[experiments] Allow experiments to opt-in to testing against all pollers (default to not) (#35683)

Closes #35683

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/35683 from ctiller:minimize2 ac22512f99
PiperOrigin-RevId: 601886350

bazel/experiments.bzl

@@ -58,6 +58,12 @@ EXPERIMENT_ENABLES = {
     "wrr_delegate_to_pick_first": "wrr_delegate_to_pick_first",
 }
 
+EXPERIMENT_POLLERS = [
+    "event_engine_client",
+    "event_engine_dns",
+    "event_engine_listener",
+]
+
 EXPERIMENTS = {
     "windows": {
         "dbg": {

bazel/grpc_build_system.bzl

@@ -29,8 +29,8 @@ Contains macros used throughout the repo.
 
 load("//bazel:cc_grpc_library.bzl", "cc_grpc_library")
 load("//bazel:copts.bzl", "GRPC_DEFAULT_COPTS")
-load("//bazel:experiments.bzl", "EXPERIMENTS", "EXPERIMENT_ENABLES")
-load("//bazel:test_experiments.bzl", "TEST_EXPERIMENTS", "TEST_EXPERIMENT_ENABLES")
+load("//bazel:experiments.bzl", "EXPERIMENTS", "EXPERIMENT_ENABLES", "EXPERIMENT_POLLERS")
+load("//bazel:test_experiments.bzl", "TEST_EXPERIMENTS", "TEST_EXPERIMENT_ENABLES", "TEST_EXPERIMENT_POLLERS")
 load("@build_bazel_rules_apple//apple:ios.bzl", "ios_unit_test")
 load("@build_bazel_rules_apple//apple/testing/default_runner:ios_test_runner.bzl", "ios_test_runner")
 load("@com_google_protobuf//bazel:upb_proto_library.bzl", "upb_proto_library", "upb_proto_reflection_library")
@@ -279,8 +279,10 @@ def ios_cc_test(
             deps = ios_test_deps,
         )
 
-def expand_tests(name, srcs, deps, tags, args, exclude_pollers, uses_polling, uses_event_engine, flaky):
-    """Common logic used to parameterize tests for every poller and EventEngine and experiment.
+def expand_poller_config(name, srcs, deps, tags, args, exclude_pollers, uses_polling, uses_event_engine, flaky):
+    """Common logic used to parameterize tests for every poller and EventEngine.
+
+    Used by expand_tests (repeatedly) to form base lists of pollers for each experiment.
 
     Args:
         name: base name of the test
@@ -297,6 +299,7 @@ def expand_tests(name, srcs, deps, tags, args, exclude_pollers, uses_polling, us
     Returns:
         A list of dictionaries containing modified values of name, srcs, deps, tags, and args.
     """
+
     poller_config = []
 
     # See work_stealing_thread_pool.cc for details.
@@ -373,6 +376,27 @@ def expand_tests(name, srcs, deps, tags, args, exclude_pollers, uses_polling, us
                     "flaky": flaky,
                 })
 
+    return poller_config
+
+def expand_tests(name, srcs, deps, tags, args, exclude_pollers, uses_polling, uses_event_engine, flaky):
+    """Common logic used to parameterize tests for every poller and EventEngine and experiment.
+
+    Args:
+        name: base name of the test
+        srcs: source files
+        deps: base deps
+        tags: base tags
+        args: base args
+        flaky: base flaky
+        exclude_pollers: list of poller names to exclude for this set of tests.
+        uses_polling: set to False if the test is not sensitive to polling methodology.
+        uses_event_engine: set to False if the test is not sensitive to
+            EventEngine implementation differences
+
+    Returns:
+        A list of dictionaries containing modified values of name, srcs, deps, tags, and args.
+    """
+
     experiments = {}
 
     # buildifier: disable=uninitialized
@@ -421,13 +445,28 @@ def expand_tests(name, srcs, deps, tags, args, exclude_pollers, uses_polling, us
                 tags.append("no_test_ios")
         return tags
 
