Supervisor分析

1.运行原理概述:

Supervisor生成主进程并将主进程变成守护进程，supervisor依次生成配置文件中的工作进程，然后依次监控工作进程的工作状态，并且主进程负责与supervisorctl客户端通信，实现主进程对子进程的控制。

2.本次分析只分析supervisor的最小实现原理部分

1).supervisor生成主进程并成为守护进程，根据配置依次生成子进程
2).supervisor与supervisorctl基于rpc通信
3).子进程与主进程的管道通信

3.源码分析

本次源码基于supervisor-2.0b1
命令行启动

[wuzi:] supervisord

此时supervisord已经启动，我们就从这个命令中开始supervisord的分析

Supervisord文件中

#!/usr/bin/python
from supervisor.supervisord import main
main()

运行的开始函数开始于main, main中主要运行代码为:

    while 1:
        # if we hup, restart by making a new Supervisor()
        # the test argument just makes it possible to unit test this code
        options = ServerOptions()
        d = Supervisor(options)
        d.main(None, test, first)

1).ServerOptions类主要进行了配置文件的优化，提供服务器的初始化和主进程变成守护进程，子进程的创建和管理等工作。
2).Supervisor类主要实现了基于异步IO的服务器运行，接受子进程、rpc客户端的通信处理等工作。
3).d.main(None, test, first),主要执行了运行时的参数日志等初始化工作，并生成子进程，打开http服务器等工作。
d.main(None, test, first)代码为:

 def main(self, args=None, test=False, first=False):
.......(省略部分初始化代码)

        self.run(test)

    def run(self, test=False):
        self.processes = {}
        for program in self.options.programs:
            name = program.name
# 根据初始化后的配置文件生成相应的子进程实例
            self.processes[name] = self.options.make_process(program)  
        try:
# 生成pid文件
            self.options.write_pidfile()
# 打开http服务器           
            self.options.openhttpserver(self)
# 设置注册的信号量
            self.options.setsignals()
# 主进程是否成为守护进程
            if not self.options.nodaemon:
                self.options.daemonize()
# 运行异步io服务器
            self.runforever(test)
        finally:
            self.options.cleanup()

    def runforever(self, test=False):
        timeout = 1
# 获取已经注册的句柄
        socket_map = self.options.get_socket_map()

        while 1:
# mood表示主进程状态1为运行
            if self.mood > 0:
                self.start_necessary()

            r, w, x = [], [], []

            process_map = {}

            # process output fds
# 子进程管道数据操作
            for proc in self.processes.values():
                proc.log_output()
                drains = proc.get_pipe_drains()
                for fd, drain in drains:
                    r.append(fd)
                    process_map[fd] = drain

            # medusa i/o fds
# 网络socket io操作
            for fd, dispatcher in socket_map.items():
                if dispatcher.readable():
                    r.append(fd)
                if dispatcher.writable():
                    w.append(fd)
# mood为主程序为停止状态
            if self.mood < 1:
                if not self.stopping:
                    self.stop_all()
                    self.stopping = True

                # if there are no delayed processes (we're done killing
                # everything), it's OK to stop or reload
                delayprocs = self.get_delay_processes()
                if delayprocs:
                    names = [ p.config.name for p in delayprocs]
                    namestr = ', '.join(names)
                    self.options.logger.info('waiting for %s to die' % namestr)
                else:
                    break

            try:
# 依次遍历注册的文件句柄
                r, w, x = select.select(r, w, x, timeout)
            except select.error, err:
                if err[0] == errno.EINTR:
                    self.options.logger.log(self.options.TRACE,
                                            'EINTR encountered in select')
                else:
                    raise
                r = w = x = []

            for fd in r:
# 如果是子进程的管道事件
                if process_map.has_key(fd):
                    drain = process_map[fd]
                    # drain the file descriptor
                    drain(fd)
# 如果是客户端的rpc读事件
                if socket_map.has_key(fd):
                    try:
                        socket_map[fd].handle_read_event()
                    except asyncore.ExitNow:
                        raise
                    except:
                        socket_map[fd].handle_error()

