好的，首先是一些背景知识。我们需要一个进程间读取器/写入器锁。我们决定使用一个文件并使用LockEx和UnlockEx锁定第一个字节。该类在创建时在系统临时文件夹中创建一个文件。使用readwrite访问创建文件并共享读写|删除。我们还指定了DeleteOnClose，因此我们不会留下大量的临时文件。显然，AcquireReader和AcquireWriter使用适当的标志调用LockEx，而ReleaseLock调用UnlockEx 我们已经使用一个小型应用程序测试了这个类，您可以运行多个实例并且它可以完美地运行。使用它的应用程序有一个问题，我们已经设法在另一个小测试应用程序中重新生成。在伪代码中它是
Create InterProcessReaderWriter Dispose InterProcessReaderWriter without acquiring any locks Launch a child process which takes a reader lock
第一次运行时，它运行正常。如果您再次尝试运行它，当第一次子进程仍然保持锁定时，我们在尝试打开文件时会收到UnauthorisedAccessException。
这似乎是权限问题，而不是共享冲突，但此测试用例中的所有进程都以同一用户身份运行。这里有没有人有任何想法？
我注意到另一个问题，建议使用互斥锁和信号量来实现我们想要的东西。我可能会改变我们的实现，但我仍然想知道造成这个问题的原因。
答案 0 :(得分：0)
听起来像子进程试图两次访问同一个文件。
临时文件名是唯一的吗？
答案 1 :(得分：0)
为什么不锁定整个文件？而不是第1个字节。下面的示例类具有以下优点：它可以跨不同机器上的进程工作，而不是仅限于一台机器。
这是一个使用下面的lockfilehelper类的简单示例。
Module Module1
Sub Main()
Using lockFile As New LockFileHelper("\\sharedfolder\simplefile.lock")
If lockFile.LockAcquire(1000) Then
' Do your work here.
Else
' Manage timeouts here.
End If
End Using
End Sub
End Module
这是Helper类的代码。
Public Class LockFileHelper
Implements IDisposable
'-------------------------------------------------------------------------------------------------
' We use lock files in various places in the system to provide a simple co-ordination mechanism
' between different threads within a process and for sharing access to resources with the same
' process running across different machines.
'-------------------------------------------------------------------------------------------------
Private _lockFileName As String
Private _ioStream As IO.FileStream
Private _acquiredLock As Boolean = False
Private _wasLocked As Boolean = False
Public Sub New(ByVal LockFileName As String)
_lockFileName = LockFileName
End Sub
Public ReadOnly Property LockFileName() As String
Get
Return _lockFileName
End Get
End Property
Public ReadOnly Property WasLocked() As Boolean
Get
Return _wasLocked
End Get
End Property
Public Function Exists() As Boolean
Return IO.File.Exists(_lockFileName)
End Function
Public Function IsLocked() As Boolean
'-------------------------------------------------------------------------------------------------
' If this file already locked?
'-------------------------------------------------------------------------------------------------
Dim Result As Boolean = False
Try
_ioStream = IO.File.Open(_lockFileName, IO.FileMode.Create, IO.FileAccess.ReadWrite, IO.FileShare.None)
_ioStream.Close()
Catch ex As System.IO.IOException
' File is in used by another process.
Result = True
Catch ex As Exception
Throw ex
End Try
Return Result
End Function
Public Sub LockAcquireWithException(ByVal TimeOutMilliseconds As Int32)
If Not LockAcquire(TimeOutMilliseconds) Then
Throw New Exception("Timed out trying to acquire a lock on the file " & _lockFileName)
End If
End Sub
Public Function LockAcquire(ByVal TimeOutMilliseconds As Int32) As Boolean
'-------------------------------------------------------------------------------------------------
' See have we already acquired the lock. THis can be useful in situations where we are passing
' locks around to various processes and each process may want to be sure it has acquired the lock.
'-------------------------------------------------------------------------------------------------
If _acquiredLock Then
Return _acquiredLock
End If
_wasLocked = False
Dim StartTicks As Int32 = System.Environment.TickCount
Dim TimedOut As Boolean = False
If Not IO.Directory.Exists(IO.Path.GetDirectoryName(_lockFileName)) Then
IO.Directory.CreateDirectory(IO.Path.GetDirectoryName(_lockFileName))
End If
Do
Try
_ioStream = IO.File.Open(_lockFileName, IO.FileMode.Create, IO.FileAccess.ReadWrite, IO.FileShare.None)
_acquiredLock = True
Catch ex As System.IO.IOException
' File is in used by another process.
_wasLocked = True
Threading.Thread.Sleep(100)
Catch ex As Exception
Throw ex
End Try
TimedOut = ((System.Environment.TickCount - StartTicks) >= TimeOutMilliseconds)
Loop Until _acquiredLock OrElse TimedOut
'-------------------------------------------------------------------------------------------------
' Return back the status of the lock acquisition.
'-------------------------------------------------------------------------------------------------
Return _acquiredLock
End Function
Public Sub LockRelease()
'-------------------------------------------------------------------------------------------------
' Release the lock (if we got it in the first place)
'-------------------------------------------------------------------------------------------------
If _acquiredLock Then
_acquiredLock = False
If Not IsNothing(_ioStream) Then
_ioStream.Close()
_ioStream = Nothing
End If
End If
End Sub
Private disposedValue As Boolean = False ' To detect redundant calls
' IDisposable
Protected Overridable Sub Dispose(ByVal disposing As Boolean)
If Not Me.disposedValue Then
If disposing Then
Call LockRelease()
End If
' TODO: free shared unmanaged resources
End If
Me.disposedValue = True
End Sub
#Region " IDisposable Support "
' This code added by Visual Basic to correctly implement the disposable pattern.
Public Sub Dispose() Implements IDisposable.Dispose
' Do not change this code. Put cleanup code in Dispose(ByVal disposing As Boolean) above.
Dispose(True)
GC.SuppressFinalize(Me)
End Sub
#End Region
End Class