mirror of
https://github.com/autc04/Retro68.git
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653 lines
22 KiB
C++
653 lines
22 KiB
C++
/* Copyright (C) 2012-2015 Free Software Foundation, Inc.
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This file is part of GCC.
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GCC is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3, or (at your option)
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any later version.
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GCC is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
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License for more details.
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Under Section 7 of GPL version 3, you are granted additional
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permissions described in the GCC Runtime Library Exception, version
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3.1, as published by the Free Software Foundation.
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You should have received a copy of the GNU General Public License
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and a copy of the GCC Runtime Library Exception along with this
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program; see the files COPYING3 and COPYING.RUNTIME respectively.
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If not, see <http://www.gnu.org/licenses/>. */
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#ifndef _VTV_SET_H
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#define _VTV_SET_H 1
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/* Code in this file manages a collection of insert-only sets. We
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have only tested the case where Key is uintptr_t, though it
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theoretically should work for some other cases. All odd keys are
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reserved, and must not be inserted into any of the sets. This code
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is intended primarily for sets of pointers, and the code is
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optimized for small sets (including size 0 and 1), but regardless
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of the set size, insert() and contains() have close to O(1) speed
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in practice.
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TODO(gpike): fix this comment.
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Recommended multithreaded use of a set:
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For speed, we want to use a lock-free test for set membership. The
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code handles simultaneous reads and inserts, as long as at most one
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insertion is in progress at a time. After an insert, other threads
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may not immediately "see" the inserted key if they perform a
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lock-free read, so we recommend retrying, as explained below.
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Also, to make data corruption less likely, we recommend using a
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"normal" RW page as well as one or pages that are typically RO
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but that can be switched to RW and back as needed. The latter
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pages should contain sets. The former should contain a lock, L,
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and an int or similar, num_writers. Then, to insert, something
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like this would be safe:
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o Acquire L.
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o Increment num_writers; if that made it 1, change pages to RW.
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o Release L.
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o while (there are insertions to do in some set, S) {
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acquire L;
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do some insertions in S;
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release L;
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}
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o Acquire L.
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o Decrement num_writers; if that made it 0, change pages to RO.
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o Release L.
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And to check if the set contains some key, one could use
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set.contains(key) ||
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({ Acquire L; bool b = set.contains(key); Release L; b; })
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In this scheme, the number of threads with reads in progress isn't
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tracked, so old sets can never be deleted. In addition, on some
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architectures the intentionally racy reads might cause contains()
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to return true when it should have returned false. This should be
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no problem on x86, and most other machines, where reading or
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writing an aligned uintptr_t is atomic. E.g., on those machines,
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if *p is 0 and one thread does *p = x while another reads *p, the
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read will see either 0 or x.
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To make the above easier, the insert_only_hash_sets class provides
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an interface to manipulate any number of hash sets. One shouldn't
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create objects of that class, as it has no member data and its
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methods are static.
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So the recommended model is to have a single lock, a single
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num_writers variable, and some number of sets. If lock contention
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becomes a problem then the sets can be divided into k groups, each
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of which has a lock and a num_writers variable; or each set can be
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represented as a set of values that equal 0 mod m, a set of values
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that equal 1 mod m, ..., plus a set of values that equal m-1 mod m.