            for fd in w:
# 如果是客户端rpc写事件
                if socket_map.has_key(fd):
                    try:
                        socket_map[fd].handle_write_event()
                    except asyncore.ExitNow:
                        raise
                    except:
                        socket_map[fd].handle_error()
# 判断配置子进程的状态，来决定该子进程是否运行(这其中是由于有些进程可以配置延迟执行),通过调用子进程实例的spwn()方法来运行子进程
            self.give_up()
# 杀死没有要杀死但还没杀死的进程
            self.kill_undead() 
# 获取已经死亡的子进程信息
            self.reap()
# 处理信号
            self.handle_signal()

            if test:
                break

其中以上比较重要的步骤为:
1).明白子进程如果将数据发送给主进程
2).明白如何处理客户端发过来的rpc请求
Supervisor将http的句柄和管道的句柄放在了同一个select中进行了处理，
一．管道数据的发送
Linux中管道是单向传输数据的，如果创建管道后，如果要读就必须关闭管道的写操作。
首先我们先找到run()函数，其中有

for program in self.options.programs:
            name = program.name
# 根据初始化后的配置文件生成相应的子进程实例
            self.processes[name] = self.options.make_process(program)  
找到options.py中，1029行，
    def make_process(self, config):
        from supervisord import Subprocess
        return Subprocess(self, config)
其中Subprocess类的主要方法:
 def spawn(self):
        """Start the subprocess.  It must not be running already.

        Return the process id.  If the fork() call fails, return 0.
        """
        pname = self.config.name
# 如果该实例已经有pid文件则该实例已经运行
        if self.pid:
            msg = 'process %r already running' % pname
            self.options.logger.critical(msg)
            return
# 相应状态的初始化
        self.killing = 0
        self.spawnerr = None
        self.exitstatus = None
        self.system_stop = 0
        self.administrative_stop = 0
        # 最后一次启动时间
        self.laststart = time.time()
# 获取配置子进程的执行命令
        filename, argv, st = self.get_execv_args()
# 检查该配置文件是否可以运行这些执行命令
        fail_msg = self.options.check_execv_args(filename, argv, st)
        if fail_msg is not None:
            self.record_spawnerr(fail_msg)
            return

        try:
# 生成管道，生成与主进程通信的管道
            self.pipes = self.options.make_pipes()
        except OSError, why:
            code = why[0]
            if code == errno.EMFILE:
                # too many file descriptors open
                msg = 'too many open files to spawn %r' % pname
            else:
                msg = 'unknown error: %s' % errno.errorcode.get(code, code)
            self.record_spawnerr(msg)
            return

        try:
# 生成子进程
            pid = self.options.fork()
        except OSError, why:
            code = why[0]
            if code == errno.EAGAIN:
                # process table full
                msg  = 'Too many processes in process table to spawn %r' % pname
            else:
                msg = 'unknown error: %s' % errno.errorcode.get(code, code)

            self.record_spawnerr(msg)
            self.options.close_pipes(self.pipes)
            return

        if pid != 0:
            # Parent
            self.pid = pid
# 关闭父进程中管道的写
            for fdname in ('child_stdin', 'child_stdout', 'child_stderr'):
                self.options.close_fd(self.pipes[fdname])
            self.options.logger.info('spawned: %r with pid %s' % (pname, pid))
            self.spawnerr = None
            self.delay = time.time() + self.config.startsecs
            self.options.pidhistory[pid] = self
            return pid

