celery源码分析
本文环境python3.5.2，celery4.0.2，django1.10.x系列celery简介
celery是一款异步任务框架，基于AMQP协议的任务调度框架。使用的场景与生产者消费者类似，生产者发送消息，发送到消息队列中，然后消费者通过消息队列获取消息然后消费掉，这样达到服务或应用(生产者)解耦。
使用场景概述
celery作为异步任务框架，不仅能完成任务的分发调度，也可以实现定时任务，同时也是一个分布式的任务调度框架。其应用场景，当在用户注册时，通常需要发送一封激活邮件来激活账户，而发邮件是一个IO开销较大的操作，此时会增加用户的等待时间；当web应用需要执行大量的文件读写操作时，为了避免提供服务的本机资源被这些文件操作占用过多资源，可以将这些任务发送到专门的服务器上进行处理；这些场景都可以利用异步任务框架进行，达到解耦提升服务响应。
celery命令简析
根据官方文档来看，选用redis作为消息队列，当安装好celery时，在终端输入celery时，如下：
(venv) wuzideMacBook-Air:~ wuzi$ celery
usage: celery <command> [options]
Show help screen and exit.
positional arguments:
args
optional arguments:
-h, --help show this help message and exit
--version show program's version number and exit
Global Options:
-A APP, --app APP
-b BROKER, --broker BROKER
--loader LOADER
--config CONFIG
--workdir WORKDIR
--no-color, -C
--quiet, -q
---- -- - - ---- Commands- -------------- --- ------------
+ Main:
| celery worker
| celery events
| celery beat
| celery shell
| celery multi
| celery amqp
+ Remote Control:
| celery status
| celery inspect --help
| celery inspect active
| celery inspect active_queues
| celery inspect clock
| celery inspect conf [include_defaults=False]
| celery inspect memdump [n_samples=10]
| celery inspect memsample
| celery inspect objgraph [object_type=Request] [num=200 [max_depth=10]]
| celery inspect ping
| celery inspect query_task [id1 [id2 [... [idN]]]]
| celery inspect registered [attr1 [attr2 [... [attrN]]]]
| celery inspect report
| celery inspect reserved
| celery inspect revoked
| celery inspect scheduled
| celery inspect stats
| celery control --help
| celery control add_consumer <queue> [exchange [type [routing_key]]]
| celery control autoscale [max [min]]
| celery control cancel_consumer <queue>
| celery control disable_events
| celery control election
| celery control enable_events
| celery control heartbeat
| celery control pool_grow [N=1]
| celery control pool_restart
| celery control pool_shrink [N=1]
| celery control rate_limit <task_name> <rate_limit (e.g., 5/s | 5/m | 5/h)>
| celery control revoke [id1 [id2 [... [idN]]]]
| celery control shutdown
| celery control terminate <signal> [id1 [id2 [... [idN]]]]
| celery control time_limit <task_name> <soft_secs> [hard_secs]
+ Utils:
| celery purge
| celery list
| celery call
| celery result
| celery migrate
| celery graph
| celery upgrade
+ Debugging:
| celery report
| celery logtool
---- -- - - --------- -- - -------------- --- ------------
Type 'celery <command> --help' for help using a specific command.根据以上输出可以看出，celery的主要命令分为worker,events,beat,shell，multi和amqp主命令组成。今天主要分析multi命令，该命令是celery提供管理celery集群的命令。
celery后台管理命令multi
此时在终端中输入:
(venv) wuzideMacBook-Air:~ wuzi$ celery multi
celery multi v4.0.0 (latentcall)
usage: multi start <node1 node2 nodeN|range> [worker options]
multi stop <n1 n2 nN|range> [-SIG (default: -TERM)]
multi restart <n1 n2 nN|range> [-SIG] [worker options]
multi kill <n1 n2 nN|range>
multi show <n1 n2 nN|range> [worker options]
multi get hostname <n1 n2 nN|range> [-qv] [worker options]
multi names <n1 n2 nN|range>
multi expand template <n1 n2 nN|range>
multi help
additional options (must appear after command name):
* --nosplash: Don't display program info.
* --quiet: Don't show as much output.
* --verbose: Show more output.
