Concurrent I/O without threads
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/* threadless.io
* Copyright (c) 2016 Justin R. Cutler
* Licensed under the MIT License. See LICENSE file in the project root for
* full license information.
*/
/** @file
* @c mmap(3) allocator implementation
* @author Justin R. Cutler <justin.r.cutler@gmail.com>
*/
#define _GNU_SOURCE
/* HAVE_* */
#include "config.h"
/* errno, ENOSYS */
#include <errno.h>
/* size_t, NULL */
#include <stddef.h>
#ifndef HAVE_MREMAP
/* memcpy */
# include <string.h>
#endif
/* mmap, munmap, PROT_*, MAP_*, mremap(optional), MREMAP_*(optional) */
#include <sys/mman.h>
/* sysconf, _SC_PAGESIZE */
#include <unistd.h>
/* ... */
#include <threadless/mmap_allocator.h>
#ifndef HAVE_MMAP
# error Need mmap()
#endif
#if defined(HAVE_MAP_ANONYMOUS) || defined(HAVE_MAP_ANON)
# ifndef HAVE_MAP_ANONYMOUS
# define MAP_ANONYMOUS MAP_ANON
# endif
#else
# error Need MAP_ANONYMOUS or MAP_ANON
#endif
static void *do_mmap(size_t size)
{
return mmap(NULL, size, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS,
-1, 0);
}
static void *do_mremap(void *memory, size_t old_size, size_t new_size)
{
void *new_memory;
#ifdef HAVE_MREMAP
new_memory = mremap(memory, old_size, new_size, MREMAP_MAYMOVE);
#else
if (old_size < new_size) {
/* slow remap: mmap + copy + munmap */
size_t copy_size = (new_size < old_size) ? new_size : old_size;
new_memory = do_mmap(new_size);
if (MAP_FAILED != new_memory) {
memcpy(new_memory, memory, copy_size);
(void) munmap(memory, old_size);
}
} else {
/* shrink via munmap */
(void) munmap((char *)memory + new_size, old_size - new_size);
new_memory = memory;
}
#endif
return new_memory;
}
static int mmap_allocate(allocation_t *allocation, size_t size)
{
static size_t page_size = 0;
static size_t page_mask = 0;
void *new_memory = MAP_FAILED;
size_t old_size = allocation->size;
size_t new_size = size;
if (!page_size) {
/* get page size */
long result = sysconf(_SC_PAGESIZE);
if (result > 0 && !(result & (result - 1))) {
page_size = (size_t) result;
page_mask = page_size - 1;
} else {
/* not a power of 2 */
errno = ENOSYS;
return -1;
}
}
/* round sizes up to multiple of page_size */
old_size = (old_size + page_size - 1) & ~page_mask;
new_size = (new_size + page_size - 1) & ~page_mask;
/* no mapping action required */
if (old_size == new_size) {
allocation->size = size;
return 0;
}
if (0 == new_size) {
if (NULL != allocation->memory && 0 != old_size) {
(void) munmap(allocation->memory, old_size);
}
new_memory = NULL;
} else if (0 == old_size) {
new_memory = do_mmap(new_size);
} else {
new_memory = do_mremap(allocation->memory, old_size, new_size);
}
if (MAP_FAILED == new_memory) {
/* operation failed */
return -1;
}
/* update allocation */
allocation->memory = new_memory;
allocation->size = size;
return 0;
}
static void mmap_destroy(allocator_t *allocator)
{
/* ignore allocator */
(void) allocator;
}
static allocator_t mmap_allocator = {
.allocate = mmap_allocate,
.destroy = mmap_destroy,
};
allocator_t *mmap_allocator_get(void)
{
return &mmap_allocator;
}