NAME

Prima::internals - Prima internal architecture

DESCRIPTION

This document describes the internal structures of the Prima toolkit, its loading considerations, object and class representation, and C coding style.

Bootstrap

Initializing

From the point of view of a perl script, Prima is no more but an average module that uses DynaLoader. As the use Prima code gets executed, the 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, the Prima module is ready to use. All wrapping code for built-in functionality that can be seen from perl is in two modules - Prima::Const and Prima::Classes.

Constants

Prima defines a lot of constants for different purposes ( e.g. colors, font styles,0 etc). Prima does not follow perl naming conventions here, for the sake 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 is used first ), Prima registers these functions during the boot_Prima stage. As soon as perl code tries to get a constant's value, an AUTOLOAD function is called, which is banded inside Prima::Const. Constants are widely used both in C and perl code and are defined in apricot.h in such a way so that perl constant definitions come along with the C ones. 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 filled with UVs ( unsigned integers ) and declares a register_fe_constants() function, which should be called at the boot_Prima stage. This way feRead becomes the C analog to the fe::Read in perl.

Classes and methods

Virtual method tables

Prima implementation of classes uses virtual method tables, or VMTs, to make the classes inheritable and their methods overridable. The VMTs are usual C structs, that contain pointers to functions. A 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.

The built-in classes already contain all the information needed for method overloading, but when a new class is derived from an existing one, a new VMT has to be created as well. The actual sub-classing is performed inside build_dynamic_vmt() and build_static_vmt(). gimme_the_vmt() function creates a new VMT instance on the fly and caches the result for every new class that is derived from a Prima built-in class.

C to Perl and Perl to C calling routines

The majority of Prima methods are 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.

Note: Do not mix XS calls with the XS language ( perlxs manpage) - the latter is a meta-language for simplification of coding tasks and is not used in the 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 the gencls tool ( prima-gencls manpage ), and the typical Prima method consists of three functions, two of which are thunks.

The first function, say Class_init(char*), would initialize a class ( for example). It is written fully in C, so to be called from perl code a registration step must be taken for the second function, Class_init_FROMPERL(), that would look like this:

newXS( "Prima::Class::init", Class_init_FROMPERL, "Prima::Class");

Class_init_FROMPERL() is the first thunk, that translates the parameters passed from perl to C and the result back from the C function to perl. This step is almost fully automatized, so one never bothers about writing the 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 the perl code too. 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 returns values from a perl function back to C. This thunk is also generated automatically by the 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 in core C files. In the class declaration files these methods are prepended with the 'public' or 'weird' modifiers, while methods with no special data handling need to use the 'method' or 'static' modifiers.

Note: functions that are not allowed to be seen from perl should have the 'c_only' modifier, and do not need the 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
            Region
            Timer
            Widget
                    Application
                    Window

These classes can be seen from perl with Prima:: prefix. Along with these, the Utils class is defined in a special way. 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 are marked with the 'package' prefix while the other classes are marked with the 'object' prefix (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 be the Prima::Object descendant object. Prima employs blessed hashes as 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 this is not enough to create Prima objects. Every Prima::Object descendant class therefore is equipped with the create() method, which allocates the object instance and calls bless() itself. Parameters that come to the create() call are formed into a hash and passed to the init() method, which is also present on every object. Note that although the perl-coded init() returns the hash, it is 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 the perl stack, using the parse_hv() and push_hv() functions.

Objects can be created from perl by using the 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);

or even

create_object("SampleObject", "si",
    "name", "Sample",
    "index", 10
);

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 the create() method, every object class has the destroy() method. An 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 a memory leak problem.

For the user code it is sufficient to overload done() and/or cleanup() methods, or just the onDestroy notification. It is highly recommended to avoid overloading the destroy() method since it can be called in a 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 Prima objects are blessed hashes, and the hash key __CMATE__ holds a C pointer to a memory that is occupied by a C data instance, or a "mate". It keeps all object variables and a pointer to the VMT. Every object has its own copy of the data instance, but the VMTs can be shared. To reach the C data instance gimme_the_mate() function is used. As the first argument, 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

There are several steps, or "stages", in every object's life cycle. Every stage is mirrored into PObject(self)-> stage integer variable, which can be one of the following csXXX constants:

csConstructing

The object is this initial stage until create() is finished. Right after init() is completed, the setup() method is called.

csNormal

After create() is finished and before destroy() starts. If an object is in either csNormal or csConstructing stage, the result of the Object_alive() method is non-zero.

csDestroying

The destroy() started. This stage runs the cleanup() and the done() methods.

csFrozen

cleanup() started.

csFinalizing

done() started

csDead

destroy() finished

Coding techniques

Accessing object data

C coding in Prima has no specific conventions, except when coding an object method. The object syntax for accessing the object's data instance is though fairly straightforward. For example, accessing the component 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 methods could be called 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

The calling of methods via the object's VMTs is preferred, compared to the direct call of Component_get_name(), primarily because get_name() is a method that can be overridden in the user code.

