pitrou commented on a change in pull request #11206:
URL: https://github.com/apache/arrow/pull/11206#discussion_r718264548
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File path: ci/docker/debian-10-go-cgo.dockerfile
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@@ -0,0 +1,34 @@
+# Licensed to the Apache Software Foundation (ASF) under one
Review comment:
Why do we need this in addition to the existing
`debian-10-go-cgo-python` dockerfile?
##########
File path: go/arrow/memory/cgo_allocator.go
##########
@@ -0,0 +1,108 @@
+// 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.
+
+// +build cgo
+// +build ccalloc
+
+package memory
+
+import (
+ "runtime"
+
+ cga "github.com/apache/arrow/go/arrow/memory/internal/cgoalloc"
+)
+
+// CgoArrowAllocator is an allocator which exposes the C++ memory pool class
+// from the Arrow C++ Library as an allocator for memory buffers to use in Go.
+// The build tag 'ccalloc' must be used in order to include it as it requires
+// linking against the arrow library.
+//
+// The primary reason to use this would be as an allocator when dealing with
+// exporting data across the cdata interface in order to ensure that the memory
+// is allocated safely on the C side so it can be held on the CGO side beyond
+// the context of a single function call. If the memory in use isn't allocated
+// on the C side, then it is not safe for any pointers to data to be held
outside
+// of Go beyond the context of a single Cgo function call as it will be
invisible
+// to the Go garbage collector and could potentially get moved without being
updated.
Review comment:
I don't understand this comment. In #11220 your `releaseData` function
seems to take care of this correctly (by defining a global container of
exported arrays).
##########
File path: go/arrow/memory/internal/cgoalloc/allocator.cc
##########
@@ -0,0 +1,75 @@
+// 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.
+
+// +build ccalloc
+
+#include "allocator.h"
+#include "arrow/memory_pool.h"
+#include "helpers.h"
+
+struct mem_holder {
+ std::unique_ptr<arrow::MemoryPool> pool;
+ arrow::MemoryPool* current_pool;
Review comment:
Why isn't this a `unique_ptr` as well?
##########
File path: go/arrow/memory/internal/cgoalloc/helpers.h
##########
@@ -0,0 +1,59 @@
+// 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.
+
+#pragma once
+
+#include <cstdint>
+#include <memory>
+
+// helper functions to be included by C++ code for interacting with Cgo
+
+// create_ref will construct a shared_ptr on the heap and return a pointer
+// to it. the returned uintptr_t can then be used with retrieve_instance
+// to get back the shared_ptr and object it refers to. This ensures that
+// the object outlives the exported function so that Go can use it.
+template <typename T>
+uintptr_t create_ref(std::shared_ptr<T> t) {
+ std::shared_ptr<T>* retained_ptr = new std::shared_ptr<T>(t);
+ return reinterpret_cast<uintptr_t>(retained_ptr);
+}
+
+// specialization for shared_ptrs to const objects
Review comment:
I'm curious: `create_ref<const T>` doesn't work by itself?
##########
File path: go/arrow/memory/internal/cgoalloc/allocator.go
##########
@@ -0,0 +1,99 @@
+// 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.
+
+// +build ccalloc
+
+package cgoalloc
+
+// #cgo !windows pkg-config: arrow
+// #cgo CXXFLAGS: -std=c++14
+// #cgo windows LDFLAGS: -larrow
+// #include "allocator.h"
+import "C"
+import (
+ "reflect"
+ "unsafe"
+)
+
+// CGOMemPool is an alias to the typedef'd uintptr from the allocator.h file
+type CGOMemPool = C.ArrowMemoryPool
+
+// CgoPoolAlloc allocates a block of memory of length 'size' using the memory
+// pool that is passed in.
+func CgoPoolAlloc(pool CGOMemPool, size int) []byte {
+ var out *C.uint8_t
+ C.arrow_pool_allocate(pool, C.int64_t(size),
(**C.uint8_t)(unsafe.Pointer(&out)))
+
+ var ret []byte
+ s := (*reflect.SliceHeader)(unsafe.Pointer(&ret))
+ s.Data = uintptr(unsafe.Pointer(out))
+ s.Len = size
+ s.Cap = size
+
+ return ret
+}
+
+// CgoPoolRealloc calls 'reallocate' on the block of memory passed in which
must
+// be a slice that was returned by CgoPoolAlloc or CgoPoolRealloc.
+func CgoPoolRealloc(pool CGOMemPool, size int, b []byte) []byte {
+ oldSize := C.int64_t(len(b))
+ data := (*C.uint8_t)(unsafe.Pointer(&b[0]))
+ C.arrow_pool_reallocate(pool, oldSize, C.int64_t(size), &data)
+
+ var ret []byte
+ s := (*reflect.SliceHeader)(unsafe.Pointer(&ret))
+ s.Data = uintptr(unsafe.Pointer(data))
+ s.Len = size
+ s.Cap = size
+
+ return ret
+}
+
+// CgoPoolFree uses the indicated memory pool to free a block of memory. The
+// slice passed in *must* be a slice which was returned by CgoPoolAlloc or
+// CgoPoolRealloc.
+func CgoPoolFree(pool CGOMemPool, b []byte) {
+ if len(b) == 0 {
Review comment:
I don't see a corresponding condition in `CgoPoolAlloc` and
`CgoPoolRealloc`, won't this leak 0-byte allocated areas?
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