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/*
* Copyright 2011-2015 Samy Al Bahra.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#ifndef CK_EPOCH_H
#define CK_EPOCH_H
/*
* The implementation here is inspired from the work described in:
* Fraser, K. 2004. Practical Lock-Freedom. PhD Thesis, University
* of Cambridge Computing Laboratory.
*/
#include <ck_cc.h>
#include <ck_md.h>
#include <ck_pr.h>
#include <ck_stack.h>
#include <ck_stdbool.h>
#ifndef CK_EPOCH_LENGTH
#define CK_EPOCH_LENGTH 4
#endif
/*
* This is used for sense detection with-respect to concurrent
* epoch sections.
*/
#define CK_EPOCH_SENSE (2)
struct ck_epoch_entry;
typedef struct ck_epoch_entry ck_epoch_entry_t;
typedef void ck_epoch_cb_t(ck_epoch_entry_t *);
/*
* This should be embedded into objects you wish to be the target of
* ck_epoch_cb_t functions (with ck_epoch_call).
*/
struct ck_epoch_entry {
ck_epoch_cb_t *function;
ck_stack_entry_t stack_entry;
};
/*
* A section object may be passed to every begin-end pair to allow for
* forward progress guarantees with-in prolonged active sections.
*/
struct ck_epoch_section {
unsigned int bucket;
};
typedef struct ck_epoch_section ck_epoch_section_t;
/*
* Return pointer to ck_epoch_entry container object.
*/
#define CK_EPOCH_CONTAINER(T, M, N) \
CK_CC_CONTAINER(struct ck_epoch_entry, T, M, N)
struct ck_epoch_ref {
unsigned int epoch;
unsigned int count;
};
struct ck_epoch_record {
struct ck_epoch *global;
unsigned int state;
unsigned int epoch;
unsigned int active;
struct {
struct ck_epoch_ref bucket[CK_EPOCH_SENSE];
} local CK_CC_CACHELINE;
unsigned int n_pending;
unsigned int n_peak;
unsigned long n_dispatch;
ck_stack_t pending[CK_EPOCH_LENGTH];
ck_stack_entry_t record_next;
} CK_CC_CACHELINE;
typedef struct ck_epoch_record ck_epoch_record_t;
struct ck_epoch {
unsigned int epoch;
char pad[CK_MD_CACHELINE - sizeof(unsigned int)];
ck_stack_t records;
unsigned int n_free;
};
typedef struct ck_epoch ck_epoch_t;
/*
* Internal functions.
*/
void _ck_epoch_addref(ck_epoch_record_t *, ck_epoch_section_t *);
void _ck_epoch_delref(ck_epoch_record_t *, ck_epoch_section_t *);
/*
* Marks the beginning of an epoch-protected section.
*/
CK_CC_FORCE_INLINE static void
ck_epoch_begin(ck_epoch_record_t *record, ck_epoch_section_t *section)
{
struct ck_epoch *epoch = record->global;
/*
* Only observe new epoch if thread is not recursing into a read
* section.
*/
if (record->active == 0) {
unsigned int g_epoch;
/*
* It is possible for loads to be re-ordered before the store
* is committed into the caller's epoch and active fields.
* For this reason, store to load serialization is necessary.
*/
#if defined(CK_MD_TSO)
ck_pr_fas_uint(&record->active, 1);
ck_pr_fence_atomic_load();
#else
ck_pr_store_uint(&record->active, 1);
ck_pr_fence_memory();
#endif
/*
* This load is allowed to be re-ordered prior to setting
* active flag due to monotonic nature of the global epoch.
* However, stale values lead to measurable performance
* degradation in some torture tests so we disallow early load
* of global epoch.
*/
g_epoch = ck_pr_load_uint(&epoch->epoch);
ck_pr_store_uint(&record->epoch, g_epoch);
} else {
ck_pr_store_uint(&record->active, record->active + 1);
}
if (section != NULL)
_ck_epoch_addref(record, section);
return;
}
/*
* Marks the end of an epoch-protected section.
*/
CK_CC_FORCE_INLINE static void
ck_epoch_end(ck_epoch_record_t *record, ck_epoch_section_t *section)
{
ck_pr_fence_release();
ck_pr_store_uint(&record->active, record->active - 1);
if (section != NULL)
_ck_epoch_delref(record, section);
return;
}
/*
* Defers the execution of the function pointed to by the "cb"
* argument until an epoch counter loop. This allows for a
* non-blocking deferral.
*/
CK_CC_FORCE_INLINE static void
ck_epoch_call(ck_epoch_record_t *record,
ck_epoch_entry_t *entry,
ck_epoch_cb_t *function)
{
struct ck_epoch *epoch = record->global;
unsigned int e = ck_pr_load_uint(&epoch->epoch);
unsigned int offset = e & (CK_EPOCH_LENGTH - 1);
record->n_pending++;
entry->function = function;
ck_stack_push_spnc(&record->pending[offset], &entry->stack_entry);
return;
}
void ck_epoch_init(ck_epoch_t *);
ck_epoch_record_t *ck_epoch_recycle(ck_epoch_t *);
void ck_epoch_register(ck_epoch_t *, ck_epoch_record_t *);
void ck_epoch_unregister(ck_epoch_record_t *);
bool ck_epoch_poll(ck_epoch_record_t *);
void ck_epoch_synchronize(ck_epoch_record_t *);
void ck_epoch_barrier(ck_epoch_record_t *);
void ck_epoch_reclaim(ck_epoch_record_t *);
#endif /* CK_EPOCH_H */
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