From 12098b900be205074160716c4d241fac2c458e7c Mon Sep 17 00:00:00 2001
From: Konstantin Osipov <kostja@tarantool.org>
Date: Wed, 13 Nov 2013 17:23:02 +0400
Subject: [PATCH] Add a simple lock-free LIFO implementation to small
allocators library.
---
include/lib/small/lf_lifo.h | 115 ++++++++++++++++++++++++++++++++++++
test/unit/CMakeLists.txt | 1 +
test/unit/lf_lifo.c | 65 ++++++++++++++++++++
test/unit/lf_lifo.result | 1 +
4 files changed, 182 insertions(+)
create mode 100644 include/lib/small/lf_lifo.h
create mode 100644 test/unit/lf_lifo.c
create mode 100644 test/unit/lf_lifo.result
diff --git a/include/lib/small/lf_lifo.h b/include/lib/small/lf_lifo.h
new file mode 100644
index 0000000000..a725c57d12
--- /dev/null
+++ b/include/lib/small/lf_lifo.h
@@ -0,0 +1,115 @@
+#ifndef INCLUDES_TARANTOOL_LF_LIFO_H
+#define INCLUDES_TARANTOOL_LF_LIFO_H
+/*
+ * 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 <COPYRIGHT HOLDER> ``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
+ * <COPYRIGHT HOLDER> 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.
+ */
+#include <assert.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <stdlib.h>
+
+/**
+ * Provide wrappers around gcc built-ins for now.
+ * These built-ins work with all numeric types - may not
+ * be the case when another implementation is used.
+ */
+#define atomic_cas(a, b, c) __sync_val_compare_and_swap(a, b, c)
+#define atomic_add(a, b) __sync_add_and_fetch(a, b)
+
+/**
+ * A very primitive implementation of lock-free
+ * LIFO (last in first out, AKA stack, AKA single-linked
+ * list with head-only add and remove).
+ *
+ * It is only usable to store free pages of a memory allocator
+ * or similar, since it assumes that all addresses are aligned,
+ * and lower 16 bits of address can be used as a counter-based
+ * solution for ABA problem.
+ */
+struct lf_lifo {
+ void *next;
+};
+
+static inline unsigned short
+aba_value(void *a)
+{
+ return (intptr_t) a & 0xffff;
+}
+
+static inline struct lf_lifo *
+lf_lifo(void *a)
+{
+ return (struct lf_lifo *) ((intptr_t) a & ~0xffff);
+}
+
+static inline void
+lf_lifo_init(struct lf_lifo *head)
+{
+ head->next = NULL;
+}
+
+struct lf_lifo *
+lf_lifo_push(struct lf_lifo *head, void *elem)
+{
+ assert(lf_lifo(elem) == elem); /* Aligned address. */
+ do {
+ void *tail = head->next;
+ lf_lifo(elem)->next = tail;
+ /*
+ * Sic: add 1 thus let ABA value overflow, *then*
+ * coerce to unsigned short
+ */
+ void *newhead = elem + aba_value(tail + 1);
+ if (atomic_cas(&head->next, tail, newhead) == tail)
+ return head;
+ } while (true);
+}
+
+void *
+lf_lifo_pop(struct lf_lifo *head)
+{
+ do {
+ void *tail = head->next;
+ struct lf_lifo *elem = lf_lifo(tail);
+ if (elem == NULL)
+ return NULL;
+ /*
+ * Discard the old tail's aba value, then save
+ * the old head's value in the tail.
+ * This way head's aba value grows monotonically
+ * regardless of the exact sequence of push/pop
+ * operations.
+ */
+ void *newhead = ((void *) lf_lifo(elem->next) +
+ aba_value(tail));
+ if (atomic_cas(&head->next, tail, newhead) == tail)
+ return elem;
+ } while (true);
+}
+
+#endif /* INCLUDES_TARANTOOL_LF_LIFO_H */
diff --git a/test/unit/CMakeLists.txt b/test/unit/CMakeLists.txt
index 99b5aa00b1..21a0fd62c1 100644
--- a/test/unit/CMakeLists.txt
+++ b/test/unit/CMakeLists.txt
@@ -25,3 +25,4 @@ add_executable(mempool.test mempool.c)
target_link_libraries(mempool.test small)
add_executable(small_alloc.test small_alloc.c)
target_link_libraries(small_alloc.test small)
+add_executable(lf_lifo.test lf_lifo.c)
diff --git a/test/unit/lf_lifo.c b/test/unit/lf_lifo.c
new file mode 100644
index 0000000000..1d42a4fa4d
--- /dev/null
+++ b/test/unit/lf_lifo.c
@@ -0,0 +1,65 @@
+#include "lib/small/lf_lifo.h"
+#include "unit.h"
+#include <sys/mman.h>
+
+static void *
+mmap_aligned(size_t size)
+{
+ assert((size & (size - 1)) == 0);
+ void *map = mmap(NULL, 2 * size,
+ PROT_READ | PROT_WRITE, MAP_PRIVATE |
+ MAP_ANONYMOUS, -1, 0);
+
+ /* Align the mapped address around slab size. */
+ size_t offset = (intptr_t) map & (size - 1);
+
+ if (offset != 0) {
+ munmap(map, size - offset);
+ map += size - offset;
+ munmap(map + size, offset);
+ } else {
+ /* The address is returned aligned. */
+ munmap(map + size, size);
+ }
+ return map;
+}
+
+#define MAP_SIZE 0x10000
+
+int main()
+{
+ struct lf_lifo head;
+ void *val1 = mmap_aligned(MAP_SIZE);
+ void *val2 = mmap_aligned(MAP_SIZE);
+ void *val3 = mmap_aligned(MAP_SIZE);
+ lf_lifo_init(&head);
+
+ fail_unless(lf_lifo_pop(&head) == NULL);
+ fail_unless(lf_lifo_pop(lf_lifo_push(&head, val1)) == val1);
+ fail_unless(lf_lifo_pop(lf_lifo_push(&head, val1)) == val1);
+ lf_lifo_push(lf_lifo_push(lf_lifo_push(&head, val1), val2), val3);
+ fail_unless(lf_lifo_pop(&head) == val3);
+ fail_unless(lf_lifo_pop(&head) == val2);
+ fail_unless(lf_lifo_pop(&head) == val1);
+ fail_unless(lf_lifo_pop(&head) == NULL);
+
+ lf_lifo_init(&head);
+
+ /* Test overflow of ABA counter. */
+
+ int i = 0;
+ do {
+ lf_lifo_push(&head, val1);
+ fail_unless(lf_lifo_pop(&head) == val1);
+ fail_unless(lf_lifo_pop(&head) == NULL);
+ i++;
+ } while (head.next != 0);
+
+ munmap(val1, MAP_SIZE);
+ munmap(val2, MAP_SIZE);
+ munmap(val3, MAP_SIZE);
+
+ printf("success\n");
+
+ return 0;
+}
diff --git a/test/unit/lf_lifo.result b/test/unit/lf_lifo.result
new file mode 100644
index 0000000000..2e9ba477f8
--- /dev/null
+++ b/test/unit/lf_lifo.result
@@ -0,0 +1 @@
+success
--
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