train_from_dataset throws PyThread_start_new_thread exception.
Created by: LihangLiu
利用train_from_dataset进行训练的时候，第一个epoch正常，到了第二个epoch就报错了，好像是跟thread有关。 系统信息：centos，fluid1.6 cpu版本。
输出如下：
==== epoch_id ==== 0
loss reduce_mean_0.tmp_0 lod: {}
dim: 1
layout: NCHW
dtype: float
data: [1.70779]
==== finished ====
==== epoch_id ==== 1
W1106 10:26:39.796146 5593 init.cc:212] *** Aborted at 1573007199 (unix time) try "date -d @1573007199" if you are using GNU date ***
W1106 10:26:39.798044 5593 init.cc:212] PC: @ 0x0 (unknown)
W1106 10:26:39.798264 5593 init.cc:212] *** SIGSEGV (@0x2) received by PID 5593 (TID 0x7ff678c76700) from PID 2; stack trace: ***
W1106 10:26:39.799917 5593 init.cc:212] @ 0x7ff679740160 (unknown)
W1106 10:26:39.801622 5593 init.cc:212] @ 0x7ff678cf47d4 __GI___libc_free
W1106 10:26:39.803226 5593 init.cc:212] @ 0x7ff67973873a __pthread_create_2_1
W1106 10:26:39.804966 5593 init.cc:212] @ 0x7ff679a61aed PyThread_start_new_thread
W1106 10:26:39.806640 5593 init.cc:212] @ 0x7ff679a65f87 thread_PyThread_start_new_thread
W1106 10:26:39.808364 5593 init.cc:212] @ 0x7ff679a34ea4 PyEval_EvalFrameEx
W1106 10:26:39.810075 5593 init.cc:212] @ 0x7ff679a3517e PyEval_EvalFrameEx
W1106 10:26:39.811789 5593 init.cc:212] @ 0x7ff679a3517e PyEval_EvalFrameEx
W1106 10:26:39.813552 5593 init.cc:212] @ 0x7ff679a366c9 PyEval_EvalCodeEx
W1106 10:26:39.815271 5593 init.cc:212] @ 0x7ff679a33b98 PyEval_EvalFrameEx
W1106 10:26:39.816990 5593 init.cc:212] @ 0x7ff679a366c9 PyEval_EvalCodeEx
W1106 10:26:39.818692 5593 init.cc:212] @ 0x7ff679a33b98 PyEval_EvalFrameEx
W1106 10:26:39.820422 5593 init.cc:212] @ 0x7ff679a3517e PyEval_EvalFrameEx
W1106 10:26:39.822183 5593 init.cc:212] @ 0x7ff679a366c9 PyEval_EvalCodeEx
W1106 10:26:39.823884 5593 init.cc:212] @ 0x7ff679a33b98 PyEval_EvalFrameEx
W1106 10:26:39.825582 5593 init.cc:212] @ 0x7ff679a366c9 PyEval_EvalCodeEx
W1106 10:26:39.827316 5593 init.cc:212] @ 0x7ff679a33b98 PyEval_EvalFrameEx
W1106 10:26:39.829082 5593 init.cc:212] @ 0x7ff679a366c9 PyEval_EvalCodeEx
W1106 10:26:39.830780 5593 init.cc:212] @ 0x7ff679a368ea PyEval_EvalCode
W1106 10:26:39.832540 5593 init.cc:212] @ 0x7ff679a4fbad run_mod
W1106 10:26:39.834237 5593 init.cc:212] @ 0x7ff679a50d28 PyRun_FileExFlags
W1106 10:26:39.835966 5593 init.cc:212] @ 0x7ff679a51f48 PyRun_SimpleFileExFlags
W1106 10:26:39.837720 5593 init.cc:212] @ 0x7ff679a6416c Py_Main
W1106 10:26:39.839462 5593 init.cc:212] @ 0x7ff678c99bd5 __libc_start_main
W1106 10:26:39.841110 5593 init.cc:212] @ 0x7ff679b3107f (unknown)