From b1101d64fcc5243106a879fc5e7e6e2e633f70c8 Mon Sep 17 00:00:00 2001
From: Nikolay Igotti <nikolay.igotti@jetbrains.com>
Date: Fri, 16 Sep 2016 16:05:32 +0300
Subject: [PATCH] Add simple explicit placer in C++.

---
 experiments/placer/Makefile  |  16 +++++
 experiments/placer/placer.cc | 122 +++++++++++++++++++++++++++++++++++
 2 files changed, 138 insertions(+)
 create mode 100644 experiments/placer/Makefile
 create mode 100644 experiments/placer/placer.cc

diff --git a/experiments/placer/Makefile b/experiments/placer/Makefile
new file mode 100644
index 00000000000..681bf6c346f
--- /dev/null
+++ b/experiments/placer/Makefile
@@ -0,0 +1,16 @@
+CXX = g++
+CXXFLAGS = -std=c++11 -g2 -Wall -Werror
+
+all: placer
+
+run: placer
+	./placer
+
+clean:
+	rm -f *.o placer
+
+placer: placer.o
+	$(CXX)  $(CXXFLAGS) -o $@ $<
+
+placer.o: placer.cc
+	$(CXX) $(CXXFLAGS) -c $<
diff --git a/experiments/placer/placer.cc b/experiments/placer/placer.cc
new file mode 100644
index 00000000000..ceb7f14fcd9
--- /dev/null
+++ b/experiments/placer/placer.cc
@@ -0,0 +1,122 @@
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <cassert>
+
+struct Container {
+  uint8_t* data_;
+  uint8_t* current_;
+  int size_;
+  int ref_count_;
+
+  Container(int size)
+    : size_(size), ref_count_(1) {
+    data_ = reinterpret_cast<uint8_t*>(calloc(size_, 1));
+    current_ = data_;
+  }
+
+  ~Container() {
+    assert(ref_count_ == 0);
+    free(data_);
+  }
+
+  void* Place(int size) {
+    if (current_ + size > data_ + size_) {
+      return nullptr;
+    }
+    void* result = current_;
+    current_ += size;
+    return result;
+  }
+
+  void AddRef() {
+    if (data_) {
+      ref_count_++;
+    }
+  }
+
+  void Release() {
+    if (data_) {
+      ref_count_--;
+    }
+  }
+
+  void Dispose() {
+    // Destroy container ignoring non-zero refcount. Use with care.
+    ref_count_ = 0;
+    free(data_);
+    data_ = nullptr;
+    current_ = nullptr;
+  }
+};
+
+template <class T>
+struct Ref {
+  T* ref_;
+  Container* container_;
+
+  Ref() : ref_(nullptr), container_(nullptr) {}
+  Ref(const Ref& other) : ref_(nullptr), container_(nullptr) {
+    Assign(other);
+  }
+  Ref(T* ref, Container* container) : ref_(ref), container_(container) {
+    if (container_) {
+      container_->AddRef();
+    }
+  }
+  ~Ref() {
+    if (ref_ && container_) {
+      container_->Release();
+    }
+  }
+  
+  static Ref<T> Alloc(Container* container) {
+    return Ref<T>(reinterpret_cast<T*>(container->Place(sizeof(T))), container);
+  }
+
+  void Assign(const Ref<T>& other) {
+    if (ref_) {
+      container_->Release();
+    }
+    container_ = other.container_;
+    container_->AddRef();
+    ref_ = other.ref_;
+  }
+
+   T* operator->() const {
+     return ref_;
+   }
+  
+  bool null() const { return ref_ == nullptr; } 
+};
+
+struct List {
+  Ref<List> next_;
+  int data_;
+};
+
+void test_placer() {
+  printf("Start placement\n");
+  Container heap(1024);
+  
+  Ref<List> head = Ref<List>::Alloc(&heap);
+  head->data_ = 1;
+  Ref<List> cur = head;
+  for (int i = 0; i < 10; ++i) {
+    cur->next_ = Ref<List>::Alloc(&heap);
+    cur = cur->next_;
+    cur->data_ = i + 2;
+  }
+  cur = head;
+  while (!cur.null()) {
+    printf("next is %d\n", cur->data_);
+    cur = cur->next_;
+  }
+
+  heap.Dispose();
+}
+
+int main() {
+  test_placer();
+}