CA1816: Call GC.SuppressFinalize correctly

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ScriptFree

TypeName	CallGCSuppressFinalizeCorrectly
CheckId	CA1816
Category	Microsoft. Usage
Breaking Change	Non Breaking

Cause

A method that is an implementation of IDisposable.Dispose does not call GC.SuppressFinalize.
A method that is not an implementation of IDisposable.Dispose calls GC.SuppressFinalize.
A method calls GC.SuppressFinalize and passes something other than this (Me in Visual Basic).

Rule Description

The IDisposable.Dispose method lets users release resources at any time before the object becoming available for garbage collection. If the IDisposable.Dispose method is called, it frees resources of the object. This makes finalization unnecessary. IDisposable.Dispose should call GC.SuppressFinalize so the garbage collector does not call the finalizer of the object.

To prevent derived types with finalizers from having to re-implement [System.IDisposable] and to call it, unsealed types without finalizers should still call GC.SuppressFinalize.

How to Fix Violations

To fix a violation of this rule:

If the method is an implementation of Dispose, add a call to GC.SuppressFinalize.

If the method is not an implementation of Dispose, either remove the call to GC.SuppressFinalize or move it to the type's Dispose implementation.

Change all calls to GC.SuppressFinalize to pass this (Me in Visual Basic).

When to Suppress Warnings

Only suppress a warning from this rule if you are deliberating using GC.SuppressFinalize to control the lifetime of other objects. Do not suppress a warning from this rule if an implementation of Dispose does not call GC.SuppressFinalize. In this situation, failing to suppress finalization degrades performance and provide no benefits.

Example

The following example shows a method that incorrectly calls GC.SuppressFinalize.

Visual Basic


Imports System
Imports System.Data.SqlClient

Namespace Samples

    Public Class DatabaseConnector
        Implements IDisposable

        Private _Connection As New SqlConnection

        Public Sub Dispose() Implements IDisposable.Dispose
            Dispose(True)
            GC.SuppressFinalize(True)   ' Violates rules
        End Sub

        Protected Overridable Sub Dispose(ByVal disposing As Boolean)
            If disposing Then
                If _Connection IsNot Nothing Then
                    _Connection.Dispose()
                    _Connection = Nothing
                End If
            End If
        End Sub

    End Class

End Namespace


using System;
using System.Data.SqlClient;
namespace Samples
{
    public class DatabaseConnector : IDisposable
    {
        private SqlConnection _Connection = new SqlConnection();

        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(true);  // Violates rule
        }

        protected virtual void Dispose(bool disposing)
        {
            if (disposing)
            {
                if (_Connection != null)
                {
                    _Connection.Dispose();
                    _Connection = null;
                }
            }
        }
    }
}

The following example shows a method that correctly calls GC.SuppressFinalize.

Visual Basic


Imports System
Imports System.Data.SqlClient

Namespace Samples

    Public Class DatabaseConnector
        Implements IDisposable

        Private _Connection As New SqlConnection

        Public Sub Dispose() Implements IDisposable.Dispose
            Dispose(True)
            GC.SuppressFinalize(Me)
        End Sub

        Protected Overridable Sub Dispose(ByVal disposing As Boolean)
            If disposing Then
                If _Connection IsNot Nothing Then
                    _Connection.Dispose()
                    _Connection = Nothing
                End If
            End If
        End Sub

    End Class

End Namespace


using System;
using System.Data.SqlClient;

namespace Samples
{
    public class DatabaseConnector : IDisposable
    {
        private SqlConnection _Connection = new SqlConnection();

        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }

        protected virtual void Dispose(bool disposing)
        {
            if (disposing)
            {
                if (_Connection != null)
                {
                    _Connection.Dispose();
                    _Connection = null;
                }
            }
        }
    }
}

CA2216: Disposable types should declare finalizer

Reference

Implementing Finalize and Dispose to Clean Up Unmanaged Resources