Mongodb with very high CPU rate - mongodb

Question

When I ran the following code and killed it immediately(that means to abnormally exit), the CPU rate of Mongodb would go extremely high(around 100%):
#-*- encoding:UTF-8 -*-
import threading
import time
import pymongo
single_conn = pymongo.Connection('localhost', 27017)
class SimpleExampleThread(threading.Thread):
def run(self):
print single_conn['scrapy'].zhaodll.count(), self.getName()
time.sleep(20)
for i in range(100):
SimpleExampleThread().start()
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
VIRT RES SHR S %CPU %MEM TIME+ COMMAND
696m 35m 6404 S 1181.7 0.1 391:45.31 mongod
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
My Mongodb version is 2.2.3. When the Mongodb worked well, ran the command "strace -c -p " for 1 minute giving the following output:
% time seconds usecs/call calls errors syscall
------ ----------- ----------- --------- --------- ----------------
33.50 0.322951 173 1867 nanosleep
33.19 0.319950 730 438 recvfrom
21.16 0.203969 16 12440 select
12.13 0.116983 19497 6 restart_syscall
0.02 0.000170 2 73 write
0.00 0.000016 0 146 sendto
0.00 0.000007 0 73 lseek
0.00 0.000000 0 2 read
0.00 0.000000 0 3 open
0.00 0.000000 0 3 close
0.00 0.000000 0 2 fstat
0.00 0.000000 0 87 mmap
0.00 0.000000 0 2 munmap
0.00 0.000000 0 1 pwrite
0.00 0.000000 0 3 msync
0.00 0.000000 0 29 mincore
0.00 0.000000 0 73 fdatasync
------ ----------- ----------- --------- --------- ----------------
100.00 0.964046 15248 total
When the cpu rate of Mongodb went very high(around 100%), ran the same command giving the following output:
% time seconds usecs/call calls errors syscall
------ ----------- ----------- --------- --------- ----------------
29.12 5.064230 3088 1640 nanosleep
28.83 5.013239 27851 180 recvfrom
22.72 3.950399 658400 6 restart_syscall
19.30 3.356491 327 10268 select
0.02 0.004026 67 60 sendto
0.01 0.001000 333 3 msync
0.00 0.000269 9 30 write
0.00 0.000125 4 30 fdatasync
0.00 0.000031 10 3 open
0.00 0.000000 0 2 read
0.00 0.000000 0 3 close
0.00 0.000000 0 2 fstat
0.00 0.000000 0 30 lseek
0.00 0.000000 0 57 mmap
0.00 0.000000 0 2 munmap
0.00 0.000000 0 1 pwrite
0.00 0.000000 0 14 mincore
------ ----------- ----------- --------- --------- ----------------
100.00 17.389810 12331 total
And if I run the command "lsof", there are many socks with the description "can't identify protocol". I don't know what goes wrong. Are there some bugs in Mongodb?
Thanks!