ARROW-13238: [C++][Compute][Dataset] Use an ExecPlan for dataset scans

cpp/src/arrow/compute/exec.cc

@@ -987,8 +987,9 @@ std::unique_ptr<KernelExecutor> KernelExecutor::MakeScalarAggregate() {
 
 }  // namespace detail
 
-ExecContext::ExecContext(MemoryPool* pool, FunctionRegistry* func_registry)
-    : pool_(pool) {
+ExecContext::ExecContext(MemoryPool* pool, ::arrow::internal::Executor* executor,
+                         FunctionRegistry* func_registry)
+    : pool_(pool), executor_(executor) {
   this->func_registry_ = func_registry == nullptr ? GetFunctionRegistry() : func_registry;
 }
 

cpp/src/arrow/compute/exec.h

@@ -34,6 +34,7 @@
 #include "arrow/result.h"
 #include "arrow/type_fwd.h"
 #include "arrow/util/macros.h"
+#include "arrow/util/type_fwd.h"
 #include "arrow/util/visibility.h"
 
 namespace arrow {
@@ -60,6 +61,7 @@ class ARROW_EXPORT ExecContext {
  public:
   // If no function registry passed, the default is used.
   explicit ExecContext(MemoryPool* pool = default_memory_pool(),
+                       ::arrow::internal::Executor* executor = NULLPTR,
                        FunctionRegistry* func_registry = NULLPTR);
 
   /// \brief The MemoryPool used for allocations, default is
@@ -68,6 +70,9 @@ class ARROW_EXPORT ExecContext {
 
   ::arrow::internal::CpuInfo* cpu_info() const;
 
+  /// \brief An Executor which may be used to parallelize execution.
+  ::arrow::internal::Executor* executor() const { return executor_; }
+
   /// \brief The FunctionRegistry for looking up functions by name and
   /// selecting kernels for execution. Defaults to the library-global function
   /// registry provided by GetFunctionRegistry.
@@ -114,6 +119,7 @@ class ARROW_EXPORT ExecContext {
 
  private:
   MemoryPool* pool_;
+  ::arrow::internal::Executor* executor_;
   FunctionRegistry* func_registry_;
   int64_t exec_chunksize_ = std::numeric_limits<int64_t>::max();
   bool preallocate_contiguous_ = true;