        else:
            # Child
            try:
                # prevent child from receiving signals sent to the
                # parent by calling os.setpgrp to create a new process
                # group for the child; this prevents, for instance,
                # the case of child processes being sent a SIGINT when
                # running supervisor in foreground mode and Ctrl-C in
                # the terminal window running supervisord is pressed.
                # Presumably it also prevents HUP, etc received by
                # supervisord from being sent to children.
                self.options.setpgrp()
# 0 将子进程的标准输入重定向到管道
                self.options.dup2(self.pipes['child_stdin'], 0)
# 1 将子进程的标准输出重定向到管道
                self.options.dup2(self.pipes['child_stdout'], 1)
# 2 将子进程的标准错误重定向到管道
                self.options.dup2(self.pipes['child_stderr'], 2)
# 关闭子进程管道的读
                for i in range(3, self.options.minfds):
                    self.options.close_fd(i)
                # sending to fd 1 will put this output in the log(s)
                msg = self.set_uid()
                if msg:
                    self.options.write(
                        1, "%s: error trying to setuid to %s!\n" %
                        (pname, self.config.uid)
                        )
                    self.options.write(1, "%s: %s\n" % (pname, msg))
                try:
# 子进程开始执行
                    self.options.execv(filename, argv)
                except OSError, why:
                    code = why[0]
                    self.options.write(1, "couldn't exec %s: %s\n" % (
                        argv[0], errno.errorcode.get(code, code)))
                except:
                    (file, fun, line), t,v,tbinfo = asyncore.compact_traceback()
                    error = '%s, %s: file: %s line: %s' % (t, v, file, line)
                    self.options.write(1, "couldn't exec %s: %s\n" % (filename,
                                                                      error))
            finally:
# 子进程执行完毕后，退出
                self.options._exit(127)
其中,make_pipes()方法位于options.py中1033行，
    def make_pipes(self):
        """ Create pipes for parent to child stdin/stdout/stderr
        communications.  Open fd in nonblocking mode so we can read them
        in the mainloop without blocking """
        pipes = {}
        try:
            # 生成一个子进程标准输入管道的读和写句柄
pipes['child_stdin'], pipes['stdin'] = os.pipe()
# 生成一个子进程标准输出管道的读和写句柄
            pipes['stdout'], pipes['child_stdout'] = os.pipe()
# 生成一个子进程标准错误管道的读和写句柄
            pipes['stderr'], pipes['child_stderr'] = os.pipe()
# 将主进程中要读的管道设置成非阻塞，使之在异步io中不阻塞整个循环
            for fd in (pipes['stdout'], pipes['stderr'], pipes['stdin']):
                fcntl(fd, F_SETFL, fcntl(fd, F_GETFL) | os.O_NDELAY)
            return pipes
        except OSError:
            self.close_pipes(pipes)
            raise

此时，在上述代码中runforever()函数中：

            for proc in self.processes.values():
                proc.log_output()
                drains = proc.get_pipe_drains()
                for fd, drain in drains:
                    r.append(fd)
                    process_map[fd] = drain

Proc为进程实例，get_pipe_drains()返回管道的标准输出和标准错误输出

    def get_pipe_drains(self):
        if not self.pipes:
            return []

        drains = ( [ self.pipes['stdout'], self.drain_stdout],
                   [ self.pipes['stderr'], self.drain_stderr] )

        return drains

其中，self.drain_stdout为

 def drain_stdout(self, *ignored):
#将管道中的内容读出并保存
        output = self.options.readfd(self.pipes['stdout'])
        if self.config.log_stdout:
            self.logbuffer += output

            for fd in r:
                if process_map.has_key(fd):
                    drain = process_map[fd]
                    # drain the file descriptor
# 其中drain就是self.drain_stdout或者self.drain_stderr
                    drain(fd)  

至此管道的数据处理方式已经完成，管道数据的传递的基本原理已经分析完成
二．Rpc事件的处理
由于rpc的处理方式，使用了python中的asyncore, asynchat这两个包作为基础进行扩展。
这里对这两个包做个简要的分析，因为后面在rpc的处理中，会用到这两个包的基础知识。
由于在服务端异步编程中，

服务器端

    ser=socket.socket(socket.AF_INET,socket.SOCK_STREAM)
    ser.bind(('127.0.0.1',8000))
    ser.listen(5)
    while 1:
        client,addr=ser.accept()
        print 'accept %s connect'%(addr,)
        data=client.recv(1024)
        print data
        client.send('get')
        client.close()