Calling perl code

The call_perl_indirect() function accepts an object, a name of the method to be called, an argument format string, and an argument list. It has several wrappers for the ease of 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 the format string represents the type of the corresponding argument, using the following characters to encode types:

'i' - integer
's' - char *
'n' - float
'H' - Handle
'S' - SV *
'P' - Point
'R' - Rect

The format string can be prepended with the '<' character, in which case an SV * scalar ( always scalar, even if the code returns nothing or an rray ) value is returned. The caller is responsible for freeing the returned value.

Exceptions

As described in the perlguts manpage, the 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 the

SvTRUE( GvSV( errgv))

statement. It is guaranteed to be false if there was raised no exception. In some situations though, namely, when no perl_call_* functions are called or an error value is already assigned before calling code, there is a wrapping technique that keeps the eventual previous error message. Such code may look like this:

dG_EVAL_ARGS;                       // define arguments
....
OPEN_G_EVAL;                        // open brackets
// call code
perl_call_method( ... | G_EVAL);    // G_EVAL is necessary
if ( SvTRUE( GvSV( errgv)) {
    CLOSE_G_EVAL;                   // close brackets
    croak( SvPV_nolen( GvSV( errgv)));// propagate exception
    // no code is executed after croak
}
CLOSE_G_EVAL;                       // close brackets
...

This technique provides a workaround to a "false alarm" situation if SvTRUE( GvSV( errgv)) is already true before perl_call_method().

Object protection

After the object destroy stage is completed, it is possible that the object's data instance is gone, and even a simple stage check might cause a segmentation fault. To avoid this, bracketing functions called protect_object() and unprotect_object() are used. protect_object() increments the reference count to the object instance, thus delaying its freeing until decrementing unprotect_object() is called.

All C code that references an object must check its stage after every routine that may potentially switch to perl code because the object might be destroyed inside the call. A typical code example would be like this:

int handle_object(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 != csNormal) return 0;

     // proceed with the object
     ...
     return 1;
}

Usually C code doesn't need to check the object stage before the call to perl is made because the gimme_the_mate() function returns NULL when the object's stage is csDead, and the majority of Prima C code is prepended with this call, thus rejecting invalid references on the early stage. If it is desired to get the C mate for objects that are in the csDead stage, use the gimme_the_real_mate() function instead.

init

Object's method init() is responsible for setting all its initial properties to the given values, however, all code that is executed inside the init() must be aware that the object's stage is csConstructing. init() consists of two parts: calling of ancestor's init() and setting the properties. Examples are many in both C and perl code, but in short, it looks like this:

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 in the profile, but the mechanism guarantees that all keys that are listed in profile_default() are conveyed to the init(). For explicit checking of key presence the pexists() macro is used, and the pdelete() macro is used for the key deletion, although is it not recommended to use pdelete() inside init().

Object creation and returning

As described in the 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-> type == dbtBitmap) ? 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() has to increase and decrease the object's reference count if some perl functions are to be executed before returning the object to perl, otherwise it might get destroyed in the middle of the execution:

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 is assigned to a scalar, for example.

Thus

$c = Prima::Object-> create();

and Prima::Object-> create;

have different results. But for some classes, namely Widget and its descendants, and also for Timer, AbstractMenu, Printer, and Clipboard the code above would have the same result - the objects would not be killed. That is because these objects call the Component_attach() method during the init-stage, automatically increasing their reference count. The Component_attach() and its reverse Component_detach() keep a list of objects that are attributed to each other. An object can be attached to more than object at a time, but cannot be attached more than once to another object.

Notifications

All descendats of the Prima::Component class are equipped with a mechanism that allows user callback routines to be called when corresponding events occur. A very similar mechanism is used typically everywhere in the event-driven programming. Component_notify() is used to call the user notifications; its format string has the same format as accepted by perl_call_indirect(). The only difference is that it always has to be prepended with '<s', - this way the call success flag can be returned, and the first parameter must be the name of the notification.

Component_notify( self, "<sH", "Paint", self);
Component_notify( self, "<sPii", "MouseDown", self, point, int, int);

The notification mechanism keeps another reference list, similar to the attach-detach mechanism so that notifications can be attributed to different objects. Objects entering the list don't get their reference counter changed.

