Convert call_combiner to C++.

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

@@ -617,7 +617,7 @@ class CallData {
   grpc_millis deadline_;
   gpr_arena* arena_;
   grpc_call_stack* owning_call_;
-  grpc_call_combiner* call_combiner_;
+  CallCombiner* call_combiner_;
   grpc_call_context_element* call_context_;
 
   RefCountedPtr<ServerRetryThrottleData> retry_throttle_data_;
@@ -3017,7 +3017,7 @@ class CallData::QueuedPickCanceller {
     GRPC_CALL_STACK_REF(calld->owning_call_, "QueuedPickCanceller");
     GRPC_CLOSURE_INIT(&closure_, &CancelLocked, this,
                       grpc_combiner_scheduler(chand->data_plane_combiner()));
-    grpc_call_combiner_set_notify_on_cancel(calld->call_combiner_, &closure_);
+    calld->call_combiner_->SetNotifyOnCancel(&closure_);
   }
 
  private:

src/core/ext/filters/client_channel/health/health_check_client.cc

@@ -37,11 +37,10 @@
 #define HEALTH_CHECK_RECONNECT_MAX_BACKOFF_SECONDS 120
 #define HEALTH_CHECK_RECONNECT_JITTER 0.2
 
-grpc_core::TraceFlag grpc_health_check_client_trace(false,
-                                                    "health_check_client");
-
 namespace grpc_core {
 
+TraceFlag grpc_health_check_client_trace(false, "health_check_client");
+
 //
 // HealthCheckClient
 //
@@ -50,7 +49,7 @@ HealthCheckClient::HealthCheckClient(
     const char* service_name,
     RefCountedPtr<ConnectedSubchannel> connected_subchannel,
     grpc_pollset_set* interested_parties,
-    grpc_core::RefCountedPtr<grpc_core::channelz::SubchannelNode> channelz_node)
+    RefCountedPtr<channelz::SubchannelNode> channelz_node)
     : InternallyRefCounted<HealthCheckClient>(&grpc_health_check_client_trace),
       service_name_(service_name),
       connected_subchannel_(std::move(connected_subchannel)),
@@ -283,9 +282,7 @@ HealthCheckClient::CallState::CallState(
       pollent_(grpc_polling_entity_create_from_pollset_set(interested_parties)),
       arena_(gpr_arena_create(health_check_client_->connected_subchannel_
                                   ->GetInitialCallSizeEstimate(0))),
-      payload_(context_) {
+      payload_(context_) {}
-  grpc_call_combiner_init(&call_combiner_);
-}
 
 HealthCheckClient::CallState::~CallState() {
   if (grpc_health_check_client_trace.enabled()) {
@@ -303,14 +300,13 @@ HealthCheckClient::CallState::~CallState() {
   // holding to the call stack. Also flush the closures on exec_ctx so that
   // filters that schedule cancel notification closures on exec_ctx do not
   // need to take a ref of the call stack to guarantee closure liveness.
-  grpc_call_combiner_set_notify_on_cancel(&call_combiner_, nullptr);
+  call_combiner_.SetNotifyOnCancel(nullptr);
-  grpc_core::ExecCtx::Get()->Flush();
+  ExecCtx::Get()->Flush();
-  grpc_call_combiner_destroy(&call_combiner_);
   gpr_arena_destroy(arena_);
 }
 
 void HealthCheckClient::CallState::Orphan() {
-  grpc_call_combiner_cancel(&call_combiner_, GRPC_ERROR_CANCELLED);
+  call_combiner_.Cancel(GRPC_ERROR_CANCELLED);
   Cancel();
 }
 

src/core/ext/filters/client_channel/health/health_check_client.h

@@ -98,7 +98,7 @@ class HealthCheckClient : public InternallyRefCounted<HealthCheckClient> {
     grpc_polling_entity pollent_;
 
     gpr_arena* arena_;
-    grpc_call_combiner call_combiner_;
+    grpc_core::CallCombiner call_combiner_;
     grpc_call_context_element context_[GRPC_CONTEXT_COUNT] = {};
 
     // The streaming call to the backend. Always non-NULL.

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

@@ -77,7 +77,7 @@ class ConnectedSubchannel : public RefCounted<ConnectedSubchannel> {
     grpc_millis deadline;
     gpr_arena* arena;
     grpc_call_context_element* context;
-    grpc_call_combiner* call_combiner;
+    grpc_core::CallCombiner* call_combiner;
     size_t parent_data_size;
   };
 

src/core/ext/filters/deadline/deadline_filter.cc

@@ -68,8 +68,7 @@ static void timer_callback(void* arg, grpc_error* error) {
     error = grpc_error_set_int(
         GRPC_ERROR_CREATE_FROM_STATIC_STRING("Deadline Exceeded"),
         GRPC_ERROR_INT_GRPC_STATUS, GRPC_STATUS_DEADLINE_EXCEEDED);
-    grpc_call_combiner_cancel(deadline_state->call_combiner,
+    deadline_state->call_combiner->Cancel(GRPC_ERROR_REF(error));
-                              GRPC_ERROR_REF(error));
     GRPC_CLOSURE_INIT(&deadline_state->timer_callback,
                       send_cancel_op_in_call_combiner, elem,
                       grpc_schedule_on_exec_ctx);
@@ -183,7 +182,7 @@ static void start_timer_after_init(void* arg, grpc_error* error) {
 
