やりがちなアンマネージドメモリのリークと対処方法 ref: http://qiita.com/Nuits/items/9ce6a205a50bf8e3dbeb

file0.cs

IntPtr srcIntPtr = System.Runtime.InteropServices.Marshal.AllocCoTaskMem(length);
try
{
    // ここに処理を記載する
}
finally
{
    System.Runtime.InteropServices.Marshal.FreeCoTaskMem(srcIntPtr);
}

file1.cs

IntPtr srcIntPtr = IntPtr.Zero;
try
{
    srcIntPtr = System.Runtime.InteropServices.Marshal.AllocCoTaskMem(length);
    // ここに処理を記載する
}
finally
{
    if(srcIntPtr != IntPtr.Zero)
    {
        System.Runtime.InteropServices.Marshal.FreeCoTaskMem(srcIntPtr);
    }
}

file2.cs

System.Runtime.CompilerServices.RuntimeHelpers.PrepareConstrainedRegions();
try { }
finally
{
    IntPtr srcIntPtr = System.Runtime.InteropServices.Marshal.AllocCoTaskMem(length);
    try
    {
        // ここに処理を記載する
    }
    finally
    {
        System.Runtime.InteropServices.Marshal.FreeCoTaskMem(srcIntPtr);
    }
}

file3.cs

IntPtr srcIntPtr = IntPtr.Zero;
try
{
    System.Runtime.CompilerServices.RuntimeHelpers.PrepareConstrainedRegions();
    try { }
    finally
    {
        srcIntPtr = System.Runtime.InteropServices.Marshal.AllocCoTaskMem(length);
    }
    // ここに処理を記載する
}
finally
{
    if(srcIntPtr != IntPtr.Zero)
    {
        System.Runtime.InteropServices.Marshal.FreeCoTaskMem(srcIntPtr);
    }
}