Synopse Open Source

2011-12-08

Avoiding Garbage Collector: Delphi and Apple side by side

By AB4327-GANDI, 2011-12-08. Pascal Programming

Among all trolling subject in forums, you'll find out the great Garbage Collection theme.

Fashion languages rely on it. At the core of the .Net and Java framework, and all scripting languages (like JavaScript, Perl, Python or Ruby), you'll find a Garbage Collector. New developers, just released from schools, do learn about handling memory only in theory, and just can't understand how is memory allocated - we all have seen such rookies involved in Delphi code maintenance, leaking memory as much as they type. In fact, most of them did not understood how a computer works. I warned you this will be a trolling subject.

And, in Delphi, there is no such collector. We handle memory in several ways:

Creating static variables - e.g. on the stack, inside a class or globally;
Creating objects with class instances allocated on heap - in at least three ways: with a try..finally Free block, with a TComponent ownership model in the VCL, or by using an interface (which creates an hidden try..finally Free block);
Creating reference-counted variables, i.e. string, array of, interface or variant kind of variables.

It is a bit complex, but it is also deadly powerful. You have several memory allocation models at hand, which can be very handy if you want to tune your performance and let program scale. Just like manual recycling at home will save the planet. Some programmers will tell you that it's a waste of cell brain, typing and time. Linux kernel gurus would not say so, I'm afraid.

Then came the big Apple company, which presented its new ARC model (introduced in Mac OS X 10.7 Lion) as a huge benefit for Objective-C in comparison with the Garbage Collection model. And let's face it: this ARC just sounds like the Delphi memory model.

2011-12-06

Automatic JOIN query

By AB4327-GANDI, 2011-12-06. Open Source › mORMot Framework

In mORMot, all the methods available to handle many-to-many relationship (ManySelect, DestGetJoined...) are used to retrieve the relations between tables from the pivot table point of view. This saves bandwidth, and can be used in most simple cases, but it is not the only way to perform requests on many-to-many relationships. And you may have several TSQLRecordMany instances in the same main record - in this case, those methods won't help you.

It is very common, in the SQL world, to create a JOINed request at the main "Source" table level, and combine records from two or more tables in a database. It creates a set that can be saved as a table or used as is. A JOIN is a means for combining fields from two or more tables by using values common to each. Writing such JOINed statements is not so easy by hand, especially because you'll have to work with several tables, and have to specify the exact fields to be retrieved; if you have several pivot tables, it may start to be a nightmare.

Let's see how our ORM will handle it.

2011-12-04

Total Commander 64 bit is using... Lazarus and FPC

By AB4327-GANDI, 2011-12-04. Pascal Programming

I'm a long-time registered user of Total Commander.

This tool is my daily file manager. I never use Windows Explorer, since Total Commander is just faster, more easy to use (especially with the keyboard), has a lot of plug-ins. I even created my own plug-ins to access some custom file formats, and navigate into them just like with any folder. And it includes a lot of well written commands for FTP access or file comparison, which made other tools (like WinMerge) unnecessary.

There is a new beta version of Total Commander available, which targets Windows 64 bit. I just thought: 'Whoo, this is a real-world Delphi XE2 64 application'. I downloaded and tried it. Worked as expected, and integrates seamlessly with Windows Seven (for the shell extensions). Then I took a look at the executable... and discovered it was not compiled with Delphi XE2... but with FPC !

2011-11-30

AJAX authentication

By AB4327-GANDI, 2011-11-30. Open Source › mORMot Framework

A nice framework user, named esmondb, did write and publish some JavaScript code to handle our RESTful authentication mechanism.

It seems to work well, and implements all secure hashing and challenging.
Our authentication mechanism is much more advanced than the one used by DataSnap - which is a basic HTTP authentication with the password transmitted in clear (this is the reason why it shall better be used over HTTPS, whereas mORMot can be used over plain HTTP).
Resulting JavaScript code seems not difficult to follow, even for a no JS expert like me.

