weston/libweston/id-number-allocator.c

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/*
* Copyright 2024 Collabora, Ltd.
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice (including the
* next paragraph) shall be included in all copies or substantial
* portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#include "config.h"
#include "id-number-allocator.h"
#include "shared/helpers.h"
#include "shared/xalloc.h"
#include "shared/weston-assert.h"
struct weston_idalloc {
struct weston_compositor *compositor;
/* Each value on this array is a bucket of size 32. Bit is 0 if the id
* is available, 1 otherwise. */
uint32_t *buckets;
uint32_t num_buckets;
uint32_t lowest_free_bucket;
};
/**
* Creates a unique id allocator
*
* \param compositor The compositor
* \return The unique id allocator
*/
WESTON_EXPORT_FOR_TESTS struct weston_idalloc *
weston_idalloc_create(struct weston_compositor *compositor)
{
struct weston_idalloc *idalloc;
idalloc = xzalloc(sizeof(*idalloc));
idalloc->compositor = compositor;
/* Start with 2 buckets. If necessary we increase that on demand. */
idalloc->num_buckets = 2;
idalloc->buckets = xzalloc(idalloc->num_buckets * sizeof(*idalloc->buckets));
/* Let's reserve id 0 for errors. So start with id 0 already taken. Set
* the first bit of the first bucket to 1. */
idalloc->buckets[idalloc->lowest_free_bucket] = 1;
return idalloc;
}
/**
* Destroys a unique id allocator
*
* \param idalloc The unique id allocator to destroy
*/
WESTON_EXPORT_FOR_TESTS void
weston_idalloc_destroy(struct weston_idalloc *idalloc)
{
/* Sanity check: id 0 should still be taken. */
weston_assert_true(idalloc->compositor, idalloc->buckets[0] & 1);
free(idalloc->buckets);
free(idalloc);
}
static void
update_lowest_free_bucket(struct weston_idalloc *idalloc)
{
uint32_t old_lowest_free_bucket = idalloc->lowest_free_bucket;
uint32_t *bucket;
unsigned int i;
for (i = old_lowest_free_bucket; i < idalloc->num_buckets; i++) {
bucket = &idalloc->buckets[i];
/* Skip full bucket */
if (*bucket == 0xffffffff)
continue;
idalloc->lowest_free_bucket = i;
return;
}
/* We didn't find any free bucket, so we need to add more buckets. The
* first one (from the new added) will be the lowest free. */
idalloc->lowest_free_bucket = idalloc->num_buckets;
idalloc->num_buckets *= 2;
idalloc->buckets = xrealloc(idalloc->buckets,
idalloc->num_buckets * sizeof(*idalloc->buckets));
}
/**
* Gets an id from unique id allocator
*
* \param idalloc The unique id allocator
* \return The unique id
*/
WESTON_EXPORT_FOR_TESTS uint32_t
weston_idalloc_get_id(struct weston_idalloc *idalloc)
{
uint32_t *bucket = &idalloc->buckets[idalloc->lowest_free_bucket];
unsigned int i;
uint32_t id;
/* Sanity check: lowest free bucket should not be full. */
weston_assert_uint32_neq(idalloc->compositor, *bucket, 0xffffffff);
for (i = 0; i < 32; i++) {
/* Id already used, skip it. */
if ((*bucket >> i) & 1)
continue;
/* Found free id, take it and set it to 1 on the bucket. */
*bucket |= 1 << i;
id = (32 * idalloc->lowest_free_bucket) + i;
/* Bucket may become full... */
if (*bucket == 0xffffffff)
update_lowest_free_bucket(idalloc);
return id;
}
/* We need to find an available id. */
weston_assert_not_reached(idalloc->compositor,
"should be able to allocate unique id");
}
/**
* Releases a id back to unique id allocator
*
* When an id from the unique id allocator will not be used anymore, users
* should call this function so that this id can be advertised again by the id
* allocator.
*
* \param idalloc The unique id allocator
* \param id The id to release
*/
WESTON_EXPORT_FOR_TESTS void
weston_idalloc_put_id(struct weston_idalloc *idalloc, uint32_t id)
{
uint32_t bucket_index = id / 32;
uint32_t id_index_on_bucket = id % 32;
uint32_t *bucket;
/* Shouldn't try to release index 0, we never advertise this id to anyone. */
weston_assert_uint32_neq(idalloc->compositor, id, 0);
/* Bucket index should be lower than num_buckets. */
weston_assert_uint32_lt(idalloc->compositor,
bucket_index, idalloc->num_buckets);
bucket = &idalloc->buckets[bucket_index];
/* Shouldn't try to release a free index. */
weston_assert_true(idalloc->compositor,
(*bucket >> id_index_on_bucket) & 1);
/* We now have an available index id on this bucket, so it may become
* the lowest bucket. */
if (bucket_index < idalloc->lowest_free_bucket)
idalloc->lowest_free_bucket = bucket_index;
/* Zero the bit on the bucket. */
*bucket &= ~(1 << id_index_on_bucket);
}