Semaphore.OpenExisting 方法

定義

開啟指定的具名號誌 (如果已經存在)。Opens a specified named semaphore, if it already exists.

多載

OpenExisting(String)

開啟指定的具名號誌 (如果已經存在)。Opens the specified named semaphore, if it already exists.

OpenExisting(String, SemaphoreRights)

使用所需的安全性存取權,開啟指定的具名號誌 (如果已經存在)。Opens the specified named semaphore, if it already exists, with the desired security access.

OpenExisting(String)

開啟指定的具名號誌 (如果已經存在)。Opens the specified named semaphore, if it already exists.

public:
 static System::Threading::Semaphore ^ OpenExisting(System::String ^ name);
public static System.Threading.Semaphore OpenExisting (string name);
[System.Runtime.Versioning.SupportedOSPlatform("windows")]
public static System.Threading.Semaphore OpenExisting (string name);
static member OpenExisting : string -> System.Threading.Semaphore
[<System.Runtime.Versioning.SupportedOSPlatform("windows")>]
static member OpenExisting : string -> System.Threading.Semaphore
Public Shared Function OpenExisting (name As String) As Semaphore

參數

name
String

要與其他處理序共用之同步物件的名稱。The name of the synchronization object to be shared with other processes. 名稱區分大小寫。The name is case-sensitive.

傳回

Semaphore

表示具名系統號誌的物件。An object that represents the named system semaphore.

屬性

例外狀況

name 為空字串。name is an empty string.

-或--or-

僅限 .NET Framework:name 的長度超過 MAX_PATH (260 個字元)。.NET Framework only: name is longer than MAX_PATH (260 characters).

name 上所宣告的預設值是 nullname is null.

無法建立具有所提供 name 的同步物件。A synchronization object with the provided name cannot be created. 不同類型的同步物件可能具有相同名稱。A synchronization object of a different type might have the same name. 在某些情況下,可能會因為名稱無效而擲回此例外狀況。In some cases, this exception may be thrown for invalid names.

name 無效。name is invalid. 這可能基於數種原因,其中包括可能由作業系統設定的一些限制,例如未知前置詞或無效字元。This can be for various reasons, including some restrictions that may be placed by the operating system, such as an unknown prefix or invalid characters. 請注意,名稱與通用前置詞 "Global" 與 "Local" 會區分大小寫。Note that the name and common prefixes "Global" and "Local" are case-sensitive.

-或--or-

發生一些其他錯誤。There was some other error. HResult 屬性可提供詳細資訊。The HResult property may provide more information.

name 太長。The name is too long. 長度限制可能會取決於作業系統或設定。Length restrictions may depend on the operating system or configuration.

具名的信號已存在,但使用者沒有使用它所需的安全性存取權。The named semaphore exists, but the user does not have the security access required to use it.

範例

下列程式碼範例將示範具有存取控制安全性之命名信號的跨進程行為。The following code example demonstrates the cross-process behavior of a named semaphore with access control security. 此範例會使用 OpenExisting(String) 方法多載來測試命名信號是否存在。The example uses the OpenExisting(String) method overload to test for the existence of a named semaphore.

如果信號不存在,就會使用最大計數(二個)和存取控制安全性來建立,以拒絕目前使用者使用該信號的許可權,但這會授與對信號的讀取和變更許可權許可權。If the semaphore does not exist, it is created with a maximum count of two and with access control security that denies the current user the right to use the semaphore, but which grants the right to read and change permissions on the semaphore.

如果您從兩個命令視窗執行已編譯的範例,則第二個複本將會在呼叫方法多載時擲回存取違規例外狀況 OpenExisting(String)If you run the compiled example from two command windows, the second copy will throw an access violation exception on the call to the OpenExisting(String) method overload. 攔截到例外狀況,而此範例會使用 OpenExisting(String, SemaphoreRights) 方法多載來開啟具有讀取和變更許可權所需許可權的信號。The exception is caught, and the example uses the OpenExisting(String, SemaphoreRights) method overload to open the semaphore with the rights needed to read and change the permissions.

變更許可權之後,就會開啟具有輸入和釋放其必要許可權的信號。After the permissions are changed, the semaphore is opened with the rights required to enter and release it. 如果您從第三個命令視窗執行已編譯的範例,它會使用新的許可權執行。If you run the compiled example from a third command window, it runs using the new permissions.

#using <System.dll>
using namespace System;
using namespace System::Threading;
using namespace System::Security::AccessControl;
using namespace System::Security::Permissions;

public ref class Example
{
public:
   [SecurityPermissionAttribute(SecurityAction::Demand, Flags = SecurityPermissionFlag::UnmanagedCode)]
   static void main()
   {
      String^ semaphoreName = L"SemaphoreExample5";

      Semaphore^ sem = nullptr;
      bool doesNotExist = false;
      bool unauthorized = false;
      
      // Attempt to open the named semaphore.
      try
      {
         // Open the semaphore with (SemaphoreRights.Synchronize
         // | SemaphoreRights.Modify), to enter and release the
         // named semaphore.
         //
         sem = Semaphore::OpenExisting( semaphoreName );
      }
      catch ( WaitHandleCannotBeOpenedException^ ex ) 
      {
         Console::WriteLine( L"Semaphore does not exist." );
         doesNotExist = true;
      }
      catch ( UnauthorizedAccessException^ ex ) 
      {
         Console::WriteLine( L"Unauthorized access: {0}", ex->Message );
         unauthorized = true;
      }