 grpc_deadline_state::grpc_deadline_state(grpc_call_element* elem,
                                          grpc_call_stack* call_stack,
-                                         grpc_call_combiner* call_combiner,
+                                         grpc_core::CallCombiner* call_combiner,
                                          grpc_millis deadline)
     : call_stack(call_stack), call_combiner(call_combiner) {
   // Deadline will always be infinite on servers, so the timer will only be

src/core/ext/filters/deadline/deadline_filter.h

@@ -32,12 +32,13 @@ enum grpc_deadline_timer_state {
 // Must be the first field in the filter's call_data.
 struct grpc_deadline_state {
   grpc_deadline_state(grpc_call_element* elem, grpc_call_stack* call_stack,
-                      grpc_call_combiner* call_combiner, grpc_millis deadline);
+                      grpc_core::CallCombiner* call_combiner,
+                      grpc_millis deadline);
   ~grpc_deadline_state();
 
   // We take a reference to the call stack for the timer callback.
   grpc_call_stack* call_stack;
-  grpc_call_combiner* call_combiner;
+  grpc_core::CallCombiner* call_combiner;
   grpc_deadline_timer_state timer_state = GRPC_DEADLINE_STATE_INITIAL;
   grpc_timer timer;
   grpc_closure timer_callback;

src/core/ext/filters/http/client/http_client_filter.cc

@@ -62,7 +62,7 @@ struct call_data {
 
   ~call_data() { GRPC_ERROR_UNREF(recv_initial_metadata_error); }
 
-  grpc_call_combiner* call_combiner;
+  grpc_core::CallCombiner* call_combiner;
   // State for handling send_initial_metadata ops.
   grpc_linked_mdelem method;
   grpc_linked_mdelem scheme;

src/core/ext/filters/http/client_authority_filter.cc

@@ -40,7 +40,7 @@ namespace {
 
 struct call_data {
   grpc_linked_mdelem authority_storage;
-  grpc_call_combiner* call_combiner;
+  grpc_core::CallCombiner* call_combiner;
 };
 
 struct channel_data {

src/core/ext/filters/http/message_compress/message_compress_filter.cc

@@ -72,7 +72,7 @@ struct call_data {
     GRPC_ERROR_UNREF(cancel_error);
   }
 
-  grpc_call_combiner* call_combiner;
+  grpc_core::CallCombiner* call_combiner;
   grpc_linked_mdelem compression_algorithm_storage;
   grpc_linked_mdelem stream_compression_algorithm_storage;
   grpc_linked_mdelem accept_encoding_storage;

src/core/ext/filters/http/server/http_server_filter.cc

@@ -61,7 +61,7 @@ struct call_data {
     }
   }
 
-  grpc_call_combiner* call_combiner;
+  grpc_core::CallCombiner* call_combiner;
 
   // Outgoing headers to add to send_initial_metadata.
   grpc_linked_mdelem status;

src/core/ext/filters/message_size/message_size_filter.cc

@@ -137,7 +137,7 @@ struct call_data {
 
   ~call_data() { GRPC_ERROR_UNREF(error); }
 
-  grpc_call_combiner* call_combiner;
+  grpc_core::CallCombiner* call_combiner;
   message_size_limits limits;
   // Receive closures are chained: we inject this closure as the
   // recv_message_ready up-call on transport_stream_op, and remember to

src/core/lib/channel/channel_stack.h

@@ -70,7 +70,7 @@ typedef struct {
   gpr_timespec start_time;
   grpc_millis deadline;
   gpr_arena* arena;
-  grpc_call_combiner* call_combiner;
+  grpc_core::CallCombiner* call_combiner;
 } grpc_call_element_args;
 
 typedef struct {

src/core/lib/channel/connected_channel.cc

@@ -41,12 +41,12 @@ typedef struct connected_channel_channel_data {
 typedef struct {
   grpc_closure closure;
   grpc_closure* original_closure;
-  grpc_call_combiner* call_combiner;
+  grpc_core::CallCombiner* call_combiner;
   const char* reason;
 } callback_state;
 
 typedef struct connected_channel_call_data {
-  grpc_call_combiner* call_combiner;
+  grpc_core::CallCombiner* call_combiner;
   // Closures used for returning results on the call combiner.
   callback_state on_complete[6];  // Max number of pending batches.
   callback_state recv_initial_metadata_ready;

src/core/lib/iomgr/call_combiner.cc

@@ -26,23 +26,43 @@
 #include "src/core/lib/debug/stats.h"
 #include "src/core/lib/profiling/timers.h"
 
-grpc_core::TraceFlag grpc_call_combiner_trace(false, "call_combiner");
+namespace grpc_core {
 
-static grpc_error* decode_cancel_state_error(gpr_atm cancel_state) {
+TraceFlag grpc_call_combiner_trace(false, "call_combiner");
+
+namespace {
+
+grpc_error* DecodeCancelStateError(gpr_atm cancel_state) {
   if (cancel_state & 1) {
     return (grpc_error*)(cancel_state & ~static_cast<gpr_atm>(1));
   }
   return GRPC_ERROR_NONE;
 }
 
-static gpr_atm encode_cancel_state_error(grpc_error* error) {
+gpr_atm EncodeCancelStateError(grpc_error* error) {
   return static_cast<gpr_atm>(1) | (gpr_atm)error;
 }
 
