[event_engine] Use durations for scheduling things (#30023)

* [event_engine] Use durations for scheduling things

* fix

* Automated change: Fix sanity tests

* run-after

* fix

* Automated change: Fix sanity tests

* rename

Co-authored-by: ctiller <ctiller@users.noreply.github.com>

BUILD

@@ -1224,7 +1224,6 @@ grpc_cc_library(
     external_deps = [
         "absl/base:core_headers",
         "absl/status",
-        "absl/time",
     ],
     tags = ["grpc-autodeps"],
     deps = [
@@ -2084,6 +2083,7 @@ grpc_cc_library(
     external_deps = ["absl/strings:str_format"],
     tags = ["grpc-autodeps"],
     deps = [
+        "event_engine_base_hdrs",
         "gpr_base",
         "gpr_codegen",
         "gpr_platform",

CMakeLists.txt

@@ -13814,6 +13814,7 @@ target_include_directories(periodic_update_test
 target_link_libraries(periodic_update_test
   ${_gRPC_PROTOBUF_LIBRARIES}
   ${_gRPC_ALLTARGETS_LIBRARIES}
+  absl::statusor
   gpr
   upb
 )
@@ -16383,6 +16384,7 @@ target_link_libraries(test_core_gprpp_time_test
   absl::memory
   absl::random_random
   absl::status
+  absl::statusor
   absl::cord
   absl::str_format
   absl::strings

build_autogenerated.yaml

@@ -7165,6 +7165,7 @@ targets:
   - src/core/lib/slice/slice_string_helpers.cc
   - test/core/resource_quota/periodic_update_test.cc
   deps:
+  - absl/status:statusor
   - gpr
   - upb
   uses_polling: false
@@ -8252,6 +8253,7 @@ targets:
   - absl/memory:memory
   - absl/random:random
   - absl/status:status
+  - absl/status:statusor
   - absl/strings:cord
   - absl/strings:str_format
   - absl/strings:strings

include/grpc/event_engine/event_engine.h

@@ -21,7 +21,6 @@
 
 #include "absl/status/status.h"
 #include "absl/status/statusor.h"
-#include "absl/time/time.h"
 
 #include <grpc/event_engine/endpoint_config.h>
 #include <grpc/event_engine/memory_allocator.h>
@@ -74,6 +73,11 @@ namespace experimental {
 ////////////////////////////////////////////////////////////////////////////////
 class EventEngine {
  public:
+  /// A duration between two events.
+  ///
+  /// Throughout the EventEngine API durations are used to express how long
+  /// until an action should be performed.
+  using Duration = std::chrono::duration<int64_t, std::nano>;
   /// A custom closure type for EventEngine task execution.
   ///
   /// Throughout the EventEngine API, \a Closure ownership is retained by the
@@ -270,7 +274,7 @@ class EventEngine {
                                    const ResolvedAddress& addr,
                                    const EndpointConfig& args,
                                    MemoryAllocator memory_allocator,
-                                   absl::Time deadline) = 0;
+                                   Duration timeout) = 0;
 
