Programming With Delphi

[Tinisha]

Delphiis a general-purpose programming language and a software product that uses the Delphi dialect of the Object Pascal programming language and provides an integrated development environment (IDE) for rapid application development of desktop, mobile, web, and console software,[3] currently developed and maintained by Embarcadero Technologies.

Delphi includes a code editor, a visual designer, an integrated debugger, a source code control component, and support for third-party plugins. The code editor features Code Insight (code completion), Error Insight (real-time error-checking), and refactoring. The visual forms designer has the option of using either the Visual Component Library (VCL) for pure Windows development or the FireMonkey (FMX) framework for cross-platform development. Database support is a key feature and is provided by FireDAC (Database Access Components). Delphi is known for its fast compilation speed, native code, and developer productivity.[citation needed]

Delphi was originally developed by Borland as a rapid application development tool for Windows as the successor of Turbo Pascal. Delphi added full object-oriented programming to the existing language, and the language has grown to support generics, anonymous methods, closures, and native Component Object Model (COM) support.

Delphi and its C++ counterpart, C++Builder, are interoperable and jointly sold under the name RAD Studio. There are Professional, Enterprise, and Architect editions, with the higher editions having more features at a higher price. There is also a free-of-charge Community edition, with most of the features of Professional, but restricted to users and companies with low revenue.[7]

Delphi uses the Pascal-based programming language Object Pascal created by Anders Hejlsberg for Borland (now IDERA) as the successor to Turbo Pascal. It supports native cross-compilation to many platforms including Windows, Linux, iOS and Android.

To better support development for Microsoft Windows and interoperate with code developed with other software development tools, Delphi supports independent interfaces of Component Object Model (COM) with reference counted class implementations, and support for many third-party components. Interface implementations can be delegated to fields or properties of classes. Message handlers are implemented by tagging a method of a class with the integer constant of the message to handle.[citation needed]

Delphi uses a strongly typed high-level programming language, intended to be easy to use and originally based on the earlier Object Pascal language. Pascal was originally developed as a general-purpose language "suitable for expressing the fundamental constructs known at the time in a concise and logical way", and "its implementation was to be efficient and competitive with existing FORTRAN compilers"[8] but without low-level programming facilities or access to hardware. Turbo Pascal and its descendants, including Delphi, support access to hardware and low-level programming, with the facility to incorporate code written in assembly language and other languages. Delphi's object orientation features only class- and interface-based polymorphism.[9] Metaclasses are first class objects. Objects are references to the objects (as in Java), which Delphi implicitly de-references, so there is usually no need to manually allocate memory for pointers to objects or use similar techniques that some other languages need. There are dedicated reference-counted string types, and also null-terminated strings.

Strings can be concatenated by using the '+' operator, rather than using functions. For dedicated string types, Delphi handles memory management without programmer intervention. Since Borland Developer Studio 2006, there are functions to locate memory leaks.

Delphi includes an integrated IDE. The Delphi products all ship with a run-time library (RTL) and a Visual Component Library (VCL), including most of its source code. Third-party components (sometimes with full source code) and tools to enhance the IDE or for other Delphi related development tasks are available, some free of charge. The IDE includes a GUI for localization and translation of created programs that may be deployed to a translator; there are also third-party tools with more features for this purpose. The VCL framework maintains a high level of source compatibility between versions, which simplifies updating existing source code to a newer Delphi version. Third-party libraries typically need updates from the vendor but, if source code is supplied, recompilation with the newer version may be sufficient. The VCL was an early adopter of dependency injection or inversion of control; it uses a reusable component model, extensible by the developer. With class helpers, new functionality can be introduced to core RTL and VCL classes without changing the original source code of the RTL or VCL.

The compiler is optimizing and is a single-pass compiler. It can optionally compile to a single executable which does not require DLLs. Delphi can also generate standard DLLs, ActiveX DLLs, COM automation servers and Windows services.

