@smth Thank you for your reply! I tried to get a stacktrace with gdb (sorry if I did it wrong, I did it for the first time)
#0  0x00002aaaab1e279b in do_futex_wait.constprop () from /lib64/libpthread.so.0
#1  0x00002aaaab1e282f in __new_sem_wait_slow.constprop.0 () from /lib64/libpthread.so.0
#2  0x00002aaaab1e28cb in sem_wait@@GLIBC_2.2.5 () from /lib64/libpthread.so.0
#3  0x00002aaaaae60313 in PyThread_acquire_lock_timed (lock=0x2aab0c000c10, microseconds=-1000000, intr_flag=1) at Python/thread_pthread.h:352
#4  0x00002aaaaae66fe4 in acquire_timed (lock=0x2aab0c000c10, timeout=-1000000000) at ./Modules/_threadmodule.c:68
#5  0x00002aaaaae67126 in lock_PyThread_acquire_lock (self=0x2aaaf903ea08, args=<optimized out>, kwds=<optimized out>) at ./Modules/_threadmodule.c:151
#6  0x00002aaaaad90df2 in _PyCFunction_FastCallDict (func_obj=0x2aaaf9bbe8b8, args=0x2aaaf9bacaf8, nargs=<optimized out>, kwargs=0x0)
    at Objects/methodobject.c:231
#7  0x00002aaaaae164ec in call_function (pp_stack=0x7fffffffc078, oparg=<optimized out>, kwnames=0x0) at Python/ceval.c:4798
#8  0x00002aaaaae1915d in _PyEval_EvalFrameDefault (f=<optimized out>, throwflag=<optimized out>) at Python/ceval.c:3284
#9  0x00002aaaaae14a60 in _PyEval_EvalCodeWithName (_co=0x2aaab2352a50, globals=<optimized out>, locals=<optimized out>, args=<optimized out>, argcount=1, 
    kwnames=0x0, kwargs=0x2aaaf9bb13a0, kwcount=0, kwstep=1, defs=0x2aaab2346f60, defcount=2, kwdefs=0x0, closure=0x0, name=0x2aaab2354420, 
    qualname=0x2aaab234f7b0) at Python/ceval.c:4128
#10 0x00002aaaaae1648a in fast_function (kwnames=<optimized out>, nargs=1, stack=<optimized out>, func=0x2aaab235dae8) at Python/ceval.c:4939
#11 call_function (pp_stack=0x7fffffffc318, oparg=<optimized out>, kwnames=<optimized out>) at Python/ceval.c:4819
#12 0x00002aaaaae1915d in _PyEval_EvalFrameDefault (f=<optimized out>, throwflag=<optimized out>) at Python/ceval.c:3284
#13 0x00002aaaaae14a60 in _PyEval_EvalCodeWithName (_co=0x2aaab23529c0, globals=<optimized out>, locals=<optimized out>, args=<optimized out>, argcount=1, 
    kwnames=0x0, kwargs=0x6a6b62e0, kwcount=0, kwstep=1, defs=0x2aaab23562c8, defcount=1, kwdefs=0x0, closure=0x0, name=0x2aaaaaae2d18, qualname=0x2aaab2351a30)
    at Python/ceval.c:4128
#14 0x00002aaaaae1648a in fast_function (kwnames=<optimized out>, nargs=1, stack=<optimized out>, func=0x2aaab235da60) at Python/ceval.c:4939
#15 call_function (pp_stack=0x7fffffffc5b8, oparg=<optimized out>, kwnames=<optimized out>) at Python/ceval.c:4819
#16 0x00002aaaaae1915d in _PyEval_EvalFrameDefault (f=<optimized out>, throwflag=<optimized out>) at Python/ceval.c:3284
#17 0x00002aaaaae14a60 in _PyEval_EvalCodeWithName (_co=0x2aaae39ceed0, globals=<optimized out>, locals=<optimized out>, args=<optimized out>, argcount=4, 
