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+/*
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+ *
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+ * Copyright 2015, Google Inc.
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+ * All rights reserved.
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+ *
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+ * Redistribution and use in source and binary forms, with or without
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+ * modification, are permitted provided that the following conditions are
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+ * met:
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+ *
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+ * * Redistributions of source code must retain the above copyright
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+ * notice, this list of conditions and the following disclaimer.
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+ * * Redistributions in binary form must reproduce the above
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+ * copyright notice, this list of conditions and the following disclaimer
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+ * in the documentation and/or other materials provided with the
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+ * distribution.
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+ * * Neither the name of Google Inc. nor the names of its
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+ * contributors may be used to endorse or promote products derived from
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+ * this software without specific prior written permission.
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+ *
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+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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+ *
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+ */
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+
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+#include "src/core/support/stack_lockfree.h"
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+
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+#include <stdlib.h>
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+#include <string.h>
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+
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+#include <grpc/support/port_platform.h>
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+#include <grpc/support/alloc.h>
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+#include <grpc/support/atm.h>
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+#include <grpc/support/log.h>
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+
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+/* The lockfree node structure is a single architecture-level
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+ word that allows for an atomic CAS to set it up. */
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+struct lockfree_node_contents {
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+ /* next thing to look at. Actual index for head, next index otherwise */
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+ gpr_uint16 index;
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+#ifdef GPR_ARCH_64
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+ gpr_uint16 pad;
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+ gpr_uint32 aba_ctr;
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+#else
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+#ifdef GPR_ARCH_32
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+ gpr_uint16 aba_ctr;
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+#else
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+#error Unsupported bit width architecture
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+#endif
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+#endif
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+};
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+
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+/* Use a union to make sure that these are in the same bits as an atm word */
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+typedef union lockfree_node {
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+ gpr_atm atm;
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+ struct lockfree_node_contents contents;
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+} lockfree_node;
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+
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+#define ENTRY_ALIGNMENT_BITS 3 /* make sure that entries aligned to 8-bytes */
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+#define INVALID_ENTRY_INDEX ((1<<16)-1) /* reserve this entry as invalid */
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+
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+struct gpr_stack_lockfree {
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+ lockfree_node *entries;
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+ lockfree_node head; /* An atomic entry describing curr head */
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+};
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+
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+gpr_stack_lockfree *gpr_stack_lockfree_create(int entries) {
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+ gpr_stack_lockfree *stack;
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+ stack = gpr_malloc(sizeof(*stack));
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+ /* Since we only allocate 16 bits to represent an entry number,
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+ * make sure that we are within the desired range */
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+ /* Reserve the highest entry number as a dummy */
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+ GPR_ASSERT(entries < INVALID_ENTRY_INDEX);
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+ stack->entries = gpr_malloc_aligned(entries * sizeof(stack->entries[0]),
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+ ENTRY_ALIGNMENT_BITS);
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+ /* Clear out all entries */
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+ memset(stack->entries, 0, entries * sizeof(stack->entries[0]));
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+
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+ /* Point the head at reserved dummy entry */
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+ stack->head.contents.index = INVALID_ENTRY_INDEX;
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+ return stack;
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+}
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+
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+void gpr_stack_lockfree_destroy(gpr_stack_lockfree *stack) {
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+ gpr_free_aligned(stack->entries);
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+ gpr_free(stack);
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+}
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+
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+void gpr_stack_lockfree_push(gpr_stack_lockfree *stack, int entry) {
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+ lockfree_node head;
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+ lockfree_node newhead;
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+
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+ /* First fill in the entry's index and aba ctr for new head */
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+ newhead.contents.index = (gpr_uint16)entry;
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+ /* Also post-increment the aba_ctr */
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+ newhead.contents.aba_ctr = stack->entries[entry].contents.aba_ctr++;
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+
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+ do {
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+ /* Atomically get the existing head value for use */
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+ head.atm = gpr_atm_no_barrier_load(&(stack->head.atm));
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+ /* Point to it */
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+ stack->entries[entry].contents.index = head.contents.index;
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+ } while (!gpr_atm_rel_cas(&(stack->head.atm),
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+ head.atm, newhead.atm));
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+ /* Use rel_cas above to make sure that entry index is set properly */
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+}
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+
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+int gpr_stack_lockfree_pop(gpr_stack_lockfree *stack) {
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+ lockfree_node head;
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+ lockfree_node newhead;
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+ do {
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+ head.atm = gpr_atm_acq_load(&(stack->head.atm));
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+ if (head.contents.index == INVALID_ENTRY_INDEX) {
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+ return -1;
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+ }
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+ newhead.contents.index = stack->entries[head.contents.index].contents.index;
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+
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+ } while (!gpr_atm_no_barrier_cas(&(stack->head.atm),
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+ head.atm,
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+ newhead.atm));
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+ return newhead.contents.index;
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+}
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Vijay Pai