Protect assignment of StripDetset() StMeasurementDetSet::getDetSet()

The assigment is a critical section and must be protected.

RecoTracker/MeasurementDet/src/TkMeasurementDetSet.h

@@ -165,7 +165,7 @@ class StMeasurementDetSet {
   void update(int i, int j) {
     assert(j >= 0);
     assert(detSet_[i].empty_);
-    assert(detSet_[i].ready_);
+    assert(detSet_[i].ready_ == ReadyState::kUnset);
     detIndex_[i] = j;
     detSet_[i].empty_ = false;
     incReady();
@@ -189,7 +189,7 @@ class StMeasurementDetSet {
     printStat();
     for (auto& d : detSet_) {
       d.empty_ = true;
-      d.ready_ = true;
+      d.ready_ = ReadyState::kUnset;
     }
     std::fill(detIndex_.begin(), detIndex_.end(), -1);
     std::fill(activeThisEvent_.begin(), activeThisEvent_.end(), true);
@@ -208,7 +208,7 @@ class StMeasurementDetSet {
   const edm::Handle<edmNew::DetSetVector<SiStripCluster>>& handle() const { return handle_; }
   // StripDetset & detSet(int i) { return detSet_[i]; }
   const StripDetset& detSet(int i) const {
-    if (detSet_[i].ready_)
+    if (detSet_[i].ready_ == ReadyState::kUnset)
       getDetSet(i);
     return detSet_[i].detSet_;
   }
@@ -236,13 +236,22 @@ class StMeasurementDetSet {
       // edmNew::DetSet<T>::set() internally does an atomic update
       det.detSet_.set(*handle_, handle_->item(detIndex_[i]));
       det.empty_ = false;  // better be false already
+      det.ready_ = ReadyState::kSet;
       incAct();
+      incSet();
     } else {  // we should not be here
-      det.detSet_ = StripDetset();
-      det.empty_ = true;
+      ReadyState expected = ReadyState::kUnset;
+      if (det.ready_.compare_exchange_strong(expected, ReadyState::kSetting, std::memory_order_acq_rel)) {
+        det.detSet_ = StripDetset();
+        det.empty_ = true;
+        det.ready_ = ReadyState::kSet;
+        incSet();
+      } else {
+        // need to wait
+        while (ReadyState::kSet != det.ready_.load(std::memory_order_acquire)) {
+        }
+      }
     }
-    det.ready_ = false;
-    incSet();
   }
 
   friend class MeasurementTrackerImpl;
@@ -252,12 +261,18 @@ class StMeasurementDetSet {
   // Globals, per-event
   edm::Handle<edmNew::DetSetVector<SiStripCluster>> handle_;
 
+  enum class ReadyState : char {
+    kUnset,
+    kSetting,
+    kSet
+  };
+
   // Helper struct to define only the vector elements as mutable and
   // to have a vector of atomics without an explicit loop over
   // elements to set their values
   struct DetSetHelper {
     mutable std::atomic<bool> empty_ = true;
-    mutable std::atomic<bool> ready_ = true;  // to be cleaned
+    mutable std::atomic<ReadyState> ready_ = ReadyState::kUnset;  // to be cleaned
     // only thread-safe non-const member functions are called from a const function
     CMS_THREAD_SAFE mutable StripDetset detSet_;
   };