The Delphi IDEs since Delphi 2005 increasingly support refactoring features such as method extraction and the possibility to create UML models from the source code or to modify the source through changes made in the model.

Delphi is one of the languages where backward compatibility is close to 100%. Although each new release of Delphi attempts to keep as much backward compatibility as possible to allow existing code reuse, new features, new libraries, and improvements sometimes make newer releases less than 100% backward compatible.

Embarcadero publishes "roadmaps" describing their future development plans. The most recent one was published in November 2020.[12] Version 10.5 referred to in the November 2020 roadmap was renamed 11.0.

The Indy components seem entirely synchronous. On the other hand, while ScktComp unit does use WSAAsyncSelect, it basically only asynchronizes a BSD-style multiplexed socket app. You get dumped in a single event callback, as if you had just returned from select() in a loop, and have to do all the state machine navigation yourself.

The .NET situation is considerably nicer, with Socket.BeginRead / Socket.EndRead, where the continuation is passed directly to Socket.BeginRead, and that's where you pick back up. A continuation coded as a closure obviously has all the context you need, and more.

@Roddy - Synchronous sockets are not what I'm after. Burning a whole thread for the sake of a possibly long-lived connection means you limit the amount of concurrent connections to the number of threads that your process can contain. Since threads use a lot of resources - reserved stack address space, committed stack memory, and kernel transitions for context switches - they do not scale when you need to support hundreds of connections, much less thousands or more.

I have found that Indy, while a simpler concept in the beginning, is awkward to manage due to the need to kill sockets to free threads at application termination. In addition, I had the Indy library stop working after an OS patch upgrade. ScktComp works well for my application.

Some of the things that don't necessarily jump out from Paul's presentation, however, are that he specified -Xss:48k to the JVM on startup, and that he's assuming that the JVM's NIO implementation is efficient in order for it to be a valid comparison.

Indy does not specify a similarly shrunken and tightly constrained stack size. There are no calls to BeginThread (the Delphi RTL thread creation routine, which you should use for such situations) or CreateThread (the raw WinAPI call) in the Indy codebase.

The default stack size is stored in the PE, and for the Delphi compiler it defaults to 1MB of reserved address space (space is committed page by page by the OS in 4K chunks; in fact, the compiler needs to generate code to touch pages if there are >4K of locals in a function, because the extension is controlled by page faults, but only for the lowest (guard) page in the stack). That means you're going to run out of address space after max 2,000 concurrent threads handling connections.

Now, you can change the default stack size in the PE using the $M minStackSize [,maxStackSize] directive, but that will affect all threads, including the main thread. I hope you don't do much recursion, because 48K or (similar) isn't a lot of space.

Now, whether Paul is right about non-performance of async I/O for Windows in particular, I'm not 100% sure - I'd have to measure it to be certain. What I do know, however, is that arguments about threaded programming being easier than async event-based programming, are presenting a false dichotomy.

Async code doesn't need to be event-based; it can be continuation-based, like it is in .NET, and if you specify a closure as your continuation, you get state maintained for you for free. Moreover, conversion from linear thread-style code to continuation-passing-style async code can be made mechanical by a compiler (CPS transform is mechanical), so there need be no cost in code clarity either.

Well, Indy has been the 'standard' library for socket I/O for a long while now - and it's based on blocking sockets. This means if you want asynchronous behaviour, you use additional thread(s) to connect/read/write data. To my mind this is actually a major advantage, as there's no need to manage any kind of state machine navigation, or worry about callback procs or similar stuff. I find the logic of my 'reading' thread is less cluttered and much more portable than non-blocking sockets would allow.

This made go "huh?" until I remembered our threading library uses an exception-based technique to kill 'waiting' threads safely. We call QueueUserAPC to queue a function which raises a C++ exception (NOT derived from class Exception) which should only be caught by our thread wrapper procedure. All destructors get called so the threads all terminate cleanly and tidy up on the way out.

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