Addressed Vijay's code review comments

test/cpp/qps/client_callback.cc

@@ -43,8 +43,7 @@ namespace testing {
  * Maintains context info per RPC
  */
 struct CallbackClientRpcContext {
-  CallbackClientRpcContext(BenchmarkService::Stub* stub)
+  CallbackClientRpcContext(BenchmarkService::Stub* stub) : stub_(stub) {}
-      : response_(), context_(), alarm_(), stub_(stub) {}
 
   ~CallbackClientRpcContext() {}
 
@@ -83,8 +82,9 @@ class CallbackClient
   std::condition_variable shutdown_cv_;
   // Number of rpcs done after thread completion
   size_t rpcs_done_;
-  // Per Thread Queue of Context data pointers for running a RPC
+  // Vector of Context data pointers for running a RPC
-  std::vector<std::vector<std::unique_ptr<CallbackClientRpcContext>>> ctxs_;
+  std::vector<std::unique_ptr<CallbackClientRpcContext>> ctx_;
+
   virtual void InitThreadFuncImpl(size_t thread_idx) = 0;
   virtual bool ThreadFuncImpl(Thread* t, size_t thread_idx) = 0;
 
@@ -93,7 +93,8 @@ class CallbackClient
     ThreadFuncImpl(t, thread_idx);
   }
 
-  virtual void ScheduleRpc(Thread* t, size_t thread_idx, size_t queue_idx) = 0;
+  virtual void ScheduleRpc(Thread* t, size_t thread_idx,
+                           size_t ctx_vector_idx) = 0;
 
   /**
    * The main thread of the benchmark will be waiting on DestroyMultithreading.
@@ -134,11 +135,9 @@ class CallbackClient
 class CallbackUnaryClient final : public CallbackClient {
  public:
   CallbackUnaryClient(const ClientConfig& config) : CallbackClient(config) {
-    ctxs_.resize(num_threads_);
+    for (size_t ch = 0; ch < config.client_channels(); ch++) {
-    for (int ch = 0; ch < config.client_channels(); ch++) {
+      for (size_t i = 0; i < config.outstanding_rpcs_per_channel(); i++) {
-      for (int i = 0; i < config.outstanding_rpcs_per_channel(); i++) {
+        ctx_.emplace_back(
-        size_t bucket = (i * ch) % num_threads_;
-        ctxs_[bucket].emplace_back(
             new CallbackClientRpcContext(channels_[ch].get_stub()));
       }
     }
@@ -148,8 +147,9 @@ class CallbackUnaryClient final : public CallbackClient {
 
  protected:
   bool ThreadFuncImpl(Thread* t, size_t thread_idx) override {
-    for (size_t i = 0; i < ctxs_[thread_idx].size(); i++) {
+    for (int vector_idx = thread_idx; vector_idx < total_outstanding_rpcs_;
-      ScheduleRpc(t, thread_idx, i);
+         vector_idx += num_threads_) {
+      ScheduleRpc(t, thread_idx, vector_idx);
     }
     return true;
   }
@@ -157,27 +157,26 @@ class CallbackUnaryClient final : public CallbackClient {
   void InitThreadFuncImpl(size_t thread_idx) override { return; }
 
  private:
-  void ScheduleRpc(Thread* t, size_t thread_idx, size_t queue_idx) override {
+  void ScheduleRpc(Thread* t, size_t thread_idx, size_t vector_idx) override {
     if (!closed_loop_) {
       gpr_timespec next_issue_time = NextIssueTime(thread_idx);
       // Start an alarm callback to run the internal callback after
       // next_issue_time
-      ctxs_[thread_idx][queue_idx]->alarm_.experimental().Set(
+      ctx_[vector_idx]->alarm_.experimental().Set(
-          next_issue_time, [this, t, thread_idx, queue_idx](bool ok) {
+          next_issue_time, [this, t, thread_idx, vector_idx](bool ok) {
-            IssueUnaryCallbackRpc(t, thread_idx, queue_idx);
+            IssueUnaryCallbackRpc(t, thread_idx, vector_idx);
           });
     } else {
-      IssueUnaryCallbackRpc(t, thread_idx, queue_idx);
+      IssueUnaryCallbackRpc(t, thread_idx, vector_idx);
     }
   }
 
-  void IssueUnaryCallbackRpc(Thread* t, size_t thread_idx, size_t queue_idx) {
+  void IssueUnaryCallbackRpc(Thread* t, size_t thread_idx, size_t vector_idx) {
     GPR_TIMER_SCOPE("CallbackUnaryClient::ThreadFunc", 0);
     double start = UsageTimer::Now();
-    ctxs_[thread_idx][queue_idx]->stub_->experimental_async()->UnaryCall(
+    ctx_[vector_idx]->stub_->experimental_async()->UnaryCall(
-        std::move(&ctxs_[thread_idx][queue_idx]->context_), &request_,
+        (&ctx_[vector_idx]->context_), &request_, &ctx_[vector_idx]->response_,
-        &ctxs_[thread_idx][queue_idx]->response_,
+        [this, t, thread_idx, start, vector_idx](grpc::Status s) {
-        [this, t, thread_idx, start, queue_idx](grpc::Status s) {
           // Update Histogram with data from the callback run
           HistogramEntry entry;
           if (s.ok()) {
@@ -191,10 +190,10 @@ class CallbackUnaryClient final : public CallbackClient {
             NotifyMainThreadOfThreadCompletion();
           } else {
             // Reallocate ctx for next RPC
-            ctxs_[thread_idx][queue_idx].reset(new CallbackClientRpcContext(
+            ctx_[vector_idx].reset(
-                ctxs_[thread_idx][queue_idx]->stub_));
+                new CallbackClientRpcContext(ctx_[vector_idx]->stub_));
             // Schedule a new RPC
-            ScheduleRpc(t, thread_idx, queue_idx);
+            ScheduleRpc(t, thread_idx, vector_idx);
           }
         });
   }