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Justine Tunney 2020-06-15 07:18:57 -07:00
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libc/runtime/ringalloc.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 2020 Justine Alexandra Roberts Tunney │
│ │
│ This program is free software; you can redistribute it and/or modify │
│ it under the terms of the GNU General Public License as published by │
│ the Free Software Foundation; version 2 of the License. │
│ │
│ This program is distributed in the hope that it will be useful, but │
│ WITHOUT ANY WARRANTY; without even the implied warranty of │
│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU │
│ General Public License for more details. │
│ │
│ You should have received a copy of the GNU General Public License │
│ along with this program; if not, write to the Free Software │
│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA │
│ 02110-1301 USA │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/assert.h"
#include "libc/calls/calls.h"
#include "libc/dce.h"
#include "libc/limits.h"
#include "libc/macros.h"
#include "libc/runtime/ring.h"
#include "libc/str/str.h"
#include "libc/sysv/consts/map.h"
#include "libc/sysv/consts/prot.h"
/**
* Allocates ring buffer.
*
* Reads/writes wrap around on overflow.
*
* ┌────────────┐
* │ 𝑓₀..𝑓ₙ₋₁ │
* └┬┬──────────┘
* │└────────────┐
* ┌┴────────────┬┴────────────┐
* │ 𝑣₀..𝑣ₙ₋₁ │ 𝑣ₙ..𝑣ₙ*₂₋₁ │
* └─────────────┴─────────────┘
*
* @param r is metadata object owned by caller, initialized to zero
* @param n is byte length
* @return r->p, or NULL w/ errno
* @see ringfree(), balloc()
*/
void *ringalloc(struct RingBuffer *r, size_t n) {
void *a2;
int fd, rc;
size_t grain;
assert(!r->p);
assert(n > 0);
assert(n <= (INT_MAX - FRAMESIZE + 1) / 2);
if ((fd = openanon("ring", 0)) != -1) {
grain = ROUNDUP(n, FRAMESIZE);
rc = ftruncate(fd, grain * 2);
assert(rc != -1);
r->_size = grain * 2;
r->_addr = mmap(NULL, grain, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
if (r->_addr != MAP_FAILED) {
a2 = mmap(r->_addr + grain, grain, PROT_READ | PROT_WRITE,
MAP_SHARED | MAP_FIXED, fd, grain - n);
assert(a2 != MAP_FAILED);
r->p = r->_addr + grain - n;
if (IsWindows()) {
memset(r->p, 0, n); /* @see ftruncate() */
}
}
}
rc = close(fd);
assert(rc != -1);
return r->p;
}