      // There are three cases: (1) The semaphore does not exist.
      // (2) The semaphore exists, but the current user doesn't
      // have access. (3) The semaphore exists and the user has
      // access.
      //
      if ( doesNotExist )
      {
         // The semaphore does not exist, so create it.
         //
         // The value of this variable is set by the semaphore
         // constructor. It is true if the named system semaphore was
         // created, and false if the named semaphore already existed.
         //
         bool semaphoreWasCreated;
         
         // Create an access control list (ACL) that denies the
         // current user the right to enter or release the
         // semaphore, but allows the right to read and change
         // security information for the semaphore.
         //
         String^ user = String::Concat( Environment::UserDomainName,
            L"\\", Environment::UserName );
         SemaphoreSecurity^ semSec = gcnew SemaphoreSecurity;

         SemaphoreAccessRule^ rule = gcnew SemaphoreAccessRule( user,
            static_cast<SemaphoreRights>(
               SemaphoreRights::Synchronize |
               SemaphoreRights::Modify ),
            AccessControlType::Deny );
         semSec->AddAccessRule( rule );

         rule = gcnew SemaphoreAccessRule( user,
            static_cast<SemaphoreRights>(
               SemaphoreRights::ReadPermissions |
               SemaphoreRights::ChangePermissions ),
            AccessControlType::Allow );
         semSec->AddAccessRule( rule );
         
         // Create a Semaphore object that represents the system
         // semaphore named by the constant 'semaphoreName', with
         // maximum count three, initial count three, and the
         // specified security access. The Boolean value that
         // indicates creation of the underlying system object is
         // placed in semaphoreWasCreated.
         //
         sem = gcnew Semaphore( 3,3,semaphoreName,semaphoreWasCreated,semSec );
         
         // If the named system semaphore was created, it can be
         // used by the current instance of this program, even
         // though the current user is denied access. The current
         // program enters the semaphore. Otherwise, exit the
         // program.
         //
         if ( semaphoreWasCreated )
         {
            Console::WriteLine( L"Created the semaphore." );
         }
         else
         {
            Console::WriteLine( L"Unable to create the semaphore." );
            return;
         }

      }
      else if ( unauthorized )
      {
         // Open the semaphore to read and change the access
         // control security. The access control security defined
         // above allows the current user to do this.
         //
         try
         {
            sem = Semaphore::OpenExisting( semaphoreName,
               static_cast<SemaphoreRights>(
                  SemaphoreRights::ReadPermissions |
                  SemaphoreRights::ChangePermissions ));
            
            // Get the current ACL. This requires
            // SemaphoreRights.ReadPermissions.
            SemaphoreSecurity^ semSec = sem->GetAccessControl();

            String^ user = String::Concat( Environment::UserDomainName,
               L"\\", Environment::UserName );
            
            // First, the rule that denied the current user
            // the right to enter and release the semaphore must
            // be removed.
            SemaphoreAccessRule^ rule = gcnew SemaphoreAccessRule( user,
               static_cast<SemaphoreRights>(
                  SemaphoreRights::Synchronize |
                  SemaphoreRights::Modify ),
               AccessControlType::Deny );
            semSec->RemoveAccessRule( rule );
            
            // Now grant the user the correct rights.
            //
            rule = gcnew SemaphoreAccessRule( user,
               static_cast<SemaphoreRights>(
                  SemaphoreRights::Synchronize |
                  SemaphoreRights::Modify ),
               AccessControlType::Allow );
            semSec->AddAccessRule( rule );
            
            // Update the ACL. This requires
            // SemaphoreRights.ChangePermissions.
            sem->SetAccessControl( semSec );

            Console::WriteLine( L"Updated semaphore security." );
            
            // Open the semaphore with (SemaphoreRights.Synchronize
            // | SemaphoreRights.Modify), the rights required to
            // enter and release the semaphore.
            //
            sem = Semaphore::OpenExisting( semaphoreName );

         }
         catch ( UnauthorizedAccessException^ ex ) 
         {
            Console::WriteLine( L"Unable to change permissions: {0}", ex->Message );
            return;
         }
      }
      
      // Enter the semaphore, and hold it until the program
      // exits.
      //
      try
      {
         sem->WaitOne();
         Console::WriteLine( L"Entered the semaphore." );
         Console::WriteLine( L"Press the Enter key to exit." );
         Console::ReadLine();
         sem->Release();
      }
      catch ( UnauthorizedAccessException^ ex ) 
      {
         Console::WriteLine( L"Unauthorized access: {0}", ex->Message );
      }
   }
};
using System;
using System.Threading;
using System.Security.AccessControl;

internal class Example
{
    internal static void Main()
    {
        const string semaphoreName = "SemaphoreExample5";

        Semaphore sem = null;
        bool doesNotExist = false;
        bool unauthorized = false;

        // Attempt to open the named semaphore.
        try
        {
            // Open the semaphore with (SemaphoreRights.Synchronize
            // | SemaphoreRights.Modify), to enter and release the
            // named semaphore.
            //
            sem = Semaphore.OpenExisting(semaphoreName);
        }
        catch(WaitHandleCannotBeOpenedException)
        {
            Console.WriteLine("Semaphore does not exist.");
            doesNotExist = true;
        }
        catch(UnauthorizedAccessException ex)
        {
            Console.WriteLine("Unauthorized access: {0}", ex.Message);
            unauthorized = true;
        }

        // There are three cases: (1) The semaphore does not exist.
        // (2) The semaphore exists, but the current user doesn't 
        // have access. (3) The semaphore exists and the user has
        // access.
        //
        if (doesNotExist)
        {
            // The semaphore does not exist, so create it.
            //
            // The value of this variable is set by the semaphore
            // constructor. It is true if the named system semaphore was
            // created, and false if the named semaphore already existed.
            //
            bool semaphoreWasCreated;

