Provided by: libprima-perl_1.28-1.4_amd64 
NAME
Prima::internals - Prima internal architecture
DESCRIPTION
This documents elucidates the internal structures of the Prima toolkit, its loading
considerations, object and class representation and C coding style.
Bootstrap
Initializing
For a perl script, Prima is no more but an average module that uses DynaLoader. As 'use
Prima' code gets executed, a bootstrap procedure boot_Prima() is called. This procedure
initializes all internal structures and built-in Prima classes. It also initializes all
system-dependent structures, calling window_subsystem_init(). After that point Prima
module is ready to use. All wrapping code for built-in functionality that can be seen from
perl is located into two modules - Prima::Const and Prima::Classes.
Constants
Prima defines lot of constants for different purposes ( e.g. colors, font styles etc).
Prima does not follow perl naming conventions here, on the reason of simplicity. It is (
arguably ) easier to write cl::White rather than Prima::cl::White. As perl constants are
functions to be called once ( that means that a constant's value is not defined until it
used first ), Prima registers these functions during boot_Prima stage. As soon as perl
code tries to get a constant's value, an AUTOLOAD function is called, which is binded
inside Prima::Const. Constants are widely used both in C and perl code, and are defined
in apricot.h in that way so perl constant definition comes along with C one. As an
example file event constants set is described here.
apricot.h:
#define FE(const_name) CONSTANT(fe,const_name)
START_TABLE(fe,UV)
#define feRead 1
FE(Read)
#define feWrite 2
FE(Write)
#define feException 4
FE(Exception)
END_TABLE(fe,UV)
#undef FE
Const.pm:
package fe; *AUTOLOAD = \&Prima::Const::AUTOLOAD;
This code creates a structure of UV's ( unsigned integers ) and a register_fe_constants()
function, which should be called at boot_Prima stage. This way feRead becomes C analog to
fe::Read in perl.
Classes and methods
Virtual method tables
Prima implementation of classes uses virtual method tables, or VMTs, in order to make the
classes inheritable and their methods overrideable. The VMTs are usual C structs, that
contain pointers to functions. Set of these functions represents a class. This chapter is
not about OO programming, you have to find a good book on it if you are not familiar with
the OO concepts, but in short, because Prima is written in C, not in C++, it uses its own
classes and objects implementation, so all object syntax is devised from scratch.
Built-in classes already contain all information needed for method overloading, but when a
new class is derived from existing one, new VMT is have to be created as well. The actual
sub-classing is performed inside build_dynamic_vmt() and build_static_vmt().
gimme_the_vmt() function creates new VMT instance on the fly and caches the result for
every new class that is derived from Prima class.
C to Perl and Perl to C calling routines
Majority of Prima methods is written in C using XS perl routines, which represent a
natural ( from a perl programmer's view ) way of C to Perl communication. perlguts
manpage describes these functions and macros.
NB - Do not mix XS calls to xs language ( perlxs manpage) - the latter is a meta-language
for simplification of coding tasks and is not used in Prima implementation.
It was decided not to code every function with XS calls, but instead use special wrapper
functions ( also called "thunks") for every function that is called from within perl.
Thunks are generated automatically by gencls tool ( gencls manpage ), and typical Prima
method consists of three functions, two of which are thunks.
First function, say Class_init(char*), would initialize a class ( for example). It is
written fully in C, so in order to be called from perl code a registration step must be
taken for a second function, Class_init_FROMPERL(), that would look like
newXS( "Prima::Class::init", Class_init_FROMPERL, "Prima::Class");
Class_init_FROMPERL() is a first thunk, that translates the parameters passed from perl to
C and the result back from C function to perl. This step is almost fully automatized, so
one never bothers about writing XS code, the gencls utility creates the thunks code
automatically.
Many C methods are called from within Prima C code using VMTs, but it is possible to
override these methods from perl code. The actions for such a situation when a function is
called from C but is an overridden method therefore must be taken. On that occasion the
third function Class_init_REDEFINED() is declared. Its task is a reverse from
Class_init_FROMPERL() - it conveys all C parameters to perl and return values from a perl
function back to C. This thunk is also generated automatically by gencls tool.
