1 files changed, 125 insertions, 0 deletions
diff --git a/include/ck_sequence.h b/include/ck_sequence.h
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+++ b/include/ck_sequence.h
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+/*
+ * Copyright 2010-2015 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_SEQUENCE_H
+#define CK_SEQUENCE_H
+
+#include <ck_cc.h>
+#include <ck_pr.h>
+#include <ck_stdbool.h>
+
+struct ck_sequence {
+	unsigned int sequence;
+};
+typedef struct ck_sequence ck_sequence_t;
+
+#define CK_SEQUENCE_INITIALIZER { .sequence = 0 }
+
+CK_CC_INLINE static void
+ck_sequence_init(struct ck_sequence *sq)
+{
+
+	ck_pr_store_uint(&sq->sequence, 0);
+	return;
+}
+
+CK_CC_INLINE static unsigned int
+ck_sequence_read_begin(const struct ck_sequence *sq)
+{
+	unsigned int version;
+
+	for (;;) {
+		version = ck_pr_load_uint(&sq->sequence);
+
+		/*
+		 * If a sequence is even then associated data may be in a
+		 * consistent state.
+		 */
+		if (CK_CC_LIKELY((version & 1) == 0))
+			break;
+
+		/*
+		 * If a sequence is odd then a thread is in the middle of an
+		 * update. Retry the read to avoid operating on inconsistent
+		 * data.
+		 */
+		ck_pr_stall();
+	}
+
+	ck_pr_fence_load();
+	return version;
+}
+
+CK_CC_INLINE static bool
+ck_sequence_read_retry(const struct ck_sequence *sq, unsigned int version)
+{
+
+	/*
+	 * If the sequence number was updated then a read should be
+	 * re-attempted.
+	 */
+	ck_pr_fence_load();
+	return ck_pr_load_uint(&sq->sequence) != version;
+}
+
+#define CK_SEQUENCE_READ(seqlock, version) 						\
+	for (*(version) = 1;								\
+	    (*(version) != 0) && (*(version) = ck_sequence_read_begin(seqlock), 1);	\
+	    *(version) = ck_sequence_read_retry(seqlock, *(version)))
+
+/*
+ * This must be called after a successful mutex acquisition.
+ */
+CK_CC_INLINE static void
+ck_sequence_write_begin(struct ck_sequence *sq)
+{
+
+	/*
+	 * Increment the sequence to an odd number to indicate
+	 * the beginning of a write update.
+	 */
+	ck_pr_store_uint(&sq->sequence, sq->sequence + 1);
+	ck_pr_fence_store();
+	return;
+}
+
+/*
+ * This must be called before mutex ownership is relinquished.
+ */
+CK_CC_INLINE static void
+ck_sequence_write_end(struct ck_sequence *sq)
+{
+
+	/*
+	 * Increment the sequence to an even number to indicate
+	 * completion of a write update.
+	 */
+	ck_pr_fence_store();
+	ck_pr_store_uint(&sq->sequence, sq->sequence + 1);
+	return;
+}
+
+#endif /* CK_SEQUENCE_H */