Fix invalidation of MeasureDescriptors. (#399)

Heap-allocate MeasureDescriptors so that references to them are stable
even if the underlying storage (std::vector) in the MeasureRegistry
moves.

Add test that fails under ASAN if this isn't done.

Author: g-easy

opencensus/stats/internal/measure_registry_impl.cc

@@ -16,6 +16,7 @@
 
 #include <iostream>
 
+#include "absl/memory/memory.h"
 #include "opencensus/stats/internal/delta_producer.h"
 #include "opencensus/stats/internal/stats_manager.h"
 #include "opencensus/stats/measure_descriptor.h"
@@ -83,7 +84,8 @@ uint64_t MeasureRegistryImpl::RegisterImpl(MeasureDescriptor descriptor) {
   const uint64_t id =
       CreateMeasureId(registered_descriptors_.size(), true, descriptor.type());
   id_map_.emplace_hint(it, descriptor.name(), id);
-  registered_descriptors_.push_back(std::move(descriptor));
+  registered_descriptors_.push_back(
+      absl::make_unique<MeasureDescriptor>(std::move(descriptor)));
   return id;
 }
 
@@ -96,7 +98,7 @@ const MeasureDescriptor& MeasureRegistryImpl::GetDescriptorByName(
         MeasureDescriptor("", "", "", MeasureDescriptor::Type::kDouble);
     return default_descriptor;
   } else {
-    return registered_descriptors_[IdToIndex(it->second)];
+    return *registered_descriptors_[IdToIndex(it->second)];
   }
 }
 

opencensus/stats/internal/measure_registry_impl.h

@@ -16,6 +16,7 @@
 #define OPENCENSUS_STATS_INTERNAL_MEASURE_REGISTRY_IMPL_H_
 
 #include <cstdint>
+#include <memory>
 #include <string>
 #include <unordered_map>
 #include <vector>
@@ -74,9 +75,12 @@ class MeasureRegistryImpl {
                                   MeasureDescriptor::Type type);
 
   mutable absl::Mutex mu_;
-  // The registered MeasureDescriptors. Measure id are indexes into this
-  // vector plus some flags in the high bits.
-  std::vector<MeasureDescriptor> registered_descriptors_ GUARDED_BY(mu_);
+  // The registered MeasureDescriptors. Measure ids are indexes into this
+  // vector plus some flags in the high bits. Heap allocated so that the
+  // descriptors themselves don't move around when the vector storage moves due
+  // to resize.
+  std::vector<std::unique_ptr<MeasureDescriptor>> registered_descriptors_
+      GUARDED_BY(mu_);
   // A map from measure names to IDs.
   std::unordered_map<std::string, uint64_t> id_map_ GUARDED_BY(mu_);
 };
@@ -100,7 +104,7 @@ const MeasureDescriptor& MeasureRegistryImpl::GetDescriptor(
         MeasureDescriptor("", "", "", MeasureDescriptor::Type::kDouble);
     return default_descriptor;
   }
-  return registered_descriptors_[IdToIndex(measure.id_)];
+  return *registered_descriptors_[IdToIndex(measure.id_)];
 }
 
 // static

opencensus/stats/internal/measure_registry_test.cc

@@ -147,6 +147,20 @@ TEST(MeasureRegistryTest, GetMeasureByNameWithWrongTypeFails) {
   EXPECT_NE(measure_int.GetDescriptor(), measure_int_mistyped.GetDescriptor());
 }
 
+TEST(MeasureRegistryTest, GrowDescriptorVector) {
+  const std::string name = MakeUniqueName();
+  ASSERT_TRUE(MeasureDouble::Register(name, "desc", "units").IsValid());
+  const MeasureDescriptor& md = MeasureRegistry::GetDescriptorByName(name);
+
+  // Add descriptors until the vector of descriptors grows, moves, and
+  // invalidates md above.
+  for (int i = 0; i < 1000; ++i) {
+    EXPECT_EQ(MeasureDescriptor::Type::kDouble, md.type());
+    ASSERT_TRUE(
+        MeasureDouble::Register(MakeUniqueName(), "desc", "units").IsValid());
+  }
+}
+
 }  // namespace
 }  // namespace stats
 }  // namespace opencensus