As one can notice, only basic data types can be converted between C and perl, and at some
point automated routines do not help. In such a situation data conversion code is written
manually and is included into core C files. In the class declaration files these methods
are prepended with 'public' or 'weird' modifiers, when methods with no special data
handling needs use 'method' or 'static' modifiers.
NB - functions that are not allowed to be seen from perl have 'c_only' modifier, and
therefore do not need thunk wrapping. These functions can nevertheless be overridden from
C.
Built-in classes
Prima defines the following built-in classes: (in hierarchy order)
Object
Component
AbstractMenu
AccelTable
Menu
Popup
Clipboard
Drawable
DeviceBitmap
Printer
Image
Icon
File
Timer
Widget
Application
Window
These classes can be seen from perl with Prima:: prefix. Along with these, Utils class is
defined. Its only difference is that it cannot be used as a prototype for an object, and
used merely as a package that binds functions. Classes that are not intended to be an
object prototype marked with 'package' prefix, when others are marked with 'object' (see
prima-gencls manpage).
Objects
This chapter deals only with Prima::Object descendants, pure perl objects are not of
interest here, so the 'object' term is thereafter referenced to Prima::Object descendant
object. Prima employs blessed hashes for its objects.
Creation
All built-in object classes and their descendants can be used for creating objects with
perl semantics. Perl objects are created by calling bless(), but it is not enough to
create Prima objects. Every Prima::Object descendant class therefore is equipped with
create() method, that allocates object instance and calls bless() itself. Parameters that
come with create() call are formed into a hash and passed to init() method, that is also
present on every object. Note the fact that although perl-coded init() returns the hash,
it not seen in C code. This is a special consideration for the methods that have 'HV *
profile' as a last parameter in their class declaration. The corresponding thunk copies
the hash content back to perl stack, using parse_hv() and push_hv() functions.
Objects can be created from perl by using following code example:
$obj = Prima::SampleObject-> create(
name => "Sample",
index => 10,
);
and from C:
Handle obj;
HV * profile = newHV();
pset_c( name, "Sample");
pset_i( index, 10);
obj = Object_create("SampleObject", profile);
sv_free(( SV*) profile);
Convenience pset_XX macros assign a value of XX type to the hash key given as a first
parameter, to a hash variable named profile. "pset_i" works with integers, "pset_c" - with
strings, etc.
Destruction
As well as create() method, every object class has destroy() method. Object can be
destroyed either from perl
$obj-> destroy
or from C
Object_destroy( obj);
An object can be automatically destroyed when its reference count reaches 0. Note that the
auto destruction would never happen if the object's reference count is not lowered after
its creation. The code
--SvREFCNT( SvRV( PAnyObject(object)-> mate));
is required if the object is to be returned to perl. If that code is not called, the
object still could be destroyed explicitly, but its reference would still live, resulting
in memory leak problem.
For user code it is sufficient to overload done() and/or cleanup() methods, or just
onDestroy notifications. It is highly recommended to avoid overloading destroy method,
since it can be called in re-entrant fashion. When overloading done(), be prepared that it
may be called inside init(), and deal with the semi-initialized object.
Data instance
All object data after their creation represent an object instance. All Prima objects are
blessed hashes, and the hash key __CMATE__ holds a C pointer to a memory which is occupied
by C data instance, or a "mate". It keeps all object variables and a pointer to VMT. Every
object has its own copy of data instance, but the VMTs can be shared. In order to reach to
C data instance gimme_the_mate() function is used. As a first parameter it accepts a
scalar (SV*), which is expected to be a reference to a hash, and returns the C data
instance if the scalar is a Prima object.
