From 92884b48bacb8cc40d16cf514a9b029f4fdd474f Mon Sep 17 00:00:00 2001
From: tatiana-yan <tatiana.kondakova@gmail.com>
Date: Fri, 7 Feb 2020 14:52:02 +0300
Subject: [PATCH] [coding] Add threadsafe get to MapUint32ToValue.

---
 .../coding_tests/map_uint32_to_val_tests.cpp  |  2 +
 coding/map_uint32_to_val.hpp                  | 57 ++++++++++++++-----
 2 files changed, 45 insertions(+), 14 deletions(-)

diff --git a/coding/coding_tests/map_uint32_to_val_tests.cpp b/coding/coding_tests/map_uint32_to_val_tests.cpp
index 0066b602e3..adf9ec1c2e 100644
--- a/coding/coding_tests/map_uint32_to_val_tests.cpp
+++ b/coding/coding_tests/map_uint32_to_val_tests.cpp
@@ -55,6 +55,8 @@ UNIT_TEST(MapUint32ValTest)
       uint32_t res;
       TEST(table->Get(d.first, res), ());
       TEST_EQUAL(res, d.second, ());
+      TEST(table->GetThreadsafe(d.first, res), ());
+      TEST_EQUAL(res, d.second, ());
     }
   }
 }
diff --git a/coding/map_uint32_to_val.hpp b/coding/map_uint32_to_val.hpp
index 3e7c9f818c..f719bc2e23 100644
--- a/coding/map_uint32_to_val.hpp
+++ b/coding/map_uint32_to_val.hpp
@@ -65,7 +65,10 @@
 // exception of the last one) is a sequence of kBlockSize variables
 // encoded by block encoding callback.
 //
-// On Get call kBlockSize consecutive variables are decoded and cached in RAM.
+// On Get call kBlockSize consecutive variables are decoded and cached in RAM. Get is not
+// threadsafe.
+//
+// GetThreadsafe does not use cache.
 
 template <typename Value>
 class MapUint32ToValue
@@ -162,23 +165,23 @@ public:
 
     auto & entry = m_cache[base];
     if (entry.empty())
-    {
-      entry.resize(kBlockSize);
+      entry = GetImpl(id);
 
-      auto const start = m_offsets.select(base);
-      auto const end = base + 1 < m_offsets.num_ones()
-                           ? m_offsets.select(base + 1)
-                           : m_header.m_endOffset - m_header.m_variablesOffset;
+    value = entry[offset];
+    return true;
+  }
 
-      std::vector<uint8_t> data(static_cast<size_t>(end - start));
+  // Tries to get |value| for key identified by |id|.  Returns
+  // false if table does not have entry for this id.
+  WARN_UNUSED_RESULT bool GetThreadsafe(uint32_t id, Value & value) const
+  {
+    if (id >= m_ids.size() || !m_ids[id])
+      return false;
 
-      m_reader.Read(m_header.m_variablesOffset + start, data.data(), data.size());
+    uint32_t const rank = static_cast<uint32_t>(m_ids.rank(id));
+    uint32_t const offset = rank % kBlockSize;
 
-      MemReader mreader(data.data(), data.size());
-      NonOwningReaderSource msource(mreader);
-
-      m_readBlockCallback(msource, kBlockSize, entry);
-    }
+    auto const entry = GetImpl(id);
 
     value = entry[offset];
     return true;
@@ -219,6 +222,32 @@ public:
   uint64_t Count() const { return m_ids.num_ones(); }
 
 private:
+  std::vector<Value> GetImpl(uint32_t id) const
+  {
+    ASSERT_LESS(id, m_ids.size(), ());
+    ASSERT(m_ids[id], ());
+
+    uint32_t const rank = static_cast<uint32_t>(m_ids.rank(id));
+    uint32_t const base = rank / kBlockSize;
+
+    std::vector<Value> values(kBlockSize);
+
+    auto const start = m_offsets.select(base);
+    auto const end = base + 1 < m_offsets.num_ones()
+                         ? m_offsets.select(base + 1)
+                         : m_header.m_endOffset - m_header.m_variablesOffset;
+
+    std::vector<uint8_t> data(static_cast<size_t>(end - start));
+
+    m_reader.Read(m_header.m_variablesOffset + start, data.data(), data.size());
+
+    MemReader mreader(data.data(), data.size());
+    NonOwningReaderSource msource(mreader);
+
+    m_readBlockCallback(msource, kBlockSize, values);
+    return values;
+  }
+
   bool Init()
   {
     m_header.Read(m_reader);