会初始化一个socket，如上例中的ser，这个ser只负责接收创建新的请求，client,addr=ser.accept()，当新接收的请求client再接收数据后然后再通过该请求client将该数据发送出去。
此时我们就有两个需求一个是专门的ser只负责接收新的请求，一个是专门处理新请求的实例，将新的请求并处理该请求的类对应到asyncore.py中dispatcher类为专门接收新请求的类和asynchat.py中就是async_chat专门处理新接收的请求。

asyncore.py简要分析

socket_map 为包全局的描述符的字典
poll()对应select模式
poll2()对应epoll模式
loop()函数根据当前的运行环境选择哪种异步IO模式
dispatcher()类
init(self, sock=None, map=None) 如果传入的sock为None则实例化为ser实例，如果sock不为None则是处理请求实例，并将该sock设置为非阻塞，加入socket_map中
add_channel(self, map=None) 添加socket_map中为自己的实例
del_channel(self, map=None) 删除socket_map中为自己的实例
create_socket(self, family=socket.AF_INET, type=socket.SOCK_STREAM) 创建ser实例，并将该实例设置为非阻塞，并加入socket_map中
set_socket(self, sock, map=None) 添加sock到socket_map中
set_reuse_addr(self) 设置ser监听的端口能够在断开监听后立马重新被监听

readable(self) 该sock是否可读
writable(self) 该sock是否可写
listen(self, num) 设置ser监听的数量
bind(self, addr) 设置ser监听的端口
connect(self, address) 设置连接地址
accept(self) 接收新的连接请求
send(self, data) 发送数据
recv(self, buffer_size) 接收数据
close(self) 关闭连接
handle_read_event(self) 处理读事件，如果是新请求则接收，如果是连接发送数据则接收
handle_connect_event(self) 处理新连接进来的请求
handle_write_event(self) 处理连接的写请求

以上为dispatcher主要的方法，
在asynchat.py中async_chat继承自dispatcher.该类的详细分析

class async_chat(asyncore.dispatcher):
    """This is an abstract class.  You must derive from this class, and add
    the two methods collect_incoming_data() and found_terminator()"""

    # these are overridable defaults
# 接收缓存区大小
ac_in_buffer_size = 65536
# 发送数据缓冲区大小
    ac_out_buffer_size = 65536

    # we don't want to enable the use of encoding by default, because that is a
    # sign of an application bug that we don't want to pass silently

    use_encoding = 0
    encoding = 'latin-1'

    def __init__(self, sock=None, map=None):
        # for string terminator matching
# 初始化接收缓冲区
        self.ac_in_buffer = b''

        # we use a list here rather than io.BytesIO for a few reasons...
        # del lst[:] is faster than bio.truncate(0)
        # lst = [] is faster than bio.truncate(0)
# 分段接收数据的列表
        self.incoming = []

        # we toss the use of the "simple producer" and replace it with
        # a pure deque, which the original fifo was a wrapping of
# 发送数据时使用的队列数据结构
        self.producer_fifo = deque()
# 调用dispatcher的构造方法，将sock设置成非阻塞，将sock添加到socket_map
        asyncore.dispatcher.__init__(self, sock, map)
# 获取接收到的数据
    def collect_incoming_data(self, data):
        raise NotImplementedError("must be implemented in subclass")

    def _collect_incoming_data(self, data):
        self.incoming.append(data)
# 将所有接收到的数据
    def _get_data(self):
        d = b''.join(self.incoming)
        del self.incoming[:]
        return d
# 查找接收数据中的分隔符
    def found_terminator(self):
        raise NotImplementedError("must be implemented in subclass")
# 设置接收数据中的分隔符
    def set_terminator(self, term):
        """Set the input delimiter.

