1 files changed, 83 insertions, 0 deletions
diff --git a/src/core/lib/support/mpscq.c b/src/core/lib/support/mpscq.c
new file mode 100644
index 0000000000..5b9323275a
--- /dev/null
+++ b/src/core/lib/support/mpscq.c
@@ -0,0 +1,83 @@
+/*
+ *
+ * Copyright 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/mpscq.h"
+
+#include <grpc/support/log.h>
+
+void gpr_mpscq_init(gpr_mpscq *q) {
+  gpr_atm_no_barrier_store(&q->head, (gpr_atm)&q->stub);
+  q->tail = &q->stub;
+  gpr_atm_no_barrier_store(&q->stub.next, (gpr_atm)NULL);
+}
+
+void gpr_mpscq_destroy(gpr_mpscq *q) {
+  GPR_ASSERT(gpr_atm_no_barrier_load(&q->head) == (gpr_atm)&q->stub);
+  GPR_ASSERT(q->tail == &q->stub);
+}
+
+void gpr_mpscq_push(gpr_mpscq *q, gpr_mpscq_node *n) {
+  gpr_atm_no_barrier_store(&n->next, (gpr_atm)NULL);
+  gpr_mpscq_node *prev =
+      (gpr_mpscq_node *)gpr_atm_full_xchg(&q->head, (gpr_atm)n);
+  gpr_atm_rel_store(&prev->next, (gpr_atm)n);
+}
+
+gpr_mpscq_node *gpr_mpscq_pop(gpr_mpscq *q) {
+  gpr_mpscq_node *tail = q->tail;
+  gpr_mpscq_node *next = (gpr_mpscq_node *)gpr_atm_acq_load(&tail->next);
+  if (tail == &q->stub) {
+    // indicates the list is actually (ephemerally) empty
+    if (next == NULL) return NULL;
+    q->tail = next;
+    tail = next;
+    next = (gpr_mpscq_node *)gpr_atm_acq_load(&tail->next);
+  }
+  if (next != NULL) {
+    q->tail = next;
+    return tail;
+  }
+  gpr_mpscq_node *head = (gpr_mpscq_node *)gpr_atm_acq_load(&q->head);
+  if (tail != head) {
+    // indicates a retry is in order: we're still adding
+    return NULL;
+  }
+  gpr_mpscq_push(q, &q->stub);
+  next = (gpr_mpscq_node *)gpr_atm_acq_load(&tail->next);
+  if (next != NULL) {
+    q->tail = next;
+    return tail;
+  }
+  // indicates a retry is in order: we're still adding
+  return NULL;
+}