Avoid memset on non-POD types for portability. (#5558)

arangod/Cache/PlainBucket.cpp

@@ -142,7 +142,14 @@ void PlainBucket::evict(CachedValue* value, bool optimizeForInsertion) {
 
 void PlainBucket::clear() {
   TRI_ASSERT(isLocked());
-  memset(this, 0, sizeof(PlainBucket));
+  _state.clear(); // "clear" will keep the lock!
+
+  for (size_t i = 0; i < slotsData; ++i) {
+    _cachedHashes[i] = 0;
+    _cachedData[i] = nullptr;
+  }
+
+  _state.unlock();
 }
 
 void PlainBucket::moveSlot(size_t slot, bool moveToFront) {

arangod/Cache/Table.cpp

@@ -34,6 +34,8 @@ using namespace arangodb::cache;
 const uint32_t Table::minLogSize = 8;
 const uint32_t Table::maxLogSize = 32;
 
+Table::GenericBucket::GenericBucket() : _state{}, _padding{} {}
+
 bool Table::GenericBucket::lock(uint64_t maxTries) {
   return _state.lock(maxTries);
 }
@@ -43,6 +45,16 @@ void Table::GenericBucket::unlock() {
   _state.unlock();
 }
 
+void Table::GenericBucket::clear() {
+  _state.lock(UINT64_MAX, [this]() -> void {
+    _state.clear();
+    for (size_t i = 0; i < paddingSize; i++) {
+      _padding[i] = static_cast<uint8_t>(0);
+    }
+    _state.unlock();
+  });
+}
+
 bool Table::GenericBucket::isMigrated() const {
   TRI_ASSERT(_state.isLocked());
   return _state.isSet(BucketState::Flag::migrated);
@@ -88,7 +100,19 @@ Table::Table(uint32_t logSize)
       _bucketClearer(defaultClearer),
       _slotsTotal(_size),
       _slotsUsed(static_cast<uint64_t>(0)) {
-  memset(_buckets, 0, BUCKET_SIZE * _size);
+  for (size_t i = 0; i < _size; i++) {
+    // use placement new in order to properly initialize the bucket
+    new (_buckets + i) GenericBucket();
+  }
+}
+
+Table::~Table() {
+  for (size_t i = 0; i < _size; i++) {
+    // retrieve pointer to bucket
+    GenericBucket* b = _buckets + i;
+    // call dtor
+    b->~GenericBucket();
+  }
 }
 
 uint64_t Table::allocationSize(uint32_t logSize) {
@@ -102,8 +126,8 @@ uint64_t Table::size() const { return _size; }
 
 uint32_t Table::logSize() const { return _logSize; }
 
-std::pair<void*, Table*> Table::fetchAndLockBucket(
-    uint32_t hash, uint64_t maxTries) {
+std::pair<void*, Table*> Table::fetchAndLockBucket(uint32_t hash,
+                                                   uint64_t maxTries) {
   GenericBucket* bucket = nullptr;
   Table* source = nullptr;
   bool ok = _lock.readLock(maxTries);
@@ -228,14 +252,14 @@ bool Table::isEnabled(uint64_t maxTries) {
 
 bool Table::slotFilled() {
   size_t i = _slotsUsed.fetch_add(1, std::memory_order_acq_rel);
-  return ((static_cast<double>(i + 1) /
-           static_cast<double>(_slotsTotal)) > Table::idealUpperRatio);
+  return ((static_cast<double>(i + 1) / static_cast<double>(_slotsTotal)) >
+          Table::idealUpperRatio);
 }
 
 bool Table::slotEmptied() {
   size_t i = _slotsUsed.fetch_sub(1, std::memory_order_acq_rel);
-  return (((static_cast<double>(i - 1) /
-            static_cast<double>(_slotsTotal)) < Table::idealLowerRatio) &&
+  return (((static_cast<double>(i - 1) / static_cast<double>(_slotsTotal)) <
+           Table::idealLowerRatio) &&
           (_logSize > Table::minLogSize));
 }
 

arangod/Cache/Table.h

@@ -53,9 +53,12 @@ class Table : public std::enable_shared_from_this<Table> {
  private:
   struct GenericBucket {
     BucketState _state;
-    uint8_t _filler[BUCKET_SIZE - sizeof(BucketState)];
+    static constexpr size_t paddingSize = BUCKET_SIZE - sizeof(BucketState);
+    uint8_t _padding[paddingSize];
+    GenericBucket();
     bool lock(uint64_t maxTries);
     void unlock();
+    void clear();
     bool isMigrated() const;
   };
   static_assert(sizeof(GenericBucket) == BUCKET_SIZE,
@@ -87,6 +90,11 @@ class Table : public std::enable_shared_from_this<Table> {
   //////////////////////////////////////////////////////////////////////////////
   explicit Table(uint32_t logSize);
 
+  //////////////////////////////////////////////////////////////////////////////
+  /// @brief Destroy the table
+  //////////////////////////////////////////////////////////////////////////////
+  ~Table();
+
  public:
   //////////////////////////////////////////////////////////////////////////////
   /// @brief Returns the memory usage for a table with specified logSize

arangod/Cache/TransactionalBucket.cpp

@@ -198,7 +198,16 @@ void TransactionalBucket::evict(CachedValue* value, bool optimizeForInsertion) {
 
 void TransactionalBucket::clear() {
   TRI_ASSERT(isLocked());
-  memset(this, 0, sizeof(TransactionalBucket));
+  _state.clear(); // "clear" will keep the lock!
+  for (size_t i = 0; i < slotsBlacklist; ++i) {
+    _blacklistHashes[i] = 0;
+  }
+  _blacklistTerm = 0;
+  for (size_t i = 0; i < slotsData; ++i) {
+    _cachedHashes[i] = 0;
+    _cachedData[i] = nullptr;
+  }
+  _state.unlock();
 }
 
 void TransactionalBucket::updateBlacklistTerm(uint64_t term) {