1 files changed, 185 insertions, 0 deletions
diff --git a/src/core/lib/support/stack_lockfree.c b/src/core/lib/support/stack_lockfree.c
new file mode 100644
index 0000000000..de80486132
--- /dev/null
+++ b/src/core/lib/support/stack_lockfree.c
@@ -0,0 +1,185 @@
+/*
+ *
+ * Copyright 2015-2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * 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.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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 COPYRIGHT
+ * OWNER 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 "src/core/lib/support/stack_lockfree.h"
+
+#include <stdlib.h>
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/atm.h>
+#include <grpc/support/log.h>
+#include <grpc/support/port_platform.h>
+
+/* The lockfree node structure is a single architecture-level
+   word that allows for an atomic CAS to set it up. */
+struct lockfree_node_contents {
+  /* next thing to look at. Actual index for head, next index otherwise */
+  uint16_t index;
+#ifdef GPR_ARCH_64
+  uint16_t pad;
+  uint32_t aba_ctr;
+#else
+#ifdef GPR_ARCH_32
+  uint16_t aba_ctr;
+#else
+#error Unsupported bit width architecture
+#endif
+#endif
+};
+
+/* Use a union to make sure that these are in the same bits as an atm word */
+typedef union lockfree_node {
+  gpr_atm atm;
+  struct lockfree_node_contents contents;
+} lockfree_node;
+
+/* make sure that entries aligned to 8-bytes */
+#define ENTRY_ALIGNMENT_BITS 3
+/* reserve this entry as invalid */
+#define INVALID_ENTRY_INDEX ((1 << 16) - 1)
+
+struct gpr_stack_lockfree {
+  lockfree_node *entries;
+  lockfree_node head; /* An atomic entry describing curr head */
+
+#ifndef NDEBUG
+  /* Bitmap of pushed entries to check for double-push or pop */
+  gpr_atm pushed[(INVALID_ENTRY_INDEX + 1) / (8 * sizeof(gpr_atm))];
+#endif
+};
+
+gpr_stack_lockfree *gpr_stack_lockfree_create(size_t entries) {
+  gpr_stack_lockfree *stack;
+  stack = gpr_malloc(sizeof(*stack));
+  /* Since we only allocate 16 bits to represent an entry number,
+   * make sure that we are within the desired range */
+  /* Reserve the highest entry number as a dummy */
+  GPR_ASSERT(entries < INVALID_ENTRY_INDEX);
+  stack->entries = gpr_malloc_aligned(entries * sizeof(stack->entries[0]),
+                                      ENTRY_ALIGNMENT_BITS);
+  /* Clear out all entries */
+  memset(stack->entries, 0, entries * sizeof(stack->entries[0]));
+  memset(&stack->head, 0, sizeof(stack->head));
+#ifndef NDEBUG
+  memset(&stack->pushed, 0, sizeof(stack->pushed));
+#endif
+
+  GPR_ASSERT(sizeof(stack->entries->atm) == sizeof(stack->entries->contents));
+
+  /* Point the head at reserved dummy entry */
+  stack->head.contents.index = INVALID_ENTRY_INDEX;
+/* Fill in the pad and aba_ctr to avoid confusing memcheck tools */
+#ifdef GPR_ARCH_64
+  stack->head.contents.pad = 0;
+#endif
+  stack->head.contents.aba_ctr = 0;
+  return stack;
+}
+
+void gpr_stack_lockfree_destroy(gpr_stack_lockfree *stack) {
+  gpr_free_aligned(stack->entries);
+  gpr_free(stack);
+}
+
+int gpr_stack_lockfree_push(gpr_stack_lockfree *stack, int entry) {
+  lockfree_node head;
+  lockfree_node newhead;
+  lockfree_node curent;
+  lockfree_node newent;
+
+  /* First fill in the entry's index and aba ctr for new head */
+  newhead.contents.index = (uint16_t)entry;
+#ifdef GPR_ARCH_64
+  /* Fill in the pad to avoid confusing memcheck tools */
+  newhead.contents.pad = 0;
+#endif
+
+  /* Also post-increment the aba_ctr */
+  curent.atm = gpr_atm_no_barrier_load(&stack->entries[entry].atm);
+  newhead.contents.aba_ctr = ++curent.contents.aba_ctr;
+  gpr_atm_no_barrier_store(&stack->entries[entry].atm, curent.atm);
+
+#ifndef NDEBUG
+  /* Check for double push */
+  {
+    int pushed_index = entry / (int)(8 * sizeof(gpr_atm));
+    int pushed_bit = entry % (int)(8 * sizeof(gpr_atm));
+    gpr_atm old_val;
+
+    old_val = gpr_atm_no_barrier_fetch_add(&stack->pushed[pushed_index],
+                                           ((gpr_atm)1 << pushed_bit));
+    GPR_ASSERT((old_val & (((gpr_atm)1) << pushed_bit)) == 0);
+  }
+#endif
+
+  do {
+    /* Atomically get the existing head value for use */
+    head.atm = gpr_atm_no_barrier_load(&(stack->head.atm));
+    /* Point to it */
+    newent.atm = gpr_atm_no_barrier_load(&stack->entries[entry].atm);
+    newent.contents.index = head.contents.index;
+    gpr_atm_no_barrier_store(&stack->entries[entry].atm, newent.atm);
+  } while (!gpr_atm_rel_cas(&(stack->head.atm), head.atm, newhead.atm));
+  /* Use rel_cas above to make sure that entry index is set properly */
+  return head.contents.index == INVALID_ENTRY_INDEX;
+}
+
+int gpr_stack_lockfree_pop(gpr_stack_lockfree *stack) {
+  lockfree_node head;
+  lockfree_node newhead;
+
+  do {
+    head.atm = gpr_atm_acq_load(&(stack->head.atm));
+    if (head.contents.index == INVALID_ENTRY_INDEX) {
+      return -1;
+    }
+    newhead.atm =
+        gpr_atm_no_barrier_load(&(stack->entries[head.contents.index].atm));
+
+  } while (!gpr_atm_no_barrier_cas(&(stack->head.atm), head.atm, newhead.atm));
+#ifndef NDEBUG
+  /* Check for valid pop */
+  {
+    int pushed_index = head.contents.index / (8 * sizeof(gpr_atm));
+    int pushed_bit = head.contents.index % (8 * sizeof(gpr_atm));
+    gpr_atm old_val;
+
+    old_val = gpr_atm_no_barrier_fetch_add(&stack->pushed[pushed_index],
+                                           -((gpr_atm)1 << pushed_bit));
+    GPR_ASSERT((old_val & (((gpr_atm)1) << pushed_bit)) != 0);
+  }
+#endif
+
+  return head.contents.index;
+}