X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu%2Fwfstack.h;h=9d693053117ceb93e69034e433f2196a22c3070d;hp=b3ee2e7c4585e6e2f735a81ce82b67db3f84a5e2;hb=200d100e05ed8e10c47f971939042f2406df92ef;hpb=cb3f3d6bce4faeb41e4109e12fa722f73a6f6c13 diff --git a/urcu/wfstack.h b/urcu/wfstack.h index b3ee2e7..9d69305 100644 --- a/urcu/wfstack.h +++ b/urcu/wfstack.h @@ -2,11 +2,11 @@ #define _URCU_WFSTACK_H /* - * rcuwfstack.h + * urcu/wfstack.h * - * Userspace RCU library - Stack with Wait-Free push, Blocking pop. + * Userspace RCU library - Stack with wait-free push, blocking traversal. * - * Copyright 2010 - Mathieu Desnoyers + * Copyright 2010-2012 - Mathieu Desnoyers * * This library is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public @@ -25,105 +25,333 @@ #include #include +#include #include #ifdef __cplusplus extern "C" { #endif -#if (!defined(_GNU_SOURCE) && !defined(_LGPL_SOURCE)) -#error "Dynamic loader LGPL wrappers not implemented yet" -#endif +/* + * Stack with wait-free push, blocking traversal. + * + * Stack implementing push, pop, pop_all operations, as well as iterator + * on the stack head returned by pop_all. + * + * Wait-free operations: cds_wfs_push, __cds_wfs_pop_all, cds_wfs_empty, + * cds_wfs_first. + * Blocking operations: cds_wfs_pop, cds_wfs_pop_all, cds_wfs_next, + * iteration on 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_wfs_push __cds_wfs_pop __cds_wfs_pop_all + * cds_wfs_push - - - + * __cds_wfs_pop - X X + * __cds_wfs_pop_all - X - + * + * cds_wfs_pop and cds_wfs_pop_all use an internal mutex to provide + * synchronization. + */ -#define WF_STACK_END ((void *)0x1UL) -#define WFS_ADAPT_ATTEMPTS 10 /* Retry if being set */ -#define WFS_WAIT 10 /* Wait 10 ms if being set */ +#define CDS_WFS_WOULDBLOCK ((void *) -1UL) -struct wfs_node { - struct wfs_node *next; +enum cds_wfs_state { + CDS_WFS_STATE_LAST = (1U << 0), }; -struct wfs_stack { - struct wfs_node *head; +/* + * struct cds_wfs_node is returned by __cds_wfs_pop, and also used as + * iterator on stack. It is not safe to dereference the node next + * pointer when returned by __cds_wfs_pop_blocking. + */ +struct cds_wfs_node { + struct cds_wfs_node *next; +}; + +/* + * struct cds_wfs_head is returned by __cds_wfs_pop_all, and can be used + * to begin iteration on the stack. "node" needs to be the first field of + * cds_wfs_head, so the end-of-stack pointer value can be used for both + * types. + */ +struct cds_wfs_head { + struct cds_wfs_node node; +}; + +struct __cds_wfs_stack { + struct cds_wfs_head *head; +}; + +struct cds_wfs_stack { + struct cds_wfs_head *head; pthread_mutex_t lock; }; -void wfs_node_init(struct wfs_node *node) -{ - node->next = NULL; -} +/* + * The transparent union allows calling functions that work on both + * struct cds_wfs_stack and struct __cds_wfs_stack on any of those two + * types. + */ +typedef union { + struct __cds_wfs_stack *_s; + struct cds_wfs_stack *s; +} __attribute__((__transparent_union__)) cds_wfs_stack_ptr_t; -void wfs_init(struct wfs_stack *s) -{ - int ret; +#ifdef _LGPL_SOURCE - s->head = WF_STACK_END; - ret = pthread_mutex_init(&s->lock, NULL); - assert(!ret); -} +#include -void wfs_push(struct wfs_stack *s, struct wfs_node *node) -{ - struct wfs_node *old_head; - - assert(node->next == NULL); - /* - * uatomic_xchg() implicit memory barrier orders earlier stores to node - * (setting it to NULL) before publication. - */ - old_head = uatomic_xchg(&s->head, node); - /* - * At this point, dequeuers see a NULL node->next, they should busy-wait - * until node->next is set to old_head. - */ - STORE_SHARED(node->next, old_head); -} +#define cds_wfs_node_init _cds_wfs_node_init +#define cds_wfs_init _cds_wfs_init +#define cds_wfs_destroy _cds_wfs_destroy +#define __cds_wfs_init ___cds_wfs_init +#define cds_wfs_empty _cds_wfs_empty +#define cds_wfs_push _cds_wfs_push + +/* Locking performed internally */ +#define cds_wfs_pop_blocking _cds_wfs_pop_blocking +#define cds_wfs_pop_with_state_blocking _cds_wfs_pop_with_state_blocking +#define cds_wfs_pop_all_blocking _cds_wfs_pop_all_blocking + +/* + * For iteration on cds_wfs_head returned by __cds_wfs_pop_all or + * cds_wfs_pop_all_blocking. + */ +#define cds_wfs_first _cds_wfs_first +#define cds_wfs_next_blocking _cds_wfs_next_blocking +#define cds_wfs_next_nonblocking _cds_wfs_next_nonblocking + +/* Pop locking with internal mutex */ +#define cds_wfs_pop_lock _cds_wfs_pop_lock +#define cds_wfs_pop_unlock _cds_wfs_pop_unlock + +/* Synchronization ensured by the caller. See synchronization table. */ +#define __cds_wfs_pop_blocking ___cds_wfs_pop_blocking +#define __cds_wfs_pop_with_state_blocking \ + ___cds_wfs_pop_with_state_blocking +#define __cds_wfs_pop_nonblocking ___cds_wfs_pop_nonblocking +#define __cds_wfs_pop_with_state_nonblocking \ + ___cds_wfs_pop_with_state_nonblocking +#define __cds_wfs_pop_all ___cds_wfs_pop_all + +#else /* !_LGPL_SOURCE */ + +/* + * cds_wfs_node_init: initialize wait-free stack node. + */ +extern void cds_wfs_node_init(struct cds_wfs_node *node); + +/* + * cds_wfs_init: initialize wait-free stack (with lock). Pair with + * cds_wfs_destroy(). + */ +extern void cds_wfs_init(struct cds_wfs_stack *s); + +/* + * cds_wfs_destroy: destroy wait-free stack (with lock). Pair with + * cds_wfs_init(). + */ +extern void cds_wfs_destroy(struct cds_wfs_stack *s); + +/* + * __cds_wfs_init: initialize wait-free stack (no lock). Don't pair with + * any destroy function. + */ +extern void __cds_wfs_init(struct __cds_wfs_stack *s); + +/* + * cds_wfs_empty: return whether wait-free stack is empty. + * + * No memory barrier is issued. No mutual exclusion is required. + */ +extern bool cds_wfs_empty(cds_wfs_stack_ptr_t u_stack); + +/* + * cds_wfs_push: push a node into the stack. + * + * Issues a full memory barrier before push. No mutual exclusion is + * required. + * + * Returns 0 if the stack was empty prior to adding the node. + * Returns non-zero otherwise. + */ +extern int cds_wfs_push(cds_wfs_stack_ptr_t u_stack, struct cds_wfs_node *node); + +/* + * cds_wfs_pop_blocking: pop a node from the stack. + * + * Calls __cds_wfs_pop_blocking with an internal pop mutex held. + */ +extern struct cds_wfs_node *cds_wfs_pop_blocking(struct cds_wfs_stack *s); + +/* + * cds_wfs_pop_with_state_blocking: pop a node from the stack, with state. + * + * Same as cds_wfs_pop_blocking, but stores whether the stack was + * empty into state (CDS_WFS_STATE_LAST). + */ +extern struct