Debug.ProcedureEnter(ldtoken($1()));   // WTF?

Reflector:

Crashes blatantly! Unhandled ‘ldtoken’ at offset 0000.

dotPeek:

Well well, at least it got this right! Not sure why it is an issue though…

// ISSUE: method reference
Debug.ProcedureEnter(__methodref (eval\u002Dcore\u0028003\u0029.\u00241));

public static object $1()
{
  Debug.ProcedureEnter();
  Debug.ExpressionIn();
  Debug.ExpressionOut();
  Closure.Create(new CallTarget1(eval-core(003).::foo), 1);
  Debug.ExpressionIn();
  Debug.ExpressionOut();
  Closure.Create(new CallTarget2(eval-core(003).::bar), 2);
  Debug.ExpressionIn();
  Debug.ExpressionOut();
  Debug.ExpressionIn();
  Debug.ExpressionOut();
  ::dummy$2(::foo(RuntimeHelpers.Int32ToObject(20)));
  return Builtins.Unspecified;
  Debug.ProcedureExit();
}

Output from ILSpy (almost correct):

public static object $1()
{
	Debug.ProcedureEnter();
	Delegate arg_17_0 = new CallTarget1(eval-core(003).::foo);
	int arg_17_1 = 1;
	Debug.ExpressionIn();
	Closure.Create(arg_17_0, arg_17_1);
	Debug.ExpressionOut();
	Delegate arg_34_0 = new CallTarget2(eval-core(003).::bar);
	int arg_34_1 = 2;
	Debug.ExpressionIn();
	Closure.Create(arg_34_0, arg_34_1);
	Debug.ExpressionOut();
	object arg_4B_0 = RuntimeHelpers.Int32ToObject(20);
	Debug.ExpressionIn();
	object arg_5A_0 = eval-core(003).::foo(arg_4B_0);
	Debug.ExpressionOut();
	Debug.ExpressionIn();
	eval-core(003).::dummy$2(arg_5A_0);
	Debug.ExpressionOut();
	return Builtins.Unspecified;
}

Just silly

ILSpy does seem to hide the call to Debug.ProcedureExit(). But that is my bad ;P

Here is the IL:

.method public static
	object $1 () cil managed
{
	// Method begins at RVA 0x20dc
	// Code size 112 (0x70)
	.maxstack 3

	IL_0000: call void [Microsoft.Scripting]Microsoft.Scripting.Debugging.Debug::ProcedureEnter()
	IL_0005: ldnull
	IL_0006: ldftn object 'eval-core(003)'::'::foo'(object)
	IL_000c: newobj instance void [Microsoft.Scripting]Microsoft.Scripting.CallTarget1::.ctor(object, native int)
	IL_0011: ldc.i4.1
	IL_0012: call void [Microsoft.Scripting]Microsoft.Scripting.Debugging.Debug::ExpressionIn()
	IL_0017: call class [IronScheme.Closures]IronScheme.Runtime.Callable [IronScheme.Closures]IronScheme.Runtime.Closure::Create(class [mscorlib]System.Delegate, int32)
	IL_001c: call void [Microsoft.Scripting]Microsoft.Scripting.Debugging.Debug::ExpressionOut()
	IL_0021: pop
	IL_0022: ldnull
	IL_0023: ldftn object 'eval-core(003)'::'::bar'(object, object)
	IL_0029: newobj instance void [Microsoft.Scripting]Microsoft.Scripting.CallTarget2::.ctor(object, native int)
	IL_002e: ldc.i4.2
	IL_002f: call void [Microsoft.Scripting]Microsoft.Scripting.Debugging.Debug::ExpressionIn()
	IL_0034: call class [IronScheme.Closures]IronScheme.Runtime.Callable [IronScheme.Closures]IronScheme.Runtime.Closure::Create(class [mscorlib]System.Delegate, int32)
	IL_0039: call void [Microsoft.Scripting]Microsoft.Scripting.Debugging.Debug::ExpressionOut()
	IL_003e: pop
	IL_003f: ldc.i4.s 20
	IL_0041: call object [Microsoft.Scripting]Microsoft.Scripting.RuntimeHelpers::Int32ToObject(int32)
	IL_0046: call void [Microsoft.Scripting]Microsoft.Scripting.Debugging.Debug::ExpressionIn()
	IL_004b: call object 'eval-core(003)'::'::foo'(object)
	IL_0050: call void [Microsoft.Scripting]Microsoft.Scripting.Debugging.Debug::ExpressionOut()
	IL_0055: call void [Microsoft.Scripting]Microsoft.Scripting.Debugging.Debug::ExpressionIn()
	IL_005a: call object 'eval-core(003)'::'::dummy$2'(object)
	IL_005f: call void [Microsoft.Scripting]Microsoft.Scripting.Debugging.Debug::ExpressionOut()
	IL_0064: pop
	IL_0065: ldsfld object [IronScheme]IronScheme.Runtime.Builtins::Unspecified
	IL_006a: ret

