimal working example:

using GLPK
using JuMP
using Polyhedra
using QHull

@show Threads.nthreads()

thread_libs = [QHull.Library(GLPK.Optimizer) for i = 1:Threads.nthreads()]
thread_lp_solvers = [optimizer_with_attributes(GLPK.Optimizer, "presolve" => GLPK.ON) for i = 1:Threads.nthreads()]

Threads.@threads for i = 1:10
    threadᵢ = Threads.threadid()
    println("I am thread #$(threadᵢ).")

    lib = thread_libs[threadᵢ]
    lp_solver = thread_lp_solvers[threadᵢ]

    my_points = rand(10, 3)
    my_polyhedron = polyhedron(vrep(my_points), lib)
    hchebyshevcenter(my_polyhedron, lp_solver)
end

I am not even sure I need a distinct lib and lp_solver per thread, but I tried it anyway to check whether that was the cause of the problem...

Output log:

signal (11): Segmentation fault

signal (11): Segmentation fault
in expression starting at REPL[12]:1
in expression starting at REPL[12]:1
unknown function (ip: 0x7f3a890d7936)
PyUnicode_New at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
_PyUnicodeWriter_PrepareInternal at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
PyUnicode_DecodeUTF8Stateful at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
PyUnicode_FromFormatV at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
PyErr_FormatV at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
PyErr_Format at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
PyObject_GetBuffer at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
_PyObject_Malloc at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
PyUnicode_New at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
_PyUnicodeWriter_PrepareInternal at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
PyUnicode_DecodeUTF8Stateful at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
PyUnicode_FromFormatV at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
sbuftype! at /home/henrique/.julia/packages/PyCall/zqDXB/src/pybuffer.jl:134 [inlined]
PyErr_FormatV at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
isbuftype at /home/henrique/.julia/packages/PyCall/zqDXB/src/pybuffer.jl:148 [inlined]
pysequence_query at /home/henrique/.julia/packages/PyCall/zqDXB/src/conversions.jl:756
PyErr_Format at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
PyObject_GetBuffer at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
isbuftype! at /home/henrique/.julia/packages/PyCall/zqDXB/src/pybuffer.jl:134 [inlined]
isbuftype at /home/henrique/.julia/packages/PyCall/zqDXB/src/pybuffer.jl:148 [inlined]
pysequence_query at /home/henrique/.julia/packages/PyCall/zqDXB/src/conversions.jl:756
pytype_query at /home/henrique/.julia/packages/PyCall/zqDXB/src/conversions.jl:770
pytype_query at /home/henrique/.julia/packages/PyCall/zqDXB/src/conversions.jl:803 [inlined]
convert at /home/henrique/.julia/packages/PyCall/zqDXB/src/conversions.jl:828
pytype_query at /home/henrique/.julia/packages/PyCall/zqDXB/src/conversions.jl:770
pytype_query at /home/henrique/.julia/packages/PyCall/zqDXB/src/conversions.jl:803 [inlined]
convert at /home/henrique/.julia/packages/PyCall/zqDXB/src/conversions.jl:828
getproperty at /home/henrique/.julia/packages/PyCall/zqDXB/src/PyCall.jl:306 [inlined]
chull at /home/henrique/.julia/packages/QHull/ck7jQ/src/QHull.jl:34
getproperty at /home/henrique/.julia/packages/PyCall/zqDXB/src/PyCall.jl:306 [inlined]
chull at /home/henrique/.julia/packages/QHull/ck7jQ/src/QHull.jl:34
qhull at /home/henrique/.julia/packages/QHull/ck7jQ/src/polyhedron.jl:83
qhull at /home/henrique/.julia/packages/QHull/ck7jQ/src/polyhedron.jl:83
jl_apply_generic at /opt/julia-1.4.1/bin/../lib/libjulia.so.1 (unknown line)
qhull at /home/henrique/.julia/packages/QHull/ck7jQ/src/polyhedron.jl:62
qhull at /home/henrique/.julia/packages/QHull/ck7jQ/src/polyhedron.jl:61
getine at /home/henrique/.julia/packages/QHull/ck7jQ/src/polyhedron.jl:167
hrep at /home/henrique/.julia/packages/QHull/ck7jQ/src/polyhedron.jl:211
hyperplanetype at /home/henrique/.julia/packages/Polyhedra/w0Toa/src/iterators.jl:175
_broadcast_getindex_evalf at ./broadcast.jl:631 [inlined]
_broadcast_getindex at ./broadcast.jl:604 [inlined]
#19 at ./broadcast.jl:1024 [inlined]
ntuple at ./ntuple.jl:41 [inlined]
copy at ./broadcast.jl:1024 [inlined]
materialize at ./broadcast.jl:820
hyperplanes at /home/henrique/.julia/packages/Polyhedra/w0Toa/src/iterators.jl:183 [inlined]
hchebyshevcenter at /home/henrique/.julia/packages/Polyhedra/w0Toa/src/center.jl:13
_jl_invoke at (null):0 [inlined]
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2322
macro expansion at ./REPL[12]:10 [inlined]
#12#threadsfor_fun at ./threadingconstructs.jl:61
#12#threadsfor_fun at ./threadingconstructs.jl:28
unknown function (ip: 0x7f3ab411c8ec)
_jl_invoke at (null):0 [inlined]
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2322
_jl_invoke at /buildworker/worker/package_linux64/build/src/gf.c:2144 [inlined]
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2322
qhull at /home/henrique/.julia/packages/QHull/ck7jQ/src/polyhedron.jl:62
qhull at /home/henrique/.julia/packages/QHull/ck7jQ/src/polyhedron.jl:61
getine at /home/henrique/.julia/packages/QHull/ck7jQ/src/polyhedron.jl:167
hrep at /home/henrique/.julia/packages/QHull/ck7jQ/src/polyhedron.jl:211
hyperplanetype at /home/henrique/.julia/packages/Polyhedra/w0Toa/src/iterators.jl:175
_broadcast_getindex_evalf at ./broadcast.jl:631 [inlined]
_broadcast_getindex at ./broadcast.jl:604 [inlined]
#19 at ./broadcast.jl:1024 [inlined]
ntuple at ./ntuple.jl:41 [inlined]
copy at ./broadcast.jl:1024 [inlined]
materialize at ./broadcast.jl:820
hyperplanes at /home/henrique/.julia/packages/Polyhedra/w0Toa/src/iterators.jl:183 [inlined]
hchebyshevcenter at /home/henrique/.julia/packages/Polyhedra/w0Toa/src/center.jl:13
_jl_invoke at /buildworker/worker/package_linux64/build/src/gf.c:2144 [inlined]
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2322
macro expansion at ./REPL[12]:10 [inlined]
#12#threadsfor_fun at ./threadingconstructs.jl:61
#12#threadsfor_fun at ./threadingconstructs.jl:28
unknown function (ip: 0x7f3ab411c8ec)
_jl_invoke at /buildworker/worker/package_linux64/build/src/gf.c:2144 [inlined]
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2322