   /// Request cancellation of a connection attempt.
   ///
@@ -328,21 +332,21 @@ class EventEngine {
     virtual LookupTaskHandle LookupHostname(LookupHostnameCallback on_resolve,
                                             absl::string_view name,
                                             absl::string_view default_port,
-                                            absl::Time deadline) = 0;
+                                            Duration timeout) = 0;
     /// Asynchronously perform an SRV record lookup.
     ///
     /// \a on_resolve has the same meaning and expectations as \a
     /// LookupHostname's \a on_resolve callback.
     virtual LookupTaskHandle LookupSRV(LookupSRVCallback on_resolve,
                                        absl::string_view name,
-                                       absl::Time deadline) = 0;
+                                       Duration timeout) = 0;
     /// Asynchronously perform a TXT record lookup.
     ///
     /// \a on_resolve has the same meaning and expectations as \a
     /// LookupHostname's \a on_resolve callback.
     virtual LookupTaskHandle LookupTXT(LookupTXTCallback on_resolve,
                                        absl::string_view name,
-                                       absl::Time deadline) = 0;
+                                       Duration timeout) = 0;
     /// Cancel an asynchronous lookup operation.
     ///
     /// This shares the same semantics with \a EventEngine::Cancel: successfully
@@ -384,13 +388,13 @@ class EventEngine {
   /// in some scenarios. This overload is useful in situations where performance
   /// is not a critical concern.
   virtual void Run(std::function<void()> closure) = 0;
-  /// Synonymous with scheduling an alarm to run at time \a when.
+  /// Synonymous with scheduling an alarm to run after duration \a when.
   ///
   /// The \a closure will execute when time \a when arrives unless it has been
   /// cancelled via the \a Cancel method. If cancelled, the closure will not be
   /// run, nor will it be deleted. Ownership remains with the caller.
-  virtual TaskHandle RunAt(absl::Time when, Closure* closure) = 0;
-  /// Synonymous with scheduling an alarm to run at time \a when.
+  virtual TaskHandle RunAfter(Duration when, Closure* closure) = 0;
+  /// Synonymous with scheduling an alarm to run after duration \a when.
   ///
   /// The \a closure will execute when time \a when arrives unless it has been
   /// cancelled via the \a Cancel method. If cancelled, the closure will not be
@@ -398,10 +402,10 @@ class EventEngine {
   /// version's \a closure will be deleted by the EventEngine after the closure
   /// has been run, or upon cancellation.
   ///
-  /// This version of \a RunAt may be less performant than the \a Closure
+  /// This version of \a RunAfter may be less performant than the \a Closure
   /// version in some scenarios. This overload is useful in situations where
   /// performance is not a critical concern.
-  virtual TaskHandle RunAt(absl::Time when, std::function<void()> closure) = 0;
+  virtual TaskHandle RunAfter(Duration when, std::function<void()> closure) = 0;
   /// Request cancellation of a task.
   ///
   /// If the associated closure has already been scheduled to run, it will not

src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc

@@ -78,8 +78,6 @@
 #include "absl/strings/str_join.h"
 #include "absl/strings/string_view.h"
 #include "absl/strings/strip.h"
-#include "absl/time/clock.h"
-#include "absl/time/time.h"
 #include "absl/types/optional.h"
 #include "absl/types/variant.h"
 #include "upb/upb.hpp"
@@ -996,9 +994,8 @@ void GrpcLb::BalancerCallState::StartQuery() {
 }
 
 void GrpcLb::BalancerCallState::ScheduleNextClientLoadReportLocked() {
-  client_load_report_handle_ = GetDefaultEventEngine()->RunAt(
-      absl::Now() + absl::Milliseconds(client_stats_report_interval_.millis()),
-      [this] {
+  client_load_report_handle_ =
+      GetDefaultEventEngine()->RunAfter(client_stats_report_interval_, [this] {
         ApplicationCallbackExecCtx callback_exec_ctx;
         ExecCtx exec_ctx;
         MaybeSendClientLoadReport();

src/core/ext/filters/client_channel/lb_policy/xds/xds_cluster_resolver.cc

@@ -24,6 +24,7 @@
 #include <memory>
 #include <set>
 #include <string>
+#include <type_traits>
 #include <utility>
 #include <vector>
 

src/core/ext/filters/client_channel/subchannel.cc

@@ -28,8 +28,6 @@
 #include <utility>
 
 #include "absl/status/statusor.h"
-#include "absl/time/clock.h"
-#include "absl/time/time.h"
 
 #include <grpc/grpc.h>
 #include <grpc/slice.h>
@@ -943,8 +941,6 @@ void Subchannel::OnConnectingFinishedLocked(grpc_error_handle error) {
   if (connecting_result_.transport == nullptr || !PublishTransportLocked()) {
     const Duration time_until_next_attempt =
         next_attempt_time_ - ExecCtx::Get()->Now();
-    auto ee_deadline =
-        absl::Now() + absl::Milliseconds(time_until_next_attempt.millis());
     gpr_log(GPR_INFO,
             "subchannel %p %s: connect failed (%s), backing off for %" PRId64
             " ms",
@@ -952,8 +948,9 @@ void Subchannel::OnConnectingFinishedLocked(grpc_error_handle error) {
             time_until_next_attempt.millis());
     SetConnectivityStateLocked(GRPC_CHANNEL_TRANSIENT_FAILURE,
                                grpc_error_to_absl_status(error));
-    retry_timer_handle_ = GetDefaultEventEngine()->RunAt(
-        ee_deadline, [self = WeakRef(DEBUG_LOCATION, "RetryTimer")]() mutable {
+    retry_timer_handle_ = GetDefaultEventEngine()->RunAfter(
+        time_until_next_attempt,
+        [self = WeakRef(DEBUG_LOCATION, "RetryTimer")]() mutable {
           {
             ApplicationCallbackExecCtx callback_exec_ctx;
             ExecCtx exec_ctx;

src/core/lib/channel/channel_args_preconditioning.cc

@@ -16,6 +16,7 @@
 
 #include "src/core/lib/channel/channel_args_preconditioning.h"
 