* --no-color: Don't display colors.通过终端显示可知，multi的一些基本操作命令有start、stop、restart和kill等，此时celery配合Django框架使用，所有启动的话按照官方文档与django的相关配置使用。
celery的启动过程
由于本文环境默认是django框架配合使用，在终端中输入:
celery multi start t1 -A wangqian t2 -A wangqian此时-A表示是使用app,wangqian就是django项目的跟项目位置，我们开始源码分析，找到celery的入口函数。
def main():
"""Entrypoint to the ``celery`` umbrella command."""
if 'multi' not in sys.argv: # 判断multi是否在输入参数里面,作为后台启动管理命令
maybe_patch_concurrency() # 如果不在则判断是否在参数中使用gevent或者eventlet作为pool
from celery.bin.celery import main as _main
_main() # 入口执行函数此时继续查看celery.bin.celery中的main函数；
def main(argv=None):
"""Start celery umbrella command."""
# Fix for setuptools generated scripts, so that it will
# work with multiprocessing fork emulation.
# (see multiprocessing.forking.get_preparation_data())
try:
if __name__ != '__main__': # pragma: no cover
sys.modules['__main__'] = sys.modules[__name__]
cmd = CeleryCommand() # 初始化CeleryCommand类实例
cmd.maybe_patch_concurrency() # 检查是否更换pool
from billiard import freeze_support
freeze_support()
cmd.execute_from_commandline(argv) # 执行
except KeyboardInterrupt:
pass除了检查pool参数外，进而执行了CeleryCommand实例的execute_from_commandline方法，继续查看：
class CeleryCommand(Command):
"""Base class for commands."""
commands = {
'amqp': amqp,
'beat': beat,
'call': call,
'control': control,
'events': events,
'graph': graph,
'help': help,
'inspect': inspect,
'list': list_,
'logtool': logtool,
'migrate': migrate,
'multi': multi,
'purge': purge,
'report': report,
'result': result,
'shell': shell,
'status': status,
'upgrade': upgrade,
'worker': worker,
}
ext_fmt = '{self.namespace}.commands'
enable_config_from_cmdline = True
prog_name = 'celery'
namespace = 'celery'
def execute_from_commandline(self, argv=None):
argv = sys.argv if argv is None else argv # 判断是否有传入输入参数，如果没有则使用系统的输入参数
if 'multi' in argv[1:3]: # Issue 1008
self.respects_app_option = False
try:
sys.exit(determine_exit_status(
super(CeleryCommand, self).execute_from_commandline(argv))) # 调用执行方法
except KeyboardInterrupt:
sys.exit(EX_FAILURE)由该类可以看出CeleryCommand继承自基础的Command类，此时调用的方法是调用父类的execute_from_commandline方法；
def execute_from_commandline(self, argv=None):
"""Execute application from command-line.
Arguments:
argv (List[str]): The list of command-line arguments.
Defaults to ``sys.argv``.
"""
if argv is None:
argv = list(sys.argv) # 如果没有输入参数则使用脚本的传入参数
# Should we load any special concurrency environment?
self.maybe_patch_concurrency(argv)
self.on_concurrency_setup()
# Dump version and exit if '--version' arg set.
self.early_version(argv) # 获取版本号
argv = self.setup_app_from_commandline(argv) # 将系统参数进行处理，获取相关参数信息
self.prog_name = os.path.basename(argv[0]) # 获取运行的类的名称
return self.handle_argv(self.prog_name, argv[1:]) # 进行处理此时完成会调用setup_app_from_commandline方法，该方法主要是解析输入参数值，并准备好运行的参数
def setup_app_from_commandline(self, argv):
preload_options = self.parse_preload_options(argv) # 获取参数如broker workdir等参数
quiet = preload_options.get('quiet')
if quiet is not None:
self.quiet = quiet
try:
self.no_color = preload_options['no_color'] # 设置输出字体颜色
except KeyError:
pass
workdir = preload_options.get('workdir') # 获取配置的工作目录
if workdir:
os.chdir(workdir) # 如果设置了工作目录则切换到该目录
app = (preload_options.get('app') or # 由于此时preload_options中app为输入参数wangqian
os.environ.get('CELERY_APP') or
self.app) # 获取app值
preload_loader = preload_options.get('loader') # 获取加载类
if preload_loader: # 如果参数中设置有则在环境变量中设置该加载类
# Default app takes loader from this env (Issue #1066).
os.environ['CELERY_LOADER'] = preload_loader
loader = (preload_loader,
os.environ.get('CELERY_LOADER') or
'default')
broker = preload_options.get('broker', None) # 获取broker
if broker:
os.environ['CELERY_BROKER_URL'] = broker # 如果获取到了则设置到环境变量中
config = preload_options.get('config') # 获取配置
if config:
os.environ['CELERY_CONFIG_MODULE'] = config # 获取到了则直接设置
if self.respects_app_option: # 由于在multi命令中此时该值被设置为了False,如果设置成True
if app: # 如果参数中传入了app值
self.app = self.find_app(app) # 加载并获取该app实例
elif self.app is None:
self.app = self.get_app(loader=loader)
if self.enable_config_from_cmdline: # 是否是解析命令行参数
argv = self.process_cmdline_config(argv) # 如果是则解析命令行参数
else:
self.app = Celery(fixups=[]) # 直接实例化Celery
self._handle_user_preload_options(argv)
return argv此时就将解析完成的参数返回，此时返回到execute_from_commandline函数处继续执行self.handle_argv(self.prog_name, argv[1:]) 函数，由于该函数在CeleryCommand中重写，所以会调用CeleryCommand类中的handle_argv函数，
def handle_argv(self, prog_name, argv, **kwargs):
self.prog_name = self.prepare_prog_name(prog_name) # 获取运行的名称
argv = self._relocate_args_from_start(argv) # 对参数顺序进行调整
_, argv = self.prepare_args(None, argv) # 检查参数是否合法
try:
command = argv[0] # 获取需要执行的命令
except IndexError:
command, argv = 'help', ['help']
return self.execute(command, argv) # 调用该函数执行该命令此时执行到这里，command就是输入参数的multi值，此时继续执行self.execute函数
def execute(self, command, argv=None):
try:
cls = self.commands[command] # 通过输入参数的command获取对应的处理类
except KeyError:
cls, argv = self.commands['help'], ['help'] # 如果获取不到则设置成help
cls = self.commands.get(command) or self.commands['help'] # 如果没有获取不到则默认使用help
try:
return cls(
app=self.app, on_error=self.on_error,
no_color=self.no_color, quiet=self.quiet,
on_usage_error=partial(self.on_usage_error, command=command),
).run_from_argv(self.prog_name, argv[1:], command=argv[0]) # 实例化该类，实例化之后调用run_from_argv
except self.UsageError as exc:
self.on_usage_error(exc)
return exc.status
except self.Error as exc:
self.on_error(exc)
return exc.status此时就调用了位于celery/bin/celery.py中的worker类，实例化并执行run_from_argv函数。
celery命令之multi
multi的类如下：
class multi(Command):
"""Start multiple worker instances."""
respects_app_option = False
def run_from_argv(self, prog_name, argv, command=None):
from celery.bin.multi import MultiTool
cmd = MultiTool(quiet=self.quiet, no_color=self.no_color) # 实例化MultiTool
return cmd.execute_from_commandline([command] + argv) # 调用实例的execute_from_commandline此时继续查看MultiTool类的execute_from_commandline方法：
def execute_from_commandline(self, argv, cmd=None):
# Reserve the --nosplash|--quiet|-q/--verbose options.
argv = self._handle_reserved_options(argv) # 将argv中设置reserved_options中的值更新到该类属性上
self.cmd = cmd if cmd is not None else self.cmd # 获取cmd值
self.prog_name = os.path.basename(argv.pop(0))
if not self.validate_arguments(argv): # 检查输入参数是否正确
return self.error()
return self.call_command(argv[0], argv[1:]) # 调用命令执行命令
def validate_arguments(self, argv):
return argv and argv[0][0] != '-'
def call_command(self, command, argv):
try:
return self.commands[command](*argv) or EX_OK # 执行该命令对应的方法
except KeyError:
return self.error('Invalid command: {0}'.format(command))此时对应的command就是start，此时就调用MultiTool类中的commands中start对应的方法self.start,
@splash
@using_cluster
def start(self, cluster):
self.note('> Starting nodes...')
return int(any(cluster.start()))使用了Python的装饰器，查看splash和using_cluster的两个方法。
def splash(fun):
@wraps(fun)
def _inner(self, *args, **kwargs):
self.splash()
return fun(self, *args, **kwargs)
return _inner该方法仅是调用了MultiTool类的splash方法，打印相关颜色等文案信息。
def using_cluster(fun):
@wraps(fun)
def _inner(self, *argv, **kwargs):
return fun(self, self.cluster_from_argv(argv), **kwargs)
return _inner在调用fun即最终的start方法时，将self.cluster_from_argv(argv)作为了参数传入了start方法中，MultiTool中相关方法如下，
def _nodes_from_argv(self, argv, cmd=None):
cmd = cmd if cmd is not None else self.cmd # 获取相关命令
p = self.OptionParser(argv) # 解析输出参数
p.parse()
return p, self.MultiParser(cmd=cmd).parse(p) # 解析并生成node实例
def cluster_from_argv(self, argv, cmd=None):
_, cluster = self._cluster_from_argv(argv, cmd=cmd) # 解析相关参数
return cluster
def _cluster_from_argv(self, argv, cmd=None):
p, nodes = self._nodes_from_argv(argv, cmd=cmd) # 通过参数分解成相应nodes
return p, self.Cluster(list(nodes), cmd=cmd) # 返回初始化的Cluster实例此时由self.MultiParser(cmd=cmd).parse(p)生成具体的node实例，位于MultiParser中的parse函数，
def parse(self, p):
.....