+}  // namespace
+
+CallCombiner::CallCombiner() {
+  gpr_atm_no_barrier_store(&cancel_state_, 0);
+  gpr_atm_no_barrier_store(&size_, 0);
+  gpr_mpscq_init(&queue_);
+#ifdef GRPC_TSAN_ENABLED
+  GRPC_CLOSURE_INIT(&tsan_closure_, TsanClosure, this,
+                    grpc_schedule_on_exec_ctx);
+#endif
+}
+
+CallCombiner::~CallCombiner() {
+  gpr_mpscq_destroy(&queue_);
+  GRPC_ERROR_UNREF(DecodeCancelStateError(cancel_state_));
+}
+
 #ifdef GRPC_TSAN_ENABLED
-static void tsan_closure(void* user_data, grpc_error* error) {
+void CallCombiner::TsanClosure(void* arg, grpc_error* error) {
-  grpc_call_combiner* call_combiner =
+  CallCombiner* self = static_cast<CallCombiner*>(arg);
-      static_cast<grpc_call_combiner*>(user_data);
   // We ref-count the lock, and check if it's already taken.
   // If it was taken, we should do nothing. Otherwise, we will mark it as
   // locked. Note that if two different threads try to do this, only one of
@@ -51,18 +71,18 @@ static void tsan_closure(void* user_data, grpc_error* error) {
   // TSAN will correctly produce an error.
   //
   // TODO(soheil): This only covers the callbacks scheduled by
-  //               grpc_call_combiner_(start|finish). If in the future, a
+  //               CallCombiner::Start() and CallCombiner::Stop().
-  //               callback gets scheduled using other mechanisms, we will need
+  //               If in the future, a callback gets scheduled using other
-  //               to add APIs to externally lock call combiners.
+  //               mechanisms, we will need to add APIs to externally lock
-  grpc_core::RefCountedPtr<grpc_call_combiner::TsanLock> lock =
+  //               call combiners.
-      call_combiner->tsan_lock;
+  RefCountedPtr<TsanLock> lock = self->tsan_lock_;
   bool prev = false;
   if (lock->taken.compare_exchange_strong(prev, true)) {
     TSAN_ANNOTATE_RWLOCK_ACQUIRED(&lock->taken, true);
   } else {
     lock.reset();
   }
-  GRPC_CLOSURE_RUN(call_combiner->original_closure, GRPC_ERROR_REF(error));
+  GRPC_CLOSURE_RUN(self->original_closure_, GRPC_ERROR_REF(error));
   if (lock != nullptr) {
     TSAN_ANNOTATE_RWLOCK_RELEASED(&lock->taken, true);
     bool prev = true;
@@ -71,34 +91,17 @@ static void tsan_closure(void* user_data, grpc_error* error) {
 }
 #endif
 
-static void call_combiner_sched_closure(grpc_call_combiner* call_combiner,
+void CallCombiner::ScheduleClosure(grpc_closure* closure, grpc_error* error) {
-                                        grpc_closure* closure,
-                                        grpc_error* error) {
 #ifdef GRPC_TSAN_ENABLED
-  call_combiner->original_closure = closure;
+  original_closure_ = closure;
-  GRPC_CLOSURE_SCHED(&call_combiner->tsan_closure, error);
+  GRPC_CLOSURE_SCHED(&tsan_closure_, error);
 #else
   GRPC_CLOSURE_SCHED(closure, error);
 #endif
 }
 
-void grpc_call_combiner_init(grpc_call_combiner* call_combiner) {
-  gpr_atm_no_barrier_store(&call_combiner->cancel_state, 0);
-  gpr_atm_no_barrier_store(&call_combiner->size, 0);
-  gpr_mpscq_init(&call_combiner->queue);
-#ifdef GRPC_TSAN_ENABLED
-  GRPC_CLOSURE_INIT(&call_combiner->tsan_closure, tsan_closure, call_combiner,
-                    grpc_schedule_on_exec_ctx);
-#endif
-}
-
-void grpc_call_combiner_destroy(grpc_call_combiner* call_combiner) {
-  gpr_mpscq_destroy(&call_combiner->queue);
-  GRPC_ERROR_UNREF(decode_cancel_state_error(call_combiner->cancel_state));
-}
-
 #ifndef NDEBUG
-#define DEBUG_ARGS , const char *file, int line
+#define DEBUG_ARGS const char *file, int line,
 #define DEBUG_FMT_STR "%s:%d: "
 #define DEBUG_FMT_ARGS , file, line
 #else
@@ -107,20 +110,17 @@ void grpc_call_combiner_destroy(grpc_call_combiner* call_combiner) {
 #define DEBUG_FMT_ARGS
 #endif
 