            // Create an access control list (ACL) that denies the
            // current user the right to enter or release the 
            // semaphore, but allows the right to read and change
            // security information for the semaphore.
            //
            string user = Environment.UserDomainName + "\\" 
                + Environment.UserName;
            SemaphoreSecurity semSec = new SemaphoreSecurity();

            SemaphoreAccessRule rule = new SemaphoreAccessRule(
                user, 
                SemaphoreRights.Synchronize | SemaphoreRights.Modify, 
                AccessControlType.Deny);
            semSec.AddAccessRule(rule);

            rule = new SemaphoreAccessRule(
                user, 
                SemaphoreRights.ReadPermissions | SemaphoreRights.ChangePermissions,
                AccessControlType.Allow);
            semSec.AddAccessRule(rule);

            // Create a Semaphore object that represents the system
            // semaphore named by the constant 'semaphoreName', with
            // maximum count three, initial count three, and the
            // specified security access. The Boolean value that 
            // indicates creation of the underlying system object is
            // placed in semaphoreWasCreated.
            //
            sem = new Semaphore(3, 3, semaphoreName, 
                out semaphoreWasCreated, semSec);

            // If the named system semaphore was created, it can be
            // used by the current instance of this program, even 
            // though the current user is denied access. The current
            // program enters the semaphore. Otherwise, exit the
            // program.
            // 
            if (semaphoreWasCreated)
            {
                Console.WriteLine("Created the semaphore.");
            }
            else
            {
                Console.WriteLine("Unable to create the semaphore.");
                return;
            }
        }
        else if (unauthorized)
        {
            // Open the semaphore to read and change the access
            // control security. The access control security defined
            // above allows the current user to do this.
            //
            try
            {
                sem = Semaphore.OpenExisting(
                    semaphoreName, 
                    SemaphoreRights.ReadPermissions 
                        | SemaphoreRights.ChangePermissions);

                // Get the current ACL. This requires 
                // SemaphoreRights.ReadPermissions.
                SemaphoreSecurity semSec = sem.GetAccessControl();
                
                string user = Environment.UserDomainName + "\\" 
                    + Environment.UserName;

                // First, the rule that denied the current user 
                // the right to enter and release the semaphore must
                // be removed.
                SemaphoreAccessRule rule = new SemaphoreAccessRule(
                    user, 
                    SemaphoreRights.Synchronize | SemaphoreRights.Modify, 
                    AccessControlType.Deny);
                semSec.RemoveAccessRule(rule);

                // Now grant the user the correct rights.
                // 
                rule = new SemaphoreAccessRule(user, 
                     SemaphoreRights.Synchronize | SemaphoreRights.Modify, 
                     AccessControlType.Allow);
                semSec.AddAccessRule(rule);

                // Update the ACL. This requires
                // SemaphoreRights.ChangePermissions.
                sem.SetAccessControl(semSec);

                Console.WriteLine("Updated semaphore security.");

                // Open the semaphore with (SemaphoreRights.Synchronize 
                // | SemaphoreRights.Modify), the rights required to
                // enter and release the semaphore.
                //
                sem = Semaphore.OpenExisting(semaphoreName);
            }
            catch(UnauthorizedAccessException ex)
            {
                Console.WriteLine("Unable to change permissions: {0}", ex.Message);
                return;
            }
        }

        // Enter the semaphore, and hold it until the program
        // exits.
        //
        try
        {
            sem.WaitOne();
            Console.WriteLine("Entered the semaphore.");
            Console.WriteLine("Press the Enter key to exit.");
            Console.ReadLine();
            sem.Release();
        }
        catch(UnauthorizedAccessException ex)
        {
            Console.WriteLine("Unauthorized access: {0}", ex.Message);
        }
    }
}
Imports System.Threading
Imports System.Security.AccessControl

Friend Class Example

    <MTAThread> _
    Friend Shared Sub Main()
        Const semaphoreName As String = "SemaphoreExample5"

        Dim sem As Semaphore = Nothing
        Dim doesNotExist as Boolean = False
        Dim unauthorized As Boolean = False

        ' Attempt to open the named semaphore.
        Try
            ' Open the semaphore with (SemaphoreRights.Synchronize
            ' Or SemaphoreRights.Modify), to enter and release the
            ' named semaphore.
            '
            sem = Semaphore.OpenExisting(semaphoreName)
        Catch ex As WaitHandleCannotBeOpenedException
            Console.WriteLine("Semaphore 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 semaphore does not exist.
        ' (2) The semaphore exists, but the current user doesn't 
        ' have access. (3) The semaphore exists and the user has
        ' access.
        '
        If doesNotExist Then
            ' The semaphore does not exist, so create it.
            '
            ' The value of this variable is set by the semaphore
            ' constructor. It is True if the named system semaphore was
            ' created, and False if the named semaphore already existed.
            '
            Dim semaphoreWasCreated As Boolean

            ' Create an access control list (ACL) that denies the
            ' current user the right to enter or release the 
            ' semaphore, but allows the right to read and change
            ' security information for the semaphore.
            '
            Dim user As String = Environment.UserDomainName _ 
                & "\" & Environment.UserName
            Dim semSec As New SemaphoreSecurity()

            Dim rule As New SemaphoreAccessRule(user, _
                SemaphoreRights.Synchronize Or SemaphoreRights.Modify, _
                AccessControlType.Deny)
            semSec.AddAccessRule(rule)

            rule = New SemaphoreAccessRule(user, _
                SemaphoreRights.ReadPermissions Or _
                SemaphoreRights.ChangePermissions, _
                AccessControlType.Allow)
            semSec.AddAccessRule(rule)