        Can be a fixed string of any length, an integer, or None.
        """
        if isinstance(term, str) and self.use_encoding:
            term = bytes(term, self.encoding)
        elif isinstance(term, int) and term < 0:
            raise ValueError('the number of received bytes must be positive')
        self.terminator = term
# 获取已经设置的分隔符
    def get_terminator(self):
        return self.terminator

    # grab some more data from the socket,
    # throw it to the collector method,
    # check for the terminator,
    # if found, transition to the next state.
# 处理读事件
    def handle_read(self):

        try:
            data = self.recv(self.ac_in_buffer_size)
        except BlockingIOError:
            return
        except OSError as why:
            self.handle_error()
            return

        if isinstance(data, str) and self.use_encoding:
            data = bytes(str, self.encoding)
# 将读出的数据存入到接收缓冲区
        self.ac_in_buffer = self.ac_in_buffer + data

        # Continue to search for self.terminator in self.ac_in_buffer,
        # while calling self.collect_incoming_data.  The while loop
        # is necessary because we might read several data+terminator
        # combos with a single recv(4096).

        while self.ac_in_buffer:
# 获取接收的数据长度
            lb = len(self.ac_in_buffer)
# 获取设置的分隔符
            terminator = self.get_terminator()
            if not terminator:
                # no terminator, collect it all
# 将已经接收的数据处理
                self.collect_incoming_data(self.ac_in_buffer)
# 将接收缓冲区设置为空
                self.ac_in_buffer = b''
# 如果设置分隔符是数字则接收相应长度的数据
            elif isinstance(terminator, int):
                # numeric terminator
                n = terminator
                if lb < n:
                    self.collect_incoming_data(self.ac_in_buffer)
                    self.ac_in_buffer = b''
# 将设置的分隔符长度减去已经接收的数据长度
                    self.terminator = self.terminator - lb
                else:   
# 清楚已经接收的数据
                    self.collect_incoming_data(self.ac_in_buffer[:n])
# 留下超出长度的部分
                    self.ac_in_buffer = self.ac_in_buffer[n:]
# 重置
                    self.terminator = 0
                    self.found_terminator()
            else:
                # 3 cases:
                # 1) end of buffer matches terminator exactly:
                #    collect data, transition
                # 2) end of buffer matches some prefix:
                #    collect data to the prefix
                # 3) end of buffer does not match any prefix:
                #    collect data
                terminator_len = len(terminator)
# 在接收缓冲区中查找分隔符
                index = self.ac_in_buffer.find(terminator)
                if index != -1:
                    # we found the terminator
                    if index > 0:
                        # don't bother reporting the empty string
                        # (source of subtle bugs)
                        self.collect_incoming_data(self.ac_in_buffer[:index])
# 将剩下的数据保留到接收数据缓冲区
                    self.ac_in_buffer = self.ac_in_buffer[index+terminator_len:]
                    # This does the Right Thing if the terminator
                    # is changed here.
                    self.found_terminator()
                else:
                    # check for a prefix of the terminator
# 检查接收缓冲区是否已分隔符结尾
                    index = find_prefix_at_end(self.ac_in_buffer, terminator)
                    if index:
                        if index != lb:
                            # we found a prefix, collect up to the prefix
# 如果是分隔符结尾则结束本次处理
                            self.collect_incoming_data(self.ac_in_buffer[:-index])
                            self.ac_in_buffer = self.ac_in_buffer[-index:]
                        break
                    else:
                        # no prefix, collect it all
# 将接收缓冲区数据处理并重置
                        self.collect_incoming_data(self.ac_in_buffer)
                        self.ac_in_buffer = b''

def handle_write(self):
# 将处理的数据全部发送出去
        self.initiate_send()

def handle_close(self):
# 关闭连接
        self.close()

def push(self, data):
# 将连接处理后的数据全部加入发送缓冲区
        if not isinstance(data, (bytes, bytearray, memoryview)):
            raise TypeError('data argument must be byte-ish (%r)',
                            type(data))
        sabs = self.ac_out_buffer_size
# 如果要发送出去的数据大于发送缓冲区大小，就使用生产者模式发送
        if len(data) > sabs:
            for i in range(0, len(data), sabs):
                self.producer_fifo.append(data[i:i+sabs])
        else:
            self.producer_fifo.append(data)
        self.initiate_send()

    def push_with_producer(self, producer):
        self.producer_fifo.append(producer)
        self.initiate_send()

    def readable(self):
        "predicate for inclusion in the readable for select()"
        # cannot use the old predicate, it violates the claim of the
        # set_terminator method.

