In our project we're generating a lot of xml files, which are subjects of manual changes, and repeated generations (often with slightly different generation options). This way a life flow of such an xml can be described as following:

1. generate original xml (version 1)
2. manual changes (version 2)
3. next generation (version 3)
4. manual changes integrated into the new generation (version 4)

If it were a regular text files we could use diff utility to prepare patch between versions 1 and 2, and apply it with patch utility to a version 3. Unfortunately xml has additional semantics compared to a plain text. What's an invariant or a simple modification in xml is often a drastic change in text. diff/patch does not work well for us. We need xml diff and patch.

The first guess is to google it! Not so simple. We have failed to find a tool or an API that can be used from ant. There are a lot of GUIs to show xml differences and to perform manual merge, or doing similar but different things to what we need (like MS's xmldiffpatch).

Please point us to such a program!

Meantime, we need to proceed. We don't believe that such a tool can be done on the knees, as it's a heuristical and mathematical at the same time task requiring a careful design and good statistics for the use cases. Our idea is to exploit diff/patch. To achieve the goals we're going to perform some normalization of xmls before diff to remove redundant invariants, and normalization after the patch to return it into a readable form. This includes:

• ordering attributes by their names;
• replacing unsignificant whitespaces with line breaks;
• entering line breaks after element names and before attributes, after attribute name and before it's value, and after an attribute value.

This way we expect to recieve files reacting to modifications similarly to text files.

Ladies and gentlemen of the jury, exhibit number one is what the seraphs, the misinformed, simple, noble-winged seraphs, envied. Look at this the most ancient program:

See origin

At present C# serializer knows how to print comments and do some formatting (we had to create micro xml serializer within xslt to serialize xml comments). C#'s formatting is not as advanced as java's one, but it should not be such in the first place, as C# text tends to be more neat due to properties and events. Compare:

Java: instance.getItems().get(10).setValue(value);

vs

C#: instance.Items[10].Value = value;

TODO: implement API existing in jxom and missing in C# xom. This includes:

• name normalization - rewriting tree to make names unique (duplicate names are often appear during generation from code templates);
• namespaces normalization - rewriting tree to elevate type namespaces (during generation, types are usually fully qualified);
• unreachable code detection - optional feature (in java it's required, as unreachable code is an error, while in C# it's only a warning);
• compile time expression evaluation - optional feature used in code optimization and in reachability checks;
• state machine refactoring - not sure, as C# has yield statement that does the similar thing.

Update can be found at: jxom/C# xom.

June, 24 update: name and namespace normalizations are implemented.

Writing a language serializer is an as easy task, as riding a bicycle. Once you learned it, you won't apply a mental force anymore to create a new one.

This still requires essential mechanical efforts to write and test things.

Well, this is the first draft of the C# xslt serializer. Archive contains both C# xom and jxom.

Note: no comments are still supported; nothing is done to format code except line wrapping.

Today an old book was extracted by my son on the light of God. The book was immediatly opened on this verse:

Any trifle can become
a main business of your life.
You just need be a firmly believed
that there is nothing more important that can be achieved.
And then nothing won't prevent you gasp out from delight to engage with this nonsense.

Unfortunatelly too often these facetious verses of Gregory Oster becoming a true.

I've read a popular scientific stuff about DNA, RNA, proteins, cells, prokaryotes and eukaryotes their structures, roles, operational principles, evolution.

All the computer technologies and robotics seem like a childish babbling comparing to microbiology and molecular biology.

I would wish to be so open minded, and have so capable brain with infinite work capacity (and live so long life ) to push, to break through the borders of knowledge of the humanity.

Ah, I envy to the Renaissance people who were capble to hold and drive the science and art, this contrasts so much with contemporary specializations.

Well, it's jxom no more but also csharpxom!

A project concerns demanded us to create a C# 3.0 xml schema.

Shortly we expect to create an xslt serializing an xml document in this schema into a text. Thankfully to the original design we can reuse java streamer almost without changes.

A fact: C# schema more than twice bigger than the java's.

Today, I've found a C++0x FAQ by Bjarne Stroustrup reviewing most of the new features that we shall see in the next version.

A good insight for those who don't track the WG progress.

But what attracts me is a passage:

Sounds rather pessimistic to my taste.

There is a nice ServiceLoader API in java 6 implementing a service provider idiom. It's good (good because it's standard) class resolving interface implementation using META-INF/service location.

Unfortunately, there is even no JSR implementation for this class in java 5. This makes it impossible for us to use it.

What a nuisance!

Yesterday, we've found an article "Repackaging Saxon". It's about a decision to go away from Saxon-B/Saxon-SA packaging to a more conventional product line: Home/Professional/Enterprise Editions.

The good news are that the Saxon stays open source. That's most important as an open comunity spirit will be preserved. On the other hand Professional and Enterprise Editions will not be free.

In this regard the most interesting comments are:

John Cowan> I suspect that providing packaging only for $$ (or pounds or euros) won't actually work, because someone else will step in and provide that packaging for free, as the licensing permits.

and response:

Michael Kay> This will be interesting to see. I'm relying partly on the idea that there's a fair degree of trust, and expectation of support, associated with Saxonica's reputation, and that the people who are risking their business on the product might be hesitant to rely on third parties, who won't necessarily be prompt in issuing maintenance releases etc; at the same time, such third parties may serve the needs of the hobbyists who are the real market for the open source version.

and also:

Michael Kay> ...I haven't been able to make a model based on paid services plus free software work for me. It's hard enough to get the services business; when you do get it, it's hard to get enough revenue from it to fund the time spent on developing and supporting the software. Personally, I think the culture of free software has gone too far, and it is now leading to a lack of investment in new software...

