Implement new SkipList

Reviewers: teon.banek, msantl, ipaljak

Reviewed By: teon.banek

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D1787

tests/concurrent/skip_list_insert_competitive.cpp

@@ -0,0 +1,42 @@
+#include <atomic>
+#include <thread>
+#include <vector>
+
+#include <glog/logging.h>
+
+#include "utils/skip_list.hpp"
+
+const int kNumThreads = 8;
+const uint64_t kMaxNum = 10000000;
+
+int main() {
+  utils::SkipList<uint64_t> list;
+
+  std::atomic<uint64_t> success{0};
+
+  std::vector<std::thread> threads;
+  for (int i = 0; i < kNumThreads; ++i) {
+    threads.push_back(std::thread([&list, &success] {
+      for (uint64_t num = 0; num < kMaxNum; ++num) {
+        auto acc = list.access();
+        if (acc.insert(num).second) {
+          success.fetch_add(1, std::memory_order_relaxed);
+        }
+      }
+    }));
+  }
+  for (int i = 0; i < kNumThreads; ++i) {
+    threads[i].join();
+  }
+  CHECK(success == kMaxNum);
+
+  CHECK(list.size() == kMaxNum);
+  for (uint64_t i = 0; i < kMaxNum; ++i) {
+    auto acc = list.access();
+    auto it = acc.find(i);
+    CHECK(it != acc.end());
+    CHECK(*it == i);
+  }
+
+  return 0;
+}