+#include <algorithm>
 #include <utility>
 
 namespace grpc_core {

src/core/lib/event_engine/iomgr_engine.cc

@@ -15,6 +15,7 @@
 
 #include "src/core/lib/event_engine/iomgr_engine.h"
 
+#include <algorithm>
 #include <string>
 #include <type_traits>
 #include <utility>
@@ -22,7 +23,6 @@
 #include "absl/cleanup/cleanup.h"
 #include "absl/container/flat_hash_set.h"
 #include "absl/strings/str_cat.h"
-#include "absl/time/clock.h"
 
 #include <grpc/event_engine/event_engine.h>
 #include <grpc/support/log.h>
@@ -50,15 +50,12 @@ struct ClosureData {
   EventEngine::TaskHandle handle;
 };
 
-// Timer limits due to quirks in the iomgr implementation.
-// If deadline <= Now, the callback will be run inline, which can result in lock
-// issues. And absl::InfiniteFuture yields UB.
-absl::Time Clamp(absl::Time when) {
-  absl::Time max = absl::Now() + absl::Hours(8766);
-  absl::Time min = absl::Now() + absl::Milliseconds(2);
-  if (when > max) return max;
-  if (when < min) return min;
-  return when;
+grpc_core::Timestamp ToTimestamp(EventEngine::Duration when) {
+  grpc_core::ExecCtx::Get()->InvalidateNow();
+  return grpc_core::ExecCtx::Get()->Now() +
+         std::max(grpc_core::Duration::Milliseconds(1),
+                  grpc_core::Duration::NanosecondsRoundUp(when.count())) +
+         grpc_core::Duration::Milliseconds(1);
 }
 
 std::string HandleToString(EventEngine::TaskHandle handle) {
@@ -92,14 +89,14 @@ bool IomgrEventEngine::Cancel(EventEngine::TaskHandle handle) {
   return true;
 }
 
-EventEngine::TaskHandle IomgrEventEngine::RunAt(absl::Time when,
-                                                std::function<void()> closure) {
-  return RunAtInternal(when, std::move(closure));
+EventEngine::TaskHandle IomgrEventEngine::RunAfter(
+    Duration when, std::function<void()> closure) {
+  return RunAfterInternal(when, std::move(closure));
 }
 
-EventEngine::TaskHandle IomgrEventEngine::RunAt(absl::Time when,
-                                                EventEngine::Closure* closure) {
-  return RunAtInternal(when, closure);
+EventEngine::TaskHandle IomgrEventEngine::RunAfter(
+    Duration when, EventEngine::Closure* closure) {
+  return RunAfterInternal(when, closure);
 }
 
 void IomgrEventEngine::Run(std::function<void()> closure) {
@@ -110,10 +107,10 @@ void IomgrEventEngine::Run(EventEngine::Closure* closure) {
   RunInternal(closure);
 }
 
-EventEngine::TaskHandle IomgrEventEngine::RunAtInternal(
-    absl::Time when,
+EventEngine::TaskHandle IomgrEventEngine::RunAfterInternal(
+    Duration when,
     absl::variant<std::function<void()>, EventEngine::Closure*> cb) {
-  when = Clamp(when);
+  auto when_ts = ToTimestamp(when);
   auto* cd = new ClosureData;
   cd->cb = std::move(cb);
   cd->engine = this;
@@ -134,14 +131,6 @@ EventEngine::TaskHandle IomgrEventEngine::RunAtInternal(
             [](std::function<void()> fn) { fn(); });
       },
       cd, nullptr);
-  // kludge to deal with realtime/monotonic clock conversion
-  absl::Time absl_now = absl::Now();
-  grpc_core::Duration duration = grpc_core::Duration::Milliseconds(
-      absl::ToInt64Milliseconds(when - absl_now) + 1);
-  grpc_core::ExecCtx::Get()->InvalidateNow();
-  grpc_core::Timestamp when_internal = grpc_core::ExecCtx::Get()->Now() +
-                                       duration +
-                                       grpc_core::Duration::Milliseconds(1);
   EventEngine::TaskHandle handle{reinterpret_cast<intptr_t>(cd),
                                  aba_token_.fetch_add(1)};
   grpc_core::MutexLock lock(&mu_);
@@ -149,7 +138,7 @@ EventEngine::TaskHandle IomgrEventEngine::RunAtInternal(
   cd->handle = handle;
   GRPC_EVENT_ENGINE_TRACE("IomgrEventEngine:%p scheduling callback:%s", this,
                           HandleToString(handle).c_str());
-  grpc_timer_init(&cd->timer, when_internal, &cd->closure);
+  grpc_timer_init(&cd->timer, when_ts, &cd->closure);
   return handle;
 }
 
