// SPDX-FileCopyrightText: 2010-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
//
// SPDX-License-Identifier: LGPL-2.1-or-later
#ifndef _URCU_STATIC_WFSTACK_H
#define _URCU_STATIC_WFSTACK_H
/*
* Userspace RCU library - Stack with with wait-free push, blocking traversal.
*
* TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu/wfstack.h for
* linking dynamically with the userspace rcu library.
*/
#include <pthread.h>
#include <poll.h>
#include <stdbool.h>
#include <urcu/assert.h>
#include <urcu/compiler.h>
#include <urcu/uatomic.h>
#ifdef __cplusplus
extern "C" {
#endif
#define CDS_WFS_END ((struct cds_wfs_head *) 0x1UL)
#define CDS_WFS_ADAPT_ATTEMPTS 10 /* Retry if being set */
#define CDS_WFS_WAIT 10 /* Wait 10 ms if being set */
/*
* 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.
*/
/*
* cds_wfs_node_init: initialize wait-free stack node.
*/
static inline
void _cds_wfs_node_init(struct cds_wfs_node *node)
{
node->next = NULL;
}
/*
* __cds_wfs_init: initialize wait-free stack. Don't pair with
* any destroy function.
*/
static inline void ___cds_wfs_init(struct __cds_wfs_stack *s)
{
s->head = CDS_WFS_END;
}
/*
* cds_wfs_init: initialize wait-free stack. Pair with
* cds_wfs_destroy().
*/
static inline
void _cds_wfs_init(struct cds_wfs_stack *s)
{
int ret;
s->head = CDS_WFS_END;
ret = pthread_mutex_init(&s->lock, NULL);
urcu_posix_assert(!ret);
}
/*
* cds_wfs_destroy: destroy wait-free stack. Pair with
* cds_wfs_init().
*/
static inline
void _cds_wfs_destroy(struct cds_wfs_stack *s)
{
int ret = pthread_mutex_destroy(&s->lock);
urcu_posix_assert(!ret);
}
static inline bool ___cds_wfs_end(void *node)
{
return node == CDS_WFS_END;
}
/*
* cds_wfs_empty: return whether wait-free stack is empty.
*
* No memory barrier is issued. No mutual exclusion is required.
*/
static inline bool _cds_wfs_empty(cds_wfs_stack_const_ptr_t u_stack)
{
const struct __cds_wfs_stack *s = u_stack._s;
return ___cds_wfs_end(uatomic_load(&s->head, CMM_RELAXED));
}
/*
* cds_wfs_push: push a node into the stack.
*
* Issues a full memory barrier before push. No mutual exclusion is
* required.
*
* Operations before push are consistent when observed after associated pop.
*
* Returns 0 if the stack was empty prior to adding the node.
* Returns non-zero otherwise.
*/
static inline
int _cds_wfs_push(cds_wfs_stack_ptr_t u_stack, struct cds_wfs_node *node)
{
struct __cds_wfs_stack *s = u_stack._s;
struct cds_wfs_head *old_head, *new_head;
urcu_posix_assert(node->next == NULL);
new_head = caa_container_of(node, struct cds_wfs_head, node);
/*
* uatomic_xchg() implicit memory barrier orders earlier stores
* to node (setting it to NULL) before publication.
*/
cmm_emit_legacy_smp_mb();
old_head = uatomic_xchg_mo(&s->head, new_head, CMM_SEQ_CST);
/*
* At this point, dequeuers see a NULL node->next, they should
* busy-wait until node->next is set to old_head.
*/
uatomic_store(&node->next, &old_head->node, CMM_RELEASE);
return !___cds_wfs_end(old_head);
}
/*
* Waiting for push to complete enqueue and return the next node.
*/
static inline struct cds_wfs_node *
___cds_wfs_node_sync_next(struct cds_wfs_node *node, int blocking)
{
struct cds_wfs_node *next;
int attempt = 0;
/*
* Adaptative busy-looping waiting for push to complete.
*/
while ((next = uatomic_load(&node->next, CMM_CONSUME)) == NULL) {
if (!blocking)
return CDS_WFS_WOULDBLOCK;
if (++attempt >= CDS_WFS_ADAPT_ATTEMPTS) {
(void) poll(NULL, 0, CDS_WFS_WAIT); /* Wait for 10ms */
attempt = 0;
} else {
caa_cpu_relax();
}
}
return next;
}
static inline
struct cds_wfs_node *
___cds_wfs_pop(cds_wfs_stack_ptr_t u_stack, int *state, int blocking)
{
struct cds_wfs_head *head, *new_head;
struct cds_wfs_node *next;
struct __cds_wfs_stack *s = u_stack._s;
if (state)
*state = 0;
for (;;) {
head = uatomic_load(&s->head, CMM_CONSUME);
if (___cds_wfs_end(head)) {
return NULL;
}
next = ___cds_wfs_node_sync_next(&head->node, blocking);
if (!blocking && next == CDS_WFS_WOULDBLOCK) {
return CDS_WFS_WOULDBLOCK;
}
new_head = caa_container_of(next, struct cds_wfs_head, node);
if (uatomic_cmpxchg_mo(&s->head, head, new_head,
CMM_SEQ_CST, CMM_SEQ_CST) == head) {
if (state && ___cds_wfs_end(new_head))
*state |= CDS_WFS_STATE_LAST;
cmm_emit_legacy_smp_mb();
return &head->node;
}
if (!blocking) {
return CDS_WFS_WOULDBLOCK;
}
/* busy-loop if head changed under us */
}
}
/*
* __cds_wfs_pop_with_state_blocking: pop a node from the stack, with state.