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However, we expect most or all uses of this code to call contains()
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much more frequently than anything else, so lock contention is
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likely to be low. */
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#include <algorithm>
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#ifndef HASHTABLE_STATS
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#define HASHTABLE_STATS 0
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#endif
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#ifndef HASHTABLE_STATS_ATOMIC
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#define HASHTABLE_STATS_ATOMIC 0
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#endif
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#if HASHTABLE_STATS
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#if HASHTABLE_STATS_ATOMIC
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/* Stat counters, with atomics. */
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#include <bits/atomic_word.h>
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typedef _Atomic_word _AtomicStatCounter;
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void
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inc_by (_AtomicStatCounter &stat, int amount)
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{
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__atomic_add_fetch (&stat, amount, __ATOMIC_ACQ_REL);
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}
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#else
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/* Stat counters, but without atomics. */
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typedef int _AtomicStatCounter;
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void
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inc_by (_AtomicStatCounter& stat, int amount)
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{
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stat += amount;
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}
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#endif
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/* Number of calls to contains(), insert(), etc. */
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extern _AtomicStatCounter stat_insert;
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extern _AtomicStatCounter stat_contains;
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extern _AtomicStatCounter stat_resize;
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extern _AtomicStatCounter stat_create;
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/* Sum of set size over all calls to contains(). */
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extern _AtomicStatCounter stat_contains_sizes;
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/* contains() calls in a set whose capacity is more than 1. */
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extern _AtomicStatCounter stat_contains_in_non_trivial_set;
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/* Probes in a set whose capacity is more than 1. Ideally, this will
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be pretty close to stat_contains_in_non_trivial_set. That will
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happen if our hash function is good and/or important keys were
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inserted before unimportant keys. */
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extern _AtomicStatCounter stat_probes_in_non_trivial_set;
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/* number of calls to contains() with size=0, 1, etc. */
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extern _AtomicStatCounter stat_contains_size0;
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extern _AtomicStatCounter stat_contains_size1;
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extern _AtomicStatCounter stat_contains_size2;
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extern _AtomicStatCounter stat_contains_size3;
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extern _AtomicStatCounter stat_contains_size4;
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extern _AtomicStatCounter stat_contains_size5;
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extern _AtomicStatCounter stat_contains_size6;
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extern _AtomicStatCounter stat_contains_size7;
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extern _AtomicStatCounter stat_contains_size8;
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extern _AtomicStatCounter stat_contains_size9;
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extern _AtomicStatCounter stat_contains_size10;
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extern _AtomicStatCounter stat_contains_size11;
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extern _AtomicStatCounter stat_contains_size12;
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extern _AtomicStatCounter stat_contains_size13_or_more;
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extern _AtomicStatCounter stat_grow_from_size0_to_1;
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extern _AtomicStatCounter stat_grow_from_size1_to_2;
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extern _AtomicStatCounter stat_double_the_number_of_buckets;
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extern _AtomicStatCounter stat_insert_key_that_was_already_present;
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/* Hash collisions detected during insert_no_resize(). Only counts
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hasher(k) == hasher(k'); hasher(k) % tablesize == hasher(k') %
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tablesize is not sufficient. Will count collisions that are
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detected during table resizes etc., so the same two keys may add to
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this stat multiple times. */
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extern _AtomicStatCounter stat_insert_found_hash_collision;
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#include <string>
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struct insert_only_hash_sets_logger
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{
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static char *
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log (char c, char *buf)
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{
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*buf++ = c;
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return buf;
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}
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static char *
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log (const char *s, char *buf)
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{ return strcpy (buf, s) + strlen (s); }
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static char *
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log (_AtomicStatCounter i, char *buf)
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{
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if (i < 10)
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return log ((char) ('0' + i), buf);
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else
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return log ((char) ('0' + i % 10), log (i / 10, buf));
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}
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static char *
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log (const char *label, _AtomicStatCounter i, char *buf)
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{
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buf = log (label, buf);
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buf = log (": ", buf);
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buf = log (i, buf);
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return log ('\n', buf);
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}
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};
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// Write stats to the given buffer, which should be at least 4000 bytes.