    kwnames=0x0, kwargs=0x2aaaf9baadd8, kwcount=0, kwstep=1, defs=0x2aaae3727de0, defcount=2, kwdefs=0x0, closure=0x0, name=0x2aaae39d3730, 
    qualname=0x2aaae39d3730) at Python/ceval.c:4128
#18 0x00002aaaaae1648a in fast_function (kwnames=<optimized out>, nargs=4, stack=<optimized out>, func=0x2aaae39d6510) at Python/ceval.c:4939
#19 call_function (pp_stack=0x7fffffffc858, oparg=<optimized out>, kwnames=<optimized out>) at Python/ceval.c:4819
#20 0x00002aaaaae1915d in _PyEval_EvalFrameDefault (f=<optimized out>, throwflag=<optimized out>) at Python/ceval.c:3284
#21 0x00002aaaaae13e74 in _PyFunction_FastCall (co=<optimized out>, args=<optimized out>, nargs=4, globals=<optimized out>) at Python/ceval.c:4880
#22 0x00002aaaaae165e8 in fast_function (kwnames=0x0, nargs=4, stack=<optimized out>, func=0x2aaae39ec158) at Python/ceval.c:4915
#23 call_function (pp_stack=0x7fffffffca88, oparg=<optimized out>, kwnames=0x0) at Python/ceval.c:4819
#24 0x00002aaaaae1915d in _PyEval_EvalFrameDefault (f=<optimized out>, throwflag=<optimized out>) at Python/ceval.c:3284
#25 0x00002aaaaae14a60 in _PyEval_EvalCodeWithName (_co=0x2aaae39dc150, globals=<optimized out>, locals=<optimized out>, args=<optimized out>, argcount=2, 
    kwnames=0x2aaaaaadd060, kwargs=0x2aaaaaadd068, kwcount=0, kwstep=2, defs=0x0, defcount=0, kwdefs=0x0, closure=0x0, name=0x2aaae36a8ed8, 
    qualname=0x2aaae39e15d0) at Python/ceval.c:4128
#26 0x00002aaaaae14cfc in _PyFunction_FastCallDict (func=0x2aaae39e3f28, args=0x7fffffffccc0, nargs=2, kwargs=0x2aaaf9032090) at Python/ceval.c:5031
#27 0x00002aaaaad39ba6 in _PyObject_FastCallDict (func=0x2aaae39e3f28, args=0x7fffffffccc0, nargs=<optimized out>, kwargs=0x2aaaf9032090)
    at Objects/abstract.c:2295
#28 0x00002aaaaad39dfc in _PyObject_Call_Prepend (func=0x2aaae39e3f28, obj=0x2aaaf89735f8, args=0x2aaaf9048da0, kwargs=0x2aaaf9032090) at Objects/abstract.c:2358
#29 0x00002aaaaad39e96 in PyObject_Call (func=0x2aaab4146248, args=<optimized out>, kwargs=<optimized out>) at Objects/abstract.c:2246
#30 0x00002aaaaae1a236 in do_call_core (kwdict=0x2aaaf9032090, callargs=<optimized out>, func=0x2aaab4146248) at Python/ceval.c:5067
#31 _PyEval_EvalFrameDefault (f=<optimized out>, throwflag=<optimized out>) at Python/ceval.c:3366
#32 0x00002aaaaae14a60 in _PyEval_EvalCodeWithName (_co=0x2aaae3846660, globals=<optimized out>, locals=<optimized out>, args=<optimized out>, argcount=2, 
    kwnames=0x0, kwargs=0x8, kwcount=0, kwstep=2, defs=0x0, defcount=0, kwdefs=0x0, closure=0x0, name=0x2aaaaaae0170, qualname=0x2aaae3732ab0)
    at Python/ceval.c:4128
#33 0x00002aaaaae14cfc in _PyFunction_FastCallDict (func=0x2aaae397f510, args=0x7fffffffd0b0, nargs=2, kwargs=0x0) at Python/ceval.c:5031
#34 0x00002aaaaad39ba6 in _PyObject_FastCallDict (func=0x2aaae397f510, args=0x7fffffffd0b0, nargs=<optimized out>, kwargs=0x0) at Objects/abstract.c:2295
---Type <return> to continue, or q <return> to quit---
