1 files changed, 76 insertions, 0 deletions
diff --git a/src/core/lib/support/backoff.c b/src/core/lib/support/backoff.c
new file mode 100644
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+++ b/src/core/lib/support/backoff.c
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+/*
+ *
+ * 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/backoff.h"
+
+#include <grpc/support/useful.h>
+
+void gpr_backoff_init(gpr_backoff *backoff, double multiplier, double jitter,
+                      int64_t min_timeout_millis, int64_t max_timeout_millis) {
+  backoff->multiplier = multiplier;
+  backoff->jitter = jitter;
+  backoff->min_timeout_millis = min_timeout_millis;
+  backoff->max_timeout_millis = max_timeout_millis;
+  backoff->rng_state = (uint32_t)gpr_now(GPR_CLOCK_REALTIME).tv_nsec;
+}
+
+gpr_timespec gpr_backoff_begin(gpr_backoff *backoff, gpr_timespec now) {
+  backoff->current_timeout_millis = backoff->min_timeout_millis;
+  return gpr_time_add(
+      now, gpr_time_from_millis(backoff->current_timeout_millis, GPR_TIMESPAN));
+}
+
+/* Generate a random number between 0 and 1. */
+static double generate_uniform_random_number(uint32_t *rng_state) {
+  *rng_state = (1103515245 * *rng_state + 12345) % ((uint32_t)1 << 31);
+  return *rng_state / (double)((uint32_t)1 << 31);
+}
+
+gpr_timespec gpr_backoff_step(gpr_backoff *backoff, gpr_timespec now) {
+  double new_timeout_millis =
+      backoff->multiplier * (double)backoff->current_timeout_millis;
+  double jitter_range = backoff->jitter * new_timeout_millis;
+  double jitter =
+      (2 * generate_uniform_random_number(&backoff->rng_state) - 1) *
+      jitter_range;
+  backoff->current_timeout_millis =
+      GPR_CLAMP((int64_t)(new_timeout_millis + jitter),
+                backoff->min_timeout_millis, backoff->max_timeout_millis);
+  return gpr_time_add(
+      now, gpr_time_from_millis(backoff->current_timeout_millis, GPR_TIMESPAN));
+}
+
+void gpr_backoff_reset(gpr_backoff *backoff) {
+  // forces step() to return a timeout of min_timeout_millis
+  backoff->current_timeout_millis = 0;
+}