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static inline void
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insert_only_hash_tables_stats (char *buf)
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{
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buf = insert_only_hash_sets_logger::log ("insert", stat_insert, buf);
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buf = insert_only_hash_sets_logger::log ("contains", stat_contains, buf);
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buf = insert_only_hash_sets_logger::log ("resize", stat_resize, buf);
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buf = insert_only_hash_sets_logger::log ("create", stat_create, buf);
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buf = insert_only_hash_sets_logger::log ("insert_key_that_was_already_"
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"present",
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stat_insert_key_that_was_already_present,
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buf);
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buf = insert_only_hash_sets_logger::log ("contains_sizes",
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stat_contains_sizes, buf);
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buf = insert_only_hash_sets_logger::log ("contains_in_non_trivial_set",
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stat_contains_in_non_trivial_set,
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buf);
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buf = insert_only_hash_sets_logger::log ("probes_in_non_trivial_set",
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stat_probes_in_non_trivial_set,
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buf);
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buf = insert_only_hash_sets_logger::log ("contains_size0",
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stat_contains_size0, buf);
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buf = insert_only_hash_sets_logger::log ("contains_size1",
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stat_contains_size1, buf);
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buf = insert_only_hash_sets_logger::log ("contains_size2",
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stat_contains_size2, buf);
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buf = insert_only_hash_sets_logger::log ("contains_size3",
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stat_contains_size3, buf);
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buf = insert_only_hash_sets_logger::log ("contains_size4",
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stat_contains_size4, buf);
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buf = insert_only_hash_sets_logger::log ("contains_size5",
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stat_contains_size5, buf);
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buf = insert_only_hash_sets_logger::log ("contains_size6",
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stat_contains_size6, buf);
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buf = insert_only_hash_sets_logger::log ("contains_size7",
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stat_contains_size7, buf);
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buf = insert_only_hash_sets_logger::log ("contains_size8",
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stat_contains_size8, buf);
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buf = insert_only_hash_sets_logger::log ("contains_size9",
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stat_contains_size9, buf);
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buf = insert_only_hash_sets_logger::log ("contains_size10",
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stat_contains_size10, buf);
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buf = insert_only_hash_sets_logger::log ("contains_size11",
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stat_contains_size11, buf);
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buf = insert_only_hash_sets_logger::log ("contains_size12",
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stat_contains_size12, buf);
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buf = insert_only_hash_sets_logger::log ("contains_size13_or_more",
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stat_contains_size13_or_more, buf);
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buf = insert_only_hash_sets_logger::log ("grow_from_size0_to_1",
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stat_grow_from_size0_to_1, buf);
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buf = insert_only_hash_sets_logger::log ("grow_from_size1_to_2",
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stat_grow_from_size1_to_2, buf);
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buf = insert_only_hash_sets_logger::log ("insert_found_hash_collision",
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stat_insert_found_hash_collision,
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buf);
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buf = insert_only_hash_sets_logger::log ("double_the_number_of_buckets",
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stat_double_the_number_of_buckets,
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buf);
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*buf = '\0';
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}
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#else
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/* No stats. */
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#define inc_by(statname, amount) do { } while (false && (amount))
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#endif
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#define inc(statname) inc_by (statname, 1)
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template <typename Key, class HashFcn, class Alloc>
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class insert_only_hash_sets
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{
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public:
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typedef Key key_type;
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typedef size_t size_type;
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typedef Alloc alloc_type;
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enum { illegal_key = 1 };
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enum { min_capacity = 4 };
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#if HASHTABLE_STATS
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enum { stats = true };
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#else
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enum { stats = false };
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#endif
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/* Do not directly use insert_only_hash_set. Instead, use the
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static methods below to create and manipulate objects of the
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following class.
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Implementation details: each set is represented by a pointer
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plus, perhaps, out-of-line data, which would be an object of type
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insert_only_hash_set. For a pointer, s, the interpretation is: s
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== NULL means empty set, lsb(s) == 1 means a set with one
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element, which is (uintptr_t)s - 1, and otherwise s is a pointer
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of type insert_only_hash_set*. So, to increase the size of a set
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we have to change s and/or *s. To check if a set contains some
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key we have to examine s and possibly *s. */
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class insert_only_hash_set
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{
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public:
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/* Insert a key. The key must not be a reserved key. */
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static inline insert_only_hash_set *insert (key_type key,
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insert_only_hash_set *s);
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/* Create an empty set. */
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static inline insert_only_hash_set *create (size_type capacity);
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/* Return whether the given key is present. If key is illegal_key
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then either true or false may be returned, but for all other
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reserved keys false will be returned. */
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static bool
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contains (key_type key, const insert_only_hash_set *s)
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{
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if (stats)
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{
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inc (stat_contains);
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switch (size (s))
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{
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case 0: inc (stat_contains_size0); break;
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case 1: inc (stat_contains_size1); break;
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case 2: inc (stat_contains_size2); break;
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case 3: inc (stat_contains_size3); break;
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case 4: inc (stat_contains_size4); break;
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case 5: inc (stat_contains_size5); break;
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case 6: inc (stat_contains_size6); break;
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case 7: inc (stat_contains_size7); break;
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case 8: inc (stat_contains_size8); break;
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case 9: inc (stat_contains_size9); break;
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case 10: inc (stat_contains_size10); break;
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case 11: inc (stat_contains_size11); break;
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case 12: inc (stat_contains_size12); break;
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default: inc (stat_contains_size13_or_more); break;
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}
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inc_by (stat_contains_sizes, size (s));
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}
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return (singleton (s) ?
