[GitHub] [arrow] westonpace commented on a diff in pull request #14758: ARROW-18119: [C++] Utility method to ensure an array object meetings an alignment requirement

["westonpace (via GitHub)" <gi...@apache.org>]

westonpace commented on code in PR #14758:
URL: https://github.com/apache/arrow/pull/14758#discussion_r1144027067


##########
cpp/src/arrow/util/align_util.h:
##########
@@ -19,6 +19,7 @@
 
 #include <algorithm>
 
+#include "arrow/memory_pool.h"

Review Comment:
   It must be getting included transitively but we should explicitly include `arrow/type_fwd.h` since we are relying on it with this new code.



##########
cpp/src/arrow/util/align_util.cc:
##########
@@ -0,0 +1,215 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include "arrow/util/align_util.h"
+
+#include "arrow/array.h"
+#include "arrow/chunked_array.h"
+#include "arrow/record_batch.h"
+#include "arrow/table.h"
+
+namespace arrow {
+
+namespace util {
+
+bool CheckAlignment(const Buffer& buffer, const int64_t& alignment) {
+  return buffer.address() % alignment == 0;
+}
+
+bool CheckAlignment(const ArrayData& array, const int64_t& alignment) {
+  for (const auto& buffer : array.buffers) {
+    if (buffer) {
+      if (!CheckAlignment(*buffer, alignment)) return false;
+    }
+  }
+  return true;
+}
+
+bool CheckAlignment(const Array& array, const int64_t& alignment) {
+  bool align_dictionary = true, align_children = true;
+
+  if (array.type()->id() == Type::DICTIONARY) {
+    align_dictionary = CheckAlignment(*array.data()->dictionary, alignment);
+  }
+
+  for (const auto& child : array.data()->child_data) {
+    if (child) {
+      if (!CheckAlignment(*child, alignment)) align_children = false;
+    }
+  }
+  return CheckAlignment(*array.data(), alignment) && align_dictionary && align_children;

Review Comment:
   Why are you checking dictionary and child arrays here instead of in `bool CheckAlignment(const ArrayData& array, const int64_t& alignment)`?



##########
cpp/src/arrow/util/align_util.h:
##########
@@ -63,6 +64,43 @@ inline BitmapWordAlignParams BitmapWordAlign(const uint8_t* data, int64_t bit_of
   p.aligned_start = data + (bit_offset + p.leading_bits) / 8;
   return p;
 }
-
 }  // namespace internal
+
+namespace util {
+
+ARROW_EXPORT bool CheckAlignment(const Buffer& buffer, const int64_t& alignment);
+ARROW_EXPORT bool CheckAlignment(const ArrayData& array, const int64_t& alignment);
+ARROW_EXPORT bool CheckAlignment(const Array& array, const int64_t& alignment);
+ARROW_EXPORT bool CheckAlignment(const ChunkedArray& array, const int64_t& alignment,
+                                 std::vector<bool>& needs_alignment,
+                                 const int& offset = 0);
+ARROW_EXPORT bool CheckAlignment(const RecordBatch& batch, const int64_t& alignment,
+                                 std::vector<bool>& needs_alignment);
+ARROW_EXPORT bool CheckAlignment(const Table& table, const int64_t& alignment,
+                                 std::vector<bool>& needs_alignment);

Review Comment:
   These methods will need to be documented.  Specifically the `needs_alignment` argument is not obvious.



