select是全平臺通用的IO多路復用模塊。最大連接數：1024。

poll和epoll沒有最大連接數限制，但只能用在linux平臺。

selectors是再封裝模塊，推薦使用。下篇會討論。

select.select(rlist, wlist, xlist[, timeout])?

• This is a straightforward interface to the Unix select() system call. The first three arguments are sequences of ‘waitable objects’: either integers representing file descriptors or objects with a parameterless method named fileno() returning such an integer:

  Empty sequences are allowed, but acceptance of three empty sequences is platform-dependent. (It is known to work on Unix but not on Windows.) ?The optional timeout argument specifies a time-out as a floating point number in seconds. ?When the timeout argument is omitted the function blocks until at least one file descriptor is ready. ?A time-out value of zero specifies a poll and never blocks.

  The return value is a triple of lists of objects that are ready: subsets of the first three arguments. ?When the time-out is reached without a file descriptor becoming ready, three empty lists are returned.

  Among the acceptable object types in the sequences are Python file objects (e.g. sys.stdin, or objects returned by open() or os.popen()), socket objects returned by socket.socket(). ?You may also define a wrapper class yourself, as long as it

  • rlist: wait until ready for reading

  • wlist: wait until ready for writing

  • xlist: wait for an “exceptional condition” (see the manual page for what your system considers such a condition)

import?socket
import?os
import?select
import?queue
import?jsonclass?SelectFTP(object):def?__init__(self,?ip,?port):self.server?=?socket.socket(socket.AF_INET,?socket.SOCK_STREAM)self.server.setblocking(0)self.server.bind((ip,?port))self.server.listen(20)self.inputs?=?[self.server]self.outputs?=?[]self.file_attr?=?{}#?file_attr?format:file_attr[socket]:{func:'',?filename:'',?len:999,?recv_len:0}??????self.socket_queue?=?{}def?upload(self,?sock,?write_data):#?if?os.path.isfile(self.file_attr[sock]['filename']):with?open(self.file_attr[sock]['filename'],?'a+')?as?file:file.write(data)self.file_attr[sock][recv_len]?+=?len(write_data)if?self.file_attr[sock][recv_len]?==?self.file_attr[sock][len]:del?self.file_attr[sock]file.close()def?download(self,?sock,?*args):passdef?run(self):while?self.inputs:read_active,?read_output,?exception?=?select.select(self.inputs,?self.outputs,?self.inputs)for?fd?in?read_active:if?fd?is?server:conn,?addr?=?fd.accept(1024)conn.setblocking(0)self.inputs?=?self.inputs.append(conn)self.socket_queue[fd]?=?queue.Queue()else:recv_data?=?fd.recv(1024)if?recv_data:data?=?json.loads(recv_data.decode())if?fd?not?in?self.file_attr.keys:self.file_attr[fd]?=?dataelse:try:self.socket_queue.put_nowait(data)if?fd?not?in?self.outputs:self.outputs.append(fd)except?Exception?as?e:print(e)else:self.inputs.remove(fd)if?fd?in?self.outputs:self.outputs.remove(fd)del?self.socket_queue[fd]send_data?=?for?fd?in?read_output:try:message?=?self.socket_queue.get_nowait()except?queue.Empty:self.outputs.remove(fd)print('wait...')else:getattr(self.file_attr[fd]['func'])(fd,?message)

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