Object life stages
It was decided to divide object life stage in several steps. Every stage is mirrored into
PObject(self)-> stage integer variable, which can be one of csXXX constants. Currently it
has six:
csConstructing
Initial stage, is set until create() is finished. Right after init() is completed,
setup() method is called.
csNormal
After create() is finished and before destroy() started. If an object is csNormal and
csConstructing stage, Object_alive() result would be non-zero.
csDestroying
destroy() started. This stage includes calling of cleanup() and done() routines.
csFrozen
cleanup() started.
csFinalizing
done() started
csDead
Destroy finished
Coding techniques
Accessing object data
C coding has no specific conventions, except when a code is an object method. Object
syntax for accessing object instance data is also fairly standard. For example, accessing
component's field called 'name' can be done in several ways:
((PComponent) self)-> name; // classic C
PComponent(self)-> name; // using PComponent() macro from apricot.h
var-> name; // using local var() macro
Object code could to be called also in several ways:
(((PComponent) self)-> self)-> get_name( self); // classic C
CComponent(self)-> get_name( self); // using CComponent() macro from apricot.h
my-> get_name( self); // using local my() macro
This calling is preferred, comparing to direct call of Component_get_name(), primarily
because get_name() is a method and can be overridden from user code.
Calling perl code
call_perl_indirect() function accepts object, its method name and parameters list with
parameter format string. It has several wrappers for easier use, which are:
call_perl( Handle self, char * method, char * format, ...)
sv_call_perl( SV * object, char * method, char * format, ...)
cv_call_perl( SV * object, SV * code_reference, char * format, ...)
each character of format string represents a parameters type, and characters can be:
'i' - integer
's' - char *
'n' - float
'H' - Handle
'S' - SV *
'P' - Point
'R' - Rect
The format string can be prepended with '<' character, in which case SV * scalar ( always
scalar, even if code returns nothing or array ) value is returned. The caller is
responsible for freeing the return value.
Exceptions
As descriped in perlguts manpage, G_EVAL flag is used in perl_call_sv() and
perl_call_method() to indicate that an eventual exception should never be propagated
automatically. The caller checks if the exception was taken place by evaluating
SvTRUE( GvSV( PL_errgv))
statement. It is guaranteed to be false if there was no exception condition. But in some
situations, namely, when no perl_call_* functions are called or error value is already
assigned before calling code, there is a wrapping technique that keeps previous error
message and looks like:
dG_EVAL_ARGS; // define arguments
....
OPEN_G_EVAL; // open brackets
// call code
perl_call_method( ... | G_EVAL); // G_EVAL is necessary
if ( SvTRUE( GvSV( PL_errgv)) {
CLOSE_G_EVAL; // close brackets
croak( SvPV_nolen( GvSV( PL_errgv)));// propagate exception
// no code is executed after croak
}
CLOSE_G_EVAL; // close brackets
...
This technique provides workaround to a "false alarm" situation, if SvTRUE( GvSV(
PL_errgv)) is true before perl_call_method().
Object protection
After the object destroy stage is completed, it is possible that object's data instance is
gone, and even simple stage check might cause segmentation fault. To avoid this,
bracketing functions called "protect_object()" and "unprotect_object()" are used.
protect_object() increments reference count to the object instance, thus delaying its
freeing until decrementing unprotect_object() is called.
All C code that references to an object must check for its stage after every routine that
switches to perl code, because the object might be destroyed inside the call. Typical code
example would be like:
function( Handle object) {
int stage;
protect_object( object);
// call some perl code
perl_call_method( object, "test", ...);
stage = PObject(object)-> stage;
unprotect_object( object);
if ( stage == csDead) return;
// proceed with the object
}
Usual C code never checks for object stage before the call, because gimme_the_mate()
function returns NULL if object's stage is csDead, and majority of Prima C code is
prepended with this call, thus rejecting invalid references on early stage. If it is
desired to get the C mate for objects that are in csDead stage, use
"gimme_the_real_mate()" function instead.
init
Object's method init() is responsible for setting all its initial properties to the
object, but all code that is executed inside init must be aware that the object's stage is
csConstructing. init() consists of two parts: calling of ancestor's init() and setting
properties. Examples are many in both C and perl code, but in short it looks like:
void
Class_init( Handle self, HV * profile)
{
inherited init( self, profile);
my-> set_index( pget_i( index));
my-> set_name( pget_c( name));
}
pget_XX macros call croak() if the profile key is not present into profile, but the
mechanism guarantees that all keys that are listed in profile_default() are conveyed to
init(). For explicit checking of key presence pexists() macro is used, and pdelete() is
used for key deletion, although is it not recommended to use pdelete() inside init().