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singleton_key (key) == s :
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((s != NULL) && s->contains (key)));
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}
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/* Return a set's size. */
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static size_type
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size (const insert_only_hash_set *s)
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{ return (s == NULL) ? 0 : (singleton (s) ? 1 : s->num_entries); }
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static inline insert_only_hash_set *resize (size_type target_num_buckets,
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insert_only_hash_set *s);
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private:
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/* Return whether a set has size 1. */
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static bool
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singleton (const insert_only_hash_set *s)
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{ return (uintptr_t) s & 1; }
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/* Return the representation of a singleton set containing the
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given key. */
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static insert_only_hash_set *
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singleton_key (key_type key)
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{ return (insert_only_hash_set *) ((uintptr_t) key + 1); }
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/* Given a singleton set, what key does it contain? */
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static key_type
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extract_singleton_key (const insert_only_hash_set *s)
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{
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VTV_DEBUG_ASSERT (singleton (s));
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return (key_type) ((uintptr_t) s - 1);
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}
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volatile key_type &
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key_at_index (size_type index)
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{ return buckets[index]; }
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key_type
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key_at_index (size_type index) const
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{ return buckets[index]; }
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size_type
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next_index (size_type index, size_type indices_examined) const
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{ return (index + indices_examined) & (num_buckets - 1); }
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inline void insert_no_resize (key_type key);
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inline bool contains (key_type key) const;
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inline insert_only_hash_set *resize_if_necessary (void);
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size_type num_buckets; /* Must be a power of 2 not less than
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min_capacity. */
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volatile size_type num_entries;
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volatile key_type buckets[0]; /* Actual array size is num_buckets. */
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};
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/* Create an empty set with the given capacity. Requires that n be
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0 or a power of 2. If 1 < n < min_capacity then treat n as
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min_capacity. Sets *handle. Returns true unless the allocator
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fails. Subsequent operations on this set should use the same
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handle. */
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static inline bool create (size_type n, insert_only_hash_set **handle);
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/* Force the capacity of a set to be n, unless it was more than n
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already. Requires that n be 0 or a power of 2. Sets *handle
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unless the current capacity is n or more. Returns true unless
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the allocator fails. */
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static inline bool resize (size_type n, insert_only_hash_set **handle);