-void grpc_call_combiner_start(grpc_call_combiner* call_combiner,
+void CallCombiner::Start(grpc_closure* closure, grpc_error* error,
-                              grpc_closure* closure,
+                         DEBUG_ARGS const char* reason) {
-                              grpc_error* error DEBUG_ARGS,
+  GPR_TIMER_SCOPE("CallCombiner::Start", 0);
-                              const char* reason) {
-  GPR_TIMER_SCOPE("call_combiner_start", 0);
   if (grpc_call_combiner_trace.enabled()) {
     gpr_log(GPR_INFO,
-            "==> grpc_call_combiner_start() [%p] closure=%p [" DEBUG_FMT_STR
+            "==> CallCombiner::Start() [%p] closure=%p [" DEBUG_FMT_STR
             "%s] error=%s",
-            call_combiner, closure DEBUG_FMT_ARGS, reason,
+            this, closure DEBUG_FMT_ARGS, reason, grpc_error_string(error));
-            grpc_error_string(error));
   }
-  size_t prev_size = static_cast<size_t>(
+  size_t prev_size =
-      gpr_atm_full_fetch_add(&call_combiner->size, (gpr_atm)1));
+      static_cast<size_t>(gpr_atm_full_fetch_add(&size_, (gpr_atm)1));
   if (grpc_call_combiner_trace.enabled()) {
     gpr_log(GPR_INFO, "  size: %" PRIdPTR " -> %" PRIdPTR, prev_size,
             prev_size + 1);
@@ -128,34 +128,30 @@ void grpc_call_combiner_start(grpc_call_combiner* call_combiner,
   GRPC_STATS_INC_CALL_COMBINER_LOCKS_SCHEDULED_ITEMS();
   if (prev_size == 0) {
     GRPC_STATS_INC_CALL_COMBINER_LOCKS_INITIATED();
-
     GPR_TIMER_MARK("call_combiner_initiate", 0);
     if (grpc_call_combiner_trace.enabled()) {
       gpr_log(GPR_INFO, "  EXECUTING IMMEDIATELY");
     }
     // Queue was empty, so execute this closure immediately.
-    call_combiner_sched_closure(call_combiner, closure, error);
+    ScheduleClosure(closure, error);
   } else {
     if (grpc_call_combiner_trace.enabled()) {
       gpr_log(GPR_INFO, "  QUEUING");
     }
     // Queue was not empty, so add closure to queue.
     closure->error_data.error = error;
-    gpr_mpscq_push(&call_combiner->queue,
+    gpr_mpscq_push(&queue_, reinterpret_cast<gpr_mpscq_node*>(closure));
-                   reinterpret_cast<gpr_mpscq_node*>(closure));
   }
 }
 
-void grpc_call_combiner_stop(grpc_call_combiner* call_combiner DEBUG_ARGS,
+void CallCombiner::Stop(DEBUG_ARGS const char* reason) {
-                             const char* reason) {
+  GPR_TIMER_SCOPE("CallCombiner::Stop", 0);
-  GPR_TIMER_SCOPE("call_combiner_stop", 0);
   if (grpc_call_combiner_trace.enabled()) {
-    gpr_log(GPR_INFO,
+    gpr_log(GPR_INFO, "==> CallCombiner::Stop() [%p] [" DEBUG_FMT_STR "%s]",
-            "==> grpc_call_combiner_stop() [%p] [" DEBUG_FMT_STR "%s]",
+            this DEBUG_FMT_ARGS, reason);
-            call_combiner DEBUG_FMT_ARGS, reason);
   }
-  size_t prev_size = static_cast<size_t>(
+  size_t prev_size =
-      gpr_atm_full_fetch_add(&call_combiner->size, (gpr_atm)-1));
+      static_cast<size_t>(gpr_atm_full_fetch_add(&size_, (gpr_atm)-1));
   if (grpc_call_combiner_trace.enabled()) {
     gpr_log(GPR_INFO, "  size: %" PRIdPTR " -> %" PRIdPTR, prev_size,
             prev_size - 1);
@@ -168,10 +164,10 @@ void grpc_call_combiner_stop(grpc_call_combiner* call_combiner DEBUG_ARGS,
       }
       bool empty;
       grpc_closure* closure = reinterpret_cast<grpc_closure*>(
-          gpr_mpscq_pop_and_check_end(&call_combiner->queue, &empty));
+          gpr_mpscq_pop_and_check_end(&queue_, &empty));
       if (closure == nullptr) {
         // This can happen either due to a race condition within the mpscq
-        // code or because of a race with grpc_call_combiner_start().
+        // code or because of a race with Start().
         if (grpc_call_combiner_trace.enabled()) {
           gpr_log(GPR_INFO, "  queue returned no result; checking again");
         }
@@ -181,8 +177,7 @@ void grpc_call_combiner_stop(grpc_call_combiner* call_combiner DEBUG_ARGS,
         gpr_log(GPR_INFO, "  EXECUTING FROM QUEUE: closure=%p error=%s",
                 closure, grpc_error_string(closure->error_data.error));
       }
-      call_combiner_sched_closure(call_combiner, closure,
+      ScheduleClosure(closure, closure->error_data.error);
-                                  closure->error_data.error);
       break;
     }
   } else if (grpc_call_combiner_trace.enabled()) {
@@ -190,13 +185,12 @@ void grpc_call_combiner_stop(grpc_call_combiner* call_combiner DEBUG_ARGS,
   }
 }
 
