python for line in lines_Python C程序子进程挂起“for line in iter”
这是一个块缓冲问题.
直接修复C程序中的stdout缓冲区
基于stdio的程序作为规则是行缓冲的,如果它们在终端中以交互方式运行,并且当它们的stdout被重定向到管道时阻止缓冲.在后一种情况下,在缓冲区溢出或刷新之前,您将看不到新行.
为了避免在每次printf()调用后调用fflush(),你可以通过在一开始调用C程序来强制行缓冲输出：
setvbuf(stdout, (char *) NULL, _IOLBF, 0); /* make line buffered stdout */
一旦打印换行符,就会在这种情况下刷新缓冲区.
或者修改它而不修改C程序的源代码
有stdbuf实用程序,允许您在不修改源代码的情况下更改缓冲类型,例如：
from subprocess import Popen, PIPE
process = Popen(["stdbuf", "-oL", "./main"], stdout=PIPE, bufsize=1)
for line in iter(process.stdout.readline, b''):
print line,
process.communicate() # close process' stream, wait for it to exit
或者使用伪TTY
为了让子进程认为它是以交互方式运行,你可以使用pexpect module或它的类比,对于使用pexpect和pty模块的代码示例,参见Python subprocess readlines() hangs.这里提供了pty示例的变体(它应该适用于Linux)：
#!/usr/bin/env python
import os
import pty
import sys
from select import select
from subprocess import Popen, STDOUT
master_fd, slave_fd = pty.openpty() # provide tty to enable line buffering
process = Popen("./main", stdin=slave_fd, stdout=slave_fd, stderr=STDOUT,
bufsize=0, close_fds=True)
timeout = .1 # ugly but otherwise `select` blocks on process' exit
# code is similar to _copy() from pty.py
with os.fdopen(master_fd, 'r+b', 0) as master:
input_fds = [master, sys.stdin]
while True:
fds = select(input_fds, [], [], timeout)[0]
if master in fds: # subprocess' output is ready
data = os.read(master_fd, 512) #
if not data: # EOF
input_fds.remove(master)
else:
os.write(sys.stdout.fileno(), data) # copy to our stdout
if sys.stdin in fds: # got user input
data = os.read(sys.stdin.fileno(), 512)
if not data:
input_fds.remove(sys.stdin)
else:
master.write(data) # copy it to subprocess' stdin
if not fds: # timeout in select()
if process.poll() is not None: # subprocess ended
# and no output is buffered
assert not select([master], [], [], 0)[0] # race is possible
os.close(slave_fd) # subproces don't need it anymore
break
rc = process.wait()
print("subprocess exited with status %d" % rc)
或者通过pexpect使用pty
#!/usr/bin/env python
import pexpect
child = pexpect.spawn("/.main")
for line in child:
print line,
child.close()