@@ -188,7 +177,7 @@ bool IomgrEventEngine::CancelConnect(EventEngine::ConnectionHandle /*handle*/) {
 EventEngine::ConnectionHandle IomgrEventEngine::Connect(
     OnConnectCallback /*on_connect*/, const ResolvedAddress& /*addr*/,
     const EndpointConfig& /*args*/, MemoryAllocator /*memory_allocator*/,
-    absl::Time /*deadline*/) {
+    Duration /*deadline*/) {
   GPR_ASSERT(false && "unimplemented");
 }
 

src/core/lib/event_engine/iomgr_engine.h

@@ -25,7 +25,6 @@
 #include "absl/status/status.h"
 #include "absl/status/statusor.h"
 #include "absl/strings/string_view.h"
-#include "absl/time/time.h"
 #include "absl/types/variant.h"
 
 #include <grpc/event_engine/endpoint_config.h>
@@ -65,13 +64,13 @@ class IomgrEventEngine final : public EventEngine {
     LookupTaskHandle LookupHostname(LookupHostnameCallback on_resolve,
                                     absl::string_view name,
                                     absl::string_view default_port,
-                                    absl::Time deadline) override;
+                                    Duration timeout) override;
     LookupTaskHandle LookupSRV(LookupSRVCallback on_resolve,
                                absl::string_view name,
-                               absl::Time deadline) override;
+                               Duration timeout) override;
     LookupTaskHandle LookupTXT(LookupTXTCallback on_resolve,
                                absl::string_view name,
-                               absl::Time deadline) override;
+                               Duration timeout) override;
     bool CancelLookup(LookupTaskHandle handle) override;
   };
 
@@ -89,7 +88,7 @@ class IomgrEventEngine final : public EventEngine {
                            const ResolvedAddress& addr,
                            const EndpointConfig& args,
                            MemoryAllocator memory_allocator,
-                           absl::Time deadline) override;
+                           Duration timeout) override;
 
   bool CancelConnect(ConnectionHandle handle) override;
   bool IsWorkerThread() override;
@@ -97,13 +96,13 @@ class IomgrEventEngine final : public EventEngine {
       const DNSResolver::ResolverOptions& options) override;
   void Run(Closure* closure) override;
   void Run(std::function<void()> closure) override;
-  TaskHandle RunAt(absl::Time when, Closure* closure) override;
-  TaskHandle RunAt(absl::Time when, std::function<void()> closure) override;
+  TaskHandle RunAfter(Duration when, Closure* closure) override;
+  TaskHandle RunAfter(Duration when, std::function<void()> closure) override;
   bool Cancel(TaskHandle handle) override;
 
  private:
-  EventEngine::TaskHandle RunAtInternal(
-      absl::Time when,
+  EventEngine::TaskHandle RunAfterInternal(
+      Duration when,
       absl::variant<std::function<void()>, EventEngine::Closure*> cb);
 
   void RunInternal(

src/core/lib/gprpp/time.cc

@@ -17,6 +17,7 @@
 #include "src/core/lib/gprpp/time.h"
 
 #include <atomic>
+#include <chrono>
 #include <cstdint>
 #include <limits>
 #include <string>
@@ -190,6 +191,13 @@ std::string Duration::ToJsonString() const {
   return absl::StrFormat("%d.%09ds", ts.tv_sec, ts.tv_nsec);
 }
 