-void grpc_call_combiner_set_notify_on_cancel(grpc_call_combiner* call_combiner,
+void CallCombiner::SetNotifyOnCancel(grpc_closure* closure) {
-                                             grpc_closure* closure) {
   GRPC_STATS_INC_CALL_COMBINER_SET_NOTIFY_ON_CANCEL();
   while (true) {
     // Decode original state.
-    gpr_atm original_state = gpr_atm_acq_load(&call_combiner->cancel_state);
+    gpr_atm original_state = gpr_atm_acq_load(&cancel_state_);
-    grpc_error* original_error = decode_cancel_state_error(original_state);
+    grpc_error* original_error = DecodeCancelStateError(original_state);
     // If error is set, invoke the cancellation closure immediately.
     // Otherwise, store the new closure.
     if (original_error != GRPC_ERROR_NONE) {
@@ -204,16 +198,15 @@ void grpc_call_combiner_set_notify_on_cancel(grpc_call_combiner* call_combiner,
         gpr_log(GPR_INFO,
                 "call_combiner=%p: scheduling notify_on_cancel callback=%p "
                 "for pre-existing cancellation",
-                call_combiner, closure);
+                this, closure);
       }
       GRPC_CLOSURE_SCHED(closure, GRPC_ERROR_REF(original_error));
       break;
     } else {
-      if (gpr_atm_full_cas(&call_combiner->cancel_state, original_state,
+      if (gpr_atm_full_cas(&cancel_state_, original_state, (gpr_atm)closure)) {
-                           (gpr_atm)closure)) {
         if (grpc_call_combiner_trace.enabled()) {
           gpr_log(GPR_INFO, "call_combiner=%p: setting notify_on_cancel=%p",
-                  call_combiner, closure);
+                  this, closure);
         }
         // If we replaced an earlier closure, invoke the original
         // closure with GRPC_ERROR_NONE.  This allows callers to clean
@@ -222,8 +215,8 @@ void grpc_call_combiner_set_notify_on_cancel(grpc_call_combiner* call_combiner,
           closure = (grpc_closure*)original_state;
           if (grpc_call_combiner_trace.enabled()) {
             gpr_log(GPR_INFO,
-                    "call_combiner=%p: scheduling old cancel callback=%p",
+                    "call_combiner=%p: scheduling old cancel callback=%p", this,
-                    call_combiner, closure);
+                    closure);
           }
           GRPC_CLOSURE_SCHED(closure, GRPC_ERROR_NONE);
         }
@@ -234,24 +227,23 @@ void grpc_call_combiner_set_notify_on_cancel(grpc_call_combiner* call_combiner,
   }
 }
 
-void grpc_call_combiner_cancel(grpc_call_combiner* call_combiner,
+void CallCombiner::Cancel(grpc_error* error) {
-                               grpc_error* error) {
   GRPC_STATS_INC_CALL_COMBINER_CANCELLED();
   while (true) {
-    gpr_atm original_state = gpr_atm_acq_load(&call_combiner->cancel_state);
+    gpr_atm original_state = gpr_atm_acq_load(&cancel_state_);
-    grpc_error* original_error = decode_cancel_state_error(original_state);
+    grpc_error* original_error = DecodeCancelStateError(original_state);
     if (original_error != GRPC_ERROR_NONE) {
       GRPC_ERROR_UNREF(error);
       break;
     }
-    if (gpr_atm_full_cas(&call_combiner->cancel_state, original_state,
+    if (gpr_atm_full_cas(&cancel_state_, original_state,
-                         encode_cancel_state_error(error))) {
+                         EncodeCancelStateError(error))) {
       if (original_state != 0) {
         grpc_closure* notify_on_cancel = (grpc_closure*)original_state;
         if (grpc_call_combiner_trace.enabled()) {
           gpr_log(GPR_INFO,
                   "call_combiner=%p: scheduling notify_on_cancel callback=%p",
-                  call_combiner, notify_on_cancel);
+                  this, notify_on_cancel);
         }
         GRPC_CLOSURE_SCHED(notify_on_cancel, GRPC_ERROR_REF(error));
       }
@@ -260,3 +252,5 @@ void grpc_call_combiner_cancel(grpc_call_combiner* call_combiner,
     // cas failed, try again.
   }
 }
+
+}  // namespace grpc_core

src/core/lib/iomgr/call_combiner.h

@@ -41,75 +41,37 @@
 // when it is done with the action that was kicked off by the original
 // callback.
 
-extern grpc_core::TraceFlag grpc_call_combiner_trace;
+namespace grpc_core {
-
-struct grpc_call_combiner {
-  gpr_atm size = 0;  // size_t, num closures in queue or currently executing
-  gpr_mpscq queue;
-  // Either 0 (if not cancelled and no cancellation closure set),
-  // a grpc_closure* (if the lowest bit is 0),
-  // or a grpc_error* (if the lowest bit is 1).
-  gpr_atm cancel_state = 0;
-#ifdef GRPC_TSAN_ENABLED
-  // A fake ref-counted lock that is kept alive after the destruction of
-  // grpc_call_combiner, when we are running the original closure.
-  //
-  // Ideally we want to lock and unlock the call combiner as a pointer, when the
-  // callback is called. However, original_closure is free to trigger
-  // anything on the call combiner (including destruction of grpc_call).
-  // Thus, we need a ref-counted structure that can outlive the call combiner.
-  struct TsanLock
-      : public grpc_core::RefCounted<TsanLock,
-                                     grpc_core::NonPolymorphicRefCount> {
-    TsanLock() { TSAN_ANNOTATE_RWLOCK_CREATE(&taken); }
-    ~TsanLock() { TSAN_ANNOTATE_RWLOCK_DESTROY(&taken); }
-
-    // To avoid double-locking by the same thread, we should acquire/release
-    // the lock only when taken is false. On each acquire taken must be set to
-    // true.
-    std::atomic<bool> taken{false};
-  };
-  grpc_core::RefCountedPtr<TsanLock> tsan_lock =
-      grpc_core::MakeRefCounted<TsanLock>();
-  grpc_closure tsan_closure;
-  grpc_closure* original_closure;
-#endif
-};
 