Object creation and returning
As described is previous sections, there are some precautions to be taken into account
when an object is created inside C code. A piece of real code from DeviceBitmap.c would
serve as an example:
static
Handle xdup( Handle self, char * className)
{
Handle h;
Point s;
PDrawable i;
// allocate a parameters hash
HV * profile = newHV();
// set all necessary arguments
pset_H( owner, var-> owner);
pset_i( width, var-> w);
pset_i( height, var-> h);
pset_i( type, var-> monochrome ? imBW : imRGB);
// create object
h = Object_create( className, profile);
// free profile, do not need it anymore
sv_free(( SV *) profile);
i = ( PDrawable) h;
s = i-> self-> get_size( h);
i-> self-> begin_paint( h);
i-> self-> put_image_indirect( h, self, 0, 0, 0, 0, s.x, s.y, s.x, s.y, ropCopyPut);
i-> self-> end_paint( h);
// decrement reference count
--SvREFCNT( SvRV( i-> mate));
return h;
}
Note that all code that would use this xdup(), have to increase and decrease object's
reference count if some perl functions are to be executed before returning object to perl,
otherwise it might be destroyed before its time.
Handle x = xdup( self, "Prima::Image");
++SvREFCNT( SvRV( PAnyObject(x)-> mate)); // Code without these
CImage( x)-> type( x, imbpp1);
--SvREFCNT( SvRV( PAnyObject(x)-> mate)); // brackets is unsafe
return x;
Attaching objects
The newly created object returned from C would be destroyed due perl's garbage cleaning
mechanism right away, unless the object value would be assigned to a scalar, for example.
Thus
$c = Prima::Object-> create();
and
Prima::Object-> create;
have different results. But for some classes, namely Widget ant its descendants, and also
for Timer, AbstractMenu, Printer and Clipboard the code above would have same result - the
objects would not be killed. That is because these objects call Component_attach() during
init-stage, automatically increasing their reference count. Component_attach() and its
reverse Component_detach() account list of objects, attributed to each other. Object can
be attached to multiple objects, but cannot be attached more that once to another object.
Notifications
All Prima::Component descendants are equipped with the mechanism that allows multiple user
callbacks routines to be called on different events. This mechanism is used heavily in
event-driven programming. Component_notify() is used to call user notifications, and its
format string has same format as accepted by perl_call_indirect(). The only difference
that it always has to be prepended with '<s', - this way the call success flag is set, and
first parameter have to be the name of the notification.
Component_notify( self, "<sH", "Paint", self);
Component_notify( self, "<sPii", "MouseDown", self, point, int, int);
Notifications mechanism accounts the reference list, similar to attach-detach mechanism,
because all notifications can be attributed to different objects. The membership in this
list does not affect the reference counting.
Multiple property setting
Prima::Object method set() is designed to assign several properties at one time. Sometimes
it is more convenient to write
$c-> set( index => 10, name => "Sample" );
than to invoke several methods one by one. set() performs this calling itself, but for
performance reasons it is possible to overload this method and code special conditions for
multiple assignment. As an example, Prima::Image type conversion code is exemplified:
void
Image_set( Handle self, HV * profile)
{
...
if ( pexist( type))
{
int newType = pget_i( type);
if ( !itype_supported( newType))
warn("RTC0100: Invalid image type requested (%08x) in Image::set_type",
newType);
else
if ( !opt_InPaint)
my-> reset( self, newType, pexist( palette) ?
pget_sv( palette) : my->get_palette( self));
pdelete( palette);
pdelete( type);
}
...
inherited set ( self, profile);
}
If type conversion is performed along with palette change, some efficiency is gained by
supplying both 'type' and 'palette' parameters at a time. Moreover, because ordering of
the fields is not determined by default ( although that be done by supplying '__ORDER__'
hash key to set() }, it can easily be discovered that
$image-> type( $a);
$image-> palette( $b);
and
$image-> palette( $b);
$image-> type( $a);
produce different results. Therefore it might be only solution to code Class_set()
explicitly.