##########
cpp/src/arrow/util/align_util.cc:
##########
@@ -0,0 +1,215 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include "arrow/util/align_util.h"
+
+#include "arrow/array.h"
+#include "arrow/chunked_array.h"
+#include "arrow/record_batch.h"
+#include "arrow/table.h"
+
+namespace arrow {
+
+namespace util {
+
+bool CheckAlignment(const Buffer& buffer, const int64_t& alignment) {
+  return buffer.address() % alignment == 0;
+}
+
+bool CheckAlignment(const ArrayData& array, const int64_t& alignment) {
+  for (const auto& buffer : array.buffers) {
+    if (buffer) {
+      if (!CheckAlignment(*buffer, alignment)) return false;
+    }
+  }
+  return true;
+}
+
+bool CheckAlignment(const Array& array, const int64_t& alignment) {
+  bool align_dictionary = true, align_children = true;
+
+  if (array.type()->id() == Type::DICTIONARY) {
+    align_dictionary = CheckAlignment(*array.data()->dictionary, alignment);
+  }
+
+  for (const auto& child : array.data()->child_data) {
+    if (child) {
+      if (!CheckAlignment(*child, alignment)) align_children = false;
+    }
+  }
+  return CheckAlignment(*array.data(), alignment) && align_dictionary && align_children;
+}
+
+bool CheckAlignment(const ChunkedArray& array, const int64_t& alignment,
+                    std::vector<bool>& needs_alignment, const int& offset) {
+  needs_alignment.resize(needs_alignment.size() + array.num_chunks(), false);
+  for (auto i = 0; i < array.num_chunks(); ++i) {
+    if (array.chunk(i) && !CheckAlignment(*array.chunk(i), alignment))
+      needs_alignment[i + offset] = true;
+  }
+  return std::find(needs_alignment.begin() + offset,

Review Comment:
   Instead of doing `std::find` at the end (which will loop through `needs_alignment`) could you do something like...
   
   ```
   bool at_least_one_needs_alignment = false;
   for (...) {
     if (...) {
       needs_alignment[i + offset] = true;
       at_least_one_needs_alignment = true;
     }
   }
   return at_least_one_needs_alignment;
   ```



##########
cpp/src/arrow/util/align_util_test.cc:
##########
@@ -145,6 +150,84 @@ TEST(BitmapWordAlign, UnalignedDataStart) {
   CheckBitmapWordAlign<8>(P, 1017, 64, {63, 1, 1080, A, 0, 0});
   CheckBitmapWordAlign<8>(P, 1017, 128, {63, 1, 1144, A + 128, 64, 1});
 }
-
 }  // namespace internal
+
+TEST(EnsureAlignment, Array) {
+  MemoryPool* pool = default_memory_pool();
+  auto rand = ::arrow::random::RandomArrayGenerator(1923);
+  auto random_array = rand.UInt8(/*size*/ 50, /*min*/ 0, /*max*/ 100,
+                                 /*null_probability*/ 0, /*alignment*/ 512, pool);
+  ASSERT_OK_AND_ASSIGN(auto aligned_array,

Review Comment:
   Maybe assert that `CheckAlignment(..., 1024)` returns `false` before you call `EnsureAlignment`?



##########
cpp/src/arrow/util/align_util.h:
##########
@@ -63,6 +64,43 @@ inline BitmapWordAlignParams BitmapWordAlign(const uint8_t* data, int64_t bit_of
   p.aligned_start = data + (bit_offset + p.leading_bits) / 8;
   return p;
 }
-
 }  // namespace internal
+
+namespace util {
+
+ARROW_EXPORT bool CheckAlignment(const Buffer& buffer, const int64_t& alignment);
+ARROW_EXPORT bool CheckAlignment(const ArrayData& array, const int64_t& alignment);
+ARROW_EXPORT bool CheckAlignment(const Array& array, const int64_t& alignment);
+ARROW_EXPORT bool CheckAlignment(const ChunkedArray& array, const int64_t& alignment,
+                                 std::vector<bool>& needs_alignment,
+                                 const int& offset = 0);

Review Comment:
   ```suggestion
   ARROW_EXPORT bool CheckAlignment(const ChunkedArray& array, const int64_t& alignment,
                                    std::vector<bool>* needs_alignment,
                                    const int& offset = 0);
   ```
   This works but the Arrow style guidelines prefer passing mutable parameters by pointer instead of mutable reference.
   