-// Assumes memory was initialized to zero.
+extern TraceFlag grpc_call_combiner_trace;
-void grpc_call_combiner_init(grpc_call_combiner* call_combiner);
 
-void grpc_call_combiner_destroy(grpc_call_combiner* call_combiner);
+class CallCombiner {
+ public:
+  CallCombiner();
+  ~CallCombiner();
 
 #ifndef NDEBUG
 #define GRPC_CALL_COMBINER_START(call_combiner, closure, error, reason) \
-  grpc_call_combiner_start((call_combiner), (closure), (error), __FILE__, \
+  (call_combiner)->Start((closure), (error), __FILE__, __LINE__, (reason))
-                           __LINE__, (reason))
 #define GRPC_CALL_COMBINER_STOP(call_combiner, reason) \
-  grpc_call_combiner_stop((call_combiner), __FILE__, __LINE__, (reason))
+  (call_combiner)->Stop(__FILE__, __LINE__, (reason))
-/// Starts processing \a closure on \a call_combiner.
+  /// Starts processing \a closure.
-void grpc_call_combiner_start(grpc_call_combiner* call_combiner,
+  void Start(grpc_closure* closure, grpc_error* error, const char* file,
-                              grpc_closure* closure, grpc_error* error,
+             int line, const char* reason);
-                              const char* file, int line, const char* reason);
   /// Yields the call combiner to the next closure in the queue, if any.
-void grpc_call_combiner_stop(grpc_call_combiner* call_combiner,
+  void Stop(const char* file, int line, const char* reason);
-                             const char* file, int line, const char* reason);
 #else
 #define GRPC_CALL_COMBINER_START(call_combiner, closure, error, reason) \
-  grpc_call_combiner_start((call_combiner), (closure), (error), (reason))
+  (call_combiner)->Start((closure), (error), (reason))
 #define GRPC_CALL_COMBINER_STOP(call_combiner, reason) \
-  grpc_call_combiner_stop((call_combiner), (reason))
+  (call_combiner)->Stop((reason))
-/// Starts processing \a closure on \a call_combiner.
+  /// Starts processing \a closure.
-void grpc_call_combiner_start(grpc_call_combiner* call_combiner,
+  void Start(grpc_closure* closure, grpc_error* error, const char* reason);
-                              grpc_closure* closure, grpc_error* error,
-                              const char* reason);
   /// Yields the call combiner to the next closure in the queue, if any.
-void grpc_call_combiner_stop(grpc_call_combiner* call_combiner,
+  void Stop(const char* reason);
-                             const char* reason);
 #endif
 
-/// Registers \a closure to be invoked by \a call_combiner when
+  /// Registers \a closure to be invoked when Cancel() is called.
-/// grpc_call_combiner_cancel() is called.
   ///
   /// Once a closure is registered, it will always be scheduled exactly
   /// once; this allows the closure to hold references that will be freed
@@ -118,29 +80,60 @@ void grpc_call_combiner_stop(grpc_call_combiner* call_combiner,
   /// otherwise, it will be scheduled with GRPC_ERROR_NONE.
   ///
   /// The closure will be scheduled in the following cases:
-/// - If grpc_call_combiner_cancel() was called prior to registering the
+  /// - If Cancel() was called prior to registering the closure, it will be
-///   closure, it will be scheduled immediately with the cancelation error.
+  ///   scheduled immediately with the cancelation error.
-/// - If grpc_call_combiner_cancel() is called after registering the
+  /// - If Cancel() is called after registering the closure, the closure will
-///   closure, the closure will be scheduled with the cancellation error.
+  ///   be scheduled with the cancellation error.
-/// - If grpc_call_combiner_set_notify_on_cancel() is called again to
+  /// - If SetNotifyOnCancel() is called again to register a new cancellation
-///   register a new cancellation closure, the previous cancellation
+  ///   closure, the previous cancellation closure will be scheduled with
-///   closure will be scheduled with GRPC_ERROR_NONE.
+  ///   GRPC_ERROR_NONE.
   ///
   /// If \a closure is NULL, then no closure will be invoked on
   /// cancellation; this effectively unregisters the previously set closure.
   /// However, most filters will not need to explicitly unregister their
-/// callbacks, as this is done automatically when the call is destroyed. Filters
+  /// callbacks, as this is done automatically when the call is destroyed.
-/// that schedule the cancellation closure on ExecCtx do not need to take a ref
+  /// Filters that schedule the cancellation closure on ExecCtx do not need
-/// on the call stack to guarantee closure liveness. This is done by explicitly
+  /// to take a ref on the call stack to guarantee closure liveness. This is
-/// flushing ExecCtx after the unregistration during call destruction.
+  /// done by explicitly flushing ExecCtx after the unregistration during
-void grpc_call_combiner_set_notify_on_cancel(grpc_call_combiner* call_combiner,
+  /// call destruction.
-                                             grpc_closure* closure);
+  void SetNotifyOnCancel(grpc_closure* closure);
 
   /// Indicates that the call has been cancelled.
-void grpc_call_combiner_cancel(grpc_call_combiner* call_combiner,
+  void Cancel(grpc_error* error);
-                               grpc_error* error);
 
