Incorporate C++ Buffer management and Seal global threadpool fix from arrow (#1950)

thirdparty/scripts/build_arrow.sh

@@ -44,14 +44,10 @@ if [[ ! -d $TP_DIR/../python/ray/pyarrow_files/pyarrow ]]; then
 
     pushd $TP_DIR/build/arrow
     git fetch origin master
-    # The PR for this commit is https://github.com/apache/arrow/pull/1874. We
+    # The PR for this commit is https://github.com/apache/arrow/pull/1939. We
     # include the link here to make it easier to find the right commit because
     # Arrow often rewrites git history and invalidates certain commits.
-    git checkout 0f87c12d45250ee763ac8c43b7e57e8f06a0b9f3
-
-    # Revert https://github.com/apache/arrow/pull/1807, which unfortunately
-    # introduces the issue in https://issues.apache.org/jira/browse/ARROW-2448.
-    git revert --no-commit cf396867df6f1f93948c69ce10ceb0f95e399242
+    git checkout 5f9cf9c96709f92e9ac4828cf3e106a165576ce7
 
     cd cpp
     if [ ! -d "build" ]; then

thirdparty/scripts/build_flatbuffers.sh

@@ -7,7 +7,7 @@ set -e
 
 TP_DIR=$(cd "$(dirname "${BASH_SOURCE:-$0}")"; pwd)/../
 
-FLATBUFFERS_VERSION=1.7.1
+FLATBUFFERS_VERSION=1.9.0
 
 # Download and compile flatbuffers if it isn't already present.
 if [ ! -d $TP_DIR/pkg/flatbuffers ]; then
@@ -20,6 +20,7 @@ if [ ! -d $TP_DIR/pkg/flatbuffers ]; then
   # Compile flatbuffers.
   pushd flatbuffers-$FLATBUFFERS_VERSION
     cmake -DCMAKE_CXX_FLAGS=-fPIC \
+          -DCMAKE_BUILD_TYPE=Release \
           -DCMAKE_INSTALL_PREFIX:PATH=$TP_DIR/pkg/flatbuffers \
           -DFLATBUFFERS_BUILD_TESTS=OFF
     make -j5