   For example:
   
   ```
   void Foo(int & value);
   void Bar(int * value);
   
   int x = 7;
   Foo(x); // BAD: not obvious that `x` is being modified
   Bar(&x); // GOOD: the `&` helps us know that `x` is being modified
   ```



##########
cpp/src/arrow/util/align_util.cc:
##########
@@ -0,0 +1,215 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include "arrow/util/align_util.h"
+
+#include "arrow/array.h"
+#include "arrow/chunked_array.h"
+#include "arrow/record_batch.h"
+#include "arrow/table.h"
+
+namespace arrow {
+
+namespace util {
+
+bool CheckAlignment(const Buffer& buffer, const int64_t& alignment) {
+  return buffer.address() % alignment == 0;
+}
+
+bool CheckAlignment(const ArrayData& array, const int64_t& alignment) {
+  for (const auto& buffer : array.buffers) {
+    if (buffer) {
+      if (!CheckAlignment(*buffer, alignment)) return false;
+    }
+  }
+  return true;
+}
+
+bool CheckAlignment(const Array& array, const int64_t& alignment) {
+  bool align_dictionary = true, align_children = true;
+
+  if (array.type()->id() == Type::DICTIONARY) {
+    align_dictionary = CheckAlignment(*array.data()->dictionary, alignment);
+  }
+
+  for (const auto& child : array.data()->child_data) {
+    if (child) {
+      if (!CheckAlignment(*child, alignment)) align_children = false;

Review Comment:
   Could you just return false here and break out of the loop early?



##########
cpp/src/arrow/util/align_util.h:
##########
@@ -63,6 +64,43 @@ inline BitmapWordAlignParams BitmapWordAlign(const uint8_t* data, int64_t bit_of
   p.aligned_start = data + (bit_offset + p.leading_bits) / 8;
   return p;
 }
-
 }  // namespace internal
+
+namespace util {
+
+ARROW_EXPORT bool CheckAlignment(const Buffer& buffer, const int64_t& alignment);

Review Comment:
   ```suggestion
   ARROW_EXPORT bool CheckAlignment(const Buffer& buffer, int64_t alignment);
   ```
   Passing `int64_t` by const reference is not a good idea. Primitive / simple types should be passed by value (here and in all the other functions)



##########
cpp/src/arrow/util/align_util.cc:
##########
@@ -0,0 +1,215 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include "arrow/util/align_util.h"
+
+#include "arrow/array.h"
+#include "arrow/chunked_array.h"
+#include "arrow/record_batch.h"
+#include "arrow/table.h"
+
+namespace arrow {
+
+namespace util {
+
+bool CheckAlignment(const Buffer& buffer, const int64_t& alignment) {
+  return buffer.address() % alignment == 0;
+}
+
+bool CheckAlignment(const ArrayData& array, const int64_t& alignment) {
+  for (const auto& buffer : array.buffers) {
+    if (buffer) {
+      if (!CheckAlignment(*buffer, alignment)) return false;
+    }
+  }
+  return true;
+}
+
+bool CheckAlignment(const Array& array, const int64_t& alignment) {
+  bool align_dictionary = true, align_children = true;
+
+  if (array.type()->id() == Type::DICTIONARY) {
+    align_dictionary = CheckAlignment(*array.data()->dictionary, alignment);
+  }
+
+  for (const auto& child : array.data()->child_data) {
+    if (child) {
+      if (!CheckAlignment(*child, alignment)) align_children = false;
+    }
+  }
+  return CheckAlignment(*array.data(), alignment) && align_dictionary && align_children;
+}
+
+bool CheckAlignment(const ChunkedArray& array, const int64_t& alignment,
+                    std::vector<bool>& needs_alignment, const int& offset) {
+  needs_alignment.resize(needs_alignment.size() + array.num_chunks(), false);

Review Comment:
   Why `needs_alignment.size() + array.num_chunks()` and not `offset + array.num_chunks()`?



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