return (
self._node_from_options(
p, name, prefix, suffix, cmd, append, options)
for name in names
) # 调用_node_from_options生成node实例其中,_node_from_options函数如下，
def _node_from_options(self, p, name, prefix,
suffix, cmd, append, options):
namespace, nodename, _ = build_nodename(name, prefix, suffix)
namespace = nodename if nodename in p.namespaces else namespace
return Node(nodename, cmd, append,
p.optmerge(namespace, options), p.passthrough) # 根据输入参数实例化Node实例此时继续执行start函数时，传入参数cluster就是刚刚将输入参数初始化对应node的cluster，
def start(self, cluster):
self.note('> Starting nodes...')
return int(any(cluster.start()))此时调用start方法就是调用cluster的start方法，
class Cluster(UserList):
"""Represent a cluster of workers."""
....
def start(self):
return [self.start_node(node) for node in self] # 依次遍历nodes，然后依次启动node节点
def start_node(self, node):
maybe_call(self.on_node_start, node) # 如果on_node_start能执行则调用
retcode = self._start_node(node) # 开始节点
maybe_call(self.on_node_status, node, retcode)
return retcode # 返回返回值
def _start_node(self, node):
return node.start(
self.env,
on_spawn=self.on_child_spawn,
on_signalled=self.on_child_signalled,
on_failure=self.on_child_failure,
) # 调用node实例的start方法
@property
def data(self):
return self.nodes此时就调用了start_node的方法依次运行node的start方法，
def start(self, env=None, **kwargs):
return self._waitexec(
self.argv, path=self.executable, env=env, **kwargs) # 调用_waitexec启动子进程
def _waitexec(self, argv, path=sys.executable, env=None,
on_spawn=None, on_signalled=None, on_failure=None):
argstr = self.prepare_argv(argv, path) # 获取启动传入参数
maybe_call(on_spawn, self, argstr=' '.join(argstr), env=env)
pipe = Popen(argstr, env=env) # 已子进程方式打开
return self.handle_process_exit(
pipe.wait(), # 等待子进程结束放回code
on_signalled=on_signalled,
on_failure=on_failure,
)
def handle_process_exit(self, retcode, on_signalled=None, on_failure=None):
if retcode < 0: # 如果子进程退出码小于0
maybe_call(on_signalled, self, -retcode)
return -retcode
elif retcode > 0:
maybe_call(on_failure, self, retcode) # 如果大于0，如果传入on_failure函数则调用
return retcode此时的重点在于argstr参数中添加了-m -detach参数，此时在子进程中执行时，启动的原理如上所示，但是此时的输入参数就是worker –detach -A wangqian -n t1@wuzi –pidfile=t1.pid –logfile=t1%I.log 等。
worker的后台运行
此时启动的流程如上述分析相同，只不过此时此时的CeleryCommand中获取的command就是worker,此时此处代码CeleryCommand.execute中的cls就是worker，
return cls(
app=self.app, on_error=self.on_error,
no_color=self.no_color, quiet=self.quiet,
on_usage_error=partial(self.on_usage_error, command=command),
).run_from_argv(self.prog_name, argv[1:], command=argv[0]) # 实例化该类，实例化之后调用run_from_argv查看worker对应的处理流程，
def run_from_argv(self, prog_name, argv=None, command=None):
