Improvements to C Core's backoff code and API

1 files changed, 109 insertions, 72 deletions

diff --git a/test/core/backoff/backoff_test.c b/test/core/backoff/backoff_test.c
index a29cce6cc7..e80e0b31b8 100644
--- a/test/core/backoff/backoff_test.c
+++ b/test/core/backoff/backoff_test.c
@@ -19,120 +19,157 @@
 #include "src/core/lib/backoff/backoff.h"
 
 #include <grpc/support/log.h>
+#include <grpc/support/useful.h>
 
 #include "test/core/util/test_config.h"
 
 static void test_constant_backoff(void) {
   grpc_backoff backoff;
-  grpc_backoff_init(&backoff, 200 /* initial timeout */, 1.0 /* multiplier */,
-                    0.0 /* jitter */, 100 /* min timeout */,
-                    1000 /* max timeout */);
-
+  const grpc_millis initial_backoff = 200;
+  const double multiplier = 1.0;
+  const double jitter = 0.0;
+  const grpc_millis min_connect_timeout = 100;
+  const grpc_millis max_backoff = 1000;
+  grpc_backoff_init(&backoff, initial_backoff, multiplier, jitter,
+                    min_connect_timeout, max_backoff);
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
-  grpc_millis next = grpc_backoff_begin(&exec_ctx, &backoff);
-  GPR_ASSERT(next - grpc_exec_ctx_now(&exec_ctx) == 200);
+  grpc_backoff_result next_deadlines = grpc_backoff_begin(&exec_ctx, &backoff);
+  GPR_ASSERT(next_deadlines.current_deadline - grpc_exec_ctx_now(&exec_ctx) ==
+             initial_backoff);
+  GPR_ASSERT(next_deadlines.next_attempt_start_time -
+                 grpc_exec_ctx_now(&exec_ctx) ==
+             initial_backoff);
   for (int i = 0; i < 10000; i++) {
-    next = grpc_backoff_step(&exec_ctx, &backoff);
-    GPR_ASSERT(next - grpc_exec_ctx_now(&exec_ctx) == 200);
-    exec_ctx.now = next;
+    next_deadlines = grpc_backoff_step(&exec_ctx, &backoff);
+    GPR_ASSERT(next_deadlines.current_deadline - grpc_exec_ctx_now(&exec_ctx) ==
+               initial_backoff);
+    GPR_ASSERT(next_deadlines.next_attempt_start_time -
+                   grpc_exec_ctx_now(&exec_ctx) ==
+               initial_backoff);
+    exec_ctx.now = next_deadlines.current_deadline;
   }
   grpc_exec_ctx_finish(&exec_ctx);
 }
 
 static void test_min_connect(void) {
   grpc_backoff backoff;
-  grpc_backoff_init(&backoff, 100 /* initial timeout */, 1.0 /* multiplier */,
-                    0.0 /* jitter */, 200 /* min timeout */,
-                    1000 /* max timeout */);
-
+  const grpc_millis initial_backoff = 100;
+  const double multiplier = 1.0;
+  const double jitter = 0.0;
+  const grpc_millis min_connect_timeout = 200;
+  const grpc_millis max_backoff = 1000;
+  grpc_backoff_init(&backoff, initial_backoff, multiplier, jitter,
+                    min_connect_timeout, max_backoff);
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
-  grpc_millis next = grpc_backoff_begin(&exec_ctx, &backoff);
-  GPR_ASSERT(next - grpc_exec_ctx_now(&exec_ctx) == 200);
+  grpc_backoff_result next = grpc_backoff_begin(&exec_ctx, &backoff);
+  // Because the min_connect_timeout > initial_backoff, current_deadline is used
+  // as the deadline for the current attempt.
+  GPR_ASSERT(next.current_deadline - grpc_exec_ctx_now(&exec_ctx) ==
+             min_connect_timeout);
+  // ... while, if the current attempt fails, the next one will happen after
+  // initial_backoff.
+  GPR_ASSERT(next.next_attempt_start_time - grpc_exec_ctx_now(&exec_ctx) ==
+             initial_backoff);
   grpc_exec_ctx_finish(&exec_ctx);
 }
 
