127 lines
3.3 KiB
C
127 lines
3.3 KiB
C
/*
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Copyright (C) 2024 John Cox john.cox@raspberrypi.com
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Permission is hereby granted, free of charge, to any person
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obtaining a copy of this software and associated documentation
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files (the "Software"), to deal in the Software without
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restriction, including without limitation the rights to use, copy,
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modify, merge, publish, distribute, sublicense, and/or sell copies
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of the Software, and to permit persons to whom the Software is
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furnished to do so, subject to the following conditions:
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The above copyright notice and this permission notice shall be
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included in all copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
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HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
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WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
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DEALINGS IN THE SOFTWARE.
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*/
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#include <stdlib.h>
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#include <pthread.h>
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#include <stdatomic.h>
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#include "weak_link.h"
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struct ff_weak_link_master {
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atomic_int ref_count; /* 0 is single ref for easier atomics */
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pthread_rwlock_t lock;
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void * ptr;
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};
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static inline struct ff_weak_link_master * weak_link_x(struct ff_weak_link_client * c)
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{
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return (struct ff_weak_link_master *)c;
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}
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struct ff_weak_link_master * ff_weak_link_new(void * p)
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{
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struct ff_weak_link_master * w = malloc(sizeof(*w));
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if (!w)
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return NULL;
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atomic_init(&w->ref_count, 0);
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w->ptr = p;
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if (pthread_rwlock_init(&w->lock, NULL)) {
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free(w);
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return NULL;
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}
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return w;
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}
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static void weak_link_do_unref(struct ff_weak_link_master * const w)
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{
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int n = atomic_fetch_sub(&w->ref_count, 1);
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if (n)
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return;
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pthread_rwlock_destroy(&w->lock);
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free(w);
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}
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// Unref & break link
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void ff_weak_link_break(struct ff_weak_link_master ** ppLink)
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{
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struct ff_weak_link_master * const w = *ppLink;
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if (!w)
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return;
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*ppLink = NULL;
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pthread_rwlock_wrlock(&w->lock);
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w->ptr = NULL;
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pthread_rwlock_unlock(&w->lock);
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weak_link_do_unref(w);
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}
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struct ff_weak_link_client* ff_weak_link_ref(struct ff_weak_link_master * w)
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{
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if (!w)
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return NULL;
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atomic_fetch_add(&w->ref_count, 1);
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return (struct ff_weak_link_client*)w;
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}
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void ff_weak_link_unref(struct ff_weak_link_client ** ppLink)
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{
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struct ff_weak_link_master * const w = weak_link_x(*ppLink);
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if (!w)
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return;
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*ppLink = NULL;
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weak_link_do_unref(w);
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}
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void * ff_weak_link_lock(struct ff_weak_link_client ** ppLink)
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{
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struct ff_weak_link_master * const w = weak_link_x(*ppLink);
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if (!w)
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return NULL;
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if (pthread_rwlock_rdlock(&w->lock))
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goto broken;
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if (w->ptr)
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return w->ptr;
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pthread_rwlock_unlock(&w->lock);
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broken:
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*ppLink = NULL;
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weak_link_do_unref(w);
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return NULL;
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}
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// Ignores a NULL c (so can be on the return path of both broken & live links)
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void ff_weak_link_unlock(struct ff_weak_link_client * c)
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{
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struct ff_weak_link_master * const w = weak_link_x(c);
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if (w)
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pthread_rwlock_unlock(&w->lock);
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}
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