urllib2 中重复主机查找失败
我的代码使用 Python 的 urllib2 在多个线程中发出许多 HTTP GET 请求,将响应写入文件(每个线程一个)。
在执行过程中,看起来许多主机查找失败(导致名称或服务未知错误,请参阅附加的错误日志以获取示例)。
这是由于 DNS 服务不稳定造成的吗?如果主机名没有改变,依赖 DNS 缓存是不是不好的做法?即是否应该将单个查找的结果传递到 urlopen
中?
Exception in thread Thread-16:
Traceback (most recent call last):
File "/usr/lib/python2.6/threading.py", line 532, in __bootstrap_inner
self.run()
File "/home/da/local/bin/ThreadedDownloader.py", line 61, in run
page = urllib2.urlopen(url) # get the page
File "/usr/lib/python2.6/urllib2.py", line 126, in urlopen
return _opener.open(url, data, timeout)
File "/usr/lib/python2.6/urllib2.py", line 391, in open
response = self._open(req, data)
File "/usr/lib/python2.6/urllib2.py", line 409, in _open
'_open', req)
File "/usr/lib/python2.6/urllib2.py", line 369, in _call_chain
result = func(*args)
File "/usr/lib/python2.6/urllib2.py", line 1170, in http_open
return self.do_open(httplib.HTTPConnection, req)
File "/usr/lib/python2.6/urllib2.py", line 1145, in do_open
raise URLError(err)
URLError: <urlopen error [Errno -2] Name or service not known>
更新 我的(极其简单)代码
class AsyncGet(threading.Thread):
def __init__(self,outDir,baseUrl,item,method,numPages,numRows,semaphore):
threading.Thread.__init__(self)
self.outDir = outDir
self.baseUrl = baseUrl
self.method = method
self.numPages = numPages
self.numRows = numRows
self.item = item
self.semaphore = semaphore
def run(self):
with self.semaphore: # 'with' is awesome.
with open( os.path.join(self.outDir,self.item+".xml"), 'a' ) as f:
for i in xrange(1,self.numPages+1):
url = self.baseUrl + \
"method=" + self.method + \
"&item=" + self.item + \
"&page=" + str(i) + \
"&rows=" + str(self.numRows) + \
"&prettyXML"
page = urllib2.urlopen(url)
f.write(page.read())
page.close() # Must remember to close!
信号量是一个 BoundedSemaphore,用于约束正在运行的线程总数。
I have code which issues many HTTP GET requests using Python's urllib2, in several threads, writing the responses into files (one per thread).
During execution, it looks like many of the host lookups fail (causing a name or service unknown error, see appended error log for an example).
Is this due to a flaky DNS service? Is it bad practice to rely on DNS caching, if the host name isn't changing? I.e. should a single lookup's result be passed into the urlopen
?
Exception in thread Thread-16:
Traceback (most recent call last):
File "/usr/lib/python2.6/threading.py", line 532, in __bootstrap_inner
self.run()
File "/home/da/local/bin/ThreadedDownloader.py", line 61, in run
page = urllib2.urlopen(url) # get the page
File "/usr/lib/python2.6/urllib2.py", line 126, in urlopen
return _opener.open(url, data, timeout)
File "/usr/lib/python2.6/urllib2.py", line 391, in open
response = self._open(req, data)
File "/usr/lib/python2.6/urllib2.py", line 409, in _open
'_open', req)
File "/usr/lib/python2.6/urllib2.py", line 369, in _call_chain
result = func(*args)
File "/usr/lib/python2.6/urllib2.py", line 1170, in http_open
return self.do_open(httplib.HTTPConnection, req)
File "/usr/lib/python2.6/urllib2.py", line 1145, in do_open
raise URLError(err)
URLError: <urlopen error [Errno -2] Name or service not known>
UPDATE my (extremely simple) code
class AsyncGet(threading.Thread):
def __init__(self,outDir,baseUrl,item,method,numPages,numRows,semaphore):
threading.Thread.__init__(self)
self.outDir = outDir
self.baseUrl = baseUrl
self.method = method
self.numPages = numPages
self.numRows = numRows
self.item = item
self.semaphore = semaphore
def run(self):
with self.semaphore: # 'with' is awesome.
with open( os.path.join(self.outDir,self.item+".xml"), 'a' ) as f:
for i in xrange(1,self.numPages+1):
url = self.baseUrl + \
"method=" + self.method + \
"&item=" + self.item + \
"&page=" + str(i) + \
"&rows=" + str(self.numRows) + \
"&prettyXML"
page = urllib2.urlopen(url)
f.write(page.read())
page.close() # Must remember to close!
The semaphore is a BoundedSemaphore to constrain the total number of running threads.
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这不是 Python 问题,在 Linux 系统上请确保 nscd(名称服务缓存守护进程)实际正在运行。
更新:
看看你的代码,你永远不会调用
page.close()
因此泄漏了套接字。This is not a Python problem, on Linux systems make sure
nscd (Name Service Cache Daemon)
is actually running.UPDATE:
And looking at your code you are never calling
page.close()
hence leaking sockets.