以下代码使用命名管道来允许两个脚本之间进行通信。
- 如果读者试图比写者更快地进行
read
操作,它会被阻塞。
- 如果读者跟不上写者,写者不会被阻塞。
- 操作是基于缓冲区的。目前尚未实现基于行的操作。
- 此代码应视为概念验证。延迟和缓冲区大小是任意的。
代码
import argparse
import errno
import os
from select import select
import time
class OneFifo(object):
def __init__(self, name):
self.name = name
def __enter__(self):
if os.path.exists(self.name):
os.unlink(self.name)
os.mkfifo(self.name)
return self
def __exit__(self, exc_type, exc_value, exc_traceback):
if os.path.exists(self.name):
os.unlink(self.name)
def write(self, data):
print "Waiting for client to open FIFO..."
try:
server_file = os.open(self.name, os.O_WRONLY | os.O_NONBLOCK)
except OSError as exc:
if exc.errno == errno.ENXIO:
server_file = None
else:
raise
if server_file is not None:
print "Writing line to FIFO..."
try:
os.write(server_file, data)
print "Done."
except OSError as exc:
if exc.errno == errno.EPIPE:
pass
else:
raise
os.close(server_file)
def read_nonblocking(self):
result = None
try:
client_file = os.open(self.name, os.O_RDONLY | os.O_NONBLOCK)
except OSError as exc:
if exc.errno == errno.ENOENT:
client_file = None
else:
raise
if client_file is not None:
try:
rlist = [client_file]
wlist = []
xlist = []
rlist, wlist, xlist = select(rlist, wlist, xlist, 0.01)
if client_file in rlist:
result = os.read(client_file, 1024)
except OSError as exc:
if exc.errno == errno.EAGAIN or exc.errno == errno.EWOULDBLOCK:
result = None
else:
raise
os.close(client_file)
return result
def read(self):
try:
with open(self.name, 'r') as client_file:
result = client_file.read()
except OSError as exc:
if exc.errno == errno.ENOENT:
result = None
else:
raise
if not len(result):
result = None
return result
def parse_argument():
parser = argparse.ArgumentParser()
parser.add_argument('-c', '--client', action='store_true',
help='Set this flag for the client')
parser.add_argument('-n', '--non-blocking', action='store_true',
help='Set this flag to read without blocking')
result = parser.parse_args()
return result
if __name__ == '__main__':
args = parse_argument()
if not args.client:
with OneFifo('known_name') as one_fifo:
while True:
one_fifo.write('one line')
time.sleep(0.1)
else:
one_fifo = OneFifo('known_name')
while True:
if args.non_blocking:
result = one_fifo.read_nonblocking()
else:
result = one_fifo.read()
if result is not None:
print result
服务器检查客户端是否打开了FIFO。如果客户端已经打开了FIFO,则服务器会写入一行内容。否则,服务器将继续运行。我实现了非阻塞读取,因为阻塞读取会导致一个问题:如果服务器重新启动,大多数情况下客户端会一直被阻塞,永远无法恢复。使用非阻塞客户端,更容易容忍服务器重新启动。
[user@machine:~] python onefifo.py
Waiting for client to open FIFO...
Waiting for client to open FIFO...
Writing line to FIFO...
Done.
Waiting for client to open FIFO...
Writing line to FIFO...
Done.
[user@machine:~] python onefifo.py -c
one line
one line
注意事项
启动时,如果 server
发现 FIFO 已经存在,则它会将其删除。这是通知 clients
服务器已重启的最简单方法。阻塞版本的 client
通常会忽略此通知。
os.O_NONBLOCK
来强制执行此操作? - dronus服务器
尝试打开FIFO并收到ENXIO
(设备未配置)错误,则知道客户端
尚未打开FIFO。这种测试仅在服务器
使用os.O_NONBLOCK
打开FIFO时才有效。否则,当服务器
调用open
时,它会被阻塞。 - user3657941