            ' Create a Semaphore object that represents the system
            ' semaphore named by the constant 'semaphoreName', with
            ' maximum count three, initial count three, and the
            ' specified security access. The Boolean value that 
            ' indicates creation of the underlying system object is
            ' placed in semaphoreWasCreated.
            '
            sem = New Semaphore(3, 3, semaphoreName, _
                semaphoreWasCreated, semSec)

            ' If the named system semaphore was created, it can be
            ' used by the current instance of this program, even 
            ' though the current user is denied access. The current
            ' program enters the semaphore. Otherwise, exit the
            ' program.
            ' 
            If semaphoreWasCreated Then
                Console.WriteLine("Created the semaphore.")
            Else
                Console.WriteLine("Unable to create the semaphore.")
                Return
            End If

        ElseIf unauthorized Then

            ' Open the semaphore to read and change the access
            ' control security. The access control security defined
            ' above allows the current user to do this.
            '
            Try
                sem = Semaphore.OpenExisting(semaphoreName, _
                    SemaphoreRights.ReadPermissions Or _
                    SemaphoreRights.ChangePermissions)

                ' Get the current ACL. This requires 
                ' SemaphoreRights.ReadPermissions.
                Dim semSec As SemaphoreSecurity = sem.GetAccessControl()
                
                Dim user As String = Environment.UserDomainName _ 
                    & "\" & Environment.UserName

                ' First, the rule that denied the current user 
                ' the right to enter and release the semaphore must
                ' be removed.
                Dim rule As New SemaphoreAccessRule(user, _
                    SemaphoreRights.Synchronize Or SemaphoreRights.Modify, _
                    AccessControlType.Deny)
                semSec.RemoveAccessRule(rule)

                ' Now grant the user the correct rights.
                ' 
                rule = New SemaphoreAccessRule(user, _
                    SemaphoreRights.Synchronize Or SemaphoreRights.Modify, _
                    AccessControlType.Allow)
                semSec.AddAccessRule(rule)

                ' Update the ACL. This requires
                ' SemaphoreRights.ChangePermissions.
                sem.SetAccessControl(semSec)

                Console.WriteLine("Updated semaphore security.")

                ' Open the semaphore with (SemaphoreRights.Synchronize 
                ' Or SemaphoreRights.Modify), the rights required to
                ' enter and release the semaphore.
                '
                sem = Semaphore.OpenExisting(semaphoreName)

            Catch ex As UnauthorizedAccessException
                Console.WriteLine("Unable to change permissions: {0}", _
                    ex.Message)
                Return
            End Try

        End If

        ' Enter the semaphore, and hold it until the program
        ' exits.
        '
        Try
            sem.WaitOne()
            Console.WriteLine("Entered the semaphore.")
            Console.WriteLine("Press the Enter key to exit.")
            Console.ReadLine()
            sem.Release()
        Catch ex As UnauthorizedAccessException
            Console.WriteLine("Unauthorized access: {0}", _
                ex.Message)
        End Try
    End Sub 
End Class 

備註

name可能會在前面加上 Global\Local\ 來指定命名空間。The name may be prefixed with Global\ or Local\ to specify a namespace. Global指定命名空間時,同步處理物件可能會與系統上的任何處理程式共用。When the Global namespace is specified, the synchronization object may be shared with any processes on the system. Local 指定命名空間時,如果未指定命名空間,這也是預設值,則可以與相同會話中的處理常式共用同步處理物件。When the Local namespace is specified, which is also the default when no namespace is specified, the synchronization object may be shared with processes in the same session. 在 Windows 上,會話是登入會話,而服務通常會在不同的非互動式會話中執行。On Windows, a session is a login session, and services typically run in a different non-interactive session. 在類似 Unix 的作業系統上,每個 shell 都有自己的會話。On Unix-like operating systems, each shell has its own session. 會話本機同步處理物件可能適合用來在具有父/子關聯性的進程之間進行同步處理,而且它們都會在相同的會話中執行。Session-local synchronization objects may be appropriate for synchronizing between processes with a parent/child relationship where they all run in the same session. 如需有關在 Windows 上 synchornization 物件名稱的詳細資訊,請參閱 物件名稱For more information about synchornization object names on Windows, see Object Names.

如果命名空間中有所要求之類型的同步處理物件存在,就會開啟現有的同步處理物件。If a synchronization object of the requested type exists in the namespace, the existing synchronization object is opened. 如果同步處理物件不存在於命名空間中,或命名空間中有不同類型的同步處理物件存在, WaitHandleCannotBeOpenedException 就會擲回。If a synchronization object does not exist in the namespace, or a synchronization object of a different type exists in the namespace, a WaitHandleCannotBeOpenedException is thrown.

OpenExisting方法會嘗試開啟指定的命名信號。The OpenExisting method tries to open the specified named semaphore. 若要建立尚未存在的系統信號,請使用其中一個具有參數的函式 Semaphore nameTo create the system semaphore when it does not already exist, use one of the Semaphore constructors that has a name parameter.

對這個方法使用相同值的多個呼叫 name ,不一定會傳回相同的 Semaphore 物件,即使傳回的物件代表相同的命名系統信號也是一樣。Multiple calls to this method that use the same value for name do not necessarily return the same Semaphore object, even though the objects that are returned represent the same named system semaphore.

這個方法多載相當於呼叫方法多載, OpenExistingSemaphoreRights.Synchronize SemaphoreRights.Modify 使用位 or 運算結合指定和許可權。This method overload is equivalent to calling the OpenExisting method overload and specifying SemaphoreRights.Synchronize and SemaphoreRights.Modify rights, combined by using the bitwise OR operation.