signal (11): Segmentation fault
in expression starting at REPL[12]:1
PyErr_Restore at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
PyDict_GetItem at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
unknown function (ip: 0x7f3adb8c8a5e)
unknown function (ip: (nil))
Allocations: 132736478 (Pool: 132718107; Big: 18371); GC: 137
[1]    27961 segmentation fault (core dumped)  julia

[blegat]

The hchebyshevcenter needs the H-representation so it triggers computehrep! which calls the QHull library which seems to be what is segfaulting. Could you try replacing hchebyshevcenter(my_polyhedron, lp_solver) by computehrep!(my_polyhedron) and check whether it still fails ?

[ferrolho]

Hi, @blegat! For the MWE above, I have replaced the line

hchebyshevcenter(my_polyhedron, lp_solver)

with

Polyhedra.computehrep!(my_polyhedron)

The resulting output is below:

I am thread #2.
I am thread #3.
I am thread #4.
I am thread #1.
ERROR: TaskFailedException:
MethodError: no method matching computehrep!(::QHull.Polyhedron)
Closest candidates are:
  computehrep!(::DefaultPolyhedron) at /home/henrique/.julia/packages/Polyhedra/w0Toa/src/defaultlibrary.jl:84
Stacktrace:
 [1] macro expansion at ./REPL[11]:11 [inlined]
 [2] (::var"#3#threadsfor_fun#7"{UnitRange{Int64}})(::Bool) at ./threadingconstructs.jl:61
 [3] (::var"#3#threadsfor_fun#7"{UnitRange{Int64}})() at ./threadingconstructs.jl:28
Stacktrace:
 [1] wait(::Task) at ./task.jl:267
 [2] top-level scope at ./threadingconstructs.jl:69

I am testing this using Polyhedra v0.6.3.

