Merge branch 'lockfree-stack' of github.com:vjpai/grpc into i-want-to-wait-free

2 files changed, 182 insertions, 0 deletions

diff --git a/src/core/support/stack_lockfree.c b/src/core/support/stack_lockfree.c
new file mode 100644
index 0000000000..83a68444f5
--- /dev/null
+++ b/src/core/support/stack_lockfree.c
@@ -0,0 +1,132 @@
+/*
+ *
+ * Copyright 2015, 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/support/stack_lockfree.h"
+
+#include <stdlib.h>
+#include <string.h>
+
+#include <grpc/support/port_platform.h>
+#include <grpc/support/alloc.h>
+#include <grpc/support/atm.h>
+#include <grpc/support/log.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 */
+  gpr_uint16 index;
+#ifdef GPR_ARCH_64
+  gpr_uint16 pad;
+  gpr_uint32 aba_ctr;
+#else
+#ifdef GPR_ARCH_32
+  gpr_uint16 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;
+
+#define ENTRY_ALIGNMENT_BITS 3 /* make sure that entries aligned to 8-bytes */
+#define INVALID_ENTRY_INDEX ((1<<16)-1) /* reserve this entry as invalid */
+
+struct gpr_stack_lockfree {
+  lockfree_node *entries;
+  lockfree_node head; /* An atomic entry describing curr head */
+};
+
+gpr_stack_lockfree *gpr_stack_lockfree_create(int 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));
+
+  /* Point the head at reserved dummy entry */
+  stack->head.contents.index = INVALID_ENTRY_INDEX;
+  return stack;
+}
+
+void gpr_stack_lockfree_destroy(gpr_stack_lockfree *stack) {
+  gpr_free_aligned(stack->entries);
+  gpr_free(stack);
+}
+
+void gpr_stack_lockfree_push(gpr_stack_lockfree *stack, int entry) {
+  lockfree_node head;
+  lockfree_node newhead;
+
+  /* First fill in the entry's index and aba ctr for new head */
+  newhead.contents.index = (gpr_uint16)entry;
+  /* Also post-increment the aba_ctr */
+  newhead.contents.aba_ctr = stack->entries[entry].contents.aba_ctr++;
+
+  do {
+    /* Atomically get the existing head value for use */
+    head.atm = gpr_atm_no_barrier_load(&(stack->head.atm));
+    /* Point to it */
+    stack->entries[entry].contents.index = head.contents.index;
+  } 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 */
+}
+
+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));
+  return head.contents.index;
+}
diff --git a/src/core/support/stack_lockfree.h b/src/core/support/stack_lockfree.h
new file mode 100644
index 0000000000..7919ef38cc
--- /dev/null
+++ b/src/core/support/stack_lockfree.h
@@ -0,0 +1,50 @@
+/*
+ *
+ * Copyright 2015, 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.
+ *
+ */
+
+#ifndef GRPC_INTERNAL_CORE_SUPPORT_STACK_LOCKFREE_H
+#define GRPC_INTERNAL_CORE_SUPPORT_STACK_LOCKFREE_H
+
+typedef struct gpr_stack_lockfree gpr_stack_lockfree;
+
+/* This stack must specify the maximum number of entries to track.
+   The current implementation only allows up to 65534 entries */
+gpr_stack_lockfree *gpr_stack_lockfree_create(int entries);
+void gpr_stack_lockfree_destroy(gpr_stack_lockfree *);
+
+/* Pass in a valid entry number for the next stack entry */
+void gpr_stack_lockfree_push(gpr_stack_lockfree *, int entry);
+
+/* Returns -1 on empty or the actual entry number */
+int gpr_stack_lockfree_pop(gpr_stack_lockfree *);
+
+#endif  /* GRPC_INTERNAL_CORE_SUPPORT_STACK_LOCKFREE_H */