指定 SemaphoreRights.Synchronize 旗標可讓執行緒進入信號,並指定 SemaphoreRights.Modify 旗標讓執行緒可以呼叫 Release 方法。Specifying the SemaphoreRights.Synchronize flag allows a thread to enter the semaphore, and specifying the SemaphoreRights.Modify flag allows a thread to call the Release method.

適用於

OpenExisting(String, SemaphoreRights)

使用所需的安全性存取權,開啟指定的具名號誌 (如果已經存在)。Opens the specified named semaphore, if it already exists, with the desired security access.

public:
 static System::Threading::Semaphore ^ OpenExisting(System::String ^ name, System::Security::AccessControl::SemaphoreRights rights);
public static System.Threading.Semaphore OpenExisting (string name, System.Security.AccessControl.SemaphoreRights rights);
static member OpenExisting : string * System.Security.AccessControl.SemaphoreRights -> System.Threading.Semaphore
Public Shared Function OpenExisting (name As String, rights As SemaphoreRights) As Semaphore

參數

name
String

要與其他處理序共用之同步物件的名稱。The name of the synchronization object to be shared with other processes. 名稱區分大小寫。The name is case-sensitive.

rights
SemaphoreRights

列舉值的位元組合,表示所需的安全性存取。A bitwise combination of the enumeration values that represent the desired security access.

傳回

Semaphore

表示具名系統號誌的物件。An object that represents the named system semaphore.

例外狀況

name 為空字串。name is an empty string.

-或--or-

僅限 .NET Framework:name 的長度超過 MAX_PATH (260 個字元)。.NET Framework only: name is longer than MAX_PATH (260 characters).

name 上所宣告的預設值是 nullname is null.

無法建立具有所提供 name 的同步物件。A synchronization object with the provided name cannot be created. 不同類型的同步物件可能具有相同名稱。A synchronization object of a different type might have the same name. 在某些情況下,可能會因為名稱無效而擲回此例外狀況。In some cases, this exception may be thrown for invalid names.

name 無效。name is invalid. 這可能基於數種原因,其中包括可能由作業系統設定的一些限制,例如未知前置詞或無效字元。This can be for various reasons, including some restrictions that may be placed by the operating system, such as an unknown prefix or invalid characters. 請注意,名稱與通用前置詞 "Global" 與 "Local" 會區分大小寫。Note that the name and common prefixes "Global" and "Local" are case-sensitive.

-或--or-

發生一些其他錯誤。There was some other error. HResult 屬性可提供詳細資訊。The HResult property may provide more information.

name 太長。The name is too long. 長度限制可能會取決於作業系統或設定。Length restrictions may depend on the operating system or configuration.

具名號誌已存在,但是使用者沒有所需的安全性存取權限。The named semaphore exists, but the user does not have the desired security access rights.

範例

下列程式碼範例將示範具有存取控制安全性之命名信號的跨進程行為。The following code example demonstrates the cross-process behavior of a named semaphore with access control security. 此範例會使用 OpenExisting(String) 方法多載來測試命名信號是否存在。The example uses the OpenExisting(String) method overload to test for the existence of a named semaphore.

如果信號不存在,則會使用最大計數來建立,並使用存取控制安全性來拒絕目前使用者使用該信號的許可權,但會授與對信號的讀取和變更許可權許可權。If the semaphore does not exist, it is created with a maximum count of two and with access control security that denies the current user the right to use the semaphore, but grants the right to read and change permissions on the semaphore.

如果您從兩個命令視窗執行已編譯的範例,則第二個複本將會在呼叫方法時擲回存取違規例外狀況 OpenExisting(String)If you run the compiled example from two command windows, the second copy will throw an access violation exception on the call to the OpenExisting(String) method. 攔截到例外狀況,而此範例會使用 OpenExisting(String, SemaphoreRights) 方法多載來開啟具有讀取和變更許可權所需許可權的信號。The exception is caught, and the example uses the OpenExisting(String, SemaphoreRights) method overload to open the semaphore with the rights needed to read and change the permissions.

變更許可權之後,就會開啟具有輸入和釋放其必要許可權的信號。After the permissions are changed, the semaphore is opened with the rights required to enter and release it. 如果您從第三個命令視窗執行已編譯的範例,它會使用新的許可權執行。If you run the compiled example from a third command window, it runs using the new permissions.

#using <System.dll>
using namespace System;
using namespace System::Threading;
using namespace System::Security::AccessControl;
using namespace System::Security::Permissions;

public ref class Example
{
public:
   [SecurityPermissionAttribute(SecurityAction::Demand, Flags = SecurityPermissionFlag::UnmanagedCode)]
   static void main()
   {
      String^ semaphoreName = L"SemaphoreExample5";

      Semaphore^ sem = nullptr;
      bool doesNotExist = false;
      bool unauthorized = false;
      
      // Attempt to open the named semaphore.
      try
      {
         // Open the semaphore with (SemaphoreRights.Synchronize
         // | SemaphoreRights.Modify), to enter and release the
         // named semaphore.
         //
         sem = Semaphore::OpenExisting( semaphoreName );
      }
      catch ( WaitHandleCannotBeOpenedException^ ex ) 
      {
         Console::WriteLine( L"Semaphore does not exist." );
         doesNotExist = true;
      }
      catch ( UnauthorizedAccessException^ ex ) 
      {
         Console::WriteLine( L"Unauthorized access: {0}", ex->Message );
         unauthorized = true;
      }

