Use mutext to protect drop call counts in grpclb client stats.

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

@@ -558,7 +558,7 @@ GrpcLb::PickResult GrpcLb::Picker::Pick(PickArgs* pick, grpc_error** error) {
     // subchannel call (and therefore no client_load_reporting filter)
     // for dropped calls.
     if (client_stats_ != nullptr) {
-      client_stats_->AddCallDroppedLocked(drop_token);
+      client_stats_->AddCallDropped(drop_token);
     }
     return PICK_COMPLETE;
   }
@@ -917,7 +917,7 @@ void GrpcLb::BalancerCallState::SendClientLoadReportLocked() {
   // Construct message payload.
   GPR_ASSERT(send_message_payload_ == nullptr);
   grpc_grpclb_request* request =
-      grpc_grpclb_load_report_request_create_locked(client_stats_.get());
+      grpc_grpclb_load_report_request_create(client_stats_.get());
   // Skip client load report if the counters were all zero in the last
   // report and they are still zero in this one.
   if (LoadReportCountersAreZero(request)) {

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

@@ -25,6 +25,8 @@
 #include <grpc/support/atm.h>
 #include <grpc/support/string_util.h>
 
+#include "src/core/lib/gprpp/mutex_lock.h"
+
 namespace grpc_core {
 
 void GrpcLbClientStats::AddCallStarted() {
@@ -43,11 +45,12 @@ void GrpcLbClientStats::AddCallFinished(
   }
 }
 
-void GrpcLbClientStats::AddCallDroppedLocked(const char* token) {
+void GrpcLbClientStats::AddCallDropped(const char* token) {
   // Increment num_calls_started and num_calls_finished.
   gpr_atm_full_fetch_add(&num_calls_started_, (gpr_atm)1);
   gpr_atm_full_fetch_add(&num_calls_finished_, (gpr_atm)1);
   // Record the drop.
+  MutexLock lock(&drop_count_mu_);
   if (drop_token_counts_ == nullptr) {
     drop_token_counts_.reset(New<DroppedCallCounts>());
   }
@@ -69,7 +72,7 @@ void AtomicGetAndResetCounter(int64_t* value, gpr_atm* counter) {
 
 }  // namespace
 
-void GrpcLbClientStats::GetLocked(
+void GrpcLbClientStats::Get(
     int64_t* num_calls_started, int64_t* num_calls_finished,
     int64_t* num_calls_finished_with_client_failed_to_send,
     int64_t* num_calls_finished_known_received,
@@ -80,6 +83,7 @@ void GrpcLbClientStats::GetLocked(
                            &num_calls_finished_with_client_failed_to_send_);
   AtomicGetAndResetCounter(num_calls_finished_known_received,
                            &num_calls_finished_known_received_);
+  MutexLock lock(&drop_count_mu_);
   *drop_token_counts = std::move(drop_token_counts_);
 }
 

src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb_client_stats.h

@@ -41,17 +41,16 @@ class GrpcLbClientStats : public RefCounted<GrpcLbClientStats> {
 
   typedef InlinedVector<DropTokenCount, 10> DroppedCallCounts;
 
-  GrpcLbClientStats() {}
+  GrpcLbClientStats() { gpr_mu_init(&drop_count_mu_); }
+  ~GrpcLbClientStats() { gpr_mu_destroy(&drop_count_mu_); }
 
   void AddCallStarted();
   void AddCallFinished(bool finished_with_client_failed_to_send,
                        bool finished_known_received);
 
-  // This method is not thread-safe; caller must synchronize.
+  void AddCallDropped(const char* token);
-  void AddCallDroppedLocked(const char* token);
 
-  // This method is not thread-safe; caller must synchronize.
+  void Get(int64_t* num_calls_started, int64_t* num_calls_finished,
-  void GetLocked(int64_t* num_calls_started, int64_t* num_calls_finished,
            int64_t* num_calls_finished_with_client_failed_to_send,
            int64_t* num_calls_finished_known_received,
            UniquePtr<DroppedCallCounts>* drop_token_counts);
@@ -63,13 +62,12 @@ class GrpcLbClientStats : public RefCounted<GrpcLbClientStats> {
   }
 
  private:
-  // This field must only be accessed via *_locked() methods.
-  UniquePtr<DroppedCallCounts> drop_token_counts_;
-  // These fields may be accessed from multiple threads at a time.
   gpr_atm num_calls_started_ = 0;
   gpr_atm num_calls_finished_ = 0;
   gpr_atm num_calls_finished_with_client_failed_to_send_ = 0;
   gpr_atm num_calls_finished_known_received_ = 0;
+  gpr_mu drop_count_mu_;  // Guards drop_token_counts_.
+  UniquePtr<DroppedCallCounts> drop_token_counts_;
 };
 
 }  // namespace grpc_core

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

@@ -107,7 +107,7 @@ static bool encode_drops(pb_ostream_t* stream, const pb_field_t* field,
   return true;
 }
 
-grpc_grpclb_request* grpc_grpclb_load_report_request_create_locked(
+grpc_grpclb_request* grpc_grpclb_load_report_request_create(
     grpc_core::GrpcLbClientStats* client_stats) {
   grpc_grpclb_request* req = static_cast<grpc_grpclb_request*>(
       gpr_zalloc(sizeof(grpc_grpclb_request)));
@@ -122,7 +122,7 @@ grpc_grpclb_request* grpc_grpclb_load_report_request_create_locked(
   req->client_stats.calls_finished_with_drop.funcs.encode = encode_drops;
   grpc_core::UniquePtr<grpc_core::GrpcLbClientStats::DroppedCallCounts>
       drop_counts;
-  client_stats->GetLocked(
+  client_stats->Get(
       &req->client_stats.num_calls_started,
       &req->client_stats.num_calls_finished,
       &req->client_stats.num_calls_finished_with_client_failed_to_send,

src/core/ext/filters/client_channel/lb_policy/grpclb/load_balancer_api.h

@@ -43,7 +43,7 @@ typedef struct {
 
 /** Create a request for a gRPC LB service under \a lb_service_name */
 grpc_grpclb_request* grpc_grpclb_request_create(const char* lb_service_name);
-grpc_grpclb_request* grpc_grpclb_load_report_request_create_locked(
+grpc_grpclb_request* grpc_grpclb_load_report_request_create(
     grpc_core::GrpcLbClientStats* client_stats);
 
 /** Protocol Buffers v3-encode \a request */