#35 0x00002aaaaad39dfc in _PyObject_Call_Prepend (func=0x2aaae397f510, obj=0x2aaaf89735f8, args=0x2aaaf9048d68, kwargs=0x0) at Objects/abstract.c:2358
#36 0x00002aaaaad39e96 in PyObject_Call (func=0x2aaae2b1fec8, args=<optimized out>, kwargs=<optimized out>) at Objects/abstract.c:2246
#37 0x00002aaaaadb1baf in slot_tp_call (self=0x2aaaf89735f8, args=0x2aaaf9048d68, kwds=0x0) at Objects/typeobject.c:6167
#38 0x00002aaaaad39ade in _PyObject_FastCallDict (func=0x2aaaf89735f8, args=<optimized out>, nargs=<optimized out>, kwargs=0x0) at Objects/abstract.c:2316
#39 0x00002aaaaae162bb in call_function (pp_stack=0x7fffffffd3a8, oparg=<optimized out>, kwnames=0x0) at Python/ceval.c:4822
#40 0x00002aaaaae1915d in _PyEval_EvalFrameDefault (f=<optimized out>, throwflag=<optimized out>) at Python/ceval.c:3284
#41 0x00002aaaaae13e74 in _PyFunction_FastCall (co=<optimized out>, args=<optimized out>, nargs=0, globals=<optimized out>) at Python/ceval.c:4880
#42 0x00002aaaaae165e8 in fast_function (kwnames=0x0, nargs=0, stack=<optimized out>, func=0x2aaaf8965f28) at Python/ceval.c:4915
#43 call_function (pp_stack=0x7fffffffd5d8, oparg=<optimized out>, kwnames=0x0) at Python/ceval.c:4819
#44 0x00002aaaaae1915d in _PyEval_EvalFrameDefault (f=<optimized out>, throwflag=<optimized out>) at Python/ceval.c:3284
#45 0x00002aaaaae14a60 in _PyEval_EvalCodeWithName (_co=0x2aaaaac12c90, globals=<optimized out>, locals=<optimized out>, args=<optimized out>, argcount=0, 
    kwnames=0x0, kwargs=0x8, kwcount=0, kwstep=2, defs=0x0, defcount=0, kwdefs=0x0, closure=0x0, name=0x0, qualname=0x0) at Python/ceval.c:4128
#46 0x00002aaaaae14ee3 in PyEval_EvalCodeEx (_co=<optimized out>, globals=<optimized out>, locals=<optimized out>, args=<optimized out>, 
    argcount=<optimized out>, kws=<optimized out>, kwcount=0, defs=0x0, defcount=0, kwdefs=0x0, closure=0x0) at Python/ceval.c:4149
#47 0x00002aaaaae14f2b in PyEval_EvalCode (co=<optimized out>, globals=<optimized out>, locals=<optimized out>) at Python/ceval.c:695
#48 0x00002aaaaae476c0 in run_mod (arena=0x2aaaaab2f1e0, flags=0x7fffffffd930, locals=0x2aaaaab97048, globals=0x2aaaaab97048, filename=0x2aaaaac83eb0, 
    mod=0x6bac40) at Python/pythonrun.c:980
#49 PyRun_FileExFlags (fp=0x642460, filename_str=<optimized out>, start=<optimized out>, globals=0x2aaaaab97048, locals=0x2aaaaab97048, closeit=<optimized out>, 
    flags=0x7fffffffd930) at Python/pythonrun.c:933
#50 0x00002aaaaae48c83 in PyRun_SimpleFileExFlags (fp=0x642460, filename=<optimized out>, closeit=1, flags=0x7fffffffd930) at Python/pythonrun.c:396
#51 0x00002aaaaae640b5 in run_file (p_cf=0x7fffffffd930, filename=0x604270 L"train.py", fp=0x642460) at Modules/main.c:338
#52 Py_Main (argc=<optimized out>, argv=<optimized out>) at Modules/main.c:810
#53 0x0000000000400c1d in main (argc=7, argv=<optimized out>) at ./Programs/python.c:69