If it is desired to specify exact order how atomic properties have to be called, __ORDER__
anonymous array have to be added to set() parameters.
$image-> set(
owner => $xxx,
type => 24,
__ORDER__ => [qw( type owner)],
);
API reference
Variables
primaObjects, PHash
Hash with all prima objects, where keys are their data instances
application, Handle
Pointer to an application. There can be only one Application instance at a time, or
none at all.
Macros and functions
dG_EVAL_ARGS
Defines variable for $@ value storage
OPEN_G_EVAL, CLOSE_G_EVAL
Brackets for exception catching
build_static_vmt
Bool(void * vmt)
Caches pre-built VMT for further use
build_dynamic_vmt
Bool( void * vmt, char * ancestorName, int ancestorVmtSize)
Creates a subclass from vmt and caches result under ancestorName key
gimme_the_vmt
PVMT( const char *className);
Returns VMT pointer associated with class by name.
gimme_the_mate
Handle( SV * perlObject)
Returns a C pointer to an object, if perlObject is a reference to a Prima object.
returns nilHandle if object's stage is csDead
gimme_the_real_mate
Handle( SV * perlObject)
Returns a C pointer to an object, if perlObject is a reference to a Prima object. Same
as "gimme_the_mate", but does not check for the object stage.
alloc1
alloc1(type)
To be used instead (type*)(malloc(sizeof(type))
allocn
allocn(type,n)
To be used instead (type*)(malloc((n)*sizeof(type))
alloc1z
Same as "alloc1" but fills the allocated memory with zeros
allocnz
Same as "allocn" but fills the allocated memory with zeros
prima_mallocz
Same as malloc() but fills the allocated memory with zeros
prima_hash_create
PHash(void)
Creates an empty hash
prima_hash_destroy
void(PHash self, Bool killAll);
Destroys a hash. If killAll is true, assumes that every value in the hash is a dynamic
memory pointer and calls free() on each.
prima_hash_fetch
void*( PHash self, const void *key, int keyLen);
Returns pointer to a value, if found, nil otherwise
prima_hash_delete
void*( PHash self, const void *key, int keyLen, Bool kill);
Deletes hash key and returns associated value. if kill is true, calls free() on the
value and returns nil.
prima_hash_store
void( PHash self, const void *key, int keyLen, void *val);
Stores new value into hash. If the key is already present, old value is overwritten.
prima_hash_count
int(PHash self)
Returns number of keys in the hash
prima_hash_first_that
void * ( PHash self, void *action, void *params, int *pKeyLen, void **pKey);
Enumerates all hash entries, calling action procedure on each. If the action
procedure returns true, enumeration stops and the last processed value is returned.
Otherwise nil is returned. action have to be function declared as
Bool action_callback( void * value, int keyLen, void * key, void * params);
params is a pointer to an arbitrary user data
kind_of
Bool( Handle object, void *cls);
Returns true, if the object is an exemplar of class cls or its descendant
PERL_CALL_METHOD, PERL_CALL_PV
To be used instead of perl_call_method and perl_call_pv, described in perlguts
manpage. These functions aliased to a code with the workaround of perl bug which
emerges when G_EVAL flag is combined with G_SCALAR.
eval
SV *( char *string)
Simplified perl_eval_pv() call.
sv_query_method
CV * ( SV * object, char *methodName, Bool cacheIt);
Returns perl pointer to a method searched by a scalar and a name If cacheIt true,
caches the hierarchy traverse result for a speedup.
query_method
CV * ( Handle object, char *methodName, Bool cacheIt);
Returns perl pointer to a method searched by an object and a name If cacheIt true,
caches the hierarchy traverse result for a speedup.
call_perl_indirect
SV * ( Handle self, char *subName, const char *format, Bool cdecl,
Bool coderef, va_list params);
Core function for calling Prima methods. Is used by the following three functions, but
is never called directly. Format is described in "Calling perl code" section.
call_perl
SV * ( Handle self, char *subName, const char *format, ...);
Calls method of an object pointer by a Handle
sv_call_perl
SV * ( SV * mate, char *subName, const char *format, ...);
Calls method of an object pointed by a SV*
cv_call_perl
SV * ( SV * mate, Sv * coderef, const char *format, ...);
Calls arbitrary perl code with mate as first parameter. Used in notifications
mechanism.
