python阻塞套接字，立即发送返回

Question

我正在使用 socket 模块在 Python 中编写一个多线程套接字应用程序。 服务器侦听连接，当它获得连接时，它为该套接字生成一个线程。

服务器线程向客户端发送一些数据。但是客户还没有准备好接收它。我认为这会导致服务器等到客户端启动 recv 而是立即返回

客户端然后调用recv，它被阻塞并且没有收到任何数据。

客户端套接字构造函数

self.__clientSocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
self.__clientSocket.connect((server, port))

服务器套接字构造函数

        self.servSock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        self.servSock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        #self.servSock.settimeout(None)
        self.servSock.setblocking(1)
        self.servSock.bind((self.addr,self.port))
        self.servSock.listen(5)

监听接受线程

    try:
        (cs, address) = self.servSock.accept()
    except socket.timeout:
        return
    threadName = '\r\nClient %s:%s\r\n' % (cs, address)
    print threadName
    clientSocketHandler = ClientSocket()
    clientSocketHandler.setClientSocket(cs)
    self.clients.newThread(self.clientFunc, {clientSocketHandler : "1"}, threadName).start()

服务器和客户端从 ClientSocket 内部发送/接收方法

receivedData = self.__clientSocket.recv(1024*1024)

self.__clientSocket.send(s)

知道为什么 send() 会立即返回吗？

Answer 1

知道为什么 send() 会立即返回吗？

所有 send() 所做的就是填充网络缓冲区并返回发送的字节数。

如果您想要阻止的发送，只需接收来自客户端的确认消息。

Answer 2

客户端不必准备好接收数据 - 数据将在套接字的接收缓冲区中排队，直到您准备好接收它。 Send 立即返回，因为发送缓冲区未满 - 如果它已满，send() 将阻塞，直到有空间容纳您要发送的数据。

大多数时候你永远不会填满它 - 因此你正在经历什么。另一方面，您可能不希望其中包含 1024*1024 的 recv 调用 - 这有点偏高。

Answer 3

抱歉，我在提出这个问题后不久就解决了这个问题。 @Lee 感谢您的回答，它为我指明了正确的方向。 解决方案是发送一个 4byte int 指定要遵循的数据大小。客户端总是会收到这四个字节，然后是数据的大小。

from commandClass import Command
from commandActionClass import CommandAction
import socket
from time import *
import struct

class ClientSocket():
    instance = None
    __connected = False
    __clientSocket = None

    @staticmethod
    def getInstance():
        if ClientSocket.instance == None:
            ClientSocket.instance = ClientSocket()
        return ClientSocket.instance

    def __init__(self):
        self.__connected = False
        self.receivedData = ''
        self.bufSize = 4096
        self.buffer = ''

    def connect(self, server, port):
        if self.isConnected():
            raise Exception('Already connected.')

        self.__clientSocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        self.__clientSocket.setsockopt(socket.SOL_TCP, socket.TCP_NODELAY, 1)
        self.__clientSocket.connect((server, port))
        self.__clientSocket.setblocking(1)
        self.__connected = True

    def disconnect(self):
        try:
            self.receivedData = ''
            self.buffer = ''
            self.__clientSocket.close()
        except Exception, e:
            print e
        finally:
            self.__connected = False

    def sendString(self,s):
        try:
            if (self.isConnected()):
                self.__clientSocket.send(s)
        except Exception, e:
            print e
            self.disconnect()

    def __pop(self, size):
        data = self.receivedData[:size]
        self.receivedData = self.receivedData[size:]
        return data

    def __recv(self,toRead):
        self.flush()
        while ((len(self.receivedData)<toRead)and(self.isConnected())):
            data = self.__clientSocket.recv(self.bufSize)
            if not data:
                self.disconnect()
            self.receivedData = self.receivedData + data

        return self.__pop(toRead)

    def __sendint(self, x):
        self.__sendall(struct.pack("i", x))

    def __recvint(self):
        data = self.__recv(4)
        if not data:
            raise Exception('Expected to receive buffer size')
        return struct.unpack("i", data)[0]

    def flush(self):
        if len(self.buffer)>0:
            self.__clientSocket.sendall(self.buffer)
        self.buffer = ''

    def __sendall(self, s):
        self.buffer = self.buffer + s

    def send(self,s):
        try:
            if (not self.isConnected()):
                raise Exception('Socket is not connected')
            data = s.pickle()
            self.__sendint(len(data))
            self.__sendall(data)
        except Exception, e:
            self.disconnect()
            raise e

    def sendEOC(self):
        self.send(Command(CommandAction.EOC, time()))#send our system time. can be used for ping

    def receive(self):
        if (not self.isConnected()):
            raise Exception('Socket Error. Not Connected')
        try:
            #first receive the size of packet
            buffsize = self.__recvint()
            #now receive the actual data
            data = self.__recv(buffsize)

            if not data:
                raise Exception('No data to receive')

            command = Command.unpickle(data)
        except Exception, e:
            self.disconnect()
            command = Command(CommandAction.Invalid, None)
            raise e
        #finally?
        return command

    def isConnected(self):
        return self.__connected

    def setClientSocket(self, clientSocket):
        self.__clientSocket = clientSocket
        self.__connected = True #assume its connected