TRAMPOLINE(3)TRAMPOLINE(3)NAME
trampoline - closures as first-class C functions
SYNOPSIS
#include <trampoline_r.h>
function = alloc_trampoline_r(address, data0, data1);
free_trampoline_r(function);
is_trampoline_r(function)trampoline_r_address(function)trampoline_r_data0(function)trampoline_r_data1(function)DESCRIPTION
These functions implement closures as first-class C functions. A clo‐
sure consists of a regular C function and a piece of data which gets
passed to the C function when the closure is called.
Closures as first-class C functions means that they fit into a function
pointer and can be called exactly like any other C function. function
= alloc_trampoline_r(address, data0, data1) allocates a closure. When
function gets called, it stores in a special "lexical chain register" a
pointer to a storage area containing data0 in its first word and data1
in its second word and calls the C function at address. The function
at address is responsible for fetching data0 and data1 off the pointer.
Note that the "lexical chain register" is a call-used register, i.e. is
clobbered by function calls.
This is much like gcc's local functions, except that the GNU C local
functions have dynamic extent (i.e. are deallocated when the creating
function returns), while trampoline provides functions with indefinite
extent: function is only deallocated when free_trampoline_r(function)
is called.
is_trampoline_r(function) checks whether the C function function was
produced by a call to alloc_trampoline_r. If this returns true, the
arguments given to alloc_trampoline_r can be retrieved:
trampoline_r_address(function) returns address,
trampoline_r_data0(function) returns data0,
trampoline_r_data1(function) returns data1.
SEE ALSOtrampoline(3), gcc(1), varargs(3)PORTING
The way gcc builds local functions is described in the gcc source, file
gcc-2.6.3/config/cpu/cpu.h.
AUTHOR
Bruno Haible <bruno@clisp.org>
ACKNOWLEDGEMENTS
Many ideas were cribbed from the gcc source.
22 October 1997 TRAMPOLINE(3)
