我使用subprocess模块启动子流程并连接到其输出流(标准输出)。我希望能够对其标准输出执行非阻塞读取。是否有一种方法使.readline非阻塞或在我调用.readline之前检查流上是否有数据?我希望这是可移植的,或者至少可以在Windows和Linux下工作。
下面是我现在怎么做的(如果没有数据可用,它会阻塞在.readline上):
p = subprocess.Popen('myprogram.exe', stdout = subprocess.PIPE)
output_str = p.stdout.readline()
编辑:这个实现仍然会阻塞。请用j·f·塞巴斯蒂安的答案。
我尝试了上面的答案,但是线程代码的额外风险和维护令人担忧。
通过io模块(仅限于2.6),我找到了BufferedReader。这是我的无线程、无阻塞的解决方案。
import io
from subprocess import PIPE, Popen
p = Popen(['myprogram.exe'], stdout=PIPE)
SLEEP_DELAY = 0.001
# Create an io.BufferedReader on the file descriptor for stdout
with io.open(p.stdout.fileno(), 'rb', closefd=False) as buffer:
while p.poll() == None:
time.sleep(SLEEP_DELAY)
while '\n' in bufferedStdout.peek(bufferedStdout.buffer_size):
line = buffer.readline()
# do stuff with the line
# Handle any remaining output after the process has ended
while buffer.peek():
line = buffer.readline()
# do stuff with the line
编辑:这个实现仍然会阻塞。请用j·f·塞巴斯蒂安的答案。
我尝试了上面的答案,但是线程代码的额外风险和维护令人担忧。
通过io模块(仅限于2.6),我找到了BufferedReader。这是我的无线程、无阻塞的解决方案。
import io
from subprocess import PIPE, Popen
p = Popen(['myprogram.exe'], stdout=PIPE)
SLEEP_DELAY = 0.001
# Create an io.BufferedReader on the file descriptor for stdout
with io.open(p.stdout.fileno(), 'rb', closefd=False) as buffer:
while p.poll() == None:
time.sleep(SLEEP_DELAY)
while '\n' in bufferedStdout.peek(bufferedStdout.buffer_size):
line = buffer.readline()
# do stuff with the line
# Handle any remaining output after the process has ended
while buffer.peek():
line = buffer.readline()
# do stuff with the line
我添加这个问题是为了读一些子进程。Popen stdout。
下面是我的非阻塞读解决方案:
import fcntl
def non_block_read(output):
fd = output.fileno()
fl = fcntl.fcntl(fd, fcntl.F_GETFL)
fcntl.fcntl(fd, fcntl.F_SETFL, fl | os.O_NONBLOCK)
try:
return output.read()
except:
return ""
# Use example
from subprocess import *
sb = Popen("echo test && sleep 1000", shell=True, stdout=PIPE)
sb.kill()
# sb.stdout.read() # <-- This will block
non_block_read(sb.stdout)
'test\n'
为什么要打扰线程和队列?
与readline()不同,BufferedReader.read1()不会阻塞等待\r\n,如果有任何输出进入,它会尽快返回。
#!/usr/bin/python
from subprocess import Popen, PIPE, STDOUT
import io
def __main__():
try:
p = Popen( ["ping", "-n", "3", "127.0.0.1"], stdin=PIPE, stdout=PIPE, stderr=STDOUT )
except: print("Popen failed"); quit()
sout = io.open(p.stdout.fileno(), 'rb', closefd=False)
while True:
buf = sout.read1(1024)
if len(buf) == 0: break
print buf,
if __name__ == '__main__':
__main__()
下面是一个在python中支持非阻塞读和后台写的模块:
https://pypi.python.org/pypi/python-nonblock
提供一个函数,
nonblock_read将从流中读取数据,如果可用,否则返回一个空字符串(或None,如果流在另一端关闭,并且所有可能的数据都已读取)
你也可以考虑python-subprocess2模块,
https://pypi.python.org/pypi/python-subprocess2
这将添加到子流程模块。所以在subprocess返回的对象上。Popen”被添加了一个额外的方法,runInBackground。这将启动一个线程并返回一个对象,该对象将在写入stdout/stderr时自动填充,而不会阻塞主线程。
享受吧!
在类unix系统和Python 3.5+上有os。Set_blocking,做的就是它所说的。
import os
import time
import subprocess
cmd = 'python3', '-c', 'import time; [(print(i), time.sleep(1)) for i in range(5)]'
p = subprocess.Popen(cmd, stdout=subprocess.PIPE)
os.set_blocking(p.stdout.fileno(), False)
start = time.time()
while True:
# first iteration always produces empty byte string in non-blocking mode
for i in range(2):
line = p.stdout.readline()
print(i, line)
time.sleep(0.5)
if time.time() > start + 5:
break
p.terminate()
这个输出:
1 b''
2 b'0\n'
1 b''
2 b'1\n'
1 b''
2 b'2\n'
1 b''
2 b'3\n'
1 b''
2 b'4\n'
与操作系统。Set_blocking注释它是:
0 b'0\n'
1 b'1\n'
0 b'2\n'
1 b'3\n'
0 b'4\n'
1 b''