      // There are three cases: (1) The semaphore does not exist.
      // (2) The semaphore exists, but the current user doesn't
      // have access. (3) The semaphore exists and the user has
      // access.
      //
      if ( doesNotExist )
      {
         // The semaphore does not exist, so create it.
         //
         // The value of this variable is set by the semaphore
         // constructor. It is true if the named system semaphore was
         // created, and false if the named semaphore already existed.
         //
         bool semaphoreWasCreated;
         
         // Create an access control list (ACL) that denies the
         // current user the right to enter or release the
         // semaphore, but allows the right to read and change
         // security information for the semaphore.
         //
         String^ user = String::Concat( Environment::UserDomainName,
            L"\\", Environment::UserName );
         SemaphoreSecurity^ semSec = gcnew SemaphoreSecurity;

         SemaphoreAccessRule^ rule = gcnew SemaphoreAccessRule( user,
            static_cast<SemaphoreRights>(
               SemaphoreRights::Synchronize |
               SemaphoreRights::Modify ),
            AccessControlType::Deny );
         semSec->AddAccessRule( rule );

         rule = gcnew SemaphoreAccessRule( user,
            static_cast<SemaphoreRights>(
               SemaphoreRights::ReadPermissions |
               SemaphoreRights::ChangePermissions ),
            AccessControlType::Allow );
         semSec->AddAccessRule( rule );
         
         // Create a Semaphore object that represents the system
         // semaphore named by the constant 'semaphoreName', with
         // maximum count three, initial count three, and the
         // specified security access. The Boolean value that
         // indicates creation of the underlying system object is
         // placed in semaphoreWasCreated.
         //
         sem = gcnew Semaphore( 3,3,semaphoreName,semaphoreWasCreated,semSec );
         
         // If the named system semaphore was created, it can be
         // used by the current instance of this program, even
         // though the current user is denied access. The current
         // program enters the semaphore. Otherwise, exit the
         // program.
         //
         if ( semaphoreWasCreated )
         {
            Console::WriteLine( L"Created the semaphore." );
         }
         else
         {
            Console::WriteLine( L"Unable to create the semaphore." );
            return;
         }

      }
      else if ( unauthorized )
      {
         // Open the semaphore to read and change the access
         // control security. The access control security defined
         // above allows the current user to do this.
         //
         try
         {
            sem = Semaphore::OpenExisting( semaphoreName,
               static_cast<SemaphoreRights>(
                  SemaphoreRights::ReadPermissions |
                  SemaphoreRights::ChangePermissions ));
            
            // Get the current ACL. This requires
            // SemaphoreRights.ReadPermissions.
            SemaphoreSecurity^ semSec = sem->GetAccessControl();

            String^ user = String::Concat( Environment::UserDomainName,
               L"\\", Environment::UserName );
            
            // First, the rule that denied the current user
            // the right to enter and release the semaphore must
            // be removed.
            SemaphoreAccessRule^ rule = gcnew SemaphoreAccessRule( user,
               static_cast<SemaphoreRights>(
                  SemaphoreRights::Synchronize |
                  SemaphoreRights::Modify ),
               AccessControlType::Deny );
            semSec->RemoveAccessRule( rule );
            
            // Now grant the user the correct rights.
            //
            rule = gcnew SemaphoreAccessRule( user,
               static_cast<SemaphoreRights>(
                  SemaphoreRights::Synchronize |
                  SemaphoreRights::Modify ),
               AccessControlType::Allow );
            semSec->AddAccessRule( rule );
            
            // Update the ACL. This requires
            // SemaphoreRights.ChangePermissions.
            sem->SetAccessControl( semSec );

            Console::WriteLine( L"Updated semaphore security." );
            
            // Open the semaphore with (SemaphoreRights.Synchronize
            // | SemaphoreRights.Modify), the rights required to
            // enter and release the semaphore.
            //
            sem = Semaphore::OpenExisting( semaphoreName );

         }
         catch ( UnauthorizedAccessException^ ex ) 
         {
            Console::WriteLine( L"Unable to change permissions: {0}", ex->Message );
            return;
         }
      }
      
      // Enter the semaphore, and hold it until the program
      // exits.
      //
      try
      {
         sem->WaitOne();
         Console::WriteLine( L"Entered the semaphore." );
         Console::WriteLine( L"Press the Enter key to exit." );
         Console::ReadLine();
         sem->Release();
      }
      catch ( UnauthorizedAccessException^ ex ) 
      {
         Console::WriteLine( L"Unauthorized access: {0}", ex->Message );
      }
   }
};
using System;
using System.Threading;
using System.Security.AccessControl;

internal class Example
{
    internal static void Main()
    {
        const string semaphoreName = "SemaphoreExample5";

        Semaphore sem = null;
        bool doesNotExist = false;
        bool unauthorized = false;

        // Attempt to open the named semaphore.
        try
        {
            // Open the semaphore with (SemaphoreRights.Synchronize
            // | SemaphoreRights.Modify), to enter and release the
            // named semaphore.
            //
            sem = Semaphore.OpenExisting(semaphoreName);
        }
        catch(WaitHandleCannotBeOpenedException)
        {
            Console.WriteLine("Semaphore does not exist.");
            doesNotExist = true;
        }
        catch(UnauthorizedAccessException ex)
        {
            Console.WriteLine("Unauthorized access: {0}", ex.Message);
            unauthorized = true;
        }

        // There are three cases: (1) The semaphore does not exist.
        // (2) The semaphore exists, but the current user doesn't 
        // have access. (3) The semaphore exists and the user has
        // access.
        //
        if (doesNotExist)
        {
            // The semaphore does not exist, so create it.
            //
            // The value of this variable is set by the semaphore
            // constructor. It is true if the named system semaphore was
            // created, and false if the named semaphore already existed.
            //
            bool semaphoreWasCreated;