	IL_006b: call void [Microsoft.Scripting]Microsoft.Scripting.Debugging.Debug::ProcedureExit()
} // end of method 'eval-core(003)'::$1

Output from latest dotPeek:

  public static object \u00241()
  {
    Debug.ProcedureEnter();
    CallTarget1 callTarget1 = new CallTarget1(eval\u002Dcore\u0028003\u0029.\u003A\u003Afoo);
    int paramcount1 = 1;
    Debug.ExpressionIn();
    Closure.Create((Delegate) callTarget1, paramcount1);
    Debug.ExpressionOut();
    CallTarget2 callTarget2 = new CallTarget2(eval\u002Dcore\u0028003\u0029.\u003A\u003Abar);
    int paramcount2 = 2;
    Debug.ExpressionIn();
    Closure.Create((Delegate) callTarget2, paramcount2);
    Debug.ExpressionOut();
    object x = RuntimeHelpers.Int32ToObject(20);
    Debug.ExpressionIn();
    object a = eval\u002Dcore\u0028003\u0029.\u003A\u003Afoo(x);
    Debug.ExpressionOut();
    Debug.ExpressionIn();
    eval\u002Dcore\u0028003\u0029.\u003A\u003Adummy\u00242(a);
    Debug.ExpressionOut();
    object obj = Builtins.Unspecified;
    Debug.ProcedureExit();
    return obj;
  }

  object[] a = new object[2];
  a[0] = symbol_free-id;
  s11n:8 = objArray[8];
  a[1] = s11n:8;
  $c$00BA = Builtins.List(symbol__, symbol_any, Builtins.ListStar(a, symbol_each-any));

What the actual IL is:

  L_045e: ldc.i4.2
  L_045f: newarr object
  L_0464: dup
  L_0465: ldc.i4.0
  L_0466: ldsfld object contracts::symbol_free-id
  L_046b: stelem.ref
  L_046c: dup
  L_046d: ldc.i4.1
  L_046e: ldsfld object contracts::s11n:8
  L_0473: ldloc.0
  L_0474: ldc.i4.8
  L_0475: ldelem.ref
  L_0476: stsfld object contracts::s11n:8
  L_047b: stelem.ref
  L_047c: ldsfld object contracts::symbol_each-any
  L_0481: call object [IronScheme]IronScheme.Runtime.Builtins::ListStar(object, object)
  L_0486: call object [IronScheme]IronScheme.Runtime.Builtins::List(object, object, object)
  L_048b: stsfld object contracts::$c$00BA

Note, L_046e and L_0476, completely wrong order in the C#

After my umpteenth time saying it should NOT be needed to call Dispose, I got a response from a well-respected StackOverflow user that made me think about it more. Although he did not mention why I was wrong, I could just had to figure this one out.

As we know, IDisposable is recommended primarily to release unmanaged resources in a deterministic way for managed types. If implemented correctly, you need to call GC.SuppressFinalize in your Dispose method. GC.SuppressFinalize prevents the object’s finalizer to be called.

All good up to here?

So lets run a little test:

class Foo
{
  byte[] buffer = new byte[50 * 1024];

  ~Foo()
  {
    Console.WriteLine("Finalized");
  }

  public void Moo()
  {
    Console.WriteLine("Moosposed");
    GC.SuppressFinalize(this);
  }
}

class Program
{
  static void Main(string[] args)
  {
    while (true)
    {
      new Foo();
    }
  }
}

Run the above, and within seconds you should get an OutOfMemoryException. Funny, seems the GC is not doing it’s job, or the printing in the finalizer is causing it not to be collected? This can be ‘confirmed’ by removing that printing statement. Strange indeed why something that has no reference to the object can prevent it being finalized.

