Difference between revisions of "Dynamically loading headers"
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dynlibs.pas | dynlibs.pas | ||
− | < | + | <syntaxhighlight lang=pascal> |
+ | type | ||
PLibHandler = ^TLibHandler; | PLibHandler = ^TLibHandler; | ||
Line 71: | Line 72: | ||
function LoadLibrarySymbols(const Lib: TLibHandle; const Symbols: PLibSymbol; const Count: Integer; | function LoadLibrarySymbols(const Lib: TLibHandle; const Symbols: PLibSymbol; const Count: Integer; | ||
const ErrorSym: PPLibSymbol = nil): Boolean; | const ErrorSym: PPLibSymbol = nil): Boolean; | ||
− | procedure ClearLibrarySymbols(const Symbols: PLibSymbol; const Count: Integer);</ | + | procedure ClearLibrarySymbols(const Symbols: PLibSymbol; const Count: Integer);</syntaxhighlight> |
=== Naming conventions === | === Naming conventions === | ||
Line 83: | Line 84: | ||
==== foobar.pas ==== | ==== foobar.pas ==== | ||
− | < | + | <syntaxhighlight lang=pascal> |
+ | unit foobar; | ||
{$i foobar.inc} | {$i foobar.inc} | ||
− | end.</ | + | end.</syntaxhighlight> |
==== foobardyn.pas ==== | ==== foobardyn.pas ==== | ||
− | < | + | <syntaxhighlight lang=pascal> |
+ | unit foobardyn; | ||
{$DEFINE LOAD_DYNAMICALLY} | {$DEFINE LOAD_DYNAMICALLY} | ||
{$i foobar.inc} | {$i foobar.inc} | ||
− | end.</ | + | end.</syntaxhighlight> |
==== foobar.inc ==== | ==== foobar.inc ==== | ||
− | < | + | <syntaxhighlight lang=pascal> |
+ | {$mode objfpc}{$H+} | ||
{$MACRO ON} | {$MACRO ON} | ||
// other possible compiler flags | // other possible compiler flags | ||
Line 180: | Line 184: | ||
FoobarLibrary := LibraryHandler('foobar', [foobarlib,foobarvlib, {moreversions} ], @foobar_symbols, | FoobarLibrary := LibraryHandler('foobar', [foobarlib,foobarvlib, {moreversions} ], @foobar_symbols, | ||
Length(foobar_symbols), @foobar_init, @foobar_end); | Length(foobar_symbols), @foobar_init, @foobar_end); | ||
− | {$ENDIF}</ | + | {$ENDIF}</syntaxhighlight> |
=== Usage === | === Usage === | ||
− | < | + | <syntaxhighlight lang=pascal> |
+ | program foobar_user; | ||
uses | uses | ||
Line 193: | Line 198: | ||
foobar_dosomething(2, 1.3); | foobar_dosomething(2, 1.3); | ||
ReleaseFoobar; | ReleaseFoobar; | ||
− | end.</ | + | end.</syntaxhighlight> |
=== Notes === | === Notes === | ||
Line 201: | Line 206: | ||
In Delphi 2010 they introduced "delayed" loading | In Delphi 2010 they introduced "delayed" loading | ||
− | < | + | <syntaxhighlight lang=pascal> |
+ | function GetFoobar: Integer; external 'foobar.dll' delayed;</syntaxhighlight> | ||
More Info: | More Info: |
Latest revision as of 07:14, 14 February 2020
Abstract
Currently, most library headers in fpc/packages support only static loading. Some exceptions are mysql, ibase, sqlite (and some other database headers). The idea is now to add dynamic loading support for other headers. This page should provide some place to list pro/contra, implementation details, etc...
Since dynamic loading is not supported by the compiler directly, it's required to define some framework, so that all headers are "implemented" in an uniform way and can be used easily.
Pro
- loading libraries at runtime for plugin support
Contra
- compatibility breaker (using dynamic loading is just an option, that should be choosen carefully)
- may produce strange errors, if wrong versions of libraries are loaded.
