[DRAFT] PDD 11: Extending

Abstract

The extension API for Parrot is a simple, somewhat abstract, interface to Parrot for code written in C or other compiled languages. It provides about the same level of access to Parrot that bytecode programs have.

Description

The API presents to C programs roughly the same interface presented to bytecode programs--that is, a C extension can see everything that a bytecode program can see, including Parrot's base architecture, registers, stacks, and whatnot. This view isn't required, however, and often extension code won't need or want to know what Parrot's internal structures look like. For this reason the functions in the extension API are divided into two broad groups, one that has no particular knowledge of the internals and one that does.

The stability of the two API groups is guaranteed separately. Group 1, the internals unaware group, should be good basically forever. Group 2, the internals aware group, is only guaranteed for the lifetime of the current architecture. (It's likely that both groups will last equally long; however, the Group 1 interface could reasonably be emulated on a different engine, while the Group 2 interface is more closely tied to Parrot).

Note: The extension API has not yet been completely specified. New functions may be added, and those described below may change or be removed. You have been warned...

Implementation

API - Group 1: Internals-unaware functions

These functions are the ones that are largely unaware of the structure and architecture of Parrot. They deal mainly in data as abstract entities, and Parrot itself as a black box that, at best, can make subroutine or method calls. This is sufficient for many extensions which act as black box processing units and in turn treat Parrot itself as a black box.

PMC access functions

The following functions are for storing and retrieving data inside PMCs. Note that use of the _keyed functions with non-aggregate PMCs will generally just result in Parrot throwing an exception.

Parrot_PMC_get_string(interp, pmc)

Returns a Parrot_String that represents the string value of the PMC.

Parrot_PMC_get_string_intkey(interp, pmc, Parrot_Int key)

Keyed version of Parrot_PMC_get_string. Returns a Parrot_String representing the string value of whatever is stored at the element of the PMC indexed by key.

Parrot_PMC_get_pointer(interp, pmc)

Returns a pointer to some item of data. The details of what the pointer points to depend on the particular PMC. This function is useful for dealing with PMCs that hold pointers to arbitrary data.

Parrot_PMC_get_pointer_intkey(interp, pmc, Parrot_Int key)

A keyed version of Parrot_PMC_get_pointer. Returns the pointer value of whatever is stored at the element of the PMC indexed by key.

Parrot_PMC_get_integer(interp, pmc)

Returns the integer value of the PMC.

Parrot_PMC_get_integer_keyed_int(interp, pmc, Parrot_Int key)

A keyed version of Parrot_PMC_get_integer. Returns the integer value of whatever is stored at the element of the PMC indexed by key.

Parrot_PMC_get_numval(interp, pmc)

Returns the numeric value of the PMC.

Parrot_PMC_get_numval_intkey(interp, pmc, Parrot_Int key)

A keyed version of Parrot_PMC_get_numval. Returns the numeric value of whatever is stored at the element of the PMC indexed by key.

Parrot_PMC_get_cstring(interp, pmc)

Returns a C-string (char *) that represents the string value of the PMC. The memory the char * points to is a copy of the original value, and changing it will not change the original in any way.

This memory will not be reclaimed by garbage collection, nor may it be returned to the system with free. It must be returned with Parrot_str_free_cstring.

Parrot_PMC_get_cstring_intkey(interp, pmc, Parrot_Int key)

A keyed version of Parrot_PMC_get_cstring. Returns a C-string representing the string value of whatever is stored at the element of the PMC indexed by key.

Parrot_PMC_get_cstringn(interp, pmc, &len)

Returns a C-string (char *) that represents the string value of the PMC. The memory the char * points to is a copy of the original value, and changing it will not change the original in any way. The len parameter is the address of an integer that will get the length of the string as Parrot knows it.

This memory will not be reclaimed by garbage collection, nor may it be returned to the system with free. It must be returned with Parrot_str_free_cstring.

Parrot_PMC_get_cstringn_intkey(interp, pmc, &len, Parrot_Int key)

A keyed version of Parrot_PMC_get_cstringn. Returns a C-string representing the string value of whatever is stored at the element of the PMC indexed by key. Stores the length of the string in len.

Parrot_PMC_get_pmc_intkey(interp, pmc, Parrot_Int key)

Returns the PMC stored at the element of the passed-in PMC that is indexed by key.

Parrot_PMC_set_string(interp, pmc, Parrot_String value)

Assign the passed-in Parrot_String to the passed-in PMC.

Parrot_PMC_set_string_intkey(interp, pmc, Parrot_String value, Parrot_Int key)

Keyed version of Parrot_PMC_set_string. Assigns value to the PMC stored at element <key> of the passed-in PMC.

Parrot_PMC_set_pointer(interp, pmc, void *value)

Assign the passed-in pointer to the passed-in PMC.

Parrot_PMC_set_pointer_intkey(interp, pmc, void *value, Parrot_Int key)

Keyed version of Parrot_PMC_set_pointer. Assigns value to the PMC stored at element <key> of the passed-in PMC.

Parrot_PMC_set_pmc_intkey(interp, pmc, Parrot_PMC value, Parrot_Int key)

Assigns value to the PMC stored at element <key> of the passed-in PMC.

Parrot_PMC_set_intval(interp, pmc, Parrot_Int value)

Assign the passed-in Parrot integer to the passed-in PMC.

Parrot_PMC_set_intval_intkey(interp, pmc, Parrot_Int value, Parrot_Int key)

Keyed version of Parrot_PMC_set_intval. Assigns value to the PMC stored at element <key> of the passed-in PMC.

