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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_BYTELOCK_H
+#define CK_BYTELOCK_H
+
+/*
+ * The implementations here are derived from the work described in:
+ * Dice, D. and Shavit, N. 2010. TLRW: return of the read-write lock.
+ * In Proceedings of the 22nd ACM Symposium on Parallelism in Algorithms
+ * and Architectures (Thira, Santorini, Greece, June 13 - 15, 2010).
+ * SPAA '10. ACM, New York, NY, 284-293.
+ */
+
+#include <ck_cc.h>
+#include <ck_md.h>
+#include <ck_pr.h>
+#include <ck_stdbool.h>
+#include <ck_stddef.h>
+#include <ck_limits.h>
+
+struct ck_bytelock {
+ unsigned int owner;
+ unsigned int n_readers;
+ uint8_t readers[CK_MD_CACHELINE - sizeof(unsigned int) * 2] CK_CC_ALIGN(8);
+};
+typedef struct ck_bytelock ck_bytelock_t;
+
+#define CK_BYTELOCK_INITIALIZER { 0, 0, {0} }
+#define CK_BYTELOCK_UNSLOTTED UINT_MAX
+
+CK_CC_INLINE static void
+ck_bytelock_init(struct ck_bytelock *bytelock)
+{
+ unsigned int i;
+
+ bytelock->owner = 0;
+ bytelock->n_readers = 0;
+ for (i = 0; i < sizeof bytelock->readers; i++)
+ bytelock->readers[i] = false;
+
+ ck_pr_barrier();
+ return;
+}
+
+#ifdef CK_F_PR_LOAD_64
+#define CK_BYTELOCK_LENGTH sizeof(uint64_t)
+#define CK_BYTELOCK_LOAD ck_pr_load_64
+#define CK_BYTELOCK_TYPE uint64_t
+#elif defined(CK_F_PR_LOAD_32)
+#define CK_BYTELOCK_LENGTH sizeof(uint32_t)
+#define CK_BYTELOCK_LOAD ck_pr_load_32
+#define CK_BYTELOCK_TYPE uint32_t
+#else
+#error Unsupported platform.
+#endif
+
+CK_CC_INLINE static void
+ck_bytelock_write_lock(struct ck_bytelock *bytelock, unsigned int slot)
+{
+ CK_BYTELOCK_TYPE *readers = (void *)bytelock->readers;
+ unsigned int i;
+
+ /* Announce upcoming writer acquisition. */
+ while (ck_pr_cas_uint(&bytelock->owner, 0, slot) == false)
+ ck_pr_stall();
+
+ /* If we are slotted, we might be upgrading from a read lock. */
+ if (slot <= sizeof bytelock->readers)
+ ck_pr_store_8(&bytelock->readers[slot - 1], false);
+
+ /*
+ * Wait for slotted readers to drain out. This also provides the
+ * lock acquire semantics.
+ */
+ ck_pr_fence_atomic_load();
+
+ for (i = 0; i < sizeof(bytelock->readers) / CK_BYTELOCK_LENGTH; i++) {
+ while (CK_BYTELOCK_LOAD(&readers[i]) != false)
+ ck_pr_stall();
+ }
+
+ /* Wait for unslotted readers to drain out. */
+ while (ck_pr_load_uint(&bytelock->n_readers) != 0)
+ ck_pr_stall();
+
+ ck_pr_fence_lock();
+ return;
+}
+
+#undef CK_BYTELOCK_LENGTH
+#undef CK_BYTELOCK_LOAD
+#undef CK_BYTELOCK_TYPE
+
+CK_CC_INLINE static void
+ck_bytelock_write_unlock(struct ck_bytelock *bytelock)
+{
+
+ ck_pr_fence_unlock();
+ ck_pr_store_uint(&bytelock->owner, 0);
+ return;
+}
+
+CK_CC_INLINE static void
+ck_bytelock_read_lock(struct ck_bytelock *bytelock, unsigned int slot)
+{
+
+ if (ck_pr_load_uint(&bytelock->owner) == slot) {
+ ck_pr_store_8(&bytelock->readers[slot - 1], true);
+ ck_pr_fence_strict_store();
+ ck_pr_store_uint(&bytelock->owner, 0);
+ return;
+ }
+
+ /* Unslotted threads will have to use the readers counter. */
+ if (slot > sizeof bytelock->readers) {
+ for (;;) {
+ ck_pr_inc_uint(&bytelock->n_readers);
+ ck_pr_fence_atomic_load();
+ if (ck_pr_load_uint(&bytelock->owner) == 0)
+ break;
+ ck_pr_dec_uint(&bytelock->n_readers);
+
+ while (ck_pr_load_uint(&bytelock->owner) != 0)
+ ck_pr_stall();
+ }
+
+ ck_pr_fence_lock();
+ return;
+ }
+
+ slot -= 1;
+ for (;;) {
+#ifdef CK_F_PR_FAA_8
+ ck_pr_fas_8(&bytelock->readers[slot], true);
+ ck_pr_fence_atomic_load();
+#else
+ ck_pr_store_8(&bytelock->readers[slot], true);
+ ck_pr_fence_store_load();
+#endif
+
+ /*
+ * If there is no owner at this point, our slot has
+ * already been published and it is guaranteed no
+ * write acquisition will succeed until we drain out.
+ */
+ if (ck_pr_load_uint(&bytelock->owner) == 0)
+ break;
+
+ ck_pr_store_8(&bytelock->readers[slot], false);
+ while (ck_pr_load_uint(&bytelock->owner) != 0)
+ ck_pr_stall();
+ }
+
+ ck_pr_fence_lock();
+ return;
+}
+
+CK_CC_INLINE static void
+ck_bytelock_read_unlock(struct ck_bytelock *bytelock, unsigned int slot)
+{
+
+ ck_pr_fence_unlock();
+
+ if (slot > sizeof bytelock->readers)
+ ck_pr_dec_uint(&bytelock->n_readers);
+ else
+ ck_pr_store_8(&bytelock->readers[slot - 1], false);
+
+ return;
+}
+
+#endif /* CK_BYTELOCK_H */