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Expose public garbage collector API for C language

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You can now do epic things like this:

    puts(_gc(xasprintf("%d", 123)));

The _gc() API is shorthand for _defer() which works like Go's keyword:

    const char *s = xasprintf("%d", 123);
    _defer(free, s);
    puts(s);

Be sure to always use -fno-omit-frame-pointer which makes code fast too.

Enjoy! See also #114
This commit is contained in:
Justine Tunney 2021-03-08 10:56:09 -08:00
parent 0ad609268f
commit 33e8fc8687
26 changed files with 192 additions and 182 deletions
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66
libc/mem/gc.c Normal file
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/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2021 Justine Alexandra Roberts Tunney │
│ │
│ Permission to use, copy, modify, and/or distribute this software for │
│ any purpose with or without fee is hereby granted, provided that the │
│ above copyright notice and this permission notice appear in all copies. │
│ │
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
│ PERFORMANCE OF THIS SOFTWARE. │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/nexgen32e/stackframe.h"
#include "libc/runtime/gc.h"
#include "libc/runtime/runtime.h"
/**
* Frees memory when function returns.
*
* This garbage collector overwrites the return address on the stack so
* that the RET instruction calls a trampoline which calls free(). It's
* loosely analogous to Go's defer keyword rather than a true cycle gc.
*
* const char *s = _gc(strdup("hello"));
* puts(s);
*
* This macro is equivalent to:
*
* _defer(free, ptr)
*
* @warning do not return a gc()'d pointer
* @warning do not realloc() with gc()'d pointer
* @warning be careful about static keyword due to impact of inlining
* @note you should use -fno-omit-frame-pointer
*/
void *(_gc)(void *thing) {
struct StackFrame *frame;
frame = __builtin_frame_address(0);
__deferer(frame->next, _weakfree, thing);
return thing;
}
/**
* Calls fn(arg) when function returns.
*
* This garbage collector overwrites the return address on the stack so
* that the RET instruction calls a trampoline which calls free(). It's
* loosely analogous to Go's defer keyword rather than a true cycle gc.
*
* @warning do not return a gc()'d pointer
* @warning do not realloc() with gc()'d pointer
* @warning be careful about static keyword due to impact of inlining
* @note you should use -fno-omit-frame-pointer
*/
void *(_defer)(void *fn, void *arg) {
struct StackFrame *frame;
frame = __builtin_frame_address(0);
__deferer(frame->next, fn, arg);
return arg;
}