+Duration::operator grpc_event_engine::experimental::EventEngine::Duration()
+    const {
+  return std::chrono::milliseconds(
+      Clamp(millis_, std::numeric_limits<int64_t>::min() / GPR_NS_PER_MS,
+            std::numeric_limits<int64_t>::max() / GPR_NS_PER_MS));
+}
+
 void TestOnlySetProcessEpoch(gpr_timespec epoch) {
   g_process_epoch_seconds.store(
       gpr_convert_clock_type(epoch, GPR_CLOCK_MONOTONIC).tv_sec);

src/core/lib/gprpp/time.h

@@ -23,6 +23,7 @@
 #include <ostream>
 #include <string>
 
+#include <grpc/event_engine/event_engine.h>
 #include <grpc/impl/codegen/gpr_types.h>
 #include <grpc/support/time.h>
 
@@ -207,6 +208,9 @@ class Duration {
   constexpr int64_t millis() const { return millis_; }
   double seconds() const { return static_cast<double>(millis_) / 1000.0; }
 
+  // NOLINTNEXTLINE: google-explicit-constructor
+  operator grpc_event_engine::experimental::EventEngine::Duration() const;
+
   gpr_timespec as_timespec() const;
 
   std::string ToString() const;

src/core/lib/promise/sleep.cc

@@ -16,9 +16,6 @@
 
 #include "src/core/lib/promise/sleep.h"
 
-#include "absl/time/clock.h"
-#include "absl/time/time.h"
-
 #include <grpc/event_engine/event_engine.h>
 
 #include "src/core/lib/event_engine/event_engine_factory.h"
@@ -57,16 +54,6 @@ void Sleep::OnTimer() {
   tmp_waker.Wakeup();
 }
 
-// TODO(hork): refactor gpr_base to allow a separate time_util target.
-namespace {
-absl::Time ToAbslTime(Timestamp timestamp) {
-  if (timestamp == Timestamp::InfFuture()) return absl::InfiniteFuture();
-  if (timestamp == Timestamp::InfPast()) return absl::InfinitePast();
-  return absl::Now() +
-         absl::Milliseconds((timestamp - ExecCtx::Get()->Now()).millis());
-}
-}  // namespace
-
 Poll<absl::Status> Sleep::operator()() {
   MutexLock lock(&mu_);
   switch (stage_) {
@@ -75,8 +62,8 @@ Poll<absl::Status> Sleep::operator()() {
         return absl::OkStatus();
       }
       stage_ = Stage::kStarted;
-      timer_handle_ =
-          GetDefaultEventEngine()->RunAt(ToAbslTime(deadline_), [this] {
+      timer_handle_ = GetDefaultEventEngine()->RunAfter(
+          deadline_ - ExecCtx::Get()->Now(), [this] {
             ApplicationCallbackExecCtx callback_exec_ctx;
             ExecCtx exec_ctx;
             OnTimer();

src/cpp/server/orca/orca_service.cc

@@ -21,7 +21,6 @@
 #include <utility>
 
 #include "absl/base/thread_annotations.h"
-#include "absl/time/clock.h"
 #include "absl/time/time.h"
 #include "absl/types/optional.h"
 #include "google/protobuf/duration.upb.h"
@@ -124,8 +123,8 @@ class OrcaService::Reactor : public ServerWriteReactor<ByteBuffer>,
     grpc_core::ApplicationCallbackExecCtx callback_exec_ctx;
     grpc_core::ExecCtx exec_ctx;
     grpc::internal::MutexLock lock(&timer_mu_);
-    timer_handle_ = GetDefaultEventEngine()->RunAt(
-        absl::Now() + absl::Milliseconds(report_interval_.millis()),
+    timer_handle_ = GetDefaultEventEngine()->RunAfter(
+        report_interval_,
         [self = Ref(DEBUG_LOCATION, "Orca Service")] { self->OnTimer(); });
   }
 

test/core/event_engine/fuzzing_event_engine/fuzzing_event_engine.cc

@@ -14,6 +14,8 @@
 
 #include "test/core/event_engine/fuzzing_event_engine/fuzzing_event_engine.h"
 
