1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
|
#
# Copyright 2011 Facebook
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
"""Utilities for working with multiple processes."""
import errno
import logging
import os
import sys
import time
from binascii import hexlify
from tornado import ioloop
try:
import multiprocessing # Python 2.6+
except ImportError:
multiprocessing = None
def cpu_count():
"""Returns the number of processors on this machine."""
if multiprocessing is not None:
try:
return multiprocessing.cpu_count()
except NotImplementedError:
pass
try:
return os.sysconf("SC_NPROCESSORS_CONF")
except ValueError:
pass
logging.error("Could not detect number of processors; assuming 1")
return 1
def _reseed_random():
if 'random' not in sys.modules:
return
import random
# If os.urandom is available, this method does the same thing as
# random.seed (at least as of python 2.6). If os.urandom is not
# available, we mix in the pid in addition to a timestamp.
try:
seed = long(hexlify(os.urandom(16)), 16)
except NotImplementedError:
seed = int(time.time() * 1000) ^ os.getpid()
random.seed(seed)
_task_id = None
def fork_processes(num_processes, max_restarts=100):
"""Starts multiple worker processes.
If ``num_processes`` is None or <= 0, we detect the number of cores
available on this machine and fork that number of child
processes. If ``num_processes`` is given and > 0, we fork that
specific number of sub-processes.
Since we use processes and not threads, there is no shared memory
between any server code.
Note that multiple processes are not compatible with the autoreload
module (or the debug=True option to `tornado.web.Application`).
When using multiple processes, no IOLoops can be created or
referenced until after the call to ``fork_processes``.
In each child process, ``fork_processes`` returns its *task id*, a
number between 0 and ``num_processes``. Processes that exit
abnormally (due to a signal or non-zero exit status) are restarted
with the same id (up to ``max_restarts`` times). In the parent
process, ``fork_processes`` returns None if all child processes
have exited normally, but will otherwise only exit by throwing an
exception.
"""
global _task_id
assert _task_id is None
if num_processes is None or num_processes <= 0:
num_processes = cpu_count()
if ioloop.IOLoop.initialized():
raise RuntimeError("Cannot run in multiple processes: IOLoop instance "
"has already been initialized. You cannot call "
"IOLoop.instance() before calling start_processes()")
logging.info("Starting %d processes", num_processes)
children = {}
def start_child(i):
pid = os.fork()
if pid == 0:
# child process
_reseed_random()
global _task_id
_task_id = i
return i
else:
children[pid] = i
return None
for i in range(num_processes):
id = start_child(i)
if id is not None: return id
num_restarts = 0
while children:
try:
pid, status = os.wait()
except OSError, e:
if e.errno == errno.EINTR:
continue
raise
if pid not in children:
continue
id = children.pop(pid)
if os.WIFSIGNALED(status):
logging.warning("child %d (pid %d) killed by signal %d, restarting",
id, pid, os.WTERMSIG(status))
elif os.WEXITSTATUS(status) != 0:
logging.warning("child %d (pid %d) exited with status %d, restarting",
id, pid, os.WEXITSTATUS(status))
else:
logging.info("child %d (pid %d) exited normally", id, pid)
continue
num_restarts += 1
if num_restarts > max_restarts:
raise RuntimeError("Too many child restarts, giving up")
new_id = start_child(id)
if new_id is not None: return new_id
# All child processes exited cleanly, so exit the master process
# instead of just returning to right after the call to
# fork_processes (which will probably just start up another IOLoop
# unless the caller checks the return value).
sys.exit(0)
def task_id():
"""Returns the current task id, if any.
Returns None if this process was not created by `fork_processes`.
"""
global _task_id
return _task_id
|