本文整理汇总了VB.NET中System.Threading.Mutex.OpenExisting方法的典型用法代码示例。如果您正苦于以下问题:VB.NET Mutex.OpenExisting方法的具体用法?VB.NET Mutex.OpenExisting怎么用?VB.NET Mutex.OpenExisting使用的例子?那么恭喜您, 这里精选的方法代码示例或许可以为您提供帮助。您也可以进一步了解该方法所在类System.Threading.Mutex
的用法示例。
在下文中一共展示了Mutex.OpenExisting方法的1个代码示例,这些例子默认根据受欢迎程度排序。您可以为喜欢或者感觉有用的代码点赞,您的评价将有助于系统推荐出更棒的VB.NET代码示例。
示例1: Example
' 导入命名空间
Imports System.Threading
Imports System.Security.AccessControl
Friend Class Example
<MTAThread> _
Friend Shared Sub Main()
Const mutexName As String = "MutexExample4"
Dim m As Mutex = Nothing
Dim doesNotExist as Boolean = False
Dim unauthorized As Boolean = False
' The value of this variable is set by the mutex
' constructor. It is True if the named system mutex was
' created, and False if the named mutex already existed.
'
Dim mutexWasCreated As Boolean
' Attempt to open the named mutex.
Try
' Open the mutex with (MutexRights.Synchronize Or
' MutexRights.Modify), to enter and release the
' named mutex.
'
m = Mutex.OpenExisting(mutexName)
Catch ex As WaitHandleCannotBeOpenedException
Console.WriteLine("Mutex does not exist.")
doesNotExist = True
Catch ex As UnauthorizedAccessException
Console.WriteLine("Unauthorized access: {0}", ex.Message)
unauthorized = True
End Try
' There are three cases: (1) The mutex does not exist.
' (2) The mutex exists, but the current user doesn't
' have access. (3) The mutex exists and the user has
' access.
'
If doesNotExist Then
' The mutex does not exist, so create it.
' Create an access control list (ACL) that denies the
' current user the right to enter or release the
' mutex, but allows the right to read and change
' security information for the mutex.
'
Dim user As String = Environment.UserDomainName _
& "\" & Environment.UserName
Dim mSec As New MutexSecurity()
Dim rule As New MutexAccessRule(user, _
MutexRights.Synchronize Or MutexRights.Modify, _
AccessControlType.Deny)
mSec.AddAccessRule(rule)
rule = New MutexAccessRule(user, _
MutexRights.ReadPermissions Or _
MutexRights.ChangePermissions, _
AccessControlType.Allow)
mSec.AddAccessRule(rule)
' Create a Mutex object that represents the system
' mutex named by the constant 'mutexName', with
' initial ownership for this thread, and with the
' specified security access. The Boolean value that
' indicates creation of the underlying system object
' is placed in mutexWasCreated.
'
m = New Mutex(True, mutexName, mutexWasCreated, mSec)
' If the named system mutex was created, it can be
' used by the current instance of this program, even
' though the current user is denied access. The current
' program owns the mutex. Otherwise, exit the program.
'
If mutexWasCreated Then
Console.WriteLine("Created the mutex.")
Else
Console.WriteLine("Unable to create the mutex.")
Return
End If
ElseIf unauthorized Then
' Open the mutex to read and change the access control
' security. The access control security defined above
' allows the current user to do this.
'
Try
m = Mutex.OpenExisting(mutexName, _
MutexRights.ReadPermissions Or _
MutexRights.ChangePermissions)
' Get the current ACL. This requires
' MutexRights.ReadPermissions.
Dim mSec As MutexSecurity = m.GetAccessControl()
Dim user As String = Environment.UserDomainName _
& "\" & Environment.UserName
' First, the rule that denied the current user
' the right to enter and release the mutex must
' be removed.
Dim rule As New MutexAccessRule(user, _
MutexRights.Synchronize Or MutexRights.Modify, _
AccessControlType.Deny)
mSec.RemoveAccessRule(rule)
' Now grant the user the correct rights.
'
rule = New MutexAccessRule(user, _
MutexRights.Synchronize Or MutexRights.Modify, _
AccessControlType.Allow)
mSec.AddAccessRule(rule)
' Update the ACL. This requires
' MutexRights.ChangePermissions.
m.SetAccessControl(mSec)
Console.WriteLine("Updated mutex security.")
' Open the mutex with (MutexRights.Synchronize
' Or MutexRights.Modify), the rights required to
' enter and release the mutex.
'
m = Mutex.OpenExisting(mutexName)
Catch ex As UnauthorizedAccessException
Console.WriteLine("Unable to change permissions: {0}", _
ex.Message)
Return
End Try
End If
' If this program created the mutex, it already owns
' the mutex.
'
If Not mutexWasCreated Then
' Enter the mutex, and hold it until the program
' exits.
'
Try
Console.WriteLine("Wait for the mutex.")
m.WaitOne()
Console.WriteLine("Entered the mutex.")
Catch ex As UnauthorizedAccessException
Console.WriteLine("Unauthorized access: {0}", _
ex.Message)
End Try
End If
Console.WriteLine("Press the Enter key to exit.")
Console.ReadLine()
m.ReleaseMutex()
m.Dispose()
End Sub
End Class