Suggestion w/o compiler modifications
Framework
dynlibs.pas
type
PLibHandler = ^TLibHandler;
TLibEventLoading = function(User: Pointer; Handler: PLibHandler): Boolean;
TLibEventUnloading = procedure(Handler: PLibHandler);
PPLibSymbol = ^PLibSymbol;
PLibSymbol = ^TLibSymbol;
TLibSymbol = record
pvar: PPointer; { pointer to Symbol variable }
name: String; { name of the Symbol }
weak: Boolean; { no error if this symbol don't exist }
end;
TLibHandler = record
InterfaceName: String; { abstract name of the library }
Defaults : array of String; { list of default library filenames }
Filename : String; { handle of the current loaded library }
Handle : TLibHandle; { filename of the current loaded library }
Loading : TLibEventLoading; { loading event, called after the unit is loaded }
Unloading : TLibEventUnloading; { unloading event, called before the unit is unloaded }
SymCount : Integer; { number of symbols }
Symbols : PLibSymbol; { symbol address- and namelist }
ErrorMsg : String; { last error message }
RefCount : Integer; { reference counter }
end;
{ handler definition }
function LibraryHandler(const InterfaceName: String; const DefaultLibraries: array of String;
const Symbols: PLibSymbol; const SymCount: Integer; const AfterLoading: TLibEventLoading = nil;
const BeforeUnloading: TLibEventUnloading = nil): TLibHandler;
{ initialization/finalization }
function TryInitializeLibrary(var Handler: TLibHandler; const LibraryNames: array of String;
const User: Pointer = nil; const NoSymbolErrors: Boolean = False): Integer;
function TryInitializeLibrary(var Handler: TLibHandler; const LibraryName: String = '';
const User: Pointer = nil; const NoSymbolErrors: Boolean = False): Integer;
function InitializeLibrary(var Handler: TLibHandler; const LibraryNames: array of String;
const User: Pointer = nil; const NoSymbolErrors: Boolean = False): Integer;
function InitializeLibrary(var Handler: TLibHandler; const LibraryName: String = '';
const User: Pointer = nil; const NoSymbolErrors: Boolean = False): Integer;
function ReleaseLibrary(var Handler: TLibHandler): Integer;
{ errors }
procedure AppendLibraryError(var Handler: TLibHandler; const Msg: String);
function GetLastLibraryError(var Handler: TLibHandler): String;
procedure RaiseLibraryException(var Handler: TLibHandler);
{ symbol load/clear }
function LoadLibrarySymbols(const Lib: TLibHandle; const Symbols: PLibSymbol; const Count: Integer;
const ErrorSym: PPLibSymbol = nil): Boolean;
procedure ClearLibrarySymbols(const Symbols: PLibSymbol; const Count: Integer);
Naming conventions
For the dynamic headers the suffix "dyn" is added
- static: foobar.pas
- dynamic: foobardyn.pas
Header implementation
foobar.pas
unit foobar;
{$i foobar.inc}
end.
foobardyn.pas
unit foobardyn;
{$DEFINE LOAD_DYNAMICALLY}
{$i foobar.inc}
end.
foobar.inc
{$mode objfpc}{$H+}
{$MACRO ON}
// other possible compiler flags
interface
uses
ctypes, dynlibs;
{$IFDEF UNIX}
{$DEFINE extdecl:=cdecl}
const
foobarlib = 'libfoobar.'+sharedsuffix;
foobarvlib = foobarlib+'.0.9.9';
{$ENDIF}
{$IFDEF WINDOWS}
{$DEFINE extdecl:=stdcall}
const
foobarlib = 'libfoobar.dll';
foobarvlib = foobarlib;
{$ENDIF}
{$IFDEF LOAD_DYNAMICALLY}
{$DEFINE D}
{$ELSE}
{$DEFINE S}
{$ENDIF}
// header stuff
{$IFDEF S}function{$ELSE}var{$ENDIF}foobar_dosomething{$IFDEF D}: function{$ENDIF}(a:cint; b:cdouble): cint; extdecl;{$IFDEF S}external foobarlib;{$ENDIF}
// more external functions
{$IFDEF LOAD_DYNAMICALLY}
function InitializeFoobar(const LibraryName: String = ''): Integer;
function TryInitializeFoobar(const LibraryName: string = ''): Integer;
function ReleaseFoobar: Integer;
var
FoobarLibrary: TLibHandler;
{$ENDIF LOAD_DYNAMICALLY}
implementation
{$IFDEF LOAD_DYNAMICALLY}
const
foobar_symbols: array[0..X] of TLibSymbol = (
(pvar:@foobar_dosomething; name:'foobar_dosomething'; weak:false),
// more external functions
);
function foobar_init(User: Pointer; Handler: PLibHandler): Boolean;
var
args: PMysqlArgs absolute User;
begin
// do some initialization calls
end;
procedure foobar_end(Handler: PLibHandler);
begin
// do some calls before library is unloaded
end;
function TryInitializeFoobar(const LibraryName: string): Integer;
begin
Result := TryInitializeLibrary(FoobarLibrary, LibraryName);
end;
function InitializeFoobar(const LibraryName: String): Integer;
begin
Result := InitializeLibrary(FoobarLibrary, LibraryName);
end;
function ReleaseFoobar: Integer;
begin
Result := ReleaseLibrary(FoobarLibrary);
end;
initialization
FoobarLibrary := LibraryHandler('foobar', [foobarlib,foobarvlib, {moreversions} ], @foobar_symbols,
Length(foobar_symbols), @foobar_init, @foobar_end);
{$ENDIF}
Usage
program foobar_user;
uses
foobardyn;
begin
InitializeFoobar; // if no paramter is submitted, the default library is loaded
foobar_dosomething(2, 1.3);
ReleaseFoobar;
end.
Notes
Solution of Delphi 2010 (modifying compiler)
In Delphi 2010 they introduced "delayed" loading
function GetFoobar: Integer; external 'foobar.dll' delayed;
More Info: http://docwiki.embarcadero.com/RADStudio/en/Libraries_and_Packages#Delayed_Loading
Others
Example implementations can be found in
- mysql: packages/mysql/src/mysql.inc
- sqlite: packages/sqlite/src/sqlite3.inc
- zorba: packages/zorba/src/zorba.inc