通过计算互斥量来限制最大进程实例？

Question

我已经编写了下一个通过MUTEX 防止多实例化的代码，但我想通过允许设置允许的最大实例数来扩展它的功能，所以我应该可以决定是否只允许单个实例或只有 3 个实例的多实例（例如）。

我试图弄清楚如何计算进程的互斥量，但我没有找到任何相关信息。

另一方面，我在 StackOverflow 中找到了很多帖子，解释如何通过文件名计算进程数量，我对这些都不感兴趣，因为我选择了 MUTEX 检测对我来说更安全。

有人能帮我这个心血来潮吗？

这就是我所做的一切：

Namespace My

    Partial Friend Class MyApplication

#Region " Properties "

        ''' <summary>
        ''' Gets the current process mutex identifier.
        ''' </summary>
        ''' <value>The current process mutex identifier.</value>
        ''' <exception cref="System.FormatException">The specified value is not a valid GUID format.</exception>
        Private ReadOnly Property MutexID As String
            Get
                ' Define a Golabl Unique Identifier to name the Mutex.
                Dim Id As String = "b045ce40-2863-4ce7-a7df-8afca8214454"

                If Guid.TryParse(input:=Id, result:=New Guid) Then
                    Return Id
                Else
                    Throw New FormatException("The specified value is not in a valid GUID format.")
                End If

            End Get
        End Property

        ''' <summary>
        ''' Gets the maximum instances allowed for this process.
        ''' </summary>
        ''' <value>The maximum instances allowed for this process.</value>
        Private ReadOnly Property MaxInstances As Integer
            Get
                Return 2
            End Get
        End Property

#End Region

#Region " Private Methods "

        ''' <summary>
        ''' Determines whether this is the unique instance that is running for this process.
        ''' </summary>
        ''' <returns><c>true</c> if this is the unique instance; otherwise, <c>false</c>.</returns>
        Private Function IsUniqueInstance() As Boolean

            Dim mtx As Threading.Mutex = Nothing

            Try
                mtx = Threading.Mutex.OpenExisting(name:=Me.MutexID)
                mtx.Close()
                mtx = Nothing
            Catch
                mtx = New Threading.Mutex(initiallyOwned:=True, name:=Me.MutexID)
            End Try

            Return mtx IsNot Nothing

        End Function

#End Region

#Region " Event-Handlers "

        ''' <summary>
        ''' This occurs when the application starts, before the startup Form is created.
        ''' </summary>
        ''' <param name="sender">The source of the event.</param>
        ''' <param name="e">The <see cref="ApplicationServices.StartupEventArgs"/> instance containing the event data.</param>
        Private Sub MyApplication_Startup(ByVal sender As Object, ByVal e As ApplicationServices.StartupEventArgs) _
        Handles Me.Startup

            ' If there is more than one instance running of this process with the same mutex then...
            If Not Me.IsUniqueInstance Then ' Prevent multi-instancing.

                MessageBox.Show("This is a limited demo, to run multiple instances please purchase the program.",
                               Application.Info.ProductName, MessageBoxButtons.OK, MessageBoxIcon.Error)

                ' Cancel the application execution.
                e.Cancel = True

            End If

        End Sub

#End Region

    End Class ' MyApplication

End Namespace

更新

这是我正在尝试的代码，我在应用程序事件、表单构造函数、加载和显示事件中都尝试过，但未检测到多实例。

    Private Sub test() Handles Me.Startup

        Using semaphore As New Semaphore(3I, 3I, "something")

            If Not semaphore.WaitOne(100I) Then
                MsgBox("Already max instances running")
                End
            Else
                MsgBox("test")
            End If

        End Using

    End Sub

Answer 1

Mutex 用于互斥。它最多只允许一个线程继续进行。如果您需要允许线程数（在这种情况下为进程）继续进行，您需要 Semaphore 而不是互斥锁。

C# 示例：

private static void Main()
{
    using (Semaphore semaphore = new Semaphore(3, 3, Assembly.GetExecutingAssembly().GetName().FullName))
    {
        if (!semaphore.WaitOne(100))
        {
            MessageBox.Show("Already max instances running");
            return;
        }

        //Start your application here
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run(new Form1());
    }
}

VB.Net 示例：

Private Shared Sub Main()
    Using semaphore As New Semaphore(3, 3, Assembly.GetExecutingAssembly().GetName().FullName)
        If Not semaphore.WaitOne(100) Then
            MessageBox.Show("Already max instances running")
            Return
        End If

       'Start your application here
        Application.EnableVisualStyles()
        Application.SetCompatibleTextRenderingDefault(False)
        Application.Run(New Form1())
    End Using
End Sub

P.S: 使用http://converter.telerik.com/ 将代码从 C# 转换为 VB