            // Create an access control list (ACL) that denies the
            // current user the right to enter or release the 
            // semaphore, but allows the right to read and change
            // security information for the semaphore.
            //
            string user = Environment.UserDomainName + "\\" 
                + Environment.UserName;
            SemaphoreSecurity semSec = new SemaphoreSecurity();

            SemaphoreAccessRule rule = new SemaphoreAccessRule(
                user, 
                SemaphoreRights.Synchronize | SemaphoreRights.Modify, 
                AccessControlType.Deny);
            semSec.AddAccessRule(rule);

            rule = new SemaphoreAccessRule(
                user, 
                SemaphoreRights.ReadPermissions | SemaphoreRights.ChangePermissions,
                AccessControlType.Allow);
            semSec.AddAccessRule(rule);

            // Create a Semaphore object that represents the system
            // semaphore named by the constant 'semaphoreName', with
            // maximum count three, initial count three, and the
            // specified security access. The Boolean value that 
            // indicates creation of the underlying system object is
            // placed in semaphoreWasCreated.
            //
            sem = new Semaphore(3, 3, semaphoreName, 
                out semaphoreWasCreated, semSec);

            // If the named system semaphore was created, it can be
            // used by the current instance of this program, even 
            // though the current user is denied access. The current
            // program enters the semaphore. Otherwise, exit the
            // program.
            // 
            if (semaphoreWasCreated)
            {
                Console.WriteLine("Created the semaphore.");
            }
            else
            {
                Console.WriteLine("Unable to create the semaphore.");
                return;
            }
        }
        else if (unauthorized)
        {
            // Open the semaphore to read and change the access
            // control security. The access control security defined
            // above allows the current user to do this.
            //
            try
            {
                sem = Semaphore.OpenExisting(
                    semaphoreName, 
                    SemaphoreRights.ReadPermissions 
                        | SemaphoreRights.ChangePermissions);

                // Get the current ACL. This requires 
                // SemaphoreRights.ReadPermissions.
                SemaphoreSecurity semSec = sem.GetAccessControl();
                
                string user = Environment.UserDomainName + "\\" 
                    + Environment.UserName;

                // First, the rule that denied the current user 
                // the right to enter and release the semaphore must
                // be removed.
                SemaphoreAccessRule rule = new SemaphoreAccessRule(
                    user, 
                    SemaphoreRights.Synchronize | SemaphoreRights.Modify, 
                    AccessControlType.Deny);
                semSec.RemoveAccessRule(rule);

                // Now grant the user the correct rights.
                // 
                rule = new SemaphoreAccessRule(user, 
                     SemaphoreRights.Synchronize | SemaphoreRights.Modify, 
                     AccessControlType.Allow);
                semSec.AddAccessRule(rule);

                // Update the ACL. This requires
                // SemaphoreRights.ChangePermissions.
                sem.SetAccessControl(semSec);

                Console.WriteLine("Updated semaphore security.");

                // Open the semaphore with (SemaphoreRights.Synchronize 
                // | SemaphoreRights.Modify), the rights required to
                // enter and release the semaphore.
                //
                sem = Semaphore.OpenExisting(semaphoreName);
            }
            catch(UnauthorizedAccessException ex)
            {
                Console.WriteLine("Unable to change permissions: {0}", ex.Message);
                return;
            }
        }

        // Enter the semaphore, and hold it until the program
        // exits.
        //
        try
        {
            sem.WaitOne();
            Console.WriteLine("Entered the semaphore.");
            Console.WriteLine("Press the Enter key to exit.");
            Console.ReadLine();
            sem.Release();
        }
        catch(UnauthorizedAccessException ex)
        {
            Console.WriteLine("Unauthorized access: {0}", ex.Message);
        }
    }
}
Imports System.Threading
Imports System.Security.AccessControl

Friend Class Example

    <MTAThread> _
    Friend Shared Sub Main()
        Const semaphoreName As String = "SemaphoreExample5"

        Dim sem As Semaphore = Nothing
        Dim doesNotExist as Boolean = False
        Dim unauthorized As Boolean = False

        ' Attempt to open the named semaphore.
        Try
            ' Open the semaphore with (SemaphoreRights.Synchronize
            ' Or SemaphoreRights.Modify), to enter and release the
            ' named semaphore.
            '
            sem = Semaphore.OpenExisting(semaphoreName)
        Catch ex As WaitHandleCannotBeOpenedException
            Console.WriteLine("Semaphore 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 semaphore does not exist.
        ' (2) The semaphore exists, but the current user doesn't 
        ' have access. (3) The semaphore exists and the user has
        ' access.
        '
        If doesNotExist Then
            ' The semaphore does not exist, so create it.
            '
            ' The value of this variable is set by the semaphore
            ' constructor. It is True if the named system semaphore was
            ' created, and False if the named semaphore already existed.
            '
            Dim semaphoreWasCreated As Boolean

            ' Create an access control list (ACL) that denies the
            ' current user the right to enter or release the 
            ' semaphore, but allows the right to read and change
            ' security information for the semaphore.
            '
            Dim user As String = Environment.UserDomainName _ 
                & "\" & Environment.UserName
            Dim semSec As New SemaphoreSecurity()

            Dim rule As New SemaphoreAccessRule(user, _
                SemaphoreRights.Synchronize Or SemaphoreRights.Modify, _
                AccessControlType.Deny)
            semSec.AddAccessRule(rule)

            rule = New SemaphoreAccessRule(user, _
                SemaphoreRights.ReadPermissions Or _
                SemaphoreRights.ChangePermissions, _
                AccessControlType.Allow)
            semSec.AddAccessRule(rule)