-namespace grpc_core {
+ private:
+  void ScheduleClosure(grpc_closure* closure, grpc_error* error);
+#ifdef GRPC_TSAN_ENABLED
+  static void TsanClosure(void* arg, grpc_error* error);
+#endif
+
+  gpr_atm size_ = 0;  // size_t, num closures in queue or currently executing
+  gpr_mpscq queue_;
+  // Either 0 (if not cancelled and no cancellation closure set),
+  // a grpc_closure* (if the lowest bit is 0),
+  // or a grpc_error* (if the lowest bit is 1).
+  gpr_atm cancel_state_ = 0;
+#ifdef GRPC_TSAN_ENABLED
+  // A fake ref-counted lock that is kept alive after the destruction of
+  // grpc_call_combiner, when we are running the original closure.
+  //
+  // Ideally we want to lock and unlock the call combiner as a pointer, when the
+  // callback is called. However, original_closure is free to trigger
+  // anything on the call combiner (including destruction of grpc_call).
+  // Thus, we need a ref-counted structure that can outlive the call combiner.
+  struct TsanLock : public RefCounted<TsanLock, NonPolymorphicRefCount> {
+    TsanLock() { TSAN_ANNOTATE_RWLOCK_CREATE(&taken); }
+    ~TsanLock() { TSAN_ANNOTATE_RWLOCK_DESTROY(&taken); }
+    // To avoid double-locking by the same thread, we should acquire/release
+    // the lock only when taken is false. On each acquire taken must be set to
+    // true.
+    std::atomic<bool> taken{false};
+  };
+  RefCountedPtr<TsanLock> tsan_lock_ = MakeRefCounted<TsanLock>();
+  grpc_closure tsan_closure_;
+  grpc_closure* original_closure_;
+#endif
+};
 
 // Helper for running a list of closures in a call combiner.
 //
@@ -166,7 +159,7 @@ class CallCombinerClosureList {
   // scheduled via GRPC_CLOSURE_SCHED(), which will eventually result in
   // yielding the call combiner.  If the list is empty, then the call
   // combiner will be yielded immediately.
-  void RunClosures(grpc_call_combiner* call_combiner) {
+  void RunClosures(CallCombiner* call_combiner) {
     if (closures_.empty()) {
       GRPC_CALL_COMBINER_STOP(call_combiner, "no closures to schedule");
       return;
@@ -190,7 +183,7 @@ class CallCombinerClosureList {
 
   // Runs all closures in the call combiner, but does NOT yield the call
   // combiner.  All closures will be scheduled via GRPC_CALL_COMBINER_START().
-  void RunClosuresWithoutYielding(grpc_call_combiner* call_combiner) {
+  void RunClosuresWithoutYielding(CallCombiner* call_combiner) {
     for (size_t i = 0; i < closures_.size(); ++i) {
       auto& closure = closures_[i];
       GRPC_CALL_COMBINER_START(call_combiner, closure.closure, closure.error,

src/core/lib/security/transport/client_auth_filter.cc

@@ -92,7 +92,7 @@ struct call_data {
   }
 
   grpc_call_stack* owning_call;
-  grpc_call_combiner* call_combiner;
+  grpc_core::CallCombiner* call_combiner;
   grpc_core::RefCountedPtr<grpc_call_credentials> creds;
   grpc_slice host = grpc_empty_slice();
   grpc_slice method = grpc_empty_slice();
@@ -270,11 +270,9 @@ static void send_security_metadata(grpc_call_element* elem,
     GRPC_ERROR_UNREF(error);
   } else {
     // Async return; register cancellation closure with call combiner.
-    grpc_call_combiner_set_notify_on_cancel(
+    calld->call_combiner->SetNotifyOnCancel(GRPC_CLOSURE_INIT(
-        calld->call_combiner,
+        &calld->get_request_metadata_cancel_closure,
-        GRPC_CLOSURE_INIT(&calld->get_request_metadata_cancel_closure,
+        cancel_get_request_metadata, elem, grpc_schedule_on_exec_ctx));
-                          cancel_get_request_metadata, elem,
-                          grpc_schedule_on_exec_ctx));
   }
 }
 
@@ -345,11 +343,9 @@ static void auth_start_transport_stream_op_batch(
         GRPC_ERROR_UNREF(error);
       } else {
         // Async return; register cancellation closure with call combiner.
-        grpc_call_combiner_set_notify_on_cancel(
+        calld->call_combiner->SetNotifyOnCancel(GRPC_CLOSURE_INIT(
-            calld->call_combiner,
+            &calld->check_call_host_cancel_closure, cancel_check_call_host,
-            GRPC_CLOSURE_INIT(&calld->check_call_host_cancel_closure,
+            elem, grpc_schedule_on_exec_ctx));
-                              cancel_check_call_host, elem,
-                              grpc_schedule_on_exec_ctx));
       }
       gpr_free(call_host);
       return; /* early exit */