        # return (len(self.ac_in_buffer) <= self.ac_in_buffer_size)
        return 1

    def writable(self):
        "predicate for inclusion in the writable for select()"
        return self.producer_fifo or (not self.connected)

    def close_when_done(self):
        "automatically close this channel once the outgoing queue is empty"
        self.producer_fifo.append(None)

def initiate_send(self):
# 如果当前生产者队列不为空，连接未关闭就发送数据
        while self.producer_fifo and self.connected:
            first = self.producer_fifo[0]
            # handle empty string/buffer or None entry
            if not first:
# 如果数据生产者没有数据则删除该生产者，如果为None则所有数据已经发送完成，并关闭连接
                del self.producer_fifo[0]
                if first is None:
                    self.handle_close()
                    return

            # handle classic producer behavior
            obs = self.ac_out_buffer_size
            try:
                data = first[:obs]
            except TypeError:
                data = first.more()
                if data:
                    self.producer_fifo.appendleft(data)
                else:
                    del self.producer_fifo[0]
                continue

            if isinstance(data, str) and self.use_encoding:
# 将发送数据改为字节类型
                data = bytes(data, self.encoding)

            # send the data
            try:    
# 发送数据
                num_sent = self.send(data)
            except OSError:
                self.handle_error()
                return

            if num_sent:
                if num_sent < len(data) or obs < len(first):
# 如果发送的数据还没有完成则继续发送
                    self.producer_fifo[0] = first[num_sent:]
                else:
                    del self.producer_fifo[0]
            return

    def discard_buffers(self):
        # Emergencies only!
        self.ac_in_buffer = b''
        del self.incoming[:]
        self.producer_fifo.clear()

对这两个包有大概了解后，我们开始分析run()方法中

self.options.openhttpserver(self)

该方法调用http中的make_http_server方法

def openhttpserver(self, supervisord):
        from http import make_http_server
        try:
            self.httpserver = make_http_server(self, supervisord)
        except socket.error, why:
            if why[0] == errno.EADDRINUSE:
                port = str(self.http_port.address)
                self.usage('Another program is already listening on '
                           'the port that our HTTP server is '
                           'configured to use (%s).  Shut this program '
                           'down first before starting supervisord. ' %
                           port)
        except ValueError, why:
            self.usage(why[0])

在http.py文件中，
def make_http_server(options, supervisord):
    if not options.http_port:
        return
# 配置的用户名和密码
    username = options.http_username
    password = options.http_password

    class LogWrapper:
        def log(self, msg):
            if msg.endswith('\n'):
                msg = msg[:-1]
            options.logger.info(msg)
    wrapper = LogWrapper()

    family = options.http_port.family
    # 如果是socket监听
if family == socket.AF_INET:
# 主要分析socket连接
        host, port = options.http_port.address
# 生成http_server
        hs = supervisor_af_inet_http_server(host, port, logger_object=wrapper)
# 如果是原始套接字
    elif family == socket.AF_UNIX:
        socketname = options.http_port.address
        sockchmod = options.sockchmod
        sockchown = options.sockchown
        hs = supervisor_af_unix_http_server(socketname, sockchmod, sockchown,
                                            logger_object=wrapper)
    else:
        raise ValueError('Cannot determine socket type %r' % family)

    from xmlrpc import supervisor_xmlrpc_handler
from web import supervisor_ui_handler
# 本次分析的rpchandler
    xmlrpchandler = supervisor_xmlrpc_handler(supervisord)
    tailhandler = logtail_handler(supervisord)
    here = os.path.abspath(os.path.dirname(__file__))
    templatedir = os.path.join(here, 'ui')
    filesystem = filesys.os_filesystem(templatedir)
    uihandler = supervisor_ui_handler(filesystem, supervisord)

    if username:
        # wrap the xmlrpc handler and tailhandler in an authentication handler
        users = {username:password}
        from medusa.auth_handler import auth_handler
        xmlrpchandler = auth_handler(users, xmlrpchandler)
        tailhandler = auth_handler(users, tailhandler)
        uihandler = auth_handler(users, uihandler)
    else:
        options.logger.critical('Running without any HTTP authentication '
                                'checking')
# 将handler注册到服务器类中
    hs.install_handler(uihandler)
    hs.install_handler(tailhandler)
    hs.install_handler(xmlrpchandler)
return hs