+#include <chrono>
+
 namespace grpc_event_engine {
 namespace experimental {
 
@@ -24,10 +26,10 @@ const intptr_t kTaskHandleSalt = 12345;
 FuzzingEventEngine::FuzzingEventEngine(Options options)
     : final_tick_length_(options.final_tick_length) {
   for (const auto& delay : options.actions.tick_lengths()) {
-    tick_increments_[delay.id()] += absl::Microseconds(delay.delay_us());
+    tick_increments_[delay.id()] += std::chrono::microseconds(delay.delay_us());
   }
   for (const auto& delay : options.actions.run_delay()) {
-    task_delays_[delay.id()] += absl::Microseconds(delay.delay_us());
+    task_delays_[delay.id()] += std::chrono::microseconds(delay.delay_us());
   }
 }
 
@@ -56,7 +58,7 @@ void FuzzingEventEngine::Tick() {
   }
 }
 
-absl::Time FuzzingEventEngine::Now() {
+FuzzingEventEngine::Time FuzzingEventEngine::Now() {
   grpc_core::MutexLock lock(&mu_);
   return now_;
 }
@@ -71,7 +73,7 @@ FuzzingEventEngine::CreateListener(Listener::AcceptCallback,
 
 EventEngine::ConnectionHandle FuzzingEventEngine::Connect(
     OnConnectCallback, const ResolvedAddress&, const EndpointConfig&,
-    MemoryAllocator, absl::Time) {
+    MemoryAllocator, Duration) {
   abort();
 }
 
@@ -84,19 +86,21 @@ std::unique_ptr<EventEngine::DNSResolver> FuzzingEventEngine::GetDNSResolver(
   abort();
 }
 
-void FuzzingEventEngine::Run(Closure* closure) { RunAt(Now(), closure); }
+void FuzzingEventEngine::Run(Closure* closure) {
+  RunAfter(Duration::zero(), closure);
+}
 
 void FuzzingEventEngine::Run(std::function<void()> closure) {
-  RunAt(Now(), closure);
+  RunAfter(Duration::zero(), closure);
 }
 
-EventEngine::TaskHandle FuzzingEventEngine::RunAt(absl::Time when,
+EventEngine::TaskHandle FuzzingEventEngine::RunAfter(Duration when,
                                                      Closure* closure) {
-  return RunAt(when, [closure]() { closure->Run(); });
+  return RunAfter(when, [closure]() { closure->Run(); });
 }
 
-EventEngine::TaskHandle FuzzingEventEngine::RunAt(
-    absl::Time when, std::function<void()> closure) {
+EventEngine::TaskHandle FuzzingEventEngine::RunAfter(
+    Duration when, std::function<void()> closure) {
   grpc_core::MutexLock lock(&mu_);
   const intptr_t id = next_task_id_;
   ++next_task_id_;
@@ -108,7 +112,7 @@ EventEngine::TaskHandle FuzzingEventEngine::RunAt(
   }
   auto task = std::make_shared<Task>(id, std::move(closure));
   tasks_by_id_.emplace(id, task);
-  tasks_by_time_.emplace(when, std::move(task));
+  tasks_by_time_.emplace(now_ + when, std::move(task));
   return TaskHandle{id, kTaskHandleSalt};
 }
 

test/core/event_engine/fuzzing_event_engine/fuzzing_event_engine.h

@@ -15,6 +15,7 @@
 #ifndef GRPC_TEST_CORE_EVENT_ENGINE_FUZZING_EVENT_ENGINE_H
 #define GRPC_TEST_CORE_EVENT_ENGINE_FUZZING_EVENT_ENGINE_H
 
+#include <chrono>
 #include <cstdint>
 #include <map>
 
@@ -32,7 +33,7 @@ class FuzzingEventEngine : public EventEngine {
   struct Options {
     // After all scheduled tick lengths are completed, this is the amount of
     // time Now() will be incremented each tick.
-    absl::Duration final_tick_length = absl::Seconds(1);
+    Duration final_tick_length = std::chrono::seconds(1);
     fuzzing_event_engine::Actions actions;
   };
   explicit FuzzingEventEngine(Options options);
@@ -49,7 +50,7 @@ class FuzzingEventEngine : public EventEngine {
                            const ResolvedAddress& addr,
                            const EndpointConfig& args,
                            MemoryAllocator memory_allocator,
-                           absl::Time deadline) override;
+                           Duration timeout) override;
 
   bool CancelConnect(ConnectionHandle handle) override;
 