Multi-property setting

Prima::Object method set() is designed to assign several properties at once. Sometimes it is more convenient to write

$c-> set( index => 10, name  => "Sample" );

than to invoke several methods one by one. The set() method executes these calls itself, but for the performance reasons it is possible to overload this method and code special conditions for the mult-assignment. As an example, here's Prima::Image type conversion code using this technique:

void
Image_set( Handle self, HV * profile)
{
   ...
   if ( pexist( type))
   {
      int newType = pget_i( type);
      if ( !itype_supported( newType))
         warn("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);
}

Here, if the type conversion is performed along with the palette change, some efficiency is gained by supplying both the 'type' and 'palette' parameters at once. Moreover, because the ordering of the fields is not determined by default ( although that is done by supplying the '__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 the only solution here is to code Class_set() explicitly.

If it is desired to specify the exact order of how atomic properties have to be called, __ORDER__ anonymous array has to be added to the 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 the application. There can be only one Application instance at a time, or none at all.

Macros and functions

dG_EVAL_ARGS

Defines a 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 the result under ancestorName key

gimme_the_vmt

PVMT( const char *className);

Returns the 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 NULL_HANDLE if the object 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 the pointer to a value, if found, NULL otherwise

prima_hash_delete

void*( PHash self, const void *key, int keyLen, Bool kill);

Deletes the hash key and returns the associated value. If the kill argument is true, calls free() on the value and returns NULL.

prima_hash_store

void( PHash self, const void *key, int keyLen, void *val);

Stores a new value into hash. If the key is already present, the old value is overwritten.

prima_hash_count

int(PHash self)

Returns the 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 NULL is returned. action has to be a function declared as

Bool action_callback( void * value, int keyLen, void * key, void * params);

The params argument is a pointer to 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, (see the perlguts manpage). These functions should be used to code a workaround of the perl bug which emerges when the 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 a perl pointer to a method searched by the perl object and the name. If cacheIt is true, caches the result of the hierarchy traversal for speedup.

query_method

CV * ( Handle object, char *methodName, Bool cacheIt);

Returns a perl pointer to a method searched by the C object and the name. If cacheIt is 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);

The main core function for calling Prima methods. Is used by the following three functions, but is never called directly. The format is described in the Calling perl code section.

call_perl

SV * ( Handle self, char *subName, const char *format, ...);

Calls the subName method on a C object

sv_call_perl

SV * ( SV * mate, char *subName, const char *format, ...);

Calls the subName method on a perl object

cv_call_perl

SV * ( SV * mate, Sv * coderef, const char *format, ...);

Calls arbitrary perl code with a SV mate as the first parameter. Used in notifications mechanism.

Object_create

Handle( char * className, HV * profile);

Creates an exemplar of className class with parameters in the profile hash. Never returns NULL_HANDLE, throws an exception instead.

create_object

void*( const char *objClass, const char *format, ...);

A convenience wrapper to Object_create. Uses the format specification that is described in the section Calling perl code above.

create_instance

Handle( const char * className)

Convenience call to Object_create with parameters in hash 'profile'.

Object_destroy

void( Handle self);

Destroys an object. One of the few Prima functions that can be called in the re-entrant fashion.

Object_alive

void( Handle self);

Returns non-zero if the object is alive, 0 otherwise. In particular, returns 1 if the 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);

Protects the object data from deletion after Object_destroy() is called. Can be called several times on an object. Increments Object.protectCount .

unprotect_object

void( Handle obj);

Frees the objectdatapointer 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 into 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 the result of the executed perl code and stores it into the HV hash.

pexist

Bool(char*key)

Returns true if a key is present in the hash 'profile'

pdelete

void(char*key)

Deletes a key in the hash 'profile'

pget_sv, pget_i, pget_f, pget_c, pget_H, pget_B

TYPE(char*key)

Returns a value of one of the types supported (SV*, int, float, char*, Handle or Bool) that is associated with a key in the 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 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 the hash 'profile' and increments the reference counter for the newly created scalar.

pset_sv_noinc

void(char* key, SV * sv)

Assigns a scalar value to a key in the hash 'profile' without incrementing the reference counter.

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 the list data.

plist_destroy

void ( PList self);

Destroys the list data and frees the 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 the item that is located at a given index or NULL_HANDLE if the index is out of range.

list_delete

void( PList self, Handle item);

Removes the item from the list.

list_delete_at

void( PList self, int index);

Removes the item located at a given index from a list.

list_delete_all

void ( PList self, Bool kill);

Removes all items from the list. If the kill argument is true, calls free() on every item before removing them from the list.

list_first_that

int( PList self, void * action, void * params);

Enumerates all list entries, calling action procedure on each. If the action returns true, the enumeration stops and the index is returned. Otherwise, -1 is returned. action has to be a function declared as

Bool action_callback( Handle item, void * params);

where 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

cpanm Prima

perl -MCPAN -e shell
install Prima