"OSError: [Errno 24] Too many open files" in sqlmap REST api server #1240

After run sqlmapapi.py for a long time,error below always raised.
Traceback (most recent call last):
File "/opt/sqlmap/thirdparty/bottle/bottle.py", line 763, in _handle
return route.call(*_args)
File "/opt/sqlmap/thirdparty/bottle/bottle.py", line 1627, in wrapper
rv = callback(_a, *_ka)
File "/opt/sqlmap/thirdparty/bottle/bottle.py", line 1577, in wrapper
rv = callback(_a, **ka)
File "/opt/sqlmap/lib/utils/api.py", line 459, in scan_start
DataStore.tasks[taskid].engine_start()
File "/opt/sqlmap/lib/utils/api.py", line 158, in engine_start
shell=False, stdin=PIPE, close_fds=False)
File "/usr/lib/python2.7/subprocess.py", line 672, in init
errread, errwrite) = self._get_handles(stdin, stdout, stderr)
File "/usr/lib/python2.7/subprocess.py", line 1038, in _get_handles
p2cread, p2cwrite = self.pipe_cloexec()
File "/usr/lib/python2.7/subprocess.py", line 1091, in pipe_cloexec
r, w = os.pipe()
OSError: [Errno 24] Too many open files