Parrot_PMC_set_numval(interp, pmc, Parrot_Float value)

Assign the passed-in Parrot number to the passed-in PMC.

Parrot_PMC_set_numval_intkey(interp, pmc, Parrot_Float value, Parrot_Int key)

Keyed version of Parrot_PMC_set_numval. Assigns value to the PMC stored at element <key> of the passed-in PMC.

Parrot_PMC_set_cstring(interp, pmc, const char *value)

Convert the passed-in null-terminated C string to a Parrot_String and assign it to the passed-in PMC.

Parrot_PMC_set_cstring_intkey(interp, pmc, const char *value, Parrot_Int key)

Keyed version of Parrot_PMC_set_cstring. Converts value to a Parrot_String and assigns it to the PMC stored at element <key> of the passed-in PMC.

Parrot_PMC_set_cstringn(interp, pmc, const char *value, Parrot_Int length)

Convert the passed-in null-terminated C string to a Parrot_String of length length and assign it to the passed-in PMC. If value is longer than length, then only the first length characters will be converted. If value is shorter than length, then the extra characters in the Parrot_String should be assumed to contain garbage.

Parrot_PMC_set_cstringn_intkey(interp, pmc, const char *value, Parrot_int length, Parrot_Int key)

Keyed version of Parrot_PMC_set_cstringn. Converts the first length characters of value to a Parrot_String and assigns the resulting string to the PMC stored at element <key> of the passed-in PMC.

Parrot_PMC_push_float( interp, Parrot_PMC pmc, Parrot_Float value )

Push a float onto an aggregate PMC, such as a ResizablePMCArray. Returns void.

Parrot_PMC_push_integer( interp, Parrot_PMC pmc, Parrot_Int value )

Push a integer onto an aggregate PMC, such as a ResizableIntegerArray. Returns void.

Parrot_PMC_push_pmc( interp, Parrot_PMC pmc, Parrot_PMC value )

Push a PMC value onto an aggregate PMC, such as a ResizablePMCArray. Returns void.

Parrot_PMC_push_string( interp, Parrot_PMC pmc, Parrot_String value )

Push a Parrot_String onto an aggregate PMC, such as a ResizableStringArray. Returns void.

Parrot_PMC_pop_float( interp, Parrot_PMC pmc )

Pop a Parrot_Float off of an aggregate PMC and returns it.

Parrot_PMC_pop_integer( interp, Parrot_PMC pmc )

Pop a Parrot_Int off of an aggregate PMC and returns it.

Parrot_PMC_pop_pmc( interp, Parrot_PMC pmc )

Pop a PMC off of an aggregate PMC and returns it.

Parrot_PMC_pop_string( interp, Parrot_PMC pmc )

Pop a Parrot_String off of an aggregate PMC and returns it.

Creation and destruction

Functions used to create and destroy PMCs, Parrot_Strings, etc.

Parrot_PMC_new(interp, Parrot_Int typenum)

Creates and returns a new PMC. typenum is an integer identifier that specifies the type of PMC required. The typenum corresponding to a particular PMC class name can be found using Parrot_PMC_typenum.

Parrot_PMC_typenum(interp, const char* class)

Returns the internal integer identifier corresponding to a PMC with class name class.

Parrot_PMC_null()

Returns the special NULL PMC.

Parrot_new_string(interp, char *buffer, Parrot_UInt length, const char * const encoding, Parrot_Int flags)

Create a new Parrot string from a passed-in buffer. If the encoding, charset are unspecified (i.e. if you pass in 0), then the defaults are used. Otherwise, the functions Parrot_find_encoding, or Parrot_find_chartype (both described below) can be used to find the appropriate values for a particular choice of encoding, or chartype.

Flag values are currently undocumented.

Note that a copy of the buffer is made.

Parrot_find_encoding(interp, char *encoding_name)

Find the magic token for an encoding, by name.

Parrot_find_chartype(interp, char *chartype)

Find the magic token for a chartype, by name.

Parrot_free_cstring(char* string)

Deallocates a C string that the interpreter has handed to you. This function must be used to free strings produced by Parrot_PMC_get_cstring and Parrot_PMC_get_cstringn, as these will not be reclaimed by the garbage collector. It should not be used to deallocate strings that do not come from Parrot.

Parrot_register_pmc(interp, pmc)

Add a reference to the PMC to the interpreter's GC registry. This prevents PMCs known only to extensions from getting destroyed during GC runs.

Parrot_unregister_pmc(interp, pmc)

Remove a reference to the PMC from the interpreter's GC registry. If the reference count reaches zero, the PMC will be destroyed during the next GC run.

Subroutine and method calls

Functions to call Parrot subroutines and methods

TODO: Add new call functions here

API - Group 2: Internals aware

The internals-aware functions are for those extensions that need to query or alter the state of Parrot's internals in some way.

Register access functions

The following functions allow the values stored in Parrot's registers to be accessed. An attempt to access a non-existent register (e.g. string register -123) will cause the function to throw an exception (well, it will once we actually implement some bounds-checking...). The value stored in an uninitialized register is undefined; it may well be zero (or NULL), but do not rely on this being the case.

Parrot_get_intreg(interp, Parrot_Int regnum)

Return the value of an integer register.

Parrot_get_numreg(interp, Parrot_Int regnum)

Return the value of a numeric register.

Parrot_get_strreg(interp, Parrot_Int regnum)

Return the value of a string register.

Parrot_get_pmcreg(interp, Parrot_Int regnum)

Return the value of a PMC register.

References

docs/glossary.pod