 static void test_no_jitter_backoff(void) {
   grpc_backoff backoff;
-  grpc_backoff_init(&backoff, 2 /* initial timeout */, 2.0 /* multiplier */,
-                    0.0 /* jitter */, 1 /* min timeout */,
-                    513 /* max timeout */);
+  const grpc_millis initial_backoff = 2;
+  const double multiplier = 2.0;
+  const double jitter = 0.0;
+  const grpc_millis min_connect_timeout = 1;
+  const grpc_millis max_backoff = 513;
+  grpc_backoff_init(&backoff, initial_backoff, multiplier, jitter,
+                    min_connect_timeout, max_backoff);
   // x_1 = 2
   // x_n = 2**i + x_{i-1} ( = 2**(n+1) - 2 )
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
   exec_ctx.now = 0;
   exec_ctx.now_is_valid = true;
-  grpc_millis next = grpc_backoff_begin(&exec_ctx, &backoff);
-  GPR_ASSERT(next == 2);
-  exec_ctx.now = next;
-  next = grpc_backoff_step(&exec_ctx, &backoff);
-  GPR_ASSERT(next == 6);
-  exec_ctx.now = next;
-  next = grpc_backoff_step(&exec_ctx, &backoff);
-  GPR_ASSERT(next == 14);
-  exec_ctx.now = next;
-  next = grpc_backoff_step(&exec_ctx, &backoff);
-  GPR_ASSERT(next == 30);
-  exec_ctx.now = next;
-  next = grpc_backoff_step(&exec_ctx, &backoff);
-  GPR_ASSERT(next == 62);
-  exec_ctx.now = next;
-  next = grpc_backoff_step(&exec_ctx, &backoff);
-  GPR_ASSERT(next == 126);
-  exec_ctx.now = next;
-  next = grpc_backoff_step(&exec_ctx, &backoff);
-  GPR_ASSERT(next == 254);
-  exec_ctx.now = next;
-  next = grpc_backoff_step(&exec_ctx, &backoff);
-  GPR_ASSERT(next == 510);
-  exec_ctx.now = next;
-  next = grpc_backoff_step(&exec_ctx, &backoff);
-  GPR_ASSERT(next == 1022);
-  exec_ctx.now = next;
-  next = grpc_backoff_step(&exec_ctx, &backoff);
+  grpc_backoff_result next_deadlines = grpc_backoff_begin(&exec_ctx, &backoff);
+  GPR_ASSERT(next_deadlines.current_deadline ==
+             next_deadlines.next_attempt_start_time);
+  GPR_ASSERT(next_deadlines.current_deadline == 2);
+  exec_ctx.now = next_deadlines.current_deadline;
+  next_deadlines = grpc_backoff_step(&exec_ctx, &backoff);
+  GPR_ASSERT(next_deadlines.current_deadline == 6);
+  exec_ctx.now = next_deadlines.current_deadline;
+  next_deadlines = grpc_backoff_step(&exec_ctx, &backoff);
+  GPR_ASSERT(next_deadlines.current_deadline == 14);
+  exec_ctx.now = next_deadlines.current_deadline;
+  next_deadlines = grpc_backoff_step(&exec_ctx, &backoff);
+  GPR_ASSERT(next_deadlines.current_deadline == 30);
+  exec_ctx.now = next_deadlines.current_deadline;
+  next_deadlines = grpc_backoff_step(&exec_ctx, &backoff);
+  GPR_ASSERT(next_deadlines.current_deadline == 62);
+  exec_ctx.now = next_deadlines.current_deadline;
+  next_deadlines = grpc_backoff_step(&exec_ctx, &backoff);
+  GPR_ASSERT(next_deadlines.current_deadline == 126);
+  exec_ctx.now = next_deadlines.current_deadline;
+  next_deadlines = grpc_backoff_step(&exec_ctx, &backoff);
+  GPR_ASSERT(next_deadlines.current_deadline == 254);
+  exec_ctx.now = next_deadlines.current_deadline;
+  next_deadlines = grpc_backoff_step(&exec_ctx, &backoff);
+  GPR_ASSERT(next_deadlines.current_deadline == 510);
+  exec_ctx.now = next_deadlines.current_deadline;
+  next_deadlines = grpc_backoff_step(&exec_ctx, &backoff);
+  GPR_ASSERT(next_deadlines.current_deadline == 1022);
+  exec_ctx.now = next_deadlines.current_deadline;
+  next_deadlines = grpc_backoff_step(&exec_ctx, &backoff);
   // Hit the maximum timeout. From this point onwards, retries will increase
   // only by max timeout.
-  GPR_ASSERT(next == 1535);
-  exec_ctx.now = next;
-  next = grpc_backoff_step(&exec_ctx, &backoff);
-  GPR_ASSERT(next == 2048);
-  exec_ctx.now = next;
-  next = grpc_backoff_step(&exec_ctx, &backoff);
-  GPR_ASSERT(next == 2561);
+  GPR_ASSERT(next_deadlines.current_deadline == 1535);
+  exec_ctx.now = next_deadlines.current_deadline;
+  next_deadlines = grpc_backoff_step(&exec_ctx, &backoff);
+  GPR_ASSERT(next_deadlines.current_deadline == 2048);
+  exec_ctx.now = next_deadlines.current_deadline;
+  next_deadlines = grpc_backoff_step(&exec_ctx, &backoff);
+  GPR_ASSERT(next_deadlines.current_deadline == 2561);
   grpc_exec_ctx_finish(&exec_ctx);
 }
 
