Imports System.Threading
Imports System.Net
Imports System.Net.Sockets
Imports System.IO
Imports System.Collections.Concurrent
Imports System.Reflection
Imports System.Runtime.InteropServices
Imports System.Diagnostics
Imports System.Collections.Generic

Public Class AsyncUnbuffWriter

        '''' We need the page size for best performance - so we use GetSystemInfo and dwPageSize
        ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
        ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

        Public Class clsSystemInfo

            private Class WinApi
	            <DllImport("kernel32.dll")> _
	            Public Shared Sub GetSystemInfo(<MarshalAs(UnmanagedType.Struct)> ByRef lpSystemInfo As SYSTEM_INFO)
	            End Sub

	            <StructLayout(LayoutKind.Sequential)> _
	            Public Structure SYSTEM_INFO
		            Friend uProcessorInfo As _PROCESSOR_INFO_UNION
		            Public dwPageSize As UInteger
		            Public lpMinimumApplicationAddress As IntPtr
		            Public lpMaximumApplicationAddress As IntPtr
		            Public dwActiveProcessorMask As IntPtr
		            Public dwNumberOfProcessors As UInteger
		            Public dwProcessorType As UInteger
		            Public dwAllocationGranularity As UInteger
		            Public dwProcessorLevel As UShort
		            Public dwProcessorRevision As UShort
	            End Structure

	            <StructLayout(LayoutKind.Explicit)> _
	            Public Structure _PROCESSOR_INFO_UNION
		            <FieldOffset(0)> _
		            Friend dwOemId As UInteger
		            <FieldOffset(0)> _
		            Friend wProcessorArchitecture As UShort
		            <FieldOffset(2)> _
		            Friend wReserved As UShort
	            End Structure
        End Class

	    Public Shared Function GetPageSize() As Integer
		    Dim sysinfo As New WinApi.SYSTEM_INFO()
		    WinApi.GetSystemInfo(sysinfo)
            Return CInt(sysinfo.dwPageSize)
	    End Function
    End Class

        Private target As FileStream
        Private inputBuffer As MemoryStream
        Private bufferSize As Integer
        Private running As Boolean
        Private writing As Boolean
        Private readWait As Threading.ManualResetEvent
        Private writeWait As Threading.ManualResetEvent
        Private finishedWriting As Threading.ManualResetEvent
        Private totalWritten As Int64
        Private writeTimer As Stopwatch

        Public Function GetTotalBytesWritten() As Int64
            Return totalWritten
        End Function

        Public Function IsRunning() As Boolean
            Return running
        End Function

        Public Sub Close()
            writing     = False
            writeWait   .Set
            finishedWriting.WaitOne
            readWait    .Set
        End Sub

        Public Function GetActiveMiliseconds() As Int64
            Try
                Return writeTimer.ElapsedMilliseconds
            Catch ex As Exception
                Return 0
            End Try
        End Function

        Public Shared Function GetPageSize() As Integer
            Return clsSystemInfo.GetPageSize
        End Function

        Public Sub new(ByVal dest As String, _
                    Optional ByVal unbuffered   As Boolean  = False, _
                    Optional ByVal _bufferSize  As Integer  = (1024 * 1024), _
                    Optional ByVal setLength    As Int64    = 0)
        
            bufferSize                  = _bufferSize
            Dim options As FileOptions  = FileOptions.SequentialScan
            If unbuffered then options  = FileOptions.WriteThrough or FileOptions.SequentialScan
            readWait                    = New Threading.ManualResetEvent(False)
            writeWait                   = New Threading.ManualResetEvent(False)
            finishedWriting             = New Threading.ManualResetEvent(False)

            readWait                    .Set
            writeWait                   .Reset
            finishedWriting             .Reset

            target                      = New FileStream(dest, _
                                            FileMode.Create, FileAccess.Write, FileShare.None, GetPageSize, options)
            If setLength > 0 then       target.SetLength(setLength)

            totalWritten                = 0
            inputBuffer                 = New MemoryStream(bufferSize)
            running                     = True
            writing                     = True
            writeTimer                  = New Stopwatch

            Dim asyncWriter             As New Threading.Thread(AddressOf WriteThread)

            With asyncWriter
                .Priority               = Threading.ThreadPriority.Lowest
                .IsBackground           = True
                .Name                   = "AsyncCopy writer"
                .Start()
            End With

        End Sub

        Public Function Write(ByVal someBytes() As Byte, numToWrite As Integer) As Boolean
            If Not running then Return False
            If numToWrite < 1 then Return False

            If numToWrite > inputBuffer.Capacity then
                Throw New Exception("clsAsyncUnbuffWriter: someBytes() can not be larger then buffer capacity")
            End If

            If (inputBuffer.Length + numToWrite) > inputBuffer.Capacity then
                If inputBuffer.Length > 0 then
                    readWait            .Reset
                    writeWait           .Set
                    readWait            .WaitOne
                    If Not running then Return False
                    inputBuffer.Write(someBytes, 0, numToWrite)
                End If
            Else
                inputBuffer.Write(someBytes, 0, numToWrite)
            End If

            Return True
        End Function

        Private Sub WriteThread()

            Dim bytesThisTime As Int32      = 0
            Dim internalBuffer(bufferSize)  As byte

            writeTimer                      .Stop
            writeTimer                      .Reset
            writeTimer                      .Start

            Do
                writeWait                   .WaitOne
                writeWait                   .Reset

                bytesThisTime               = CInt(inputBuffer.Length)

                Buffer.BlockCopy(inputBuffer.GetBuffer, 0, internalBuffer, 0, bytesThisTime)

                inputBuffer                 .SetLength(0)
                readWait                    .Set()

                target.Write(internalBuffer, 0, bytesThisTime)
                totalWritten                += bytesThisTime

            Loop While writing

            ' Flush inputBuffer
            If inputBuffer.Length > 0 then
                bytesThisTime               = CInt(inputBuffer.Length)
                Buffer.BlockCopy(inputBuffer.GetBuffer, 0, internalBuffer, 0, bytesThisTime)
                target.Write(internalBuffer, 0, bytesThisTime)
                totalWritten                += bytesThisTime
            End If

            running                         = False
            writeTimer                      .Stop

            Try
                target                      .Close
                target                      .Dispose
            Catch ex As Exception
            End Try

            inputBuffer                     .Close()
            finishedWriting                 .Set
            inputBuffer                     .Dispose()
            inputBuffer                     = Nothing
            internalBuffer                  = Nothing
            target                          = Nothing

            GC.GetTotalMemory(True)
        End Sub
    End Class