src/core/lib/security/transport/server_auth_filter.cc

@@ -74,7 +74,7 @@ struct call_data {
 
   ~call_data() { GRPC_ERROR_UNREF(recv_initial_metadata_error); }
 
-  grpc_call_combiner* call_combiner;
+  grpc_core::CallCombiner* call_combiner;
   grpc_call_stack* owning_call;
   grpc_transport_stream_op_batch* recv_initial_metadata_batch;
   grpc_closure* original_recv_initial_metadata_ready;
@@ -219,8 +219,7 @@ static void recv_initial_metadata_ready(void* arg, grpc_error* error) {
       // to drop the call combiner early if we get cancelled.
       GRPC_CLOSURE_INIT(&calld->cancel_closure, cancel_call, elem,
                         grpc_schedule_on_exec_ctx);
-      grpc_call_combiner_set_notify_on_cancel(calld->call_combiner,
+      calld->call_combiner->SetNotifyOnCancel(&calld->cancel_closure);
-                                              &calld->cancel_closure);
       GRPC_CALL_STACK_REF(calld->owning_call, "server_auth_metadata");
       calld->md = metadata_batch_to_md_array(
           batch->payload->recv_initial_metadata.recv_initial_metadata);

src/core/lib/surface/call.cc

@@ -131,7 +131,6 @@ struct grpc_call {
         is_client(args.server_transport_data == nullptr),
         stream_op_payload(context) {
     gpr_ref_init(&ext_ref, 1);
-    grpc_call_combiner_init(&call_combiner);
     for (int i = 0; i < 2; i++) {
       for (int j = 0; j < 2; j++) {
         metadata_batch[i][j].deadline = GRPC_MILLIS_INF_FUTURE;
@@ -141,12 +140,11 @@ struct grpc_call {
 
   ~grpc_call() {
     gpr_free(static_cast<void*>(const_cast<char*>(final_info.error_string)));
-    grpc_call_combiner_destroy(&call_combiner);
   }
 
   gpr_refcount ext_ref;
   gpr_arena* arena;
-  grpc_call_combiner call_combiner;
+  grpc_core::CallCombiner call_combiner;
   grpc_completion_queue* cq;
   grpc_polling_entity pollent;
   grpc_channel* channel;
@@ -589,7 +587,7 @@ void grpc_call_unref(grpc_call* c) {
     // holding to the call stack. Also flush the closures on exec_ctx so that
     // filters that schedule cancel notification closures on exec_ctx do not
     // need to take a ref of the call stack to guarantee closure liveness.
-    grpc_call_combiner_set_notify_on_cancel(&c->call_combiner, nullptr);
+    c->call_combiner.SetNotifyOnCancel(nullptr);
     grpc_core::ExecCtx::Get()->Flush();
   }
   GRPC_CALL_INTERNAL_UNREF(c, "destroy");
@@ -685,7 +683,7 @@ static void cancel_with_error(grpc_call* c, grpc_error* error) {
   // any in-flight asynchronous actions that may be holding the call
   // combiner.  This ensures that the cancel_stream batch can be sent
   // down the filter stack in a timely manner.
-  grpc_call_combiner_cancel(&c->call_combiner, GRPC_ERROR_REF(error));
+  c->call_combiner.Cancel(GRPC_ERROR_REF(error));
   cancel_state* state = static_cast<cancel_state*>(gpr_malloc(sizeof(*state)));
   state->call = c;
   GRPC_CLOSURE_INIT(&state->finish_batch, done_termination, state,

src/core/lib/surface/lame_client.cc

@@ -39,7 +39,7 @@ namespace grpc_core {
 namespace {
 
 struct CallData {
-  grpc_call_combiner* call_combiner;
+  grpc_core::CallCombiner* call_combiner;
   grpc_linked_mdelem status;
   grpc_linked_mdelem details;
   grpc_core::Atomic<bool> filled_metadata;

src/core/lib/surface/server.cc

@@ -190,7 +190,7 @@ struct call_data {
   grpc_closure publish;
 
   call_data* pending_next = nullptr;
-  grpc_call_combiner* call_combiner;
+  grpc_core::CallCombiner* call_combiner;
 };
 
 struct request_matcher {

src/core/lib/transport/transport.cc

@@ -174,7 +174,7 @@ grpc_endpoint* grpc_transport_get_endpoint(grpc_transport* transport) {
 // it's grpc_transport_stream_op_batch_finish_with_failure
 void grpc_transport_stream_op_batch_finish_with_failure(
     grpc_transport_stream_op_batch* batch, grpc_error* error,
-    grpc_call_combiner* call_combiner) {
+    grpc_core::CallCombiner* call_combiner) {
   if (batch->send_message) {
     batch->payload->send_message.send_message.reset();
   }

src/core/lib/transport/transport.h

@@ -379,7 +379,7 @@ void grpc_transport_destroy_stream(grpc_transport* transport,
 
 void grpc_transport_stream_op_batch_finish_with_failure(
     grpc_transport_stream_op_batch* op, grpc_error* error,
-    grpc_call_combiner* call_combiner);
+    grpc_core::CallCombiner* call_combiner);
 
 char* grpc_transport_stream_op_batch_string(grpc_transport_stream_op_batch* op);
 char* grpc_transport_op_string(grpc_transport_op* op);

test/cpp/microbenchmarks/bm_call_create.cc

@@ -609,7 +609,7 @@ BENCHMARK_TEMPLATE(BM_IsolatedFilter, MessageSizeFilter, SendEmptyMetadata);
 namespace isolated_call_filter {
 
 typedef struct {
-  grpc_call_combiner* call_combiner;
+  grpc_core::CallCombiner* call_combiner;
 } call_data;
 
 static void StartTransportStreamOp(grpc_call_element* elem,