Explicitly Freeing Memory in C#

Explicitly freeing memory in c#

Private bytes reflect the process' memory usage. When objects are collected the associated memory segment may or may not be freed to the OS. The CLR manages memory at the OS level and since allocating and freeing memory isn't free there's no reason to free each piece of memory immediately as chances are that the application will probably request more memory later.

What is the correct way to free memory in C#

1.If I have something like Foo o = new Foo(); inside the method, does that
mean that each time the timer ticks,
I'm creating a new object and a new
reference to that object?

Yes.

2.If I have string foo = null and then I just put something temporal in foo,
is it the same as above?

If you are asking if the behavior is the same then yes.

3.Does the garbage collector ever delete the object and the reference or
objects are continually created and
stay in memory?

The memory used by those objects is most certainly collected after the references are deemed to be unused.

4.If I just declare Foo o; and not point it to any instance, isn't that
disposed when the method ends?

No, since no object was created then there is no object to collect (dispose is not the right word).

5.If I want to ensure that everything is deleted, what is the best way of
doing it

If the object's class implements IDisposable then you certainly want to greedily call Dispose as soon as possible. The using keyword makes this easier because it calls Dispose automatically in an exception-safe way.

Other than that there really is nothing else you need to do except to stop using the object. If the reference is a local variable then when it goes out of scope it will be eligible for collection.¹ If it is a class level variable then you may need to assign null to it to make it eligible before the containing class is eligible.

---

¹This is technically incorrect (or at least a little misleading). An object can be eligible for collection long before it goes out of scope. The CLR is optimized to collect memory when it detects that a reference is no longer used. In extreme cases the CLR can collect an object even while one of its methods is still executing!

Update:

Here is an example that demonstrates that the GC will collect objects even though they may still be in-scope. You have to compile a Release build and run this outside of the debugger.

static void Main(string[] args)
{
    Console.WriteLine("Before allocation");
    var bo = new BigObject();
    Console.WriteLine("After allocation");
    bo.SomeMethod();
    Console.ReadLine();
    // The object is technically in-scope here which means it must still be rooted.
}

private class BigObject
{
    private byte[] LotsOfMemory = new byte[Int32.MaxValue / 4];

    public BigObject()
    {
        Console.WriteLine("BigObject()");
    }

    ~BigObject()
    {
        Console.WriteLine("~BigObject()");
    }

    public void SomeMethod()
    {
        Console.WriteLine("Begin SomeMethod");
        GC.Collect();
        GC.WaitForPendingFinalizers();
        Console.WriteLine("End SomeMethod");
    }
}

On my machine the finalizer is run while SomeMethod is still executing!

Free memory explicitly

Don't worry about it! Trying to "encourage" the garbage collector to reclaim memory isn't a great idea - just leave it to do its work in the background.

Just load your different set of data. If memory is getting low the GC will kick in to reclaim the memory without you having to do anything, and if there's plenty of memory available then you'll be able to load the new set without taking the hit of a garbage collection.

How free memory used by a large list in C#?

The problem may be that Clear is not doing what you think it is. Clear simply marks the List as being empty without resizing the internal array that it uses behind the scenes. It will, however, remove all references to the individual BasePopulation instances. So if no other data structure has a reference to them they will be eligible for garbage collection. But, it will not reduce the size of the List directly. I just verified this using ILSpy.

You have two options.

1. Set Population = null. This will unroot the entire object instance making it eligible for garbage collection.

2. Call TrimExcess on this List. This will resize the internal array.

C#: Releasing memory usage

I think I found an explanation, thanks to @ScottChamberlain's answer at: Why Garbage Collector doesn't collect Tasks objects

I think the memory gets increasing because TaskScheduler is static, and still stores the task's reference, despite the task is finished. So the amount of references is which keeps increasing the memory, not the memory usage of each task itself.

I have not figure out yet how to remove that references, but, as an alternative solution, I could refactorize the code the use threads. For example, this code is an alternative of the "Update 1" in my question. And the memory remains stable on 18mb.

private static List<Thread> LThreads = new List<Thread>();
private static void manageThreadholdLimit()
{
    waitForAll();
    realeaseMemory();
}

private static void waitForAll()
{
    LThreads.ForEach(x => x.Join());
    LThreads.ForEach(x => x = null);
    LThreads.Clear();
    LThreads = null;
}
private static void realeaseMemory()
{

    GC.Collect();
    GC.WaitForPendingFinalizers();

    LTasks = new List<Task>();
    LThreads = new List<Thread>();
}
public static void Main(string[] args)
{
    int i = 0;

    while (true)
    {
        i++;

        var t = new Thread(() => Thread.Sleep(100));
        LThreads.Add(t);
        t.Start();

        if (i % 1000 == 0) manageThreadholdLimit();

    }
}

How to free memory in C# that is allocated in C++

You need to call the corresponding "free" method in the library you're using.

Memory allocated via new is part of the C++ runtime, and calling FreeHGlobal won't work. You need to call (one way or the other) delete[] against the memory.

