版权声明 本站原创文章 由 萌叔 发表 转载请注明 萌叔 | http://vearne.cc 我们在编写程序的时候经常喜欢这样写代码
import MySQLdb import time from multiprocessing import Process conn = MySQLdb.connect('localhost', 'vearne', 'xx', 'test') def f(name): for i in xrange(10): cursor = conn.cursor() sql = "insert into car(name) values(%s)" param = [(name)] print param #time.sleep(1) n = cursor.execute(sql,param) cursor.close() conn.commit() if __name__ == '__main__': for i in xrange(10): p = Process(target=f, args=('bob',)) p.start() 上面的程序有问题吗? 以上的程序在单进程的情况下，应该是没有问题，但是在多进程的情况下，它是有错误的。
首先看看下面的源码
class Process(object): ''' Process objects represent activity that is run in a separate process The class is analagous to `threading.Thread` ''' _Popen = None def __init__(self, group=None, target=None, name=None, args=(), kwargs={}): assert group is None, 'group argument must be None for now' count = _current_process._counter.next() self._identity = _current_process._identity + (count,) self._authkey = _current_process._authkey self._daemonic = _current_process._daemonic self._tempdir = _current_process._tempdir self._parent_pid = os.getpid() self._popen = None self._target = target self._args = tuple(args) self._kwargs = dict(kwargs) self._name = name or type(self).__name__ + '-' + \ ':'.join(str(i) for i in self._identity) def run(self): ''' Method to be run in sub-process; can be overridden in sub-class ''' if self._target: self._target(*self._args, **self._kwargs) def start(self): ''' Start child process ''' assert self._popen is None, 'cannot start a process twice' assert self._parent_pid == os.getpid(), \ 'can only start a process object created by current process' assert not _current_process._daemonic, \ 'daemonic processes are not allowed to have children' _cleanup() if self._Popen is not None: Popen = self._Popen else: from .forking import Popen self._popen = Popen(self) # -- 创建 Popen 对象 -- _current_process._children.add(self) # 省略部分代码 ... ... def _bootstrap(self): # -- _bootstrap 函数 -- from . import util global _current_process try: self._children = set() self._counter = itertools.count(1) try: sys.stdin.close() sys.stdin = open(os.devnull) except (OSError, ValueError): pass _current_process = self util._finalizer_registry.clear() util._run_after_forkers() util.info('child process calling self.run()') try: self.run() # -- 调用run函数 -- exitcode = 0 finally: util._exit_function() except SystemExit, e: if not e.args: exitcode = 1 elif isinstance(e.args[0], int): exitcode = e.args[0] else: sys.stderr.write(str(e.args[0]) + '\n') sys.stderr.flush() exitcode = 0 if isinstance(e.args[0], str) else 1 except: exitcode = 1 import traceback sys.stderr.write('Process %s:\n' % self.name) sys.stderr.flush() traceback.print_exc() util.info('process exiting with exitcode %d' % exitcode) return exitcode from .forking import Popen 定义
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