fix: Reduce lock cost in AsciiInfo updates (#12363)

Summary:
Pull Request resolved: #12363

In some cases (e.g. row-wise deserialization) we need to resize the
string vector frequently.  In that case none of the ASCII info is valid, but we
still pay the price to lock and check the state.  Fix the cost by using an
atomic boolean for fast path check.

Reviewed By: kevinwilfong

Differential Revision: D69750090

fbshipit-source-id: c930fb10ed0c2a38fcbd1bb9a55bde39fe65cbfe

velox/vector/SimpleVector.h

@@ -57,6 +57,14 @@ struct AsciiInfo {
     isAllAscii_ = f;
   }
 
+  bool asciiComputedRowsEmpty() const {
+    return asciiComputedRowsEmpty_;
+  }
+
+  void setAsciiComputedRowsEmpty(bool value) {
+    asciiComputedRowsEmpty_ = value;
+  }
+
   /// Returns locked for read bit vector with bits set for rows where ascii was
   /// processed.
   auto readLockedAsciiComputedRows() const {
@@ -69,12 +77,6 @@ struct AsciiInfo {
     return asciiComputedRows_.wlock();
   }
 
-  /// Returns upgradable locked bit vector with bits set for rows where ascii
-  /// was processed.
-  auto upgradableLockedAsciiComputedRows() {
-    return asciiComputedRows_.ulock();
-  }
-
  private:
   // isAllAscii_ and asciiComputedRows_ are thread-safe because input vectors
   // can be shared across threads, hence this make their mutation thread safe.
@@ -84,6 +86,8 @@ struct AsciiInfo {
   // True is all strings in asciiComputedRows_ are ASCII.
   std::atomic_bool isAllAscii_{false};
 
+  std::atomic_bool asciiComputedRowsEmpty_{true};
+
   // If T is StringView, store set of rows where we have computed asciiness.
   // A set bit means the row was processed.
   folly::Synchronized<SelectivityVector> asciiComputedRows_;
@@ -341,14 +345,21 @@ class SimpleVector : public BaseVector {
     }
 
     wlockedAsciiComputedRows->select(rows);
+    asciiInfo.setAsciiComputedRowsEmpty(
+        !wlockedAsciiComputedRows->hasSelections());
     return asciiInfo.isAllAscii();
   }
 
   /// Clears asciiness state.
   template <typename U = T>
   typename std::enable_if_t<std::is_same_v<U, StringView>, void>
   invalidateIsAscii() {
-    asciiInfo.writeLockedAsciiComputedRows()->clearAll();
+    if (asciiInfo.asciiComputedRowsEmpty()) {
+      return;
+    }
+    auto wlock = asciiInfo.writeLockedAsciiComputedRows();
+    wlock->clearAll();
+    asciiInfo.setAsciiComputedRowsEmpty(true);
     asciiInfo.setIsAllAscii(false);
   }
 
@@ -367,14 +378,18 @@ class SimpleVector : public BaseVector {
     }
 
     wlockedAsciiComputedRows->select(rows);
+    asciiInfo.setAsciiComputedRowsEmpty(
+        !wlockedAsciiComputedRows->hasSelections());
   }
 
   template <typename U = T>
   typename std::enable_if_t<std::is_same_v<U, StringView>, void> setAllIsAscii(
       bool ascii) {
     ensureIsAsciiCapacity();
+    auto wlock = asciiInfo.writeLockedAsciiComputedRows();
+    wlock->setAll();
     asciiInfo.setIsAllAscii(ascii);
-    asciiInfo.writeLockedAsciiComputedRows()->setAll();
+    asciiInfo.setAsciiComputedRowsEmpty(!wlock->hasSelections());
   }
 
   template <typename U = T>
@@ -438,26 +453,40 @@ class SimpleVector : public BaseVector {
   template <typename U = T>
   typename std::enable_if_t<std::is_same_v<U, StringView>, void>
   ensureIsAsciiCapacity() {
-    auto ulockedAsciiComputedRows{
-        asciiInfo.upgradableLockedAsciiComputedRows()};
-    if (ulockedAsciiComputedRows->size() < length_) {
-      ulockedAsciiComputedRows.moveFromUpgradeToWrite()->resize(length_, false);
+    {
+      auto rlock = asciiInfo.readLockedAsciiComputedRows();
+      if (rlock->size() >= length_) {
+        return;
+      }
     }
+    auto wlock = asciiInfo.writeLockedAsciiComputedRows();
+    if (wlock->size() >= length_) {
+      return;
+    }
+    wlock->resize(length_, false);
+    asciiInfo.setAsciiComputedRowsEmpty(!wlock->hasSelections());
   }
 
   /// Ensure asciiInfo is of the correct size. But only if it is not empty.
   template <typename U = T>
   typename std::enable_if_t<std::is_same_v<U, StringView>, void>
   resizeIsAsciiIfNotEmpty(vector_size_t size, bool newAscii) {
-    auto ulockedAsciiComputedRows{
-        asciiInfo.upgradableLockedAsciiComputedRows()};
-    if (ulockedAsciiComputedRows->hasSelections()) {
-      if (ulockedAsciiComputedRows->size() < size) {
-        ulockedAsciiComputedRows.moveFromUpgradeToWrite()->resize(
-            size, newAscii);
-        asciiInfo.setIsAllAscii(asciiInfo.isAllAscii() & newAscii);
+    if (asciiInfo.asciiComputedRowsEmpty()) {
+      return;
+    }
+    {
+      auto rlock = asciiInfo.readLockedAsciiComputedRows();
+      if (!rlock->hasSelections() || rlock->size() >= size) {
+        return;
       }
     }
+    auto wlock = asciiInfo.writeLockedAsciiComputedRows();
+    if (!wlock->hasSelections() || wlock->size() >= size) {
+      return;
+    }
+    wlock->resize(size, newAscii);
+    asciiInfo.setIsAllAscii(asciiInfo.isAllAscii() & newAscii);
+    asciiInfo.setAsciiComputedRowsEmpty(!wlock->hasSelections());
   }
 
   /**
@@ -493,7 +522,9 @@ class SimpleVector : public BaseVector {
 
     if constexpr (std::is_same_v<T, StringView>) {
       if (rows) {
-        asciiInfo.writeLockedAsciiComputedRows()->deselect(*rows);
+        auto wlock = asciiInfo.writeLockedAsciiComputedRows();
+        wlock->deselect(*rows);
+        asciiInfo.setAsciiComputedRowsEmpty(!wlock->hasSelections());
       } else {
         invalidateIsAscii();
       }