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Prima::internals - Prima internal architecture |
Prima::internals - Prima internal architecture
This documents elucidates the internal structures of the Prima toolkit, its loading considerations, object and class representation and C coding style.
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.
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.
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.
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. the perlguts manpage manpage describes these functions and macros.
NB - Do not mix XS calls to xs language ( the perlxs manpage 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.
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).
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.
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.
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.
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.
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:
create() is finished.
Right after init() is completed, setup() method
is called.
create() is finished and before destroy() started.
If an object is csNormal and csConstructing stage,
Object_alive() result would be non-zero.
destroy() started. This stage includes calling of cleanup()
and done() routines.
cleanup() started.
done() started
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.
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.
As descriped in the perlguts manpage 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( 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( errgv)) {
CLOSE_G_EVAL; // close brackets
croak( SvPV( GvSV( errgv), na));// 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( errgv)) is true before perl_call_method().
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.
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().
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;
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;
i-> self-> begin_paint( h);
i-> self-> put_image( h, 0, 0, self);
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;
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.
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.
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)],
);
=item application, Handle
Pointer to an application. There can be only one Application instance at a time, or none at all.
Bool(void * vmt)
Caches pre-built VMT for further use
Bool( void * vmt, char * ancestorName, int ancestorVmtSize)
Creates a subclass from vmt and caches result under ancestorName key
PVMT( const char *className);
Returns VMT pointer associated with class by name.
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
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(type)
To be used instead (type*)(malloc(sizeof(type))
allocn(type,n)
To be used instead (type*)(malloc((n)*sizeof(type))
alloc1 but fills the allocated memory with zeros
allocn but fills the allocated memory with zeros
malloc() but fills the allocated memory with zeros
PHash(void)
Creates an empty hash
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.
void*( PHash self, const void *key, int keyLen);
Returns pointer to a value, if found, nil otherwise
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.
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.
int(PHash self)
Returns number of keys in the hash
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
Bool( Handle object, void *cls);
Returns true, if the object is an exemplar of class cls or its descendant
SV *( char *string)
Simplified perl_eval_pv() call.
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.
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.
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.
SV * ( Handle self, char *subName, const char *format, ...);
Calls method of an object pointer by a Handle
SV * ( SV * mate, char *subName, const char *format, ...);
Calls method of an object pointed by a SV*
SV * ( SV * mate, Sv * coderef, const char *format, ...);
Calls arbitrary perl code with mate as first parameter. Used in notifications mechanism.
Handle( char * className, HV * profile);
Creates an exemplar of className class with parameters in profile. Never returns nilHandle, throws an exception instead.
void*( const char *objClass, const char *format, ...);
Convenience wrapper to Object_create. Uses format
specification that is described in Calling perl code.
Handle( const char * className)
Convenience call to Object_create with parameters in hash 'profile'.
void( Handle self);
Destroys object. One of few Prima function that can be called in re-entrant fashion.
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.
void( Handle obj);
restricts object pointer from deletion after Object_destroy(). Can be called several times on an object. Increments Object. protectCount.
void( Handle obj);
Frees object pointer after Object. protectCount hits zero. Can be called several times on an object.
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.
void ( I32 ax, SV **sp, I32 items, SV **mark, int callerReturns, HV *hv);
Puts all hv contents back to perl stack.
SV **( SV **sp, HV *hv);
Puts hv content as arguments to perl code to be called
int ( SV **sp, int count, HV *hv, int shouldBe);
Reads result of executed perl code and stores them into hv.
Bool(char*key)
Return true if a key is present into hash 'profile'
void(char*key)
Deletes a key in hash 'profile'
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.
void( char*key, TYPE value)
Assigns a value to a key in hash 'profile' and increments reference count to a newly created scalar.
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.
void(char* key, SV * sv)
Assigns scalar value to a key in hash 'profile' without reference count increment.
char*( const char *)
Returns copy of a string
void ( PList self, int size, int delta);
Creates a list instance with a static List structure.
PList( int size, int delta);
Created list instance and returns newly allocated List structure.
void( PList self);
Destroys list data.
void ( PList self);
Destroys list data and frees list instance.
int( PList self, Handle item);
Adds new item into a list, returns its index or -1 on error.
int ( PList self, Handle item, int pos);
Inserts new item into a list at a given position, returns its position or -1 on error.
Handle ( PList self, int index);
Returns items that is located at given index or nilHandle if the index is out of range.
void( PList self, Handle item);
Removes the item from list.
void( PList self, int index);
Removes the item located at given index from a list.
void ( PList self, Bool kill);
Removes all items from the list. If kill is true,
calls free() on every item before.
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
int( PList self, Handle item);
Returns index of an item, or -1 if the item is not in the list.
Dmitry Karasik, <dmitry@karasik.eu.org>.
Prima
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Prima::internals - Prima internal architecture |