Now change the code to:

class Program
{
  static void Main(string[] args)
  {
    while (true)
    {
      new Foo().Moo();
    }
  }
}

Now the program runs happily till the cows come home, with barely any memory usage (under 18MB on my PC). So what is happening? Is GC.SuppressFinalize actually freeing the objects memory deterministically when called? It would appear so, but nowhere in any documentation is this extremely important fact noted. It also does not appear so, as adding GC.SuppressFinalize(this) to the finalizer after the printing statement also causes an OutOfMemoryException. Also, why is MS recommending calling GC.SuppressFinalize from the finalizer? This does not make sense. Can it be GC’d twice?

So all in all, one should never call Console.WriteLine() from within the finalizer else it will prevent the object from being considered for immediate garbage collection. What else can you not call from the finalizer? Clearly, when dealing with unmanaged resources, you will have to at least free them in your Dispose method, but if this is called from the finalizer, it seems you are in the same boat. What happens if your unmanaged component logs stuff to the console when you ‘close it’s handle’ ? Are you doomed?

I think the moral of the story is that one should at all costs prevent calling any unknown code (and Console methods) from the finalizer. This might be the reason why Dispose is pushed so heavily by MS.

On a side note, given we have ‘clean’ finalizers, it does not really matter if you call Dispose or not on an IDisposable object. The GC will take care of it, unless something happens like above.

I still stick to my point I made several months back. You should call Dispose, however it is not a must. It is only a must if it prints something or something that prevents the immediate GC of the object.

Here follows a simple example on how to achieve it:

class DynamicConsole : TextWriter
{
  readonly TextWriter orig;
  readonly TextWriter output;

  public DynamicConsole(string filename)
  {
     orig = Console.Out;
    output = File.AppendText(filename);
    Console.SetOut(output);
  }

  public override System.Text.Encoding Encoding
  {
    get { return output.Encoding; }
  }

  public override void Write(char value)
  {
    output.Write(value);
  }

  protected override void Dispose(bool disposing)
  {
    Console.SetOut(orig);
    output.Dispose();
  }
}

Usage:

Console.WriteLine("Real 1");

using (new DynamicConsole("Foo.txt"))
{
  Console.WriteLine("Moo");

  using (new DynamicConsole("Bar.txt"))
  {
    Console.WriteLine("Ork");
  }

  Console.WriteLine("Bar");
}

Console.WriteLine("Real 2");

When running you get the following:

This will print to the Console:

Real 1
Real 2

It will append to Foo.txt:

Moo
Bar

It will append to Bar.txt:

Ork

I will update the code later to make it generic, so any property, method or field can be used for the dynamic binding. Stay tuned!

Update:

Posted an article on CodeProject last Friday. This is a generic implementation: Dynamic binding in C#

See http://forum.unity3d.com/threads/76266-Facilities-for-script-languages-Scheme-in-particular for details. You can also view the initial discussion @ http://ironscheme.codeplex.com/Thread/View.aspx?ThreadId=243958.

Thanks a lot!