cds_wfs_node * + cds_wfs_pop_with_state_blocking(struct cds_wfs_stack *s, int *state); + +/* + * cds_wfs_pop_all_blocking: pop all nodes from a stack. + * + * Calls __cds_wfs_pop_all with an internal pop mutex held. + */ +extern struct cds_wfs_head *cds_wfs_pop_all_blocking(struct cds_wfs_stack *s); /* + * cds_wfs_first: get first node of a popped stack. + * + * Content written into the node before enqueue is guaranteed to be + * consistent, but no other memory ordering is ensured. + * + * Used by for-like iteration macros in urcu/wfstack.h: + * cds_wfs_for_each_blocking() + * cds_wfs_for_each_blocking_safe() + * + * Returns NULL if popped stack is empty, top stack node otherwise. + */ +extern struct cds_wfs_node *cds_wfs_first(struct cds_wfs_head *head); + +/* + * cds_wfs_next_blocking: get next node of a popped stack. + * + * Content written into the node before enqueue is guaranteed to be + * consistent, but no other memory ordering is ensured. + * + * Used by for-like iteration macros in urcu/wfstack.h: + * cds_wfs_for_each_blocking() + * cds_wfs_for_each_blocking_safe() + * + * Returns NULL if reached end of popped stack, non-NULL next stack + * node otherwise. + */ +extern struct cds_wfs_node *cds_wfs_next_blocking(struct cds_wfs_node *node); + +/* + * cds_wfs_next_nonblocking: get next node of a popped stack. + * + * Same as cds_wfs_next_blocking, but returns CDS_WFS_WOULDBLOCK if it + * needs to block. + */ +extern struct cds_wfs_node *cds_wfs_next_nonblocking(struct cds_wfs_node *node); + +/* + * cds_wfs_pop_lock: lock stack pop-protection mutex. + */ +extern void cds_wfs_pop_lock(struct cds_wfs_stack *s); + +/* + * cds_wfs_pop_unlock: unlock stack pop-protection mutex. + */ +extern void cds_wfs_pop_unlock(struct cds_wfs_stack *s); + +/* + * __cds_wfs_pop_blocking: pop a node from the stack. + * * Returns NULL if stack is empty. + * + * __cds_wfs_pop_blocking needs to be synchronized using one of the + * following techniques: + * + * 1) Calling __cds_wfs_pop_blocking under rcu read lock critical + * section. The caller must wait for a grace period to pass before + * freeing the returned node or modifying the cds_wfs_node structure. + * 2) Using mutual exclusion (e.g. mutexes) to protect + * __cds_wfs_pop_blocking and __cds_wfs_pop_all callers. + * 3) Ensuring that only ONE thread can call __cds_wfs_pop_blocking() + * and __cds_wfs_pop_all(). (multi-provider/single-consumer scheme). */ -struct wfs_node * -__wfs_pop_blocking(struct wfs_stack *s) -{ - struct wfs_node *head, *next; - int attempt = 0; - -retry: - head = LOAD_SHARED(s->head); - if (head == WF_STACK_END) - return NULL; - /* - * Adaptative busy-looping waiting for push to complete. - */ - while ((next = LOAD_SHARED(head->next)) == NULL) { - if (++attempt >= WFS_ADAPT_ATTEMPTS) { - poll(NULL, 0, WFS_WAIT); /* Wait for 10ms */ - attempt = 0; - } else - cpu_relax(); - } - if (uatomic_cmpxchg(&s->head, head, next) == head) - return head; - else - goto retry; /* Concurrent modification. Retry. */ -} +extern struct cds_wfs_node *__cds_wfs_pop_blocking(cds_wfs_stack_ptr_t u_stack); -struct wfs_node * -wfs_pop_blocking(struct wfs_stack *s) -{ - struct wfs_node *retnode; - int ret; - - ret = pthread_mutex_lock(&s->lock); - assert(!ret); - retnode = __wfs_pop_blocking(s); - ret = pthread_mutex_unlock(&s->lock); - assert(!ret); - return retnode; -} +/* + * __cds_wfs_pop_with_state_blocking: pop a node from the stack, with state. + * + * Same as __cds_wfs_pop_blocking, but stores whether the stack was + * empty into state (CDS_WFS_STATE_LAST). + */ +extern struct cds_wfs_node * + __cds_wfs_pop_with_state_blocking(cds_wfs_stack_ptr_t u_stack, + int *state); + +/* + * __cds_wfs_pop_nonblocking: pop a node from the stack. + * + * Same as __cds_wfs_pop_blocking, but returns CDS_WFS_WOULDBLOCK if + * it needs to block. + */ +extern struct cds_wfs_node *__cds_wfs_pop_nonblocking(cds_wfs_stack_ptr_t u_stack); + +/* + * __cds_wfs_pop_with_state_nonblocking: pop a node from the stack, with state. + * + * Same as __cds_wfs_pop_nonblocking, but stores whether the stack was + * empty into state (CDS_WFS_STATE_LAST). + */ +extern struct cds_wfs_node * + __cds_wfs_pop_with_state_nonblocking(cds_wfs_stack_ptr_t u_stack, + int *state); + +/* + * __cds_wfs_pop_all: pop all nodes from a stack. + * + * __cds_wfs_pop_all does not require any synchronization with other + * push, nor with other __cds_wfs_pop_all, but requires synchronization + * matching the technique used to synchronize __cds_wfs_pop_blocking: + * + * 1) If __cds_wfs_pop_blocking is called under rcu read lock critical + * section, both __cds_wfs_pop_blocking and cds_wfs_pop_all callers + * must wait for a grace period to pass before freeing the returned + * node or modifying the cds_wfs_node structure. However, no RCU + * read-side critical section is needed around __cds_wfs_pop_all. + * 2) Using mutual exclusion (e.g. mutexes) to protect + * __cds_wfs_pop_blocking and __cds_wfs_pop_all callers. + * 3) Ensuring that only ONE thread can call __cds_wfs_pop_blocking() + * and __cds_wfs_pop_all(). (multi-provider/single-consumer scheme). + */ +extern struct cds_wfs_head *__cds_wfs_pop_all(cds_wfs_stack_ptr_t u_stack); + +#endif /* !_LGPL_SOURCE */ #ifdef __cplusplus } #endif +/* + * cds_wfs_for_each_blocking: Iterate over all nodes returned by + * __cds_wfs_pop_all(). + * @head: head of the queue (struct cds_wfs_head pointer). + * @node: iterator (struct cds_wfs_node pointer). + * + * Content written into each node before enqueue is guaranteed to be + * consistent, but no other memory ordering is ensured. + */ +#define cds_wfs_for_each_blocking(head, node) \ + for (node = cds_wfs_first(head); \ + node != NULL; \ + node = cds_wfs_next_blocking(node)) + +/* + * cds_wfs_for_each_blocking_safe: Iterate over all nodes returned by + * __cds_wfs_pop_all(). Safe against deletion. + * @head: head of the queue (struct cds_wfs_head pointer). + * @node: iterator (struct cds_wfs_node pointer). + * @n: struct cds_wfs_node pointer holding the next pointer (used + * internally). + * + * Content written into each node before enqueue is guaranteed to be + * consistent, but no other memory ordering is ensured. + */ +#define cds_wfs_for_each_blocking_safe(head, node, n) \ + for (node = cds_wfs_first(head), \ + n = (node ? cds_wfs_next_blocking(node) : NULL); \ + node != NULL; \ + node = n, n = (node ? cds_wfs_next_blocking(node) : NULL)) + #endif /* _URCU_WFSTACK_H */