            ' Create a Semaphore object that represents the system
            ' semaphore named by the constant 'semaphoreName', with
            ' maximum count three, initial count three, and the
            ' specified security access. The Boolean value that 
            ' indicates creation of the underlying system object is
            ' placed in semaphoreWasCreated.
            '
            sem = New Semaphore(3, 3, semaphoreName, _
                semaphoreWasCreated, semSec)

            ' If the named system semaphore was created, it can be
            ' used by the current instance of this program, even 
            ' though the current user is denied access. The current
            ' program enters the semaphore. Otherwise, exit the
            ' program.
            ' 
            If semaphoreWasCreated Then
                Console.WriteLine("Created the semaphore.")
            Else
                Console.WriteLine("Unable to create the semaphore.")
                Return
            End If

        ElseIf unauthorized Then

            ' Open the semaphore to read and change the access
            ' control security. The access control security defined
            ' above allows the current user to do this.
            '
            Try
                sem = Semaphore.OpenExisting(semaphoreName, _
                    SemaphoreRights.ReadPermissions Or _
                    SemaphoreRights.ChangePermissions)

                ' Get the current ACL. This requires 
                ' SemaphoreRights.ReadPermissions.
                Dim semSec As SemaphoreSecurity = sem.GetAccessControl()
                
                Dim user As String = Environment.UserDomainName _ 
                    & "\" & Environment.UserName

                ' First, the rule that denied the current user 
                ' the right to enter and release the semaphore must
                ' be removed.
                Dim rule As New SemaphoreAccessRule(user, _
                    SemaphoreRights.Synchronize Or SemaphoreRights.Modify, _
                    AccessControlType.Deny)
                semSec.RemoveAccessRule(rule)

                ' Now grant the user the correct rights.
                ' 
                rule = New SemaphoreAccessRule(user, _
                    SemaphoreRights.Synchronize Or SemaphoreRights.Modify, _
                    AccessControlType.Allow)
                semSec.AddAccessRule(rule)

                ' Update the ACL. This requires
                ' SemaphoreRights.ChangePermissions.
                sem.SetAccessControl(semSec)

                Console.WriteLine("Updated semaphore security.")

                ' Open the semaphore with (SemaphoreRights.Synchronize 
                ' Or SemaphoreRights.Modify), the rights required to
                ' enter and release the semaphore.
                '
                sem = Semaphore.OpenExisting(semaphoreName)

            Catch ex As UnauthorizedAccessException
                Console.WriteLine("Unable to change permissions: {0}", _
                    ex.Message)
                Return
            End Try

        End If

        ' Enter the semaphore, and hold it until the program
        ' exits.
        '
        Try
            sem.WaitOne()
            Console.WriteLine("Entered the semaphore.")
            Console.WriteLine("Press the Enter key to exit.")
            Console.ReadLine()
            sem.Release()
        Catch ex As UnauthorizedAccessException
            Console.WriteLine("Unauthorized access: {0}", _
                ex.Message)
        End Try
    End Sub 
End Class 

備註

name可能會在前面加上 Global\Local\ 來指定命名空間。The name may be prefixed with Global\ or Local\ to specify a namespace. Global指定命名空間時,同步處理物件可能會與系統上的任何處理程式共用。When the Global namespace is specified, the synchronization object may be shared with any processes on the system. Local 指定命名空間時,如果未指定命名空間,這也是預設值,則可以與相同會話中的處理常式共用同步處理物件。When the Local namespace is specified, which is also the default when no namespace is specified, the synchronization object may be shared with processes in the same session. 在 Windows 上,會話是登入會話,而服務通常會在不同的非互動式會話中執行。On Windows, a session is a login session, and services typically run in a different non-interactive session. 在類似 Unix 的作業系統上,每個 shell 都有自己的會話。On Unix-like operating systems, each shell has its own session. 會話本機同步處理物件可能適合用來在具有父/子關聯性的進程之間進行同步處理,而且它們都會在相同的會話中執行。Session-local synchronization objects may be appropriate for synchronizing between processes with a parent/child relationship where they all run in the same session. 如需有關在 Windows 上 synchornization 物件名稱的詳細資訊,請參閱 物件名稱For more information about synchornization object names on Windows, see Object Names.

如果命名空間中有所要求之類型的同步處理物件存在,就會開啟現有的同步處理物件。If a synchronization object of the requested type exists in the namespace, the existing synchronization object is opened. 如果同步處理物件不存在於命名空間中,或命名空間中有不同類型的同步處理物件存在, WaitHandleCannotBeOpenedException 就會擲回。If a synchronization object does not exist in the namespace, or a synchronization object of a different type exists in the namespace, a WaitHandleCannotBeOpenedException is thrown.

rights參數必須包含 SemaphoreRights.Synchronize 允許執行緒進入信號的旗標,以及 SemaphoreRights.Modify 允許執行緒呼叫方法的旗標 ReleaseThe rights parameter must include the SemaphoreRights.Synchronize flag to allow threads to enter the semaphore, and the SemaphoreRights.Modify flag to allow threads to call the Release method.

OpenExisting方法會嘗試開啟現有的已命名信號。The OpenExisting method tries to open an existing named semaphore. 若要建立尚未存在的系統信號,請使用其中一個具有參數的函式 Semaphore nameTo create the system semaphore when it does not already exist, use one of the Semaphore constructors that has a name parameter.

對這個方法使用相同值的多個呼叫 name ,不一定會傳回相同的 Semaphore 物件,即使傳回的物件代表相同的命名系統信號也是一樣。Multiple calls to this method that use the same value for name do not necessarily return the same Semaphore object, even though the objects that are returned represent the same named system semaphore.

適用於