用 C# 来守护 Python 进程

背景

目前我主要负责的一个项目是一个 C/S 架构的客户端开发，前端主要是通过

WPF

Python

MQ

Python

守护进程

实现

对于我们的系统而言，我们的 Python 进程只允许存在一个，因此，对应的服务类型要采用单例模式，这一部分代码相对简单，就直接贴出来了，示例代码如下所示：

public partial class PythonService
{
private static readonly object _locker = new object();

private static PythonService _instance;
public static PythonService Current
{
get
{
if (_instance == null)
{
lock (_locker)
{
if (_instance == null)
{
_instance = new PythonService();
}
}
}
return _instance;
}
}

private PythonService()
{

}
}

创建独立进程

由于后端的 Python 代码运行需要安装一些第三方的扩展库，所以为了方便，我们采用的方式是总结将 python 安装文件及扩展包和他们的代码一并打包到我们的项目目录中，然后创建一个 Python 进程，在该进程中通过设置环境变量的方式来为 Python 进程进行一些环境配置。示例代码如下所示：

public partial class PythonService
{
private string _workPath => Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "scripts");
private string _pythonPath => Path.Combine(_workPath, "python27");

private bool isRunning = false;
private int taskPID = -1;

public void Start()
{
taskPID = CreateProcess();
isRunning = taskPID != -1;

var msg = isRunning ? "服务启动成功..." : "服务启动失败...";
Trace.WriteLine(msg);
}

public void Stop()
{
KillProcessAndChildren(taskPID);

isRunning = false;
taskPID = -1;
}

private int CreateProcess()
{
KillProcessAndChildren(taskPID);

int pid = -1;
var psi = new ProcessStartInfo(Path.Combine(_pythonPath, "python.exe"))
{
UseShellExecute = false,
WorkingDirectory = _workPath,
ErrorDialog = false
};

psi.CreateNoWindow = true;

var path = psi.EnvironmentVariables["PATH"];
if (path != null)
{
var array = path.Split(new[] { ';' }).Where(p => !p.ToLower().Contains("python")).ToList();
array.AddRange(new[] { _pythonPath, Path.Combine(_pythonPath, "Scripts"), _workPath });
psi.EnvironmentVariables["PATH"] = string.Join(";", array);
}
var ps = new Process { StartInfo = psi };
if (ps.Start())
{
pid = ps.Id;
}
return pid;
}

private static void KillProcessAndChildren(int pid)
{
// Cannot close 'system idle process'.
if (pid <= 0)
{
return;
}

ManagementObjectSearcher searcher = new ManagementObjectSearcher("Select * From Win32_Process Where ParentProcessID=" + pid);
ManagementObjectCollection moc = searcher.Get();
foreach (ManagementObject mo in moc)
{
KillProcessAndChildren(Convert.ToInt32(mo["ProcessID"]));
}
try
{
Process proc = Process.GetProcessById(pid);
proc.Kill();
}
catch (ArgumentException)
{
// Process already exited.
}
catch (Win32Exception)
{
// Access denied
}
}
}

创建守护进程

上面我们的通过记录当前正在运行的进程的 PID 来标识我们的进程，那对应守护进程，我们就可以通过进程列表查询的方式来进行创建，在轮询的过程中，如果未找到对应 PID 的进程则表明该进程已经退出，需要重新创建该进程，否则就不执行任何操作，示例代码如下所示：

public partial class PythonService
{
private CancellationTokenSource cts;

private void StartWatch(CancellationToken token)
{
Task.Factory.StartNew(() =>
{
while (!token.IsCancellationRequested)
{
var has = Process.GetProcesses().Any(p => p.Id == taskPID);
Trace.WriteLine($"MQ状态：{DateTime.Now}-{has}");
if (!has)
{
taskPID = CreateProcess(_reqhost, _subhost, _debug);
isRunning = taskPID > 0;

var msg = isRunning ? "MQ重启成功" : "MQ重启失败，等待下次重启";
Trace.WriteLine($"MQ状态：{DateTime.Now}-{msg}");
}

Thread.Sleep(2000);
}
}, token);
}
}

Thread.Sleep(2000)

await Task.Delay(2000,token)

TaskCanceledException

接着，完善我们的

Start

Stop

public void Start()
{
taskPID = CreateProcess();
isRunning = taskPID != -1;

if (isRunning)
{
cts = new CancellationTokenSource();
StartWatch(cts.Token);
}

var msg = isRunning ? "服务启动成功..." : "服务启动失败...";
Trace.WriteLine(msg);
}

public void Stop()
{
cts?.Cancel(false);
cts?.Dispose();

KillProcessAndChildren(taskPID);
taskPID = -1;

isRunning = false;
}

最后，上层调用就相对简单一下，直接调用

Start

Stop

总结

在我们的实际项目代码中，

PythonService

相关参考

• Kill a one-file Python process in C#
• 用c#实现通用守护进程