134 lines
3.4 KiB
C++
134 lines
3.4 KiB
C++
/*
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Copyright (c) 2011, 2018, Oracle and/or its affiliates. All rights reserved.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License, version 2.0,
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as published by the Free Software Foundation.
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This program is also distributed with certain software (including
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but not limited to OpenSSL) that is licensed under separate terms,
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as designated in a particular file or component or in included license
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documentation. The authors of MySQL hereby grant you an additional
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permission to link the program and your derivative works with the
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separately licensed software that they have included with MySQL.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License, version 2.0, for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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/* Lock-free SPSC queue. Safe for one consumer thread and one producer.
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*
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*/
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#include <stdlib.h>
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#include "ndbmemcache_global.h"
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#include "atomics.h"
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#define VPSZ sizeof(void *)
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#define CACHE_PADDING (CACHE_LINE_SIZE - VPSZ)
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template<typename T> class Queue {
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private:
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struct Node {
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T * value;
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Node * volatile next;
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};
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Node *head;
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char padding1[CACHE_PADDING];
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Node *sep;
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char padding2[CACHE_PADDING];
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Node *tail;
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Node *nodelist;
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char *nodepool;
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atomic_int32_t is_active;
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public: /* public instance variable */
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public: /* public interface methods */
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Queue(int maxnodes) {
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/* Initialize the node allocation pool */
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maxnodes += 1; // add one for a dummy node at the head.
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assert(sizeof(Node) < CACHE_LINE_SIZE);
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nodepool = (char *) calloc(maxnodes, CACHE_LINE_SIZE);
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nodelist = 0;
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for(int i = 0; i < maxnodes; i++) {
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Node *n = (Node *) (nodepool + (i * CACHE_LINE_SIZE));
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n->next = nodelist;
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nodelist = n;
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}
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/* Initialize the queue */
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head = node_alloc(0); // a dummy node
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sep = head;
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tail = sep; // an empty queue
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is_active = 1;
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}
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~Queue() {
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free(nodepool);
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}
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T * consume() {
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T * val = 0;
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Node *nxt = sep->next;
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if(nxt) { /* queue is non-empty */
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val = nxt->value; /* the value to be returned. */
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nxt->value = 0; /* This node becomes the new (empty) dummy node... */
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sep = nxt; /* at the head of the queue. */
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}
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return val;
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}
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void produce(T *t) {
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/* First do deferred cleanup of the old nodes between head and sep */
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while(head != sep) {
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Node *tmp = head;
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assert(tmp->value == 0);
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head = tmp->next;
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node_free(tmp);
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}
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/* Now add a node at the tail of the queue */
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Node * n = node_alloc(t);
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atomic_set_ptr((void * volatile *)& tail->next, n);
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atomic_barrier();
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tail = n;
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}
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void abort() {
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atomic_cmp_swap_int(& is_active, 1, 0);
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}
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bool is_aborted() {
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return (is_active == 0);
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}
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private: /* internal allocator */
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Node *node_alloc(T *val) {
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assert(nodelist);
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Node *n = nodelist;
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nodelist = n->next;
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n->next = 0;
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n->value = val;
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return n;
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}
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void node_free(Node *n) {
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n->next = nodelist;
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nodelist = n;
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}
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};
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