 static void test_jitter_backoff(void) {
-  const int64_t initial_timeout = 500;
+  const grpc_millis initial_backoff = 500;
+  grpc_millis current_backoff = initial_backoff;
+  const grpc_millis max_backoff = 1000;
+  const grpc_millis min_connect_timeout = 100;
+  const double multiplier = 1.0;
   const double jitter = 0.1;
   grpc_backoff backoff;
-  grpc_backoff_init(&backoff, (grpc_millis)initial_timeout,
-                    1.0 /* multiplier */, jitter, 100 /* min timeout */,
-                    1000 /* max timeout */);
+  grpc_backoff_init(&backoff, initial_backoff, multiplier, jitter,
+                    min_connect_timeout, max_backoff);
 
   backoff.rng_state = 0;  // force consistent PRNG
 
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
-  grpc_millis next = grpc_backoff_begin(&exec_ctx, &backoff);
-  GPR_ASSERT(next - grpc_exec_ctx_now(&exec_ctx) == 500);
-
-  int64_t expected_next_lower_bound =
-      (int64_t)((double)initial_timeout * (1 - jitter));
-  int64_t expected_next_upper_bound =
-      (int64_t)((double)initial_timeout * (1 + jitter));
+  grpc_backoff_result next_deadlines = grpc_backoff_begin(&exec_ctx, &backoff);
+  GPR_ASSERT(next_deadlines.current_deadline - grpc_exec_ctx_now(&exec_ctx) ==
+             initial_backoff);
+  GPR_ASSERT(next_deadlines.next_attempt_start_time -
+                 grpc_exec_ctx_now(&exec_ctx) ==
+             initial_backoff);
+
+  grpc_millis expected_next_lower_bound =
+      (grpc_millis)((double)current_backoff * (1 - jitter));
+  grpc_millis expected_next_upper_bound =
+      (grpc_millis)((double)current_backoff * (1 + jitter));
 
   for (int i = 0; i < 10000; i++) {
-    next = grpc_backoff_step(&exec_ctx, &backoff);
-
-    // next-now must be within (jitter*100)% of the previous timeout.
-    const int64_t timeout_millis = next - grpc_exec_ctx_now(&exec_ctx);
+    next_deadlines = grpc_backoff_step(&exec_ctx, &backoff);
+    // next-now must be within (jitter*100)% of the current backoff (which
+    // increases by * multiplier up to max_backoff).
+    const grpc_millis timeout_millis =
+        next_deadlines.current_deadline - grpc_exec_ctx_now(&exec_ctx);
     GPR_ASSERT(timeout_millis >= expected_next_lower_bound);
     GPR_ASSERT(timeout_millis <= expected_next_upper_bound);
-
+    current_backoff = GPR_MIN(
+        (grpc_millis)((double)current_backoff * multiplier), max_backoff);
     expected_next_lower_bound =
-        (int64_t)((double)timeout_millis * (1 - jitter));
+        (grpc_millis)((double)current_backoff * (1 - jitter));
     expected_next_upper_bound =
-        (int64_t)((double)timeout_millis * (1 + jitter));
-    exec_ctx.now = next;
+        (grpc_millis)((double)current_backoff * (1 + jitter));
+    exec_ctx.now = next_deadlines.current_deadline;
   }
   grpc_exec_ctx_finish(&exec_ctx);
 }