[fpc-devel] Discussion about "Dynamic packages"

[Michael Van Canneyt]

On Wed, 12 Apr 2017, Bishop via fpc-devel wrote:

> I had some fears concerning idea development of "Dynamic packages" in FreePascal and possible performance penalties of programs from these changes. This why i
> start this discussion and try wrote some of my ideas or/and proposal that, as i think, can help make FreePascal better.
> 
> At first I would like to designate a circle of tasks which in principle can effectively decide by means of system of dynamic packets. Lets remember for what
> DLL`s and SO`s was be created. It was for memory saving (by sharing code and static conts parts from many applications in memory). Now there is so many memory
> even on phones, that this almoust have no sence (its still work for things like LibC, ZLib and so.). But this kind of libraries better make with C-style
> interface (or use COM/CORBA interfaces like in DirectX if it`s realy needed). Yes, sometimes someone make libraries for C++ only, but it because of a dominant
> position of this language. Pascal didn`t have it. So, as i think, dynamic packages can be usefull only for something like plugin system in editors like 3Ds
> Max, Photoshop and etc. But Sven Bart wrote that "Package libraries can however only be used by a binary compiled with the same compiler as they rely on quite
> a bit of compiler magic.", so they be usefull only for projects that target to have plugins writed in pascal only. I try to say, that there is not so many
> situations that we realy need this system. I dont say that we dont need it at all, no. But disadvantages from this system must no effect on all other projects.
> This why i have some propositions.
> 
> Во время моего общения с Sven Barth он писал "With dynamic packages you can share classes, strings, memory, etc. between the modules (the main binary and the
> different package libraries)". Let's look at the most widespread operating systems. This will be Windows and Unix-family. In Windows every application starts
> from ntdll.dll and walk via kernel32.dll and only after that go to "main"-function in EXE file. So kernel32.dll always loaded. And its already have not bad
> memory manager (Process heap functions group). Why dont use it? It allow share memory with C code too (and strings with pascal code). Its already exist in
> application memory. In Linux if application use shared libraries it use libdl.so witch need libc.so. So we already have libc heap. As i know in FreeBSD and
> Solaris situation same.
> 
> And the second of my proposal it make dynamic packages like 2nd way in compiler (like it maked in MSVS where we can select link CRT staticaly or dunamicaly).
> Add some switch to compiler (and have 2 compiler variants of RTL, now we have this in RTL source with {$IFDEF FPC_3_0_0} macro) that will allow generate or not
> generate compiler magic for dynamic packages. They need in not so many cases, but all this indirect memory accesses make all applications slow (memory, first
> of all memory latency, in bottleneck of all today computers).

Dynamic Packages will in each case be optional, they will not be not mandatory.

Michael.