[blegat]

Arf, this is an issue with QHull.jl (opened in https://github.com/JuliaPolyhedra/QHull.jl/issues/33), replace it with hrep(my_polyhedron) then

[ferrolho]

Thanks for opening the issue on the right place. I replaced Polyhedra.computehrep!(my_polyhedron) with hrep(my_polyhedron) and it went back to segfaulting; output follows below:

I am thread #2.
I am thread #4.
I am thread #3.
I am thread #1.

signal (11): Segmentation fault

signal (11): Segmentation fault
in expression starting at REPL[10]:1
in expression starting at REPL[10]:1
_PyObject_Malloc at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
_PyObject_Malloc at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
PyUnicode_New at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
_PyUnicodeWriter_PrepareInternal at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
PyUnicode_DecodeUTF8Stateful at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
PyObject_GetAttrString at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
PyUnicode_New at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
_PyUnicodeWriter_PrepareInternal at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
PyUnicode_DecodeUTF8Stateful at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
PyUnicode_FromFormatV at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
PyErr_FormatV at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
PyErr_Format at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
PyObject_GetBuffer at /home/henrique/miniconda3/lib/libpython3.7m.so.1.0 (unknown line)
isbuftype! at /home/henrique/.julia/packages/PyCall/zqDXB/src/pybuffer.jl:134 [inlined]
isbuftype at /home/henrique/.julia/packages/PyCall/zqDXB/src/pybuffer.jl:148 [inlined]
pysequence_query at /home/henrique/.julia/packages/PyCall/zqDXB/src/conversions.jl:756
getproperty at /home/henrique/.julia/packages/PyCall/zqDXB/src/PyCall.jl:298
pytype_query at /home/henrique/.julia/packages/PyCall/zqDXB/src/conversions.jl:770
pytype_query at /home/henrique/.julia/packages/PyCall/zqDXB/src/conversions.jl:803 [inlined]
convert at /home/henrique/.julia/packages/PyCall/zqDXB/src/conversions.jl:828
getproperty at /home/henrique/.julia/packages/PyCall/zqDXB/src/PyCall.jl:306 [inlined]
chull at /home/henrique/.julia/packages/QHull/ck7jQ/src/QHull.jl:34
getproperty at /home/henrique/.julia/packages/PyCall/zqDXB/src/PyCall.jl:306 [inlined]
chull at /home/henrique/.julia/packages/QHull/ck7jQ/src/QHull.jl:34
qhull at /home/henrique/.julia/packages/QHull/ck7jQ/src/polyhedron.jl:83
qhull at /home/henrique/.julia/packages/QHull/ck7jQ/src/polyhedron.jl:83
jl_apply_generic at /opt/julia-1.4.1/bin/../lib/libjulia.so.1 (unknown line)
qhull at /home/henrique/.julia/packages/QHull/ck7jQ/src/polyhedron.jl:62
qhull at /home/henrique/.julia/packages/QHull/ck7jQ/src/polyhedron.jl:61
getine at /home/henrique/.julia/packages/QHull/ck7jQ/src/polyhedron.jl:167
hrep at /home/henrique/.julia/packages/QHull/ck7jQ/src/polyhedron.jl:211
jl_apply_generic at /opt/julia-1.4.1/bin/../lib/libjulia.so.1 (unknown line)
macro expansion at ./REPL[10]:11 [inlined]
#3#threadsfor_fun at ./threadingconstructs.jl:61
#3#threadsfor_fun at ./threadingconstructs.jl:28
unknown function (ip: 0x7f375a84d42c)
[1]    2167 segmentation fault (core dumped)  julia