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x/sys/callback

C function pointers that call x functions: a stub per callback, for a C library that takes a function pointer.

Class Callback

A C function pointer that calls an x function: (Callback make f nargs), then hand (cb address) to a C library that takes a function pointer.

The C caller passes up to four integer or pointer arguments; F gets each as an integer and answers the C result, #t as 1 and anything else that is not an integer as 0.

Keep the Callback while the library may call the address: it holds F, and the stub reaches F through its address.

An error raised in F unwinds through the C caller’s frames; a callback that can fail should catch its own errors.

target

The function the stub calls: the one made with, answering its result as an integer

Field: data carried by a Callback instance.

nargs

How many arguments the C caller passes, 0 to 4

Field: data carried by a Callback instance.

asm

The assembler buffer the stub was written into, or nil between an image write and its load

Field: data carried by a Callback instance.

address

The stub’s address, the integer to hand a C library; 0 between an image write and its load

Field: data carried by a Callback instance.

(remake!)

Write the stub again – what the recache hook does after an image load; a consumer never needs to call it.

Instance method: called on a Callback instance.

Returns: INTEGER — The stub’s new address

(free!)

Release the stub. The address is not callable afterwards.

Instance method: called on a Callback instance.

Returns: ANY — nil

(Callback make f nargs)

A C function pointer that calls f: the stub is written and its address is (cb address).

Parameters:

• f : CALLABLE — The x function to call, taking NARGS integers
• nargs : INTEGER — How many arguments the C caller passes, 0 to 4

Returns: Callback — The callback

(Callback %door name)

(Callback %write f nargs)