beginning nov: call MTN regarding the availability of advertised phone (HTC Desire HD), no stock
22 nov: eligible for upgrade, MTN says still no stock
30 nov: get call from MTN to say phone is now in stock, proceed upgrade process
2 dec: receive phone (very fast courier service)
2-5 dec: phone has a random reboot problem
6-10 dec: reboot problem stops
11-13 dec: reboot problem comes back
13 dec: report fault with MTNSP and Leaf/HTC (HTC confirms it is a known problem affecting a few phones)
13 dec: phone service get suspended due to account going over R1000, yet the account was only R635, had to increase limit to get activated again
15 dec: took phone into shop (Capegate A, James), said I needed the papers to make repair process go faster
15 dec: went home to fetch papers, tried to book in phone (Capegate A), at last minute MTN system goes offline
15 dec: go to the other shop (Capegate B, Dominique) to do a manual check in for repairs, assistant says she will tell her manager to prioritize it
23 dec: call MTN high volume repair centre for update on repairs, they say they have not received it
23 dec: go back to MTN shop (Capegate B), phone still in the shop, take phone back with me due to lack of service
29 dec: call MTN to discuss service issues, advised to go to MTN service centre in Century City
29 dec: book in phone at MTN service centre (Century City, Sakeena/Francisco), system offline again (MTN TFR# 020149)
31 dec: I changed my bank details when doing the upgrade, yet the money was taken from previous account details
3 jan: called MTN to change banking details, they confirm the change
3 jan: call MTN high volume repair centre for update on repairs, phone has not been booked in yet
3 jan: call MTN service centre (Century City) to find out what is happening, number forwards to 808, no info available
3 jan: called same number again (Century City), got through to someone (Cheryl, the switchboard operator) that says I cannot contact Century City directly, they have open an enquiry for the location of my phone
3 jan: reported to hellopeter out of desperation http://www.hellopeter.com/mtn-complaint-[505188]
3 jan: MTN responded on hellopeter.com with a generic remark which is hardly relevant
3 jan: Cannot contact MTN service centre (Century City), due to broken number (17:15, 17:30, 17:45)
3 jan: Sent this shittogram to the only 2 email addresses advertised for MTN
4 jan: Try call MTN service centre (Century City) again, again Cheryl answers and let me know she will try get someone to contact me
4 jan: Cheryl calls me back to let me know she has reached Sakeena at the service centre and will be in contact with me
4 jan: Sakeena calls me back, and informs me Francisco has taken over the issue, but he is not at work today, but she will ask him to contact me the following day
4 jan: Received feedback on email to confirm my banking details are in order, and my issue has been forwarded to the complaints department
6 jan: Gave feedback on hellopeter
6 jan: Contacted MTN HV repair centre, they confirm the phone has been sent to HTC, and should be back on Monday or Tuesday
10 jan: Called MTN HV repair centre, no further feedback available
10 jan: Called HTC, they can’t confirm receipt of phone, escalating issue, promised to call me back
11 jan: Called MTN HV repair centre (Thepo), apparently phone has been returned to cape town, but no repair actions were logged, waiting for feedback
11 jan: Thepo called, confirmed phone is at HTC, will be ready before end of the week
11 jan: Called HTC (Chris), informed them I wanted to make sure they find the fault, and not just reload the software. Chris informed me the issue will be escalated to his supervisor, and that they will be in contact with me
13 jan: Called MTN HV repair centre (Nolene), phone still at HTC, no further feedback
17 jan: Called MTN HV repair centre (Thepo), phone still at HTC, ‘should’ be back to MTN today
18 jan: Called MTN HV repair centre (Mpho), phone still at HTC, awaiting couriers to MTN
18 jan: Called HTC support (James) to try get a repair report, was told I will get it when collecting the phone
19 jan: Called MTN HV repair centre (Helen), phone was collected from HTC by RTT (assume this is the couriers), not at MTN HVRC yet
20 jan: Phoned everyone from MTN HVRC in JHB and CPT, called LEAF and RTT. The phone is being sent overnite to the CPT HVRC (confirmed by RTT) and that will take several working days before being sent to MTN Century City… Estimate around 25 jan.
25 jan: Expecting to get phone back today
25 jan: Been in contact with MTN HVRC Cape Town manager (Kevin) who confirmed the phone will be at MTN Century City after 1pm. Informed me that Leaf/HTC did not include a job card with the phone.
25 jan: Contacted HTC support (Chris), have no information about phone repairs
25 jan: Contacted Leaf Repairs, they tell me the software was updated and no other repairs was done… Spoke to Amit to explain the situation, demanding a replacement phone before the end of the week. He cannot make that decision and told me that the manager (Zach) will contact me tomorrow.
25 jan: Collected the phone at MTN Century City, spoke with Kevin and Noleen about my problems. While there, the phone rebooted 3 times, witnessed by Kevin. There was a repair report from LEAF stating only software was reloaded. Seems no other work was done.
25 jan: Tested a spare backup battery to eliminate the possibility of a faulty battery, but had a reboot within 2 hours after a full charge

25 jan: Still waiting for my phone call from Francisco/feedback regarding complaint from MTN, waiting on feedback from HTC (HTC said a repair report will be attached to the phone, never did get back to me…) and waiting for HTC to contact me on or before Friday.