这里分析supervisor_af_inet_http_server类，该类继承自supervisor_http_server，supervisor_http_server继承自http_server.http_server，http_server.http_server继承自asyncore.dispatcher，所以hs就是上例中的接收新请求的类，因为该实例的主要作用就是在新请求进来时处理

class http_server (asyncore.dispatcher):
   SERVER_IDENT = 'HTTP Server (V%s)' % VERSION_STRING
    channel_class = http_channel

def handle_accept (self):
        self.total_clients.increment()
        try:
# 接收新请求
            conn, addr = self.accept()
        except socket.error:
            # linux: on rare occasions we get a bogus socket back from
            # accept.  socketmodule.c:makesockaddr complains that the
            # address family is unknown.  We don't want the whole server
            # to shut down because of this.
            self.log_info ('warning: server accept() threw an exception', 'warning')
            return
        except TypeError:
            # unpack non-sequence.  this can happen when a read event
            # fires on a listening socket, but when we call accept()
            # we get EWOULDBLOCK, so dispatcher.accept() returns None.
            # Seen on FreeBSD3.
            self.log_info ('warning: server accept() threw EWOULDBLOCK', 'warning')
            return
# 将新请求用该类实例化处理
        self.channel_class (self, conn, addr)

supervisor_http_server类的定义
channel_class = deferring_http_channel
所以通过deferring_http_channel处理该请求
deferring_http_channel继承自http_server.http_channel
http_server.http_channel继承自asynchat.async_chat
由于当该链接有可读数据时，就出触发handle_read函数，而该函数在接收数据放入接收缓冲区后，就会调用 found_terminator函数，
我们分析一下deferring_http_channel函数

    def found_terminator (self):
        """ We only override this to use 'deferring_http_request' class
        instead of the normal http_request class; it sucks to need to override
        this """
# 如果当前请求实例存在则继续处理接收数据
        if self.current_request:
            self.current_request.found_terminator()
# 如果不存在当前初始化实例
        else:
# 第一次接收的数据
            header = self.in_buffer
# 将接收缓冲区清空
            self.in_buffer = ''
# 将头部信息分离出来
            lines = string.split (header, '\r\n')

            # --------------------------------------------------
            # crack the request header
            # --------------------------------------------------

            while lines and not lines[0]:
                # as per the suggestion of http-1.1 section 4.1, (and
                # Eric Parker <eparker@zyvex.com>), ignore a leading
                # blank lines (buggy browsers tack it onto the end of
                # POST requests)
                lines = lines[1:]

            if not lines:
                self.close_when_done()
                return
# 第一行头部数据
            request = lines[0]
# 第一行数据的命令，uri,版本
            command, uri, version = http_server.crack_request (request)
# 处理剩下的头部信息
            header = http_server.join_headers (lines[1:])

            # unquote path if necessary (thanks to Skip Montanaro for pointing
            # out that we must unquote in piecemeal fashion).
            rpath, rquery = http_server.splitquery(uri)
            if '%' in rpath:
                if rquery:
                    uri = http_server.unquote (rpath) + '?' + rquery
                else:
                    uri = http_server.unquote (rpath)
# 实例化一个http_request实例
            r = deferring_http_request (self, request, command, uri, version,
                                         header)
            self.request_counter.increment()
            self.server.total_requests.increment()

            if command is None:
                self.log_info ('Bad HTTP request: %s' % repr(request), 'error')
                r.error (400)
                return