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/* Insert a key. *handle is unmodified unless (1) a resize occurs,
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or (2) the set was initially empty. Returns true unless the
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allocator fails during a resize. If the allocator fails during a
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resize then the set is reset to be the empty set. The key must
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not be a reserved key. */
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static inline bool insert (key_type key, insert_only_hash_set **handle);
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/* Check for the presence of a key. If key is illegal_key then
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either true or false may be returned, but for all other reserved
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keys false will be returned. */
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static inline bool
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contains (key_type key, /* const */ insert_only_hash_set **handle)
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{ return insert_only_hash_set::contains (key, *handle); }
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/* Return the size of the given set. */
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static size_type
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size (const insert_only_hash_set **handle)
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{ return insert_only_hash_set::size (*handle); }
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static bool
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is_reserved_key (key_type key)
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{ return ((uintptr_t) key % 2) == 1; }
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};
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template <typename Key, class HashFcn, class Alloc>
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typename insert_only_hash_sets <Key, HashFcn, Alloc>::insert_only_hash_set *
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insert_only_hash_sets <Key, HashFcn, Alloc>::insert_only_hash_set::resize
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(size_type n, insert_only_hash_set *s)
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{
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if (s == NULL)
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return create (n);
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size_type capacity = singleton (s) ? 1 : s->num_buckets;
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if (n <= capacity)
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return s;
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insert_only_hash_set *result =
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create (std::max<size_type> (n, min_capacity));
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if (result != NULL)
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{
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if (singleton (s))
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{
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result->insert_no_resize (extract_singleton_key (s));
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}
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else
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{
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for (size_type i = 0; i < s->num_buckets; i++)
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if (s->buckets[i] != (key_type) illegal_key)
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result->insert_no_resize (s->buckets[i]);
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}
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VTV_DEBUG_ASSERT (size (result) == size (s));
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}
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return result;
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}
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template <typename Key, class HashFcn, class Alloc>
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typename insert_only_hash_sets <Key, HashFcn, Alloc>::insert_only_hash_set *
|
|
insert_only_hash_sets <Key, HashFcn, Alloc>::insert_only_hash_set::insert
|
|
(key_type key, insert_only_hash_set *s)
|
|
{
|
|
VTV_DEBUG_ASSERT (!is_reserved_key (key));
|
|
|
|
inc_by (stat_grow_from_size0_to_1, s == NULL);
|
|
|
|
if (s == NULL)
|
|
return singleton_key (key);
|
|
|
|
if (singleton (s))
|
|
{
|
|
const key_type old_key = extract_singleton_key (s);
|
|
if (old_key == key)
