子进程弹出标准输出锁定？

Question

您好，使用 subprocess.Popen 时读取标准输出有问题

daniel@desktop:~$ python -V
Python 2.7.3

代码如下：（注释代码是我尝试过的一些东西）

import subprocess

RUN = './hlds_run -game cstrike -maxplayers 11'

p = subprocess.Popen(RUN.split(), shell=False, stdout=subprocess.PIPE, stdin=subprocess.PIPE, stderr=subprocess.PIPE)

while 1:
    try:
        out = p.stdout.readline()
        #if out == '':
        #   out = p.stdout.read()
        #p.stdout.flush()
    except: 
        p.terminate()
        break

    try:
        err = p.stderr.readline()
        #if err == '':
        #   err = p.stderr.read()
        #p.stderr.flush()
    except:
        p.terminate()
        break
    if out != '':
        print out.rstrip()

    if err != '':
        print err.rstrip()


    #print '\n' #constantly prints new lines until "Calling BreakpadMiniDumpSystemInit."

这是连接到服务器并断开连接时得到的输出：

daniel@desktop:~/hlds$ python hlds.py 
Auto detecting CPU
Using breakpad crash handler
Using Pentium II Optimised binary.
Setting breakpad minidump AppID = 10
Auto-restarting the server on crash
Forcing breakpad minidump interfaces to load

Looking up breakpad interfaces from steamclient
Console initialized.
Calling BreakpadMiniDumpSystemInit
scandir failed:/home/daniel/hlds/./valve/SAVE
Installing breakpad exception handler for appid(10)/version(5447)
scandir failed:/home/daniel/hlds/./platform/SAVE
Looking up breakpad interfaces from steamclient
Protocol version 48
Calling BreakpadMiniDumpSystemInit

while 循环在之后锁定：

Calling BreakpadMiniDumpSystemInit.

但服务器仍在运行，我可以连接、运行命令等...

---

如果我运行：

 ./hlds_run -game cstrike -maxplayers 11 >> stdout.log 2>&1

我在 stdout.log 中得到以下输出：

daniel@desktop:~/hlds$ cat stdout.log 
Auto detecting CPU
Using Pentium II Optimised binary.
Auto-restarting the server on crash

Console initialized.
Using breakpad crash handler
Setting breakpad minidump AppID = 10
Forcing breakpad minidump interfaces to load
Looking up breakpad interfaces from steamclient
Calling BreakpadMiniDumpSystemInit
Installing breakpad exception handler for appid(10)/version(5447)
scandir failed:/home/daniel/hlds/./valve/SAVE
scandir failed:/home/daniel/hlds/./platform/SAVE
Protocol version 48
Exe version 1.1.2.6/Stdio (cstrike)
Exe build: 14:06:24 Sep 23 2011 (5447)
STEAM Auth Server
Server IP address 127.0.1.1:27015
couldn't exec listip.cfg
couldn't exec banned.cfg
Looking up breakpad interfaces from steamclient
Calling BreakpadMiniDumpSystemInit
scandir failed:/home/daniel/hlds/./valve/SAVE
scandir failed:/home/daniel/hlds/./platform/SAVE

Could not establish connection to Steam servers.
Reconnected to Steam servers.
   VAC secure mode is activated.
ERROR: couldn't open custom.hpk.
JAMES HETFIELD : hello!
Dropped JAMES HETFIELD from server
Reason:  Client sent 'drop'
Sat Apr 14 00:10:54 CEST 2012: Server Quit

但是，如果我不执行 2>&1，我仍然会在 stdout 中获得此输出，而其余的则在 stdout.log 中：

daniel@desktop:~/hlds$ ./hlds_run -game cstrike -maxplayers 11 >> stdout.log
Using breakpad crash handler
Setting breakpad minidump AppID = 10
Forcing breakpad minidump interfaces to load
Looking up breakpad interfaces from steamclient
Calling BreakpadMiniDumpSystemInit
Installing breakpad exception handler for appid(10)/version(5447)
Looking up breakpad interfaces from steamclient
Calling BreakpadMiniDumpSystemInit

尝试创建 servermanager 和 dispatcher 作为子流程学习体验：]

感谢所有帮助！ :)

Answer 1

发生的情况是其中一个管道被数据填满，从而阻塞了子进程，而您的 python 进程被阻塞试图从另一个管道读取一行，从而导致死锁。您可能想要使用某种轮询（select/poll/epoll）而不是在管道上进行阻塞读取。

一个快速的技巧是在你的 while 循环中进行非阻塞读取，但这会导致你的 python 进程使用大量 CPU。

查看select 模块的文档，了解有关以非骇客方式解决问题的更多信息。

Answer 2

您是否能够使用 select 解决此问题？我发现当我启动 SRCDS 时，即使是非阻塞的，它也不会超过“调用 BreakpadMiniDumpSystemInit”：

p = subprocess.Popen(cmd, shell=False, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, close_fds=True)
fcntl.fcntl(p.stdout, fcntl.F_SETFL, fcntl.fcntl(p.stdout, fcntl.F_GETFL) | os.O_NONBLOCK)
print p.stdout.read()

这会打印到“BreakpadMiniDumpSystemInit”消息，进一步调用 read() 会抛出“资源暂时不可用”，直到将某些内容写入 p.stdin。