2011-11-27

SOLID design principles

By AB4327-GANDI, 2011-11-27. Pascal Programming

Delphi is sometimes assimilated to a RAD product - and this is a marketing label - but IMHO Delphi is much more than RAD.
With Delphi, you can make very serious and clean programming.

Including SOLID style of coding.

The acronym SOLID is derived from the following OOP principles (quoted from the corresponding Wikipedia article):

Single responsibility principle: the notion that an object should have only a single responsibility;
Open/closed principle: the notion that “software entities ... should be open for extension, but closed for modification”;
Liskov substitution principle: the notion that “objects in a program should be replaceable with instances of their subtypes without altering the correctness of that program” - also named as "design by contract";
Interface segregation principle: the notion that “many client specific interfaces are better than one general purpose interface.”;
Dependency inversion principle: the notion that one should “Depend upon Abstractions. Do not depend upon concretions.”. Dependency injection is one method of following this principle.

If you have some programming skills, those principles are general statements you may already found out by yourself. If you start doing serious object-oriented coding, those principles are best-practice guidelines you would gain following.

They certainly help to fight the three main code weaknesses:

Rigidity – Hard to change something because every change affects too many other parts of the system;
Fragility – When you make a change, unexpected parts of the system break;
Immobility – Hard to reuse in another application because it cannot be disentangled from the current application.

Modification of TSQLRestServerCallBack method prototype

By AB4327-GANDI, 2011-11-27. Open Source › mORMot Framework

In order to implement some RESTful Services, a callback has to be defined on the server side.

The prototype of these method has been modified, to supply an additional aSession: cardinal parameter: this is a CODE BREAK change and you shall refresh ALL your server-side code to match the new signature.

2011-11-23

Does speed matters?

By AB4327-GANDI, 2011-11-23. Pascal Programming

Luigi Sandon wrote on Embarcadero's forum:

And then you ask yourself: "why use a native compiler if its code may be even slower than jitted one?". Hope the new developers will also develop better and faster code - and not viceversa.

Embarcadero is just following the Wirth's law slower than others:

"Software is getting slower more rapidly than hardware becomes faster"

Speed is only a matter of compiler for mathematical computing intensive tasks.
Most of the time, in real apps (like business apps), the main speed issue is more the framework size (and the number of dll invoked), memory consumption, and general design (e.g. how caching and SQL are written).

Delphi, Java or .Net can do slow apps.
Delphi, Java or .Net can do fast apps.

You can do small and fast stand-alone apps with Delphi, running from Windows 2000 to Windows 8.
It is not possible with Java nor .Net.

This is the main difference IMHO with native code and JIT - about memory use, ease of distribution and no need of an external runtime framework.

2011-11-08

Currency is your friend

By AB4327-GANDI, 2011-11-08. Pascal Programming

The currency type is the standard Delphi type to be used when storing and handling monetary values. It will avoid any rounding problems, with 4 decimals precision. It is able to safely store numbers in the range -922337203685477.5808 .. 922337203685477.5807. Should be enough for your pocket change.

As stated by the official Delphi documentation:

Currency is a fixed-point data type that minimizes rounding errors in monetary calculations. On the Win32 platform, it is stored as a scaled 64-bit integer with the four least significant digits implicitly representing decimal places. When mixed with other real types in assignments and expressions, Currency values are automatically divided or multiplied by 10000.

In fact, this type matches the corresponding OLE and .Net implementation of currency, and the one used by most database providers (when it comes to money, a dedicated type is worth the cost in a "rich man's world"). It is still implemented the same in the Win64 platform (since XE 2). The Int64 binary representation of the currency type (i.e. value*10000 as accessible via PInt64(aCurrencyValue)^) is a safe and fast implementation pattern.

In our framework, we tried to avoid any unnecessary conversion to float values when dealing with currency values. Some dedicated functions have been implemented for fast and secure access to currency published properties via RTTI, especially when converting values to or from JSON text. Using the Int64 binary representation can be not only faster, but also safer: you will avoid any rounding problem which may be introduced by the conversion to a float type. Rounding issues are a nightmare to track - it sounds safe to have a framework handling natively a currency type from the ground up.