If this is your own library then create a function (eg VideoSource_FreeFrame) that deletes the memory. Eg:

void VideoSource_FreeFrame(unsigned char *buffer)
{
  delete[] buffer;
}

And then call this from C#, passing in the IntPtr you got back.

How to release the memory which is occupied but large object as soon as possible?

first of all. Large objects, i.e. larger than 85kb, will be allocated on the large object heap (LOH). The large object heap is only collected in gen 2 collections, i.e. collections are expensive. Because of this it is generally recommended to avoid frequent LOH allocations. If at all possible, reuse the same object, or use a memory pool to avoid frequent allocations.

There are no way to explicitly free managed memory without letting the GC do its thing. While the standard recommendation is to leave the GC alone, there are cases where it may make sense to run it manually. Like if you have recently released large amount of memory, and the performance impact of a collection is acceptable at that point in time.

If the object is small enough to fit in the Small object heap then you should not need to worry about it. Gen 1 collections are fairly cheap, and while collections will need to run more frequently if you do many allocations, the time to run a collection is not proportional to the amount of freed memory. That said, reusing memory might still be a good idea.

In the end, if you suspect it is a problem, do some profiling. Some of the profilers give you the time spent in garbage collection, and also the allocation rate. Do not try to fix a imaginary problem before confirming that it actually is a problem, and you can verify that the fix actually is an improvement.

How to release the occupied memory

Using as suggested by Pranay will work as it will by default call Dispose method. else explicitly you have to call this.dispose() after calling this.close() on your child forms. But be sure you are not going to use child form elements or value after close. Since dispose will finally clear everything.

MSDN example for disposing unmanaged resource

Imports System
Imports System.ComponentModel

' The following example demonstrates how to create
' a resource class that implements the IDisposable interface
' and the IDisposable.Dispose method.
Public Class DisposeExample

   ' A class that implements IDisposable.
   ' By implementing IDisposable, you are announcing that 
   ' instances of this type allocate scarce resources.
   Public Class MyResource
      Implements IDisposable
      ' Pointer to an external unmanaged resource.
      Private handle As IntPtr
      ' Other managed resource this class uses.
      Private component As component
      ' Track whether Dispose has been called.
      Private disposed As Boolean = False

      ' The class constructor.
      Public Sub New(ByVal handle As IntPtr)
         Me.handle = handle
      End Sub

      ' Implement IDisposable.
      ' Do not make this method virtual.
      ' A derived class should not be able to override this method.
      Public Overloads Sub Dispose() Implements IDisposable.Dispose
         Dispose(True)
         ' This object will be cleaned up by the Dispose method.
         ' Therefore, you should call GC.SupressFinalize to
         ' take this object off the finalization queue 
         ' and prevent finalization code for this object
         ' from executing a second time.
         GC.SuppressFinalize(Me)
      End Sub

      ' Dispose(bool disposing) executes in two distinct scenarios.
      ' If disposing equals true, the method has been called directly
      ' or indirectly by a user's code. Managed and unmanaged resources
      ' can be disposed.
      ' If disposing equals false, the method has been called by the 
      ' runtime from inside the finalizer and you should not reference 
      ' other objects. Only unmanaged resources can be disposed.
      Protected Overridable Overloads Sub Dispose(ByVal disposing As Boolean)
         ' Check to see if Dispose has already been called.
         If Not Me.disposed Then
            ' If disposing equals true, dispose all managed 
            ' and unmanaged resources.
            If disposing Then
               ' Dispose managed resources.
               component.Dispose()
            End If

            ' Call the appropriate methods to clean up 
            ' unmanaged resources here.
            ' If disposing is false, 
            ' only the following code is executed.
            CloseHandle(handle)
            handle = IntPtr.Zero

            ' Note disposing has been done.
            disposed = True

         End If
      End Sub

      ' Use interop to call the method necessary  
      ' to clean up the unmanaged resource.
      <System.Runtime.InteropServices.DllImport("Kernel32")> _
      Private Shared Function CloseHandle(ByVal handle As IntPtr) As [Boolean]
      End Function

      ' This finalizer will run only if the Dispose method 
      ' does not get called.
      ' It gives your base class the opportunity to finalize.
      ' Do not provide finalize methods in types derived from this class.
      Protected Overrides Sub Finalize()
         ' Do not re-create Dispose clean-up code here.
         ' Calling Dispose(false) is optimal in terms of
         ' readability and maintainability.
         Dispose(False)
         MyBase.Finalize()
      End Sub
   End Class

   Public Shared Sub Main()
      ' Insert code here to create
      ' and use the MyResource object.
   End Sub

End Class

(Update)[Check]

If your child form has the signature. These are by default added to a form.

'Form overrides dispose to clean up the component list.
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then
            If Not (components Is Nothing) Then
                components.Dispose()
            End If
        End If
    MyBase.Dispose(disposing)
End Sub

---

Related Topics