1 files changed, 279 insertions, 0 deletions
diff --git a/include/ck_brlock.h b/include/ck_brlock.h
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+++ b/include/ck_brlock.h
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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_BRLOCK_H
+#define CK_BRLOCK_H
+
+/*
+ * Big reader spinlocks provide cache-local contention-free read
+ * lock acquisition in the absence of writers. This comes at the
+ * cost of O(n) write lock acquisition. They were first implemented
+ * in the Linux kernel by Ingo Molnar and David S. Miller around the
+ * year 2000.
+ *
+ * This implementation is thread-agnostic which comes at the cost
+ * of larger reader objects due to necessary linkage overhead. In
+ * order to cut down on TLB pressure, it is recommended to allocate
+ * these objects on the same page.
+ */
+
+#include <ck_pr.h>
+#include <ck_stdbool.h>
+#include <ck_stddef.h>
+
+struct ck_brlock_reader {
+	unsigned int n_readers;
+	struct ck_brlock_reader *previous;
+	struct ck_brlock_reader *next;
+};
+typedef struct ck_brlock_reader ck_brlock_reader_t;
+
+#define CK_BRLOCK_READER_INITIALIZER {0}
+
+struct ck_brlock {
+	struct ck_brlock_reader *readers;
+	unsigned int writer;
+};
+typedef struct ck_brlock ck_brlock_t;
+
+#define CK_BRLOCK_INITIALIZER {NULL, false}
+
+CK_CC_INLINE static void
+ck_brlock_init(struct ck_brlock *br)
+{
+
+	br->readers = NULL;
+	br->writer = false;
+	ck_pr_barrier();
+	return;
+}
+
+CK_CC_INLINE static void
+ck_brlock_write_lock(struct ck_brlock *br)
+{
+	struct ck_brlock_reader *cursor;
+
+	/*
+	 * As the frequency of write acquisitions should be low,
+	 * there is no point to more advanced contention avoidance.
+	 */
+	while (ck_pr_fas_uint(&br->writer, true) == true)
+		ck_pr_stall();
+
+	ck_pr_fence_atomic_load();
+
+	/* The reader list is protected under the writer br. */
+	for (cursor = br->readers; cursor != NULL; cursor = cursor->next) {
+		while (ck_pr_load_uint(&cursor->n_readers) != 0)
+			ck_pr_stall();
+	}
+
+	ck_pr_fence_lock();
+	return;
+}
+
+CK_CC_INLINE static void
+ck_brlock_write_unlock(struct ck_brlock *br)
+{
+
+	ck_pr_fence_unlock();
+	ck_pr_store_uint(&br->writer, false);
+	return;
+}
+
+CK_CC_INLINE static bool
+ck_brlock_write_trylock(struct ck_brlock *br, unsigned int factor)
+{
+	struct ck_brlock_reader *cursor;
+	unsigned int steps = 0;
+
+	while (ck_pr_fas_uint(&br->writer, true) == true) {
+		if (++steps >= factor)
+			return false;
+
+		ck_pr_stall();
+	}
+
+	/*
+	 * We do not require a strict fence here as atomic RMW operations
+	 * are serializing.
+	 */
+	ck_pr_fence_atomic_load();
+
+	for (cursor = br->readers; cursor != NULL; cursor = cursor->next) {
+		while (ck_pr_load_uint(&cursor->n_readers) != 0) {
+			if (++steps >= factor) {
+				ck_brlock_write_unlock(br);
+				return false;
+			}
+
+			ck_pr_stall();
+		}
+	}
+
+	ck_pr_fence_lock();
+	return true;
+}
+
+CK_CC_INLINE static void
+ck_brlock_read_register(struct ck_brlock *br, struct ck_brlock_reader *reader)
+{
+
+	reader->n_readers = 0;
+	reader->previous = NULL;
+
+	/* Implicit compiler barrier. */
+	ck_brlock_write_lock(br);
+
+	reader->next = ck_pr_load_ptr(&br->readers);
+	if (reader->next != NULL)
+		reader->next->previous = reader;
+	ck_pr_store_ptr(&br->readers, reader);
+
+	ck_brlock_write_unlock(br);
+	return;
+}
+
+CK_CC_INLINE static void
+ck_brlock_read_unregister(struct ck_brlock *br, struct ck_brlock_reader *reader)
+{
+
+	ck_brlock_write_lock(br);
+
+	if (reader->next != NULL)
+		reader->next->previous = reader->previous;
+
+	if (reader->previous != NULL)
+		reader->previous->next = reader->next;
+	else
+		br->readers = reader->next;
+
+	ck_brlock_write_unlock(br);
+	return;
+}
+
+CK_CC_INLINE static void
+ck_brlock_read_lock(struct ck_brlock *br, struct ck_brlock_reader *reader)
+{
+
+	if (reader->n_readers >= 1) {
+		ck_pr_store_uint(&reader->n_readers, reader->n_readers + 1);
+		return;
+	}
+
+	for (;;) {
+		while (ck_pr_load_uint(&br->writer) == true)
+			ck_pr_stall();
+
+#if defined(__x86__) || defined(__x86_64__)
+		ck_pr_fas_uint(&reader->n_readers, 1);
+
+		/*
+		 * Serialize reader counter update with respect to load of
+		 * writer.
+		 */
+		ck_pr_fence_atomic_load();
+#else
+		ck_pr_store_uint(&reader->n_readers, 1);
+
+		/*
+		 * Serialize reader counter update with respect to load of
+		 * writer.
+		 */
+		ck_pr_fence_store_load();
+#endif
+
+		if (ck_pr_load_uint(&br->writer) == false)
+			break;
+
+		ck_pr_store_uint(&reader->n_readers, 0);
+	}
+
+	ck_pr_fence_lock();
+	return;
+}
+
+CK_CC_INLINE static bool
+ck_brlock_read_trylock(struct ck_brlock *br,
+		       struct ck_brlock_reader *reader,
+		       unsigned int factor)
+{
+	unsigned int steps = 0;
+
+	if (reader->n_readers >= 1) {
+		ck_pr_store_uint(&reader->n_readers, reader->n_readers + 1);
+		return true;
+	}
+
+	for (;;) {
+		while (ck_pr_load_uint(&br->writer) == true) {
+			if (++steps >= factor)
+				return false;
+
+			ck_pr_stall();
+		}
+
+#if defined(__x86__) || defined(__x86_64__)
+		ck_pr_fas_uint(&reader->n_readers, 1);
+
+		/*
+		 * Serialize reader counter update with respect to load of
+		 * writer.
+		 */
+		ck_pr_fence_atomic_load();
+#else
+		ck_pr_store_uint(&reader->n_readers, 1);
+
+		/*
+		 * Serialize reader counter update with respect to load of
+		 * writer.
+		 */
+		ck_pr_fence_store_load();
+#endif
+
+		if (ck_pr_load_uint(&br->writer) == false)
+			break;
+
+		ck_pr_store_uint(&reader->n_readers, 0);
+
+		if (++steps >= factor)
+			return false;
+	}
+
+	ck_pr_fence_lock();
+	return true;
+}
+
+CK_CC_INLINE static void
+ck_brlock_read_unlock(struct ck_brlock_reader *reader)
+{
+
+	ck_pr_fence_unlock();
+	ck_pr_store_uint(&reader->n_readers, reader->n_readers - 1);
+	return;
+}
+
+#endif /* CK_BRLOCK_H */