|
|
return s;
|
|
|
|
/* Grow from size 1 to size 2. */
|
|
inc (stat_grow_from_size1_to_2);
|
|
s = create (2);
|
|
if (s == NULL)
|
|
return NULL;
|
|
|
|
s->insert_no_resize (old_key);
|
|
s->insert_no_resize (key);
|
|
VTV_DEBUG_ASSERT (size (s) == 2);
|
|
return s;
|
|
}
|
|
s = s->resize_if_necessary();
|
|
if (s != NULL)
|
|
s->insert_no_resize (key);
|
|
return s;
|
|
}
|
|
|
|
template <typename Key, class HashFcn, class Alloc>
|
|
typename insert_only_hash_sets <Key, HashFcn, Alloc>::insert_only_hash_set *
|
|
insert_only_hash_sets <Key, HashFcn, Alloc>::insert_only_hash_set::create
|
|
(size_type capacity)
|
|
{
|
|
if (capacity <= 1)
|
|
return NULL;
|
|
|
|
VTV_DEBUG_ASSERT (capacity > 1 && (capacity & (capacity - 1)) == 0);
|
|
VTV_DEBUG_ASSERT (sizeof (insert_only_hash_set) == 2 * sizeof (size_type));
|
|
capacity = std::max <size_type> (capacity, min_capacity);
|
|
const size_t num_bytes = sizeof (insert_only_hash_set) +
|
|
sizeof (key_type) * capacity;
|
|
alloc_type alloc;
|
|
insert_only_hash_set *result = (insert_only_hash_set *) alloc (num_bytes);
|
|
result->num_buckets = capacity;
|
|
result->num_entries = 0;
|
|
for (size_type i = 0; i < capacity; i++)
|
|
result->buckets[i] = (key_type) illegal_key;
|
|
return result;
|
|
}
|
|
|
|
template <typename Key, class HashFcn, class Alloc>
|
|
void
|
|
insert_only_hash_sets<Key, HashFcn,
|
|
Alloc>::insert_only_hash_set::insert_no_resize
|
|
(key_type key)
|
|
{
|
|
HashFcn hasher;
|
|
const size_type capacity = num_buckets;
|
|
VTV_DEBUG_ASSERT (capacity >= min_capacity);
|
|
VTV_DEBUG_ASSERT (!is_reserved_key (key));
|
|
size_type index = hasher (key) & (capacity - 1);
|
|
key_type k = key_at_index (index);
|
|
size_type indices_examined = 0;
|
|
while (k != key)
|
|
{
|
|
++indices_examined;
|
|
if (k == (key_type) illegal_key)
|
|
{
|
|
key_at_index (index) = key;
|
|
++num_entries;
|
|
return;
|
|
}
|
|
else
|
|
{
|
|
inc_by (stat_insert_found_hash_collision,
|
|
hasher (k) == hasher (key));
|
|
}
|
|
VTV_DEBUG_ASSERT (indices_examined < capacity);
|
|
index = next_index (index, indices_examined);
|
|
k = key_at_index (index);
|
|
}
|
|
}
|
|
|
|
template<typename Key, class HashFcn, class Alloc>
|
|
bool
|
|
insert_only_hash_sets<Key, HashFcn, Alloc>::insert_only_hash_set::contains
|
|
(key_type key) const
|
|
{
|
|
inc (stat_contains_in_non_trivial_set);
|
|
HashFcn hasher;
|
|
const size_type capacity = num_buckets;
|
|
size_type index = hasher (key) & (capacity - 1);
|
|
key_type k = key_at_index (index);
|
|
size_type indices_examined = 0;
|
|
inc (stat_probes_in_non_trivial_set);
|
|
while (k != key)
|
|
{
|
|
++indices_examined;
|
|
if (/*UNLIKELY*/(k == (key_type) illegal_key
|
|
|| indices_examined == capacity))
|
|
return false;
|
|
|
|
index = next_index (index, indices_examined);
|
|
k = key_at_index (index);
|
|
inc (stat_probes_in_non_trivial_set);
|
|
}
|
|
return true;
|
|
}
|
|
|
|
template <typename Key, class HashFcn, class Alloc>
|
|
typename insert_only_hash_sets <Key, HashFcn, Alloc>::insert_only_hash_set *
|
|
insert_only_hash_sets<Key, HashFcn,
|
|
Alloc>::insert_only_hash_set::resize_if_necessary (void)
|
|
{
|
|
VTV_DEBUG_ASSERT (num_buckets >= min_capacity);
|
|
size_type unused = num_buckets - num_entries;
|
|
if (unused < (num_buckets >> 2))
|
|
{
|
|
inc (stat_double_the_number_of_buckets);
|
|
size_type new_num_buckets = num_buckets * 2;
|
|
insert_only_hash_set *s = create (new_num_buckets);
|
|
for (size_type i = 0; i < num_buckets; i++)
|
|
if (buckets[i] != (key_type) illegal_key)
|
|
s->insert_no_resize (buckets[i]);
|
|
VTV_DEBUG_ASSERT (size (this) == size (s));
|
|
return s;
|
|
}
|
|
else
|
|
return this;
|
|
}
|
|
|
|
template<typename Key, class HashFcn, class Alloc>
|
|
bool
|
|
insert_only_hash_sets<Key, HashFcn, Alloc>::create (size_type n,
|
|
insert_only_hash_set **handle)
|
|
|
|
{
|
|
inc (stat_create);
|
|
*handle = insert_only_hash_set::create (n);
|
|
return (n <= 1) || (*handle != NULL);
|
|
}
|
|
|
|
template<typename Key, class HashFcn, class Alloc>
|
|
bool
|
|
insert_only_hash_sets<Key, HashFcn, Alloc>::resize (size_type n,
|
|
insert_only_hash_set **handle)
|
|
{
|
|
inc (stat_resize);
|
|
*handle = insert_only_hash_set::resize (n, *handle);
|
|
return (n <= 1) || (*handle != NULL);
|
|
}
|
|
|
|
template<typename Key, class HashFcn, class Alloc>
|
|
bool
|
|
insert_only_hash_sets<Key, HashFcn, Alloc>::insert (key_type key,
|
|
insert_only_hash_set **handle)
|
|
{
|
|
inc (stat_insert);
|
|
const size_type old_size = insert_only_hash_set::size (*handle);
|
|
*handle = insert_only_hash_set::insert (key, *handle);
|
|
if (*handle != NULL)
|
|
{
|
|
const size_type delta = insert_only_hash_set::size (*handle) - old_size;
|
|
inc_by (stat_insert_key_that_was_already_present, delta == 0);
|
|
}
|
|
return *handle != NULL;
|
|
}
|
|
|
|
#endif /* VTV_SET_H */
|