arrow git commit: ARROW-360: C++: Add method to shrink PoolBuffer using realloc

[we...@apache.org]

Repository: arrow
Updated Branches:
  refs/heads/master 74685f386 -> 7d1f1cf91


ARROW-360: C++: Add method to shrink PoolBuffer using realloc

Added no explicit unit test for this as I want to keep the freedom to
the allocator in the future to advise the PoolBuffer on an acceptable
minimal size. In some cases it might be worth it to occupy a whole
page.

Resizing to a smaller size is tested though, so we already have a unit test ensuring that this code runs smoothly.

Author: Uwe L. Korn <uw...@xhochy.com>

Closes #272 from xhochy/ARROW-360 and squashes the following commits:

f4992ee [Uwe L. Korn] Adjust DCHECK for zero size arrays
040d3b4 [Uwe L. Korn] ARROW-360: C++: Add method to shrink PoolBuffer using realloc


Project: http://git-wip-us.apache.org/repos/asf/arrow/repo
Commit: http://git-wip-us.apache.org/repos/asf/arrow/commit/7d1f1cf9
Tree: http://git-wip-us.apache.org/repos/asf/arrow/tree/7d1f1cf9
Diff: http://git-wip-us.apache.org/repos/asf/arrow/diff/7d1f1cf9

Branch: refs/heads/master
Commit: 7d1f1cf91b798259de18ebd772b213e12a6dd194
Parents: 74685f3
Author: Uwe L. Korn <uw...@xhochy.com>
Authored: Sat Jan 7 16:16:31 2017 -0500
Committer: Wes McKinney <we...@twosigma.com>
Committed: Sat Jan 7 16:16:31 2017 -0500

----------------------------------------------------------------------
 cpp/src/arrow/buffer.cc   | 20 +++++++++++++++++++-
 cpp/src/arrow/test-util.h |  2 +-
 2 files changed, 20 insertions(+), 2 deletions(-)
----------------------------------------------------------------------


http://git-wip-us.apache.org/repos/asf/arrow/blob/7d1f1cf9/cpp/src/arrow/buffer.cc
----------------------------------------------------------------------
diff --git a/cpp/src/arrow/buffer.cc b/cpp/src/arrow/buffer.cc
index 6d55f88..2e64ffd 100644
--- a/cpp/src/arrow/buffer.cc
+++ b/cpp/src/arrow/buffer.cc
@@ -92,7 +92,25 @@ Status PoolBuffer::Reserve(int64_t new_capacity) {
 }
 
 Status PoolBuffer::Resize(int64_t new_size) {
-  RETURN_NOT_OK(Reserve(new_size));
+  if (new_size > size_) {
+    RETURN_NOT_OK(Reserve(new_size));
+  } else {
+    // Buffer is not growing, so shrink to the requested size without
+    // excess space.
+    if (capacity_ != new_size) {
+      // Buffer hasn't got yet the requested size.
+      if (new_size == 0) {
+        pool_->Free(mutable_data_, capacity_);
+        capacity_ = 0;
+        mutable_data_ = nullptr;
+        data_ = nullptr;
+      } else {
+        RETURN_NOT_OK(pool_->Reallocate(capacity_, new_size, &mutable_data_));
+        data_ = mutable_data_;
+        capacity_ = new_size;
+      }
+    }
+  }
   size_ = new_size;
   return Status::OK();
 }

http://git-wip-us.apache.org/repos/asf/arrow/blob/7d1f1cf9/cpp/src/arrow/test-util.h
----------------------------------------------------------------------
diff --git a/cpp/src/arrow/test-util.h b/cpp/src/arrow/test-util.h
index e595749..f2da824 100644
--- a/cpp/src/arrow/test-util.h
+++ b/cpp/src/arrow/test-util.h
@@ -184,7 +184,7 @@ static inline void random_ascii(int n, uint32_t seed, uint8_t* out) {
 
 template <typename T>
 void rand_uniform_int(int n, uint32_t seed, T min_value, T max_value, T* out) {
-  DCHECK(out);
+  DCHECK(out || (n == 0));
   std::mt19937 gen(seed);
   std::uniform_int_distribution<T> d(min_value, max_value);
   for (int i = 0; i < n; ++i) {