argv = [x for x in argv if x not in self.removed_flags] # 判断输入参数是否是需要删除的参数
command = sys.argv[0] if command is None else command # 获取执行任务的command
argv = sys.argv[1:] if argv is None else argv # 获取输入参数
# parse options before detaching so errors can be handled.
options, args = self.prepare_args(
*self.parse_options(prog_name, argv, command)) # 获取解析之后的参数值
self.maybe_detach([command] + argv) # 判断是否是后台运行
return self(*args, **options) # 调用__call__方法
def maybe_detach(self, argv, dopts=['-D', '--detach']):
if any(arg in argv for arg in dopts): # 如果输入参数中有-D或者--detach
argv = [v for v in argv if v not in dopts] # 移除-D 或者 --detach
# will never return
detached_celeryd(self.app).execute_from_commandline(argv) # 后台运行该任务
raise SystemExit(0) # 抛出退出码0此时我们继续分析detached_celeryd该类，
def execute_from_commandline(self, argv=None):
argv = sys.argv if argv is None else argv
prog_name = os.path.basename(argv[0])
config, argv = self._split_command_line_config(argv)
options, leftovers = self.parse_options(prog_name, argv[1:])
sys.exit(detach(
app=self.app, path=self.execv_path,
argv=self.execv_argv + leftovers + config,
**vars(options)
))在经过相关参数的检查调用后，就调用detach方法，
def detach(path, argv, logfile=None, pidfile=None, uid=None,
gid=None, umask=None, workdir=None, fake=False, app=None,
executable=None, hostname=None):
"""Detach program by argv'."""
hostname = default_nodename(hostname) # 获取hostname
logfile = node_format(logfile, hostname) # 序列化logfile
pidfile = node_format(pidfile, hostname) # 序列化pidfile
fake = 1 if C_FAKEFORK else fake
with detached(logfile, pidfile, uid, gid, umask, workdir, fake,
after_forkers=False):
try:
if executable is not None:
path = executable
os.execv(path, [path] + argv) # 调用execv重新加载程序
except Exception: # pylint: disable=broad-except
if app is None:
from celery import current_app
app = current_app
app.log.setup_logging_subsystem(
'ERROR', logfile, hostname=hostname)
logger.critical("Can't exec %r", ' '.join([path] + argv),
exc_info=True)
return EX_FAILURE继续查看detached函数，该函数的返回值实现了Python的上下文协议，即实现了enter和exit方法，
def detached(logfile=None, pidfile=None, uid=None, gid=None, umask=0,
workdir=None, fake=False, **opts):
"""Detach the current process in the background (daemonize).
if not resource:
raise RuntimeError('This platform does not support detach.')
workdir = os.getcwd() if workdir is None else workdir # 获取当前的工作目录
signals.reset('SIGCLD') # Make sure SIGCLD is using the default handler.
maybe_drop_privileges(uid=uid, gid=gid)
def after_chdir_do(): # 检查logfile能否打开并创建pidfile
# Since without stderr any errors will be silently suppressed,
# we need to know that we have access to the logfile.
logfile and open(logfile, 'a').close()
# Doesn't actually create the pidfile, but makes sure it's not stale.
if pidfile:
_create_pidlock(pidfile).release()
return DaemonContext(
umask=umask, workdir=workdir, fake=fake, after_chdir=after_chdir_do,
)此时查看DaemonContext类实现了上下文协议并且实现了fork让最后的子进程去重新加载执行该程序，并且完成退出。
class DaemonContext(object):
"""Context manager daemonizing the process."""
_is_open = False
def __init__(self, pidfile=None, workdir=None, umask=None,
fake=False, after_chdir=None, after_forkers=True,
**kwargs):
if isinstance(umask, string_t):
# octal or decimal, depending on initial zero.
umask = int(umask, 8 if umask.startswith('0') else 10)
self.workdir = workdir or DAEMON_WORKDIR
self.umask = umask
self.fake = fake
self.after_chdir = after_chdir
self.after_forkers = after_forkers
self.stdfds = (sys.stdin, sys.stdout, sys.stderr)
def redirect_to_null(self, fd):
if fd is not None:
dest = os.open(os.devnull, os.O_RDWR)
os.dup2(dest, fd)
def open(self):
if not self._is_open:
if not self.fake:
self._detach() # 实现后台进程
os.chdir(self.workdir)
if self.umask is not None:
os.umask(self.umask)
if self.after_chdir:
self.after_chdir()
if not self.fake:
