Garbage Collection
- From: saurabhgarg2k@xxxxxxxxx
- Date: 6 Apr 2005 03:00:38 -0700
Hi there,
I am attaching a snippet of code here which tries to explain that if u
have a class which contains both Unamanged resources and allocates a
lot of memeory and have a finalize method, then u should divides it
into two classes , one contains the memory part and other manages the
unmanaged resources and implement finalize in the second class so that
the memory will be released quick enough for first Class which
allocates large memory as classes implementing finalize method requires
at least 2 GC cycles to release the objects.
Here is the first class with contains both large memory and Unamaged
resources in one class
Class SimpleObject
Private Declare Function CreateSemaphore _
Lib "kernel32" Alias "CreateSemaphoreA" _
(ByVal lpSemaphoreAttributes As Integer, _
ByVal lInitialCount As Integer, _
ByVal lMaximumCount As Integer, _
ByVal lpName As String) As Integer
Private Declare Function ReleaseSemaphore _
Lib "kernel32" Alias "ReleaseSemaphore" _
(ByVal hSemaphore As Integer, _
ByVal lReleaseCount As Integer, ByVal _
lpPreviousCount As Integer) As Integer
Dim arr() As Integer
Dim handle As Integer
Sub New()
ReDim arr(10000) ' a lot of memory
' directly allocate an unmanaged resource
handle = CreateSemaphore(0, 1, 1000, _
"testsemaphore")
End Sub
Protected Overrides Sub Finalize()
' release the unmanaged resource
If handle <> 0 Then _
ReleaseSemaphore(handle, 1, 0)
End Sub
End Class
Here is the Next Class which divides the functionality which is
embedded in the outer class.
Class CompoundObject
Dim arr() As Integer
Dim wrapper As SemaphoreWrapper
Sub New()
ReDim arr(10000) ' a lot of memory
' allocate another (managed) resource
' (no need to release it in Finalize)
wrapper = New SemaphoreWrapper
End Sub
' a class that wraps the unmanaged resource
Private Class SemaphoreWrapper
Private Declare Function CreateSemaphore _
Lib "kernel32" Alias "CreateSemaphoreA" _
(ByVal lpSemaphoreAttributes As Integer, _
ByVal lInitialCount As Integer, _
ByVal lMaximumCount As Integer, _
ByVal lpName As String) As Integer
Private Declare Function ReleaseSemaphore _
Lib "kernel32" Alias "ReleaseSemaphore" _
(ByVal hSemaphore As Integer, _
ByVal lReleaseCount As Integer, _
ByVal lpPreviousCount As Integer) As Integer
Public Handle As Integer
Sub New()
' allocate the unmanaged resource
Handle = CreateSemaphore(0, 1, 1000, _
"testsemaphore")
End Sub
Protected Overrides Sub Finalize()
' release the unmanaged resource
If Handle <> 0 Then _
ReleaseSemaphore(Handle, 1, 0)
End Sub
End Class
End Class
Here is the Client Code
Module Module1
Sub Main()
Dim i As Integer
Const TIMES As Integer = 10000
Dim t As Date = Now
For i = 1 To TIMES
Dim so As New SimpleObject
Next
Console.WriteLine("Simple object: {0}", _
Now.Subtract(t))
' force a garbage collection to clean up
GC.Collect()
GC.WaitForPendingFinalizers()
t = Now
For i = 1 To TIMES
Dim co As New CompoundObject
Next
Console.WriteLine("Compound object: {0}", _
Now.Subtract(t))
Console.ReadLine
End Sub
End Module
Now the author claims that the first for loop will take more time as it
requires more GC cycles to deallocate the large chunk of memory it
allocates and the second will release it quickly as the class
allocating the Large memory does not implement finalize method so it
will be deallocated in one GC cycle unlike the class with unmamaged
resource
My question:
As GC will only fire when managed heap runs out of space, so in first
for loop when after allocating a few objects, heap is full and the GC
fires but no objects will be allocated as the class implements the
Finalize method and it requires at least two GC cycles to deallocate,
so if no object is deallocated, from where the runtime gets the space
to allocate the next object,will GC be fired again for these kind of
cases when it does not able to release enough memory for the next
object.
Note:
The code works fine.No Exceptions so there is something missing in my
understanding.
Excuse me for such a long posting but i would highly appreciate if
someone clears my doubt where i am wrong.
Thanks and Regards
Saurabh Garg
.
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