X-Git-Url: http://git.liburcu.org/?p=userspace-rcu.git;a=blobdiff_plain;f=include%2Furcu%2Fstatic%2Flfstack.h;fp=include%2Furcu%2Fstatic%2Flfstack.h;h=05d0bb478b8b169a03864272810d1b5c76bfa4f8;hp=0000000000000000000000000000000000000000;hb=6893800a4d1cc14dff0395ddcd660a5138db183d;hpb=a59f39055b5ecb77b68cf78b9839aa9e8e4ec332 diff --git a/include/urcu/static/lfstack.h b/include/urcu/static/lfstack.h new file mode 100644 index 0000000..05d0bb4 --- /dev/null +++ b/include/urcu/static/lfstack.h @@ -0,0 +1,318 @@ +#ifndef _URCU_STATIC_LFSTACK_H +#define _URCU_STATIC_LFSTACK_H + +/* + * urcu/static/lfstack.h + * + * Userspace RCU library - Lock-Free Stack + * + * Copyright 2010-2012 - Mathieu Desnoyers + * + * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu/lfstack.h for + * linking dynamically with the userspace rcu library. + * + * This library is free software; you can redistribute it and/or + * modify it under the terms of the GNU Lesser General Public + * License as published by the Free Software Foundation; either + * version 2.1 of the License, or (at your option) any later version. + * + * This library 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 + * Lesser General Public License for more details. + * + * You should have received a copy of the GNU Lesser General Public + * License along with this library; if not, write to the Free Software + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA + */ + +#include +#include +#include +#include +#include + +#ifdef __cplusplus +extern "C" { +#endif + +/* + * Lock-free stack. + * + * Stack implementing push, pop, pop_all operations, as well as iterator + * on the stack head returned by pop_all. + * + * Synchronization table: + * + * External synchronization techniques described in the API below is + * required between pairs marked with "X". No external synchronization + * required between pairs marked with "-". + * + * cds_lfs_push __cds_lfs_pop __cds_lfs_pop_all + * cds_lfs_push - - - + * __cds_lfs_pop - X X + * __cds_lfs_pop_all - X - + * + * cds_lfs_pop_blocking and cds_lfs_pop_all_blocking use an internal + * mutex to provide synchronization. + */ + +/* + * cds_lfs_node_init: initialize lock-free stack node. + */ +static inline +void _cds_lfs_node_init(struct cds_lfs_node *node) +{ +} + +/* + * cds_lfs_init: initialize lock-free stack (with lock). Pair with + * cds_lfs_destroy(). + */ +static inline +void _cds_lfs_init(struct cds_lfs_stack *s) +{ + int ret; + + s->head = NULL; + ret = pthread_mutex_init(&s->lock, NULL); + assert(!ret); +} + +/* + * cds_lfs_destroy: destroy lock-free stack (with lock). Pair with + * cds_lfs_init(). + */ +static inline +void _cds_lfs_destroy(struct cds_lfs_stack *s) +{ + int ret = pthread_mutex_destroy(&s->lock); + assert(!ret); +} + +/* + * ___cds_lfs_init: initialize lock-free stack (without lock). + * Don't pair with any destroy function. + */ +static inline +void ___cds_lfs_init(struct __cds_lfs_stack *s) +{ + s->head = NULL; +} + +static inline +bool ___cds_lfs_empty_head(struct cds_lfs_head *head) +{ + return head == NULL; +} + +/* + * cds_lfs_empty: return whether lock-free stack is empty. + * + * No memory barrier is issued. No mutual exclusion is required. + */ +static inline +bool _cds_lfs_empty(cds_lfs_stack_ptr_t s) +{ + return ___cds_lfs_empty_head(CMM_LOAD_SHARED(s._s->head)); +} + +/* + * cds_lfs_push: push a node into the stack. + * + * Does not require any synchronization with other push nor pop. + * + * Lock-free stack push is not subject to ABA problem, so no need to + * take the RCU read-side lock. Even if "head" changes between two + * uatomic_cmpxchg() invocations here (being popped, and then pushed + * again by one or more concurrent threads), the second + * uatomic_cmpxchg() invocation only cares about pushing a new entry at + * the head of the stack, ensuring consistency by making sure the new + * node->next is the same pointer value as the value replaced as head. + * It does not care about the content of the actual next node, so it can + * very well be reallocated between the two uatomic_cmpxchg(). + * + * We take the approach of expecting the stack to be usually empty, so + * we first try an initial uatomic_cmpxchg() on a NULL old_head, and + * retry if the old head was non-NULL (the value read by the first + * uatomic_cmpxchg() is used as old head for the following loop). The + * upside of this scheme is to minimize the amount of cacheline traffic, + * always performing an exclusive cacheline access, rather than doing + * non-exclusive followed by exclusive cacheline access (which would be + * required if we first read the old head value). This design decision + * might be revisited after more thorough benchmarking on various + * platforms. + * + * Returns 0 if the stack was empty prior to adding the node. + * Returns non-zero otherwise. + */ +static inline +bool _cds_lfs_push(cds_lfs_stack_ptr_t u_s, + struct cds_lfs_node *node) +{ + struct __cds_lfs_stack *s = u_s._s; + struct cds_lfs_head *head = NULL; + struct cds_lfs_head *new_head = + caa_container_of(node, struct cds_lfs_head, node); + + for (;;) { + struct cds_lfs_head *old_head = head; + + /* + * node->next is still private at this point, no need to + * perform a _CMM_STORE_SHARED(). + */ + node->next = &head->node; + /* + * uatomic_cmpxchg() implicit memory barrier orders earlier + * stores to node before publication. + */ + head = uatomic_cmpxchg(&s->head, old_head, new_head); + if (old_head == head) + break; + } + return !