# We need to keep /dev/urandom from closing because
# shelve needs it, and Beat needs shelve to start.
keep = list(self.stdfds) + fd_by_path(['/dev/urandom'])
close_open_fds(keep)
for fd in self.stdfds:
self.redirect_to_null(maybe_fileno(fd))
if self.after_forkers and mputil is not None:
mputil._run_after_forkers()
self._is_open = True
__enter__ = open
def close(self, *args):
if self._is_open:
self._is_open = False
__exit__ = close
def _detach(self):
if os.fork() == 0: # first child
os.setsid() # create new session
if os.fork() > 0: # pragma: no cover
# second child
os._exit(0)
else:
os._exit(0)
return self此时子进程os.execve中执行的可执行程序就是本程序，去掉-D,–detach参数后重新执行的进程，此时在node中的pipe.wait()的返回状态码为0，此时就执行下一个node，至此完成所有node的启动，至此，所有的子节点的启动就完成了。
multi停止命令stop
后台节点启动之后，如果想要停止该node节点的话，只需要在终端上输入，
celery multi stop t1 -A wangqian此时就调用MultiTool类中的commands中stop对应的方法self.stop,
@splash
@using_cluster_and_sig
def stop(self, cluster, sig, **kwargs):
return cluster.stop(sig=sig, **kwargs)此时与上文分析同理也是调用了splash和using_cluster_and_sig作为装饰器，此时我们看下using_cluster_and_sig,
def using_cluster_and_sig(fun):
@wraps(fun)
def _inner(self, *argv, **kwargs):
p, cluster = self._cluster_from_argv(argv) # 生成cluster
sig = self._find_sig_argument(p) # 查看输入参数中是否传入了信号值
return fun(self, cluster, sig, **kwargs)
return _inner此时就调用了cluster的stop方法，此时查看该stop方法的作用，
def stop(self, retry=None, callback=None, sig=signal.SIGTERM):
return self._stop_nodes(retry=retry, on_down=callback, sig=sig) # 调用该方法停止node节点运行
def stopwait(self, retry=2, callback=None, sig=signal.SIGTERM):
return self._stop_nodes(retry=retry, on_down=callback, sig=sig)
def _stop_nodes(self, retry=None, on_down=None, sig=signal.SIGTERM):
on_down = on_down if on_down is not None else self.on_node_down # 判断是否有传入on_node_down对应的回调函数
nodes = list(self.getpids(on_down=on_down)) # 获取所有有pid的node
if nodes:
for node in self.shutdown_nodes(nodes, sig=sig, retry=retry): # 调用该函数停止node运行
maybe_call(on_down, node)
def shutdown_nodes(self, nodes, sig=signal.SIGTERM, retry=None):
P = set(nodes) # 去重
maybe_call(self.on_stopping_preamble, nodes) # 如果注册则执行该函数
to_remove = set() # 需要移除的Node节点
for node in P:
maybe_call(self.on_send_signal, node, signal_name(sig)) # 如果有则执行该函数
if not node.send(sig, self.on_node_signal_dead): # 调用node的send方法发送信号，并传入on_node_signal_dead回调函数
to_remove.add(node) # 停止成功则添加到已删除列表中
yield node # 返回已停止的node
P -= to_remove # P中减去已经停止的node
if retry: # 如果传入值
maybe_call(self.on_still_waiting_for, P)
its = 0
while P:
to_remove = set() # 设置已移除列表
for node in P: # 遍历P
its += 1
maybe_call(self.on_still_waiting_progress, P)
if not node.alive(): # 通过向该进程发送信号0,检查该进程是否还活着，如果已经死亡
maybe_call(self.on_node_shutdown_ok, node)
to_remove.add(node) # 则添加到移除列表中
yield node # 返回该node
maybe_call(self.on_still_waiting_for, P)
break
P -= to_remove # 从P中减去已经移除的node
if P and not its % len(P): # 如果P不为空，并且its的计数值对P列表的求摸值为0
sleep(float(retry)) # sleep retry秒
maybe_call(self.on_still_waiting_end)从以上代码可以看出，停止node节点是通过调用node.send方法发送相关操作信号给node去执行，
def send(self, sig, on_error=None):
pid = self.pid # 获取node的pid
if pid: # 如果有
try:
os.kill(pid, sig) # 系统调用去向该进程发送信号sig
except OSError as exc:
if exc.errno != errno.ESRCH:
raise
maybe_call(on_error, self)
return False # 失败返回false
return True # 成功返回true
maybe_call(on_error, self)至此，stop命令就完成了停止运行相关的node节点。
相关总结multi
celery的multi的相关命令，如start、stop等基本命令的解析，目前已基本完成，multi的指令的大致的实现思路是，通过生成一个Cluster来管理生成的子节点，通过生成后台进程的worker进程并生成worker进程的pid文件记录工作进程的pid，当想要停止摸个后台worker进程时，通过pid文件获取相关进程的pid并向该进程发送相关信号，达到控制管理的功能。
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