            # --------------------------------------------------
            # handler selection and dispatch
            # --------------------------------------------------
# 通过第一行信息来匹配注册的handlers
            for h in self.server.handlers:
# 调用handler中的match方法，如果匹配rpc方法就返回rpchandler
                if h.match (r):
                    try:
# 将该处理实例保存
                        self.current_request = r
                        # This isn't used anywhere.
                        # r.handler = h # CYCLE
# handler处理该请求
                        h.handle_request (r)
                    except:
                        self.server.exceptions.increment()
                        (file, fun, line), t, v, tbinfo = \
                               asyncore.compact_traceback()
                        self.log_info(
                            'Server Error: %s, %s: file: %s line: %s' %
                            (t,v,file,line),
                            'error')
                        try:
                            r.error (500)
                        except:
                            pass
                    return

            # no handlers, so complain
            r.error (404)

由于此次只分析rpchandler，supervisor_xmlrpc_handler继承自xmlrpc_handler分析xmlrpc_handler,通过协议来匹配该handler

    def match (self, request):
        # Note: /RPC2 is not required by the spec, so you may override this method.
        if request.uri[:5] == '/RPC2':
            return 1
        else:
            return 0

class supervisor_xmlrpc_handler(xmlrpc_handler):
def __init__(self, supervisord):
# rpc调用类方发接口，通过该类实现rpc客户端的对主进程的操作
        self.rpcinterface = RPCInterface(supervisord)
# supervisord实例
        self.supervisord = supervisord

    def continue_request (self, data, request):
        logger = self.supervisord.options.logger

        try:
# 解析出上传的内容，并通过xmlrpclib解析成方法
            params, method = xmlrpclib.loads(data)

            try:
                logger.debug('XML-RPC method called: %s()' % method)
# 调用方法执行
                value = self.call(method, params)
                logger.debug('XML-RPC method %s() returned successfully' %
                             method)
            except RPCError, err:
                # turn RPCError reported by method into a Fault instance
                value = xmlrpclib.Fault(err.code, err.text)
                logger.warn('XML-RPC method %s() returned fault: [%d] %s' % (
                    method,
                    err.code, err.text))

            if isinstance(value, types.FunctionType):
                # returning a function from an RPC method implies that
                # this needs to be a deferred response (it needs to block).
                pushproducer = request.channel.push_with_producer
                pushproducer(DeferredXMLRPCResponse(request, value))

            else:
                # if we get anything but a function, it implies that this
                # response doesn't need to be deferred, we can service it
                # right away.
# 将方法执行的结果返回
                body = xmlrpc_marshal(value)
                request['Content-Type'] = 'text/xml'
                request['Content-Length'] = len(body)
# 调用request.push方法，将body信息压入该内容自行阅读源码
                request.push(body)
# 执行完后将数据发送出去，该内容自行阅读源码
                request.done()

        except:
            io = StringIO.StringIO()
            traceback.print_exc(file=io)
            val = io.getvalue()
            logger.critical(val)
            # internal error, report as HTTP server error
            request.error(500)

def call(self, method, params):
# 调用rpcinterface的方法
        return traverse(self.rpcinterface, method, params)

该方法就是调用一个实例的方法
def traverse(ob, method, params):
    path = method.split('.')
    for name in path:
        if name.startswith('_'):
            # security (don't allow things that start with an underscore to
            # be called remotely)
            raise RPCError(Faults.UNKNOWN_METHOD)
        ob = getattr(ob, name, None)
        if ob is None:
            raise RPCError(Faults.UNKNOWN_METHOD)

    try:
        return ob(*params)
    except TypeError:
        raise RPCError(Faults.INCORRECT_PARAMETERS)

至此一个rpchandle的处理就完成了

总结

[supervisor_demo](https://github.com/xiaowuzidaxia/sp_demo)
本文只是简要介绍了supervisor运行时的基本原理，由于水平有限，不能详细介绍其他更多功能，但是supervisor的基本原理已经介绍了，此时附一个基于python实现的简单的supervisor的demo希望对大家理解有帮助。[简单supervisor模型](https://github.com/xiaowuzidaxia/sp_demo)