2 files changed, 139 insertions, 0 deletions
diff --git a/src/core/lib/backoff/backoff.cc b/src/core/lib/backoff/backoff.cc
new file mode 100644
index 0000000000..fe0a751817
--- /dev/null
+++ b/src/core/lib/backoff/backoff.cc
@@ -0,0 +1,73 @@
+/*
+ *
+ * Copyright 2016 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include "src/core/lib/backoff/backoff.h"
+
+#include <grpc/support/useful.h>
+
+void grpc_backoff_init(grpc_backoff *backoff,
+                       grpc_millis initial_connect_timeout, double multiplier,
+                       double jitter, grpc_millis min_timeout_millis,
+                       grpc_millis max_timeout_millis) {
+  backoff->initial_connect_timeout = initial_connect_timeout;
+  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;
+}
+
+grpc_millis grpc_backoff_begin(grpc_exec_ctx *exec_ctx, grpc_backoff *backoff) {
+  backoff->current_timeout_millis = backoff->initial_connect_timeout;
+  const grpc_millis first_timeout =
+      GPR_MAX(backoff->current_timeout_millis, backoff->min_timeout_millis);
+  return grpc_exec_ctx_now(exec_ctx) + first_timeout;
+}
+
+/* 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);
+}
+
+grpc_millis grpc_backoff_step(grpc_exec_ctx *exec_ctx, grpc_backoff *backoff) {
+  const double new_timeout_millis =
+      backoff->multiplier * (double)backoff->current_timeout_millis;
+  backoff->current_timeout_millis =
+      GPR_MIN((grpc_millis)new_timeout_millis, backoff->max_timeout_millis);
+
+  const double jitter_range_width = backoff->jitter * new_timeout_millis;
+  const double jitter =
+      (2 * generate_uniform_random_number(&backoff->rng_state) - 1) *
+      jitter_range_width;
+
+  backoff->current_timeout_millis =
+      (grpc_millis)((double)(backoff->current_timeout_millis) + jitter);
+
+  const grpc_millis current_deadline =
+      grpc_exec_ctx_now(exec_ctx) + backoff->current_timeout_millis;
+
+  const grpc_millis min_deadline =
+      grpc_exec_ctx_now(exec_ctx) + backoff->min_timeout_millis;
+
+  return GPR_MAX(current_deadline, min_deadline);
+}
+
+void grpc_backoff_reset(grpc_backoff *backoff) {
+  backoff->current_timeout_millis = backoff->initial_connect_timeout;
+}
diff --git a/src/core/lib/backoff/backoff.h b/src/core/lib/backoff/backoff.h
new file mode 100644
index 0000000000..80e49ea52a
--- /dev/null
+++ b/src/core/lib/backoff/backoff.h
@@ -0,0 +1,66 @@
+/*
+ *
+ * Copyright 2016 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_LIB_BACKOFF_BACKOFF_H
+#define GRPC_CORE_LIB_BACKOFF_BACKOFF_H
+
+#include "src/core/lib/iomgr/exec_ctx.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct {
+  /// const:  how long to wait after the first failure before retrying
+  grpc_millis initial_connect_timeout;
+  /// const: factor with which to multiply backoff after a failed retry
+  double multiplier;
+  /// const: amount to randomize backoffs
+  double jitter;
+  /// const: minimum time between retries in milliseconds
+  grpc_millis min_timeout_millis;
+  /// const: maximum time between retries in milliseconds
+  grpc_millis max_timeout_millis;
+
+  /// random number generator
+  uint32_t rng_state;
+
+  /// current retry timeout in milliseconds
+  grpc_millis current_timeout_millis;
+} grpc_backoff;
+
+/// Initialize backoff machinery - does not need to be destroyed
+void grpc_backoff_init(grpc_backoff *backoff,
+                       grpc_millis initial_connect_timeout, double multiplier,
+                       double jitter, grpc_millis min_timeout_millis,
+                       grpc_millis max_timeout_millis);
+
+/// Begin retry loop: returns a timespec for the NEXT retry
+grpc_millis grpc_backoff_begin(grpc_exec_ctx *exec_ctx, grpc_backoff *backoff);
+/// Step a retry loop: returns a timespec for the NEXT retry
+grpc_millis grpc_backoff_step(grpc_exec_ctx *exec_ctx, grpc_backoff *backoff);
+/// Reset the backoff, so the next grpc_backoff_step will be a
+/// grpc_backoff_begin
+/// instead
+void grpc_backoff_reset(grpc_backoff *backoff);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* GRPC_CORE_LIB_BACKOFF_BACKOFF_H */