From: Mathieu Desnoyers Date: Thu, 11 Oct 2012 19:08:57 +0000 (-0400) Subject: lfstack: implement lock-free stack X-Git-Tag: v0.8.0~181 X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=d3bfcb24240b01619686641ddd92ae8222b3ad32;p=urcu.git lfstack: implement lock-free stack This stack does not require to hold RCU read-side lock across push, and allows multiple strategies to be used for pop. Signed-off-by: Mathieu Desnoyers --- diff --git a/Makefile.am b/Makefile.am index ffdca9a..195b89a 100644 --- a/Makefile.am +++ b/Makefile.am @@ -17,6 +17,7 @@ nobase_dist_include_HEADERS = urcu/compiler.h urcu/hlist.h urcu/list.h \ urcu/wfqueue.h urcu/rculfstack.h urcu/rculfqueue.h \ urcu/ref.h urcu/cds.h urcu/urcu_ref.h urcu/urcu-futex.h \ urcu/uatomic_arch.h urcu/rculfhash.h urcu/wfcqueue.h \ + urcu/lfstack.h \ $(top_srcdir)/urcu/map/*.h \ $(top_srcdir)/urcu/static/*.h \ urcu/tls-compat.h @@ -72,7 +73,8 @@ liburcu_signal_la_LIBADD = liburcu-common.la liburcu_bp_la_SOURCES = urcu-bp.c urcu-pointer.c $(COMPAT) liburcu_bp_la_LIBADD = liburcu-common.la -liburcu_cds_la_SOURCES = rculfqueue.c rculfstack.c $(RCULFHASH) $(COMPAT) +liburcu_cds_la_SOURCES = rculfqueue.c rculfstack.c lfstack.c \ + $(RCULFHASH) $(COMPAT) liburcu_cds_la_LIBADD = liburcu-common.la pkgconfigdir = $(libdir)/pkgconfig diff --git a/lfstack.c b/lfstack.c new file mode 100644 index 0000000..74ffd4f --- /dev/null +++ b/lfstack.c @@ -0,0 +1,51 @@ +/* + * lfstack.c + * + * Userspace RCU library - Lock-Free Stack + * + * 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 + * 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 + */ + +/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ +#undef _LGPL_SOURCE +#include "urcu/lfstack.h" +#define _LGPL_SOURCE +#include "urcu/static/lfstack.h" + +/* + * library wrappers to be used by non-LGPL compatible source code. + */ + +void cds_lfs_node_init(struct cds_lfs_node *node) +{ + _cds_lfs_node_init(node); +} + +void cds_lfs_init(struct cds_lfs_stack *s) +{ + _cds_lfs_init(s); +} + +int cds_lfs_push(struct cds_lfs_stack *s, struct cds_lfs_node *node) +{ + return _cds_lfs_push(s, node); +} + +struct cds_lfs_node *cds_lfs_pop(struct cds_lfs_stack *s) +{ + return _cds_lfs_pop(s); +} diff --git a/urcu/cds.h b/urcu/cds.h index d9e7984..78534bb 100644 --- a/urcu/cds.h +++ b/urcu/cds.h @@ -33,5 +33,6 @@ #include #include #include +#include #endif /* _URCU_CDS_H */ diff --git a/urcu/lfstack.h b/urcu/lfstack.h new file mode 100644 index 0000000..d068739 --- /dev/null +++ b/urcu/lfstack.h @@ -0,0 +1,87 @@ +#ifndef _URCU_LFSTACK_H +#define _URCU_LFSTACK_H + +/* + * lfstack.h + * + * Userspace RCU library - Lock-Free Stack + * + * 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 + * 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 + */ + +#ifdef __cplusplus +extern "C" { +#endif + +struct cds_lfs_node { + struct cds_lfs_node *next; +}; + +struct cds_lfs_stack { + struct cds_lfs_node *head; +}; + +#ifdef _LGPL_SOURCE + +#include + +#define cds_lfs_node_init _cds_lfs_node_init +#define cds_lfs_init _cds_lfs_init +#define cds_lfs_push _cds_lfs_push +#define cds_lfs_pop _cds_lfs_pop + +#else /* !_LGPL_SOURCE */ + +extern void cds_lfs_node_init(struct cds_lfs_node *node); +extern void cds_lfs_init(struct cds_lfs_stack *s); + +/* + * cds_lfs_push: push a node into the stack. + * + * Does not require any synchronization with other push nor pop. + * + * Returns 0 if the stack was empty prior to adding the node. + * Returns non-zero otherwise. + */ +extern int cds_lfs_push(struct cds_lfs_stack *s, + struct cds_lfs_node *node); + +/* + * 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. The + * caller must wait for a grace period to pass before freeing the + * returned node or modifying the cds_lfs_node structure. + * 2) Using mutual exclusion (e.g. mutexes) to protect cds_lfs_pop + * callers. + * 3) Ensuring that only ONE thread can call cds_lfs_pop(). + * (multi-provider/single-consumer scheme). + */ +extern struct cds_lfs_node *cds_lfs_pop(struct cds_lfs_stack *s); + +#endif /* !_LGPL_SOURCE */ + +#ifdef __cplusplus +} +#endif + +#endif /* _URCU_LFSTACK_H */ diff --git a/urcu/static/lfstack.h b/urcu/static/lfstack.h new file mode 100644 index 0000000..7acbf54 --- /dev/null +++ b/urcu/static/lfstack.h @@ -0,0 +1,151 @@ +#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 rculfstack.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 + +#ifdef __cplusplus +extern "C" { +#endif + +static inline +void _cds_lfs_node_init(struct cds_lfs_node *node) +{ +} + +static inline +void _cds_lfs_init(struct cds_lfs_stack *s) +{ + s->head = NULL; +} + +/* + * 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 throrough benchmarking on various + * platforms. + * + * Returns 0 if the stack was empty prior to adding the node. + * Returns non-zero otherwise. + */ +static inline +int _cds_lfs_push(struct cds_lfs_stack *s, + struct cds_lfs_node *node) +{ + struct cds_lfs_node *head = NULL; + + for (;;) { + struct cds_lfs_node *old_head = head; + + /* + * node->next is still private at this point, no need to + * perform a _CMM_STORE_SHARED(). + */ + node->next = head; + /* + * uatomic_cmpxchg() implicit memory barrier orders earlier + * stores to node before publication. + */ + head = uatomic_cmpxchg(&s->head, old_head, node); + if (old_head == head) + break; + } + return (int) !!((unsigned long) 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. The + * caller must wait for a grace period to pass before freeing the + * returned node or modifying the cds_lfs_node structure. + * 2) Using mutual exclusion (e.g. mutexes) to protect cds_lfs_pop + * callers. + * 3) Ensuring that only ONE thread can call cds_lfs_pop(). + * (multi-provider/single-consumer scheme). + */ +static inline +struct cds_lfs_node *_cds_lfs_pop(struct cds_lfs_stack *s) +{ + for (;;) { + struct cds_lfs_node *head; + + head = _CMM_LOAD_SHARED(s->head); + if (head) { + struct cds_lfs_node *next; + + /* + * 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->next); + if (uatomic_cmpxchg(&s->head, head, next) == head) { + return head; + } else { + /* Concurrent modification. Retry. */ + continue; + } + } else { + /* Empty stack */ + return NULL; + } + } +} + +#ifdef __cplusplus +} +#endif + +#endif /* _URCU_STATIC_LFSTACK_H */