Today we have seen an article: "The Death of XSLT in Web Frameworks". Who wants, please read.

Both Arthur's and mine reactions were equal...

Fabula of the article: I never read Pasternak but I disapprove him.

Background idea: What's not being hyped is dead.

See also: Web Application Frameworks.

Sunny> Look what have I found! Consider a C#:

public class T
{
  public T free;
}

public void NewTest()
{
  T cache = new T();

  Stopwatch timer = new Stopwatch();

  timer.Reset();
  timer.Start();

  for(int i = 0; i < 10000000; ++i)
  {
    // Get from cache.
    T t;

    if (cache.free == null)
    {
      cache.free = new T();
    }

    t = cache.free;

    // Release
    cache.free = t;
    t = null;
  }

  timer.Stop();

  long cacheTicks = timer.ElapsedTicks;

  timer.Reset();
  timer.Start();

  for(int i = 0; i < 10000000; ++i)
  {
    new T();
  }

  timer.Stop();

  long newTicks = timer.ElapsedTicks;

  Console.WriteLine("cache: {0}, new: {1}", cacheTicks, newTicks);
}

Gloomy> And?

Sunny> Tests show that new T() is almost as fast as caching! GC's "new" probably has a fast route, where it shifts free memory border in an atomic way, thus allocation takes just several cycles.

Gloomy> Well, you're probably right, there is a fast route. I, however, have a different opinion. To track references, a generational garbage collector implements field assign as a call rather than a mov. This routine, except move itself, marks touched memory page in a special card table (who said GC is cheap?); thus, I think, a reference field setter is almost as slow as the "new" call.

.Net is known for its array covariance. That means that any array can be cast to an array of base elements:

public class T: B
{
}

T[] tlist = ...
B[] blist = tlist;

This feature comes at cost:

B b = ...
T t = ...

blist[0] = b; // This efficiently is: blist[0] = (T)b;
tlist[0] = t; // This is the same: tlist[0] = (T)t;

We pay the cost of additional cast, just for nothing. Let this dubious design decision opresses .Net/Java inventors.

You can eliminate the cast. Just use array of structs:

struct S<T>
{
  public T t;
}

S<T>[] slist = ...

slist[0].t = t; // Works without cast.

Measurment show that S[] is ~35% faster than T[] on write, and slower (JIT could do better) on read.

Well, ugly workaround of ugly design.

P.S. In java there is no relief...

This happens in .NET Framework 3.5, 32 bit, VS 2008.

C#:

namespace NesterovskyBros.Test
{

  using Microsoft.VisualStudio.TestTools.UnitTesting;

  [TestClass]
  public class CharAtUnitTest
  {
    private TestContext testContextInstance;

    public TestContext TestContext
    {
      get { return testContextInstance; }
      set { testContextInstance = value; }
    }

    [TestMethod]
    public void CharAtTest()
    {
      this.text = "1";

      string token = Read(1, false);

      TestContext.WriteLine("token: {0}", token);
    }

    private string Read(int offset, bool flag)
    {
      string token = null;
      int c = 0;

      if (flag)
      {
        goto Whitespace;
      }

    Scan:
      c = CharAt(offset);

      switch(c)
      {
        case -1:
        {
          return "<Eof>";
        }
        case '\'':
        {
          token = "Literal";

          goto Literal;
        }
      }

    Whitespace:
      if (c == ' ')
      {
        return "Space";
      }

      return "Unknown";

    Literal:
      while(true)
      {
        int d = CharAt(offset);

        if (token != "Literal")
        {
          goto Scan;
        }

        if (d == c)
        {
          return token;
        }
      }
    }

    string text;

    private int CharAt(int offset)
    {
      string text = this.text;

      return (uint)offset >= (uint)text.Length ? -1 : text[offset];
    }
  }
}

In debug mode this test prints: "token: <Eof>". In release - "token: Unknown". The bug is so fragile that even slightest change in code removes it. Looking into disassembly we can see that the problem is near the switch:

    Scan:
      c = CharAt(offset); /* Our old friend, CharAt(). Inlined! */
00000017 mov edx,dword ptr [edi+8]
0000001a cmp dword ptr [edx+8],esi
0000001d jbe 00000032
0000001f cmp esi,dword ptr [edx+8]
00000022 jae 000000CE
00000028 movzx eax,word ptr [edx+esi*2+0Ch]
0000002d mov dword ptr [ebp-10h],eax
00000030 jmp 00000039
00000032 mov dword ptr [ebp-10h],0FFFFFFFFh /* Move -1 (four bytes) into stack. */
00000039 movzx edx,word ptr [ebp-10h] /* Get two bytes into edx (0FFFFh) */

      switch(c)
0000003d cmp edx,0FFFFFFFFh /* Never true. */
00000040 je 0000004A
00000042 cmp dword ptr [ebp-10h],27h
00000046 je 0000005A
00000048 jmp 00000062
      {
        case -1:
        {
          return "<Eof>";
0000004a mov eax,dword ptr ds:[022EDE68h]
00000050 lea esp,[ebp-0Ch]
00000053 pop ebx
00000054 pop esi
00000055 pop edi
00000056 pop ebp
00000057 ret 4

This looks like a tremendous bug, like one of those shaking belief in computer's infallibility.

It would be nice if you would verify the case on your computer.