@@ -60,11 +61,13 @@ class FuzzingEventEngine : public EventEngine {
 
   void Run(Closure* closure) override;
   void Run(std::function<void()> closure) override;
-  TaskHandle RunAt(absl::Time when, Closure* closure) override;
-  TaskHandle RunAt(absl::Time when, std::function<void()> closure) override;
+  TaskHandle RunAfter(Duration when, Closure* closure) override;
+  TaskHandle RunAfter(Duration when, std::function<void()> closure) override;
   bool Cancel(TaskHandle handle) override;
 
-  absl::Time Now() ABSL_LOCKS_EXCLUDED(mu_);
+  using Time = std::chrono::time_point<FuzzingEventEngine, Duration>;
+
+  Time Now() ABSL_LOCKS_EXCLUDED(mu_);
 
  private:
   struct Task {
@@ -74,17 +77,17 @@ class FuzzingEventEngine : public EventEngine {
     std::function<void()> closure;
   };
 
-  const absl::Duration final_tick_length_;
+  const Duration final_tick_length_;
 
   grpc_core::Mutex mu_;
 
   intptr_t next_task_id_ ABSL_GUARDED_BY(mu_) = 1;
   intptr_t current_tick_ ABSL_GUARDED_BY(mu_) = 0;
-  absl::Time now_ ABSL_GUARDED_BY(mu_) = absl::Now();
-  std::map<intptr_t, absl::Duration> tick_increments_ ABSL_GUARDED_BY(mu_);
-  std::map<intptr_t, absl::Duration> task_delays_ ABSL_GUARDED_BY(mu_);
+  Time now_ ABSL_GUARDED_BY(mu_) = Time::min();
+  std::map<intptr_t, Duration> tick_increments_ ABSL_GUARDED_BY(mu_);
+  std::map<intptr_t, Duration> task_delays_ ABSL_GUARDED_BY(mu_);
   std::map<intptr_t, std::shared_ptr<Task>> tasks_by_id_ ABSL_GUARDED_BY(mu_);
-  std::multimap<absl::Time, std::shared_ptr<Task>> tasks_by_time_
+  std::multimap<Time, std::shared_ptr<Task>> tasks_by_time_
       ABSL_GUARDED_BY(mu_);
 };
 

test/core/event_engine/test_suite/fuzzing_event_engine_test.cc

@@ -14,8 +14,11 @@
 
 #include "test/core/event_engine/fuzzing_event_engine/fuzzing_event_engine.h"
 
+#include <chrono>
 #include <thread>
 
+#include "absl/time/clock.h"
+
 #include <grpc/grpc.h>
 
 #include "test/core/event_engine/test_suite/event_engine_test.h"
@@ -29,12 +32,15 @@ class ThreadedFuzzingEventEngine : public FuzzingEventEngine {
   ThreadedFuzzingEventEngine()
       : FuzzingEventEngine([]() {
           Options options;
-          options.final_tick_length = absl::Milliseconds(10);
+          options.final_tick_length = std::chrono::milliseconds(10);
           return options;
         }()),
         main_([this]() {
           while (!done_.load()) {
-            absl::SleepFor(absl::Milliseconds(10));
+            auto tick_start = absl::Now();
+            while (absl::Now() - tick_start < absl::Milliseconds(10)) {
+              absl::SleepFor(absl::Milliseconds(1));
+            }
             Tick();
           }
         }) {}

test/core/event_engine/test_suite/timer_test.cc

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+#include <chrono>
 #include <random>
 #include <thread>
 
@@ -29,6 +30,7 @@
 #include "test/core/event_engine/test_suite/event_engine_test.h"
 
 using ::testing::ElementsAre;
+using namespace std::chrono_literals;
 
 class EventEngineTimerTest : public EventEngineTest {
  public:
@@ -45,7 +47,7 @@ TEST_F(EventEngineTimerTest, ImmediateCallbackIsExecutedQuickly) {
   grpc_core::ExecCtx exec_ctx;
   auto engine = this->NewEventEngine();
   grpc_core::MutexLock lock(&mu_);
-  engine->RunAt(absl::Now(), [this]() {
+  engine->RunAfter(0ms, [this]() {
     grpc_core::MutexLock lock(&mu_);
     signaled_ = true;
     cv_.Signal();
@@ -57,7 +59,7 @@ TEST_F(EventEngineTimerTest, ImmediateCallbackIsExecutedQuickly) {
 TEST_F(EventEngineTimerTest, SupportsCancellation) {
   grpc_core::ExecCtx exec_ctx;
   auto engine = this->NewEventEngine();
-  auto handle = engine->RunAt(absl::InfiniteFuture(), []() {});
+  auto handle = engine->RunAfter(24h, []() {});
   ASSERT_TRUE(engine->Cancel(handle));
 }
 
