只允许一个进程运行的实例

using System;
using System.Runtime.InteropServices;
using System.Windows.Forms;
using System.Diagnostics;
using System.Reflection;
public class OneInstnace
{
[STAThread]
public static void Main()
{
//得到正在运行的例程
        Process instance = RunningInstance();
if (instance == null)
{
//如果没有其它例程，就新建一个窗体
            Application.Run(new Form());
}
else
{
//处理发现的例程
            HandleRunningInstance(instance);
}
}
public static Process RunningInstance()
{
Process current = Process.GetCurrentProcess();
Process[] processes = Process.GetProcessesByName(current.ProcessName);
//遍历正在有相同名字运行的例程
        foreach (Process process in processes)
{
//忽略现有的例程
            if (process.Id != current.Id)
{
//确保例程从EXE文件运行
                if (Assembly.GetExecutingAssembly().Location.Replace("/", "\\") ==
current.MainModule.FileName)
{
//返回另一个例程实例
                    return process;
}
}
}
//没有其它的例程，返回Null
        return null;
}
public static void HandleRunningInstance(Process instance)
{
//确保窗口没有被最小化或最大化
        ShowWindowAsync(instance.MainWindowHandle, WS_SHOWNORMAL);
//设置真实例程为foreground window
        SetForegroundWindow(instance.MainWindowHandle);
}
[DllImport("User32.dll")]
private static extern bool ShowWindowAsync(IntPtr hWnd, int cmdShow);
[DllImport("User32.dll")]
private static extern bool SetForegroundWindow(IntPtr hWnd);
private const int WS_SHOWNORMAL = 1;
}