___cds_lfs_empty_head(head); +} + +/* + * __cds_lfs_pop: pop a node from the stack. + * + * Returns NULL if stack is empty. + * + * __cds_lfs_pop needs to be synchronized using one of the following + * techniques: + * + * 1) Calling __cds_lfs_pop under rcu read lock critical section. + * Both __cds_lfs_pop and __cds_lfs_pop_all callers must wait for a + * grace period to pass before freeing the returned node or pushing + * the node back into the stack. It is valid to overwrite the content + * of cds_lfs_node immediately after __cds_lfs_pop and + * __cds_lfs_pop_all. No RCU read-side critical section is needed + * around __cds_lfs_pop_all. + * 2) Using mutual exclusion (e.g. mutexes) to protect __cds_lfs_pop + * and __cds_lfs_pop_all callers. + * 3) Ensuring that only ONE thread can call __cds_lfs_pop() and + * __cds_lfs_pop_all(). (multi-provider/single-consumer scheme). + */ +static inline +struct cds_lfs_node *___cds_lfs_pop(cds_lfs_stack_ptr_t u_s) +{ + struct __cds_lfs_stack *s = u_s._s; + + for (;;) { + struct cds_lfs_head *head, *next_head; + struct cds_lfs_node *next; + + head = _CMM_LOAD_SHARED(s->head); + if (___cds_lfs_empty_head(head)) + return NULL; /* Empty stack */ + + /* + * Read head before head->next. Matches the implicit + * memory barrier before uatomic_cmpxchg() in + * cds_lfs_push. + */ + cmm_smp_read_barrier_depends(); + next = _CMM_LOAD_SHARED(head->node.next); + next_head = caa_container_of(next, + struct cds_lfs_head, node); + if (uatomic_cmpxchg(&s->head, head, next_head) == head) + return &head->node; + /* busy-loop if head changed under us */ + } +} + +/* + * __cds_lfs_pop_all: pop all nodes from a stack. + * + * __cds_lfs_pop_all does not require any synchronization with other + * push, nor with other __cds_lfs_pop_all, but requires synchronization + * matching the technique used to synchronize __cds_lfs_pop: + * + * 1) If __cds_lfs_pop is called under rcu read lock critical section, + * both __cds_lfs_pop and __cds_lfs_pop_all callers must wait for a + * grace period to pass before freeing the returned node or pushing + * the node back into the stack. It is valid to overwrite the content + * of cds_lfs_node immediately after __cds_lfs_pop and + * __cds_lfs_pop_all. No RCU read-side critical section is needed + * around __cds_lfs_pop_all. + * 2) Using mutual exclusion (e.g. mutexes) to protect __cds_lfs_pop and + * __cds_lfs_pop_all callers. + * 3) Ensuring that only ONE thread can call __cds_lfs_pop() and + * __cds_lfs_pop_all(). (multi-provider/single-consumer scheme). + */ +static inline +struct cds_lfs_head *___cds_lfs_pop_all(cds_lfs_stack_ptr_t u_s) +{ + struct __cds_lfs_stack *s = u_s._s; + + /* + * Implicit memory barrier after uatomic_xchg() matches implicit + * memory barrier before uatomic_cmpxchg() in cds_lfs_push. It + * ensures that all nodes of the returned list are consistent. + * There is no need to issue memory barriers when iterating on + * the returned list, because the full memory barrier issued + * prior to each uatomic_cmpxchg, which each write to head, are + * taking care to order writes to each node prior to the full + * memory barrier after this uatomic_xchg(). + */ + return uatomic_xchg(&s->head, NULL); +} + +/* + * cds_lfs_pop_lock: lock stack pop-protection mutex. + */ +static inline void _cds_lfs_pop_lock(struct cds_lfs_stack *s) +{ + int ret; + + ret = pthread_mutex_lock(&s->lock); + assert(!ret); +} + +/* + * cds_lfs_pop_unlock: unlock stack pop-protection mutex. + */ +static inline void _cds_lfs_pop_unlock(struct cds_lfs_stack *s) +{ + int ret; + + ret = pthread_mutex_unlock(&s->lock); + assert(!ret); +} + +/* + * Call __cds_lfs_pop with an internal pop mutex held. + */ +static inline +struct cds_lfs_node * +_cds_lfs_pop_blocking(struct cds_lfs_stack *s) +{ + struct cds_lfs_node *retnode; + + _cds_lfs_pop_lock(s); + retnode = ___cds_lfs_pop(s); + _cds_lfs_pop_unlock(s); + return retnode; +} + +/* + * Call __cds_lfs_pop_all with an internal pop mutex held. + */ +static inline +struct cds_lfs_head * +_cds_lfs_pop_all_blocking(struct cds_lfs_stack *s) +{ + struct cds_lfs_head *rethead; + + _cds_lfs_pop_lock(s); + rethead = ___cds_lfs_pop_all(s); + _cds_lfs_pop_unlock(s); + return rethead; +} + +#ifdef __cplusplus +} +#endif + +#endif /* _URCU_STATIC_LFSTACK_H */