@@ -65,7 +67,7 @@ TEST_F(EventEngineTimerTest, CancelledCallbackIsNotExecuted) {
   grpc_core::ExecCtx exec_ctx;
   {
     auto engine = this->NewEventEngine();
-    auto handle = engine->RunAt(absl::InfiniteFuture(), [this]() {
+    auto handle = engine->RunAfter(24h, [this]() {
       grpc_core::MutexLock lock(&mu_);
       signaled_ = true;
     });
@@ -78,20 +80,20 @@ TEST_F(EventEngineTimerTest, CancelledCallbackIsNotExecuted) {
 
 TEST_F(EventEngineTimerTest, TimersRespectScheduleOrdering) {
   grpc_core::ExecCtx exec_ctx;
-  // Note: this is a brittle test if the first call to `RunAt` takes longer than
-  // the second callback's wait time.
+  // Note: this is a brittle test if the first call to `RunAfter` takes longer
+  // than the second callback's wait time.
   std::vector<uint8_t> ordered;
   uint8_t count = 0;
   grpc_core::MutexLock lock(&mu_);
   {
     auto engine = this->NewEventEngine();
-    engine->RunAt(absl::Now() + absl::Milliseconds(100), [&]() {
+    engine->RunAfter(100ms, [&]() {
       grpc_core::MutexLock lock(&mu_);
       ordered.push_back(2);
       ++count;
       cv_.Signal();
     });
-    engine->RunAt(absl::Now(), [&]() {
+    engine->RunAfter(0ms, [&]() {
       grpc_core::MutexLock lock(&mu_);
       ordered.push_back(1);
       ++count;
@@ -110,7 +112,7 @@ TEST_F(EventEngineTimerTest, CancellingExecutedCallbackIsNoopAndReturnsFalse) {
   grpc_core::ExecCtx exec_ctx;
   auto engine = this->NewEventEngine();
   grpc_core::MutexLock lock(&mu_);
-  auto handle = engine->RunAt(absl::Now(), [this]() {
+  auto handle = engine->RunAfter(0ms, [this]() {
     grpc_core::MutexLock lock(&mu_);
     signaled_ = true;
     cv_.Signal();
@@ -130,10 +132,9 @@ void EventEngineTimerTest::ScheduleCheckCB(absl::Time when,
   // to the lowest common denominator until EventEngines can compare relative
   // times with supported resolution.
   grpc_core::ExecCtx exec_ctx;
-  int64_t now_millis = absl::ToUnixMillis(absl::Now());
-  int64_t when_millis = absl::ToUnixMillis(when);
-  EXPECT_LE(when_millis, now_millis);
-  if (when_millis > now_millis) ++(*fail_count);
+  auto now = absl::Now();
+  EXPECT_LE(when, now);
+  if (when > now) ++(*fail_count);
   if (++(*call_count) == total_expected) {
     grpc_core::MutexLock lock(&mu_);
     signaled_ = true;
@@ -160,10 +161,12 @@ TEST_F(EventEngineTimerTest, StressTestTimersNotCalledBeforeScheduled) {
       std::uniform_real_distribution<> dis(timeout_min_seconds,
                                            timeout_max_seconds);
       for (int call_n = 0; call_n < call_count_per_thread; ++call_n) {
-        absl::Time when = absl::Now() + absl::Seconds(dis(gen));
-        engine->RunAt(
-            when, absl::bind_front(&EventEngineTimerTest::ScheduleCheckCB, this,
-                                   when, &call_count, &failed_call_count,
+        const auto dur = static_cast<int64_t>(1e9 * dis(gen));
+        auto deadline = absl::Now() + absl::Nanoseconds(dur);
+        engine->RunAfter(
+            std::chrono::nanoseconds(dur),
+            absl::bind_front(&EventEngineTimerTest::ScheduleCheckCB, this,
+                             deadline, &call_count, &failed_call_count,
                              thread_count * call_count_per_thread));
       }
     });