27 jan: Contacted LEAF’s technical manager to discuss problems. They arranged for ‘express’ repair service. Told them they had to replace the mainboard (as was done with others in my situation).
28 jan: Courier collected phone.
1 feb: LEAF contacts me to inform overnight courier. Phone ‘will’ be back tomorrow.
2 feb: Courier delivered the phone this morning with a new mainboard. Will be testing today. Finally after 42 days, I hope I can lay this fiasco to rest.

10 feb: All going well still. No hardware problems.

On 2 Feb, total time phone been @ MTN/HTC = 42 days, @ me = 20 days since receiving the phone. That sucks…

Finally, I have an idea where me phone is, not too happy still, but less stressed. Tomorrow I will see if the phone has actually reached the HV repair centre.

I must say Cheryl, the switchboard operator for MTN (Century City) has been by far the kindest and most helpful person in this whole fiasco. Someone make her a manager or give her a raise/bonus, she deserves it. Sakeena has also tried to help. The MTN HVRC (Cape Town) manager, Kevin has been extremely helpful too in tracking down my phone.

Also, the IronScheme source code is now under a BSD license. The DLR goodies stays on MSPL however, as moving it to the new Apache license DLR would be too much effort. Now for the rest of the post.

So the general feeling is that most ‘dynamic’ languages are pretty poor with number crunching. This is true, as code is mostly generic and have no static typing. The same goes for IronScheme, but you can make code (read hotspots) behave much better with only a little extra effort.

Let’s take the naive Fibonacci algorithm to use for this example.

(define (fib n)
  (if (< n 2)
      n
      (+ (fib (- n 2)) (fib (- n 1)))))

The main problem here is the usage of generic math operators. They are generally slow, as they cover the entire number hierarchy of Scheme. This can be improved by using the fixnum specific procedures.

(define fibf (lambda (n)
  (if (fx<? n 2)
      n
      (fx+ (fibf (fx- n 1)) (fibf (fx- n 2))))))

While the above run significantly faster (about 5 times faster), there is still quite a bit of overhead due to boxing of value types, and overflow checks. This can now be improved by using a statically typed variant of lambda called typed-lambda, and by using some ‘unsafe’ operators provided by IronScheme.

(define fibt (typed-lambda (n) ((Int32) Int32)
  (if ($fx<? n 2)
      n
      ($fx+ (fibt ($fx- n 1)) (fibt ($fx- n 2))))))

The above only requires minor changes again, that could be easily made transparent with a macro or 2. The result is a very fast procedure that runs optimally on .NET (when compared to the same code generated by the C# compiler). My tests show it running almost 13 times faster than the fixnum version and subsequently around 60 times faster than the original generic approach.

Here are timings for all of the above:

isc fibs.sps
Statistics for '(fib 35)':
  Real Time:  8357ms
  CPU Time:   8344ms
  User Time:  8344ms
  GC's:       0
Statistics for '(fibf 35)':
  Real Time:  1826ms
  CPU Time:   1828ms
  User Time:  1828ms
  GC's:       0
Statistics for '(fibt 35)':
  Real Time:  147ms
  CPU Time:   141ms
  User Time:  141ms
  GC's:       0 

Update:

On the same PC, IronPython 2.6 takes 3150ms for a naive fib.

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A question came up how StackOverflow, blah.

I have heard about this behaviour being valid in C++, so I thought I would test it on the CLR.

.class Program
{
  .method static void  Main(string[] args)
  {
    .entrypoint
    .locals init ([0] class Program p)
    ldloc.0 // but wait, it's still null!
    call   instance void Program::Awesome()
    ret
  } 

  .method instance void Awesome()
  {
    ldstr      "Awesome!"
    call       void [mscorlib]System.Console::WriteLine(string)
    ret
  } 

  .method public specialname rtspecialname instance void  .ctor()
  {
    ldarg.0
    call       instance void [mscorlib]System.Object::.ctor()
    ret
  }
}

As you can see if you compile the program, “Awesome!” is printed.

Now run PEVerify. As you can see, perfect valid CLR code.

But how? And why wont in work in C#?

The C# compiler will in all cases (even weirdly, but probably for good reason) emit a callvirt instead of the call I used. This causes the runtime to perform a null check.

Secondly, the is no instance member access, so no references to ‘this’ need to be made.

Why is this like this? Not sure, but if I would guess, they left this specification loose, to allow for more flexibility in other languages.