Merge pull request #13676 from markdroth/inlined_vector

Implement InlinedVector independently of absl.

1 files changed, 82 insertions, 2 deletions

diff --git a/src/core/lib/support/vector.h b/src/core/lib/support/vector.h
index 4a7db80676..2f249a5b9e 100644
--- a/src/core/lib/support/vector.h
+++ b/src/core/lib/support/vector.h
@@ -19,13 +19,93 @@
 #ifndef GRPC_CORE_LIB_SUPPORT_VECTOR_H
 #define GRPC_CORE_LIB_SUPPORT_VECTOR_H
 
-#include "absl/container/inlined_vector.h"
+#include <cassert>
+
 #include "src/core/lib/support/memory.h"
 
 namespace grpc_core {
 
+// NOTE: We eventually want to use absl::InlinedVector here.  However,
+// there are currently build problems that prevent us from using absl.
+// In the interim, we define a custom implementation as a place-holder,
+// with the intent to eventually replace this with the absl
+// implementation.
+//
+// This place-holder implementation does not implement the full set of
+// functionality from the absl version; it has just the methods that we
+// currently happen to need in gRPC.  If additional functionality is
+// needed before this gets replaced with the absl version, it can be
+// added, with the following proviso:
+//
+// ANY METHOD ADDED HERE MUST COMPLY WITH THE INTERFACE IN THE absl
+// IMPLEMENTATION!
+//
+// TODO(ctiller, nnoble, roth): Replace this with absl::InlinedVector
+// once we integrate absl into the gRPC build system in a usable way.
 template <typename T, size_t N>
-using InlinedVector = absl::InlinedVector<T, N, Allocator<T>>;
+class InlinedVector {
+ public:
+  InlinedVector() {}
+  ~InlinedVector() {
+    for (size_t i = 0; i < size_ && i < N; ++i) {
+      T& value = *reinterpret_cast<T*>(inline_ + i);
+      value.~T();
+    }
+    if (size_ > N) {  // Avoid subtracting two signed values.
+      for (size_t i = 0; i < size_ - N; ++i) {
+        dynamic_[i].~T();
+      }
+    }
+    gpr_free(dynamic_);
+  }
+
+  // For now, we do not support copying.
+  InlinedVector(const InlinedVector&) = delete;
+  InlinedVector& operator=(const InlinedVector&) = delete;
+
+  T& operator[](size_t offset) {
+    assert(offset < size_);
+    if (offset < N) {
+      return *reinterpret_cast<T*>(inline_ + offset);
+    } else {
+      return dynamic_[offset - N];
+    }
+  }
+
+  template <typename... Args>
+  void emplace_back(Args&&... args) {
+    if (size_ < N) {
+      new (&inline_[size_]) T(std::forward<Args>(args)...);
+    } else {
+      if (size_ - N == dynamic_capacity_) {
+        size_t new_capacity =
+            dynamic_capacity_ == 0 ? 2 : dynamic_capacity_ * 2;
+        T* new_dynamic = static_cast<T*>(gpr_malloc(sizeof(T) * new_capacity));
+        for (size_t i = 0; i < dynamic_capacity_; ++i) {
+          new (&new_dynamic[i]) T(std::move(dynamic_[i]));
+          dynamic_[i].~T();
+        }
+        gpr_free(dynamic_);
+        dynamic_ = new_dynamic;
+        dynamic_capacity_ = new_capacity;
+      }
+      new (&dynamic_[size_ - N]) T(std::forward<Args>(args)...);
+    }
+    ++size_;
+  }
+
+  void push_back(const T& value) { emplace_back(value); }
+
+  void push_back(T&& value) { emplace_back(std::move(value)); }
+
+  size_t size() const { return size_; }
+
+ private:
+  typename std::aligned_storage<sizeof(T)>::type inline_[N];
+  T* dynamic_ = nullptr;
+  size_t size_ = 0;
+  size_t dynamic_capacity_ = 0;
+};
 
 }  // namespace grpc_core