Object_create
Handle( char * className, HV * profile);
Creates an exemplar of className class with parameters in profile. Never returns
nilHandle, throws an exception instead.
create_object
void*( const char *objClass, const char *format, ...);
Convenience wrapper to Object_create. Uses format specification that is described in
"Calling perl code".
create_instance
Handle( const char * className)
Convenience call to "Object_create" with parameters in hash 'profile'.
Object_destroy
void( Handle self);
Destroys object. One of few Prima function that can be called in re-entrant fashion.
Object_alive
void( Handle self);
Returns non-zero is object is alive, 0 otherwise. In particular, current
implementation returns 1 if object's stage is csNormal and 2 if it is csConstructing.
Has virtually no use in C, only used in perl code.
protect_object
void( Handle obj);
restricts object pointer from deletion after Object_destroy(). Can be called several
times on an object. Increments Object. protectCount.
unprotect_object
void( Handle obj);
Frees object pointer after Object. protectCount hits zero. Can be called several
times on an object.
parse_hv
HV *( I32 ax, SV **sp, I32 items, SV **mark, int expected, const char *methodName);
Transfers arguments in perl stack to a newly created HV and returns it.
push_hv
void ( I32 ax, SV **sp, I32 items, SV **mark, int callerReturns, HV *hv);
Puts all hv contents back to perl stack.
push_hv_for_REDEFINED
SV **( SV **sp, HV *hv);
Puts hv content as arguments to perl code to be called
pop_hv_for_REDEFINED
int ( SV **sp, int count, HV *hv, int shouldBe);
Reads result of executed perl code and stores them into hv.
pexist
Bool(char*key)
Return true if a key is present into hash 'profile'
pdelete
void(char*key)
Deletes a key in hash 'profile'
pget_sv, pget_i, pget_f, pget_c, pget_H, pget_B
TYPE(char*key)
Returns value of ( SV*, int, float, char*, Handle or Bool) that is associated to a key
in hash 'profile'. Calls croak() if the key is not present.
pset_sv, pset_i, pset_f, pset_c, pset_H
void( char*key, TYPE value)
Assigns a value to a key in hash 'profile' and increments reference count to a newly
created scalar.
pset_b
void( char*key, void* data, int length)
Assigns binary data to a key in hash 'profile' and increments reference count to a
newly created scalar.
pset_sv_noinc
void(char* key, SV * sv)
Assigns scalar value to a key in hash 'profile' without reference count increment.
duplicate_string
char*( const char *)
Returns copy of a string
list_create
void ( PList self, int size, int delta);
Creates a list instance with a static List structure.
plist_create
PList( int size, int delta);
Created list instance and returns newly allocated List structure.
list_destroy
void( PList self);
Destroys list data.
plist_destroy
void ( PList self);
Destroys list data and frees list instance.
list_add
int( PList self, Handle item);
Adds new item into a list, returns its index or -1 on error.
list_insert_at
int ( PList self, Handle item, int pos);
Inserts new item into a list at a given position, returns its position or -1 on error.
list_at
Handle ( PList self, int index);
Returns items that is located at given index or nilHandle if the index is out of
range.
list_delete
void( PList self, Handle item);
Removes the item from list.
list_delete_at
void( PList self, int index);
Removes the item located at given index from a list.
list_delete_all
void ( PList self, Bool kill);
Removes all items from the list. If kill is true, calls free() on every item before.
list_first_that
int( PList self, void * action, void * params);
Enumerates all list entries, calling action procedure on each. If action returns
true, enumeration stops and the index is returned. Otherwise -1 is returned. action
have to be a function declared as
Bool action_callback( Handle item, void * params);
params is a pointer to an arbitrary user data
list_index_of
int( PList self, Handle item);
Returns index of an item, or -1 if the item is not in the list.
AUTHOR
Dmitry Karasik, <dmitry@karasik.eu.org>.
SEE ALSO
Prima