*
* Returns NULL if stack is empty.
*
* Operations after pop push are consistent when observed before associated push.
*
* __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).
*
* "state" saves state flags atomically sampled with pop operation.
*/
static inline
struct cds_wfs_node *
___cds_wfs_pop_with_state_blocking(cds_wfs_stack_ptr_t u_stack, int *state)
{
return ___cds_wfs_pop(u_stack, state, 1);
}
static inline
struct cds_wfs_node *
___cds_wfs_pop_blocking(cds_wfs_stack_ptr_t u_stack)
{
return ___cds_wfs_pop_with_state_blocking(u_stack, NULL);
}
/*
* __cds_wfs_pop_with_state_nonblocking: pop a node from the stack.
*
* Same as __cds_wfs_pop_with_state_blocking, but returns
* CDS_WFS_WOULDBLOCK if it needs to block.
*
* "state" saves state flags atomically sampled with pop operation.
*/
static inline
struct cds_wfs_node *
___cds_wfs_pop_with_state_nonblocking(cds_wfs_stack_ptr_t u_stack, int *state)
{
return ___cds_wfs_pop(u_stack, state, 0);
}
/*
* __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.
*/
static inline
struct cds_wfs_node *
___cds_wfs_pop_nonblocking(cds_wfs_stack_ptr_t u_stack)
{
return ___cds_wfs_pop_with_state_nonblocking(u_stack, NULL);
}
/*
* __cds_wfs_pop_all: pop all nodes from a stack.
*
* Operations after pop push are consistent when observed before associated push.
*
* __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).
*/
static inline
struct cds_wfs_head *
___cds_wfs_pop_all(cds_wfs_stack_ptr_t u_stack)
{
struct __cds_wfs_stack *s = u_stack._s;
struct cds_wfs_head *head;
/*
* Implicit memory barrier after uatomic_xchg() matches implicit
* memory barrier before uatomic_xchg() in cds_wfs_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().
*/
head = uatomic_xchg_mo(&s->head, CDS_WFS_END, CMM_SEQ_CST);
cmm_emit_legacy_smp_mb();
if (___cds_wfs_end(head))
return NULL;
return head;
}
/*
* cds_wfs_pop_lock: lock stack pop-protection mutex.
*/
static inline void _cds_wfs_pop_lock(struct cds_wfs_stack *s)
{
int ret;
ret = pthread_mutex_lock(&s->lock);
urcu_posix_assert(!ret);
}
/*
* cds_wfs_pop_unlock: unlock stack pop-protection mutex.
*/
static inline void _cds_wfs_pop_unlock(struct cds_wfs_stack *s)
{
int ret;
ret = pthread_mutex_unlock(&s->lock);
urcu_posix_assert(!ret);
}
/*
* Call __cds_wfs_pop_with_state_blocking with an internal pop mutex held.
*/
static inline
struct cds_wfs_node *
_cds_wfs_pop_with_state_blocking(struct cds_wfs_stack *s, int *state)
{
struct cds_wfs_node *retnode;
cds_wfs_stack_ptr_t stack;
_cds_wfs_pop_lock(s);
stack.s = s;
retnode = ___cds_wfs_pop_with_state_blocking(stack, state);
_cds_wfs_pop_unlock(s);
return retnode;
}
/*
* Call _cds_wfs_pop_with_state_blocking without saving any state.
*/
static inline
struct cds_wfs_node *
_cds_wfs_pop_blocking(struct cds_wfs_stack *s)
{
return _cds_wfs_pop_with_state_blocking(s, NULL);
}
/*
* Call __cds_wfs_pop_all with an internal pop mutex held.
*/
static inline
struct cds_wfs_head *
_cds_wfs_pop_all_blocking(struct cds_wfs_stack *s)
{
struct cds_wfs_head *rethead;
cds_wfs_stack_ptr_t stack;
_cds_wfs_pop_lock(s);
stack.s = s;
rethead = ___cds_wfs_pop_all(stack);
_cds_wfs_pop_unlock(s);
return rethead;
}
/*
* 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.
*/
static inline struct cds_wfs_node *
_cds_wfs_first(struct cds_wfs_head *head)
{
if (___cds_wfs_end(head))
return NULL;
return &head->node;
}
static inline struct cds_wfs_node *
___cds_wfs_next(struct cds_wfs_node *node, int blocking)
{
struct cds_wfs_node *next;
next = ___cds_wfs_node_sync_next(node, blocking);
/*
* CDS_WFS_WOULDBLOCK != CSD_WFS_END, so we can check for end
* even if ___cds_wfs_node_sync_next returns CDS_WFS_WOULDBLOCK,
* and still return CDS_WFS_WOULDBLOCK.
*/
if (___cds_wfs_end(next))
return NULL;
return next;
}
/*
* 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.
*/
static inline struct cds_wfs_node *
_cds_wfs_next_blocking(struct cds_wfs_node *node)
{
return ___cds_wfs_next(node, 1);
}
/*
* 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.
*/
static inline struct cds_wfs_node *
_cds_wfs_next_nonblocking(struct cds_wfs_node *node)
{
return ___cds_wfs_next(node, 0);
}
#ifdef __cplusplus
}
#endif
#endif /* _URCU_STATIC_WFSTACK_H */