-    experiment_config = list(poller_config)
+    base_params = {
+        "name": name,
+        "srcs": srcs,
+        "deps": deps,
+        "tags": tags,
+        "args": args,
+        "exclude_pollers": exclude_pollers,
+        "uses_polling": uses_polling,
+        "uses_event_engine": uses_event_engine,
+        "flaky": flaky,
+    }
+
+    experiment_config = expand_poller_config(**base_params)
     experiment_enables = {k: v for k, v in EXPERIMENT_ENABLES.items() + TEST_EXPERIMENT_ENABLES.items()}
+    experiment_pollers = EXPERIMENT_POLLERS + TEST_EXPERIMENT_POLLERS
     for mode, config in mode_config.items():
         enabled_tags, disabled_tags = config
         if enabled_tags != None:
             for experiment in experiments[mode].keys():
-                for config in poller_config:
+                experiment_params = dict(base_params)
+                experiment_params["uses_polling"] = uses_polling and (experiment in experiment_pollers)
+                for config in expand_poller_config(**experiment_params):
                     config = dict(config)
                     config["name"] = config["name"] + "@experiment=" + experiment
                     env = dict(config["env"])
@@ -443,7 +482,9 @@ def expand_tests(name, srcs, deps, tags, args, exclude_pollers, uses_polling, us
                     experiment_config.append(config)
         if disabled_tags != None:
             for experiment in experiments[mode].keys():
-                for config in poller_config:
+                experiment_params = dict(base_params)
+                experiment_params["uses_polling"] = uses_polling and (experiment in experiment_pollers)
+                for config in expand_poller_config(**experiment_params):
                     config = dict(config)
                     config["name"] = config["name"] + "@experiment=no_" + experiment
                     env = dict(config["env"])

bazel/test_experiments.bzl

@@ -23,6 +23,9 @@ TEST_EXPERIMENT_ENABLES = {
     "test_experiment_4": "test_experiment_4",
 }
 
+TEST_EXPERIMENT_POLLERS = [
+]
+
 TEST_EXPERIMENTS = {
     "windows": {
         "dbg": {

src/core/lib/experiments/experiments.yaml

@@ -26,6 +26,9 @@
 #              Defaults to the empty list.
 #              If any of the experiments in the required list is determined to
 #              be disabled at runtime, this experiment is disabled at runtime.
+# uses_polling: optional boolean (false if not specified) that indicates that
+#              this experiment should be tested with all different polling
+#              engines.
 #
 # Well known test tags:
 #   core_end2end_test:   all tests, fixtures in the core end2end suite
@@ -68,6 +71,7 @@
   expiry: 2024/04/01
   owner: hork@google.com
   test_tags: ["core_end2end_test", "event_engine_client_test"]
+  uses_polling: true
 - name: event_engine_dns
   description:
     If set, use EventEngine DNSResolver for client channel resolution
@@ -75,11 +79,13 @@
   owner: yijiem@google.com
   test_tags: ["cancel_ares_query_test", "resolver_component_tests_runner_invoker"]
   allow_in_fuzzing_config: false
+  uses_polling: true
 - name: event_engine_listener
   description: Use EventEngine listeners instead of iomgr's grpc_tcp_server
   expiry: 2024/04/01
   owner: vigneshbabu@google.com
   test_tags: ["core_end2end_test", "event_engine_listener_test"]
+  uses_polling: true
 - name: free_large_allocator
   description: If set, return all free bytes from a "big" allocator
   expiry: 2024/04/01

tools/codegen/core/experiments_compiler.py

@@ -192,6 +192,7 @@ class ExperimentDefinition(object):
             print("Failed to create experiment definition")
             return
         self._allow_in_fuzzing_config = True
+        self._uses_polling = False
         self._name = attributes["name"]
         self._description = attributes["description"]
         self._expiry = attributes["expiry"]
@@ -200,6 +201,9 @@ class ExperimentDefinition(object):
         self._test_tags = []
         self._requires = set()
 
+        if "uses_polling" in attributes:
+            self._uses_polling = attributes["uses_polling"]
+
         if "allow_in_fuzzing_config" in attributes:
             self._allow_in_fuzzing_config = attributes[
                 "allow_in_fuzzing_config"
@@ -683,6 +687,17 @@ class ExperimentsCompiler(object):
                 )
             print("}", file=B)
 
+            # Generate a list of experiments that use polling.
+            print(file=B)
+            if mode == "test":
+                print("TEST_EXPERIMENT_POLLERS = [", file=B)
+            else:
+                print("EXPERIMENT_POLLERS = [", file=B)
+            for name, exp in self._experiment_definitions.items():
+                if exp._uses_polling:
+                    print(f'    "{name}",', file=B)
+            print("]", file=B)
+
             print(file=B)
             if mode == "test":
                 print("TEST_EXPERIMENTS = {", file=B)