88 lines
3.3 KiB
C++
88 lines
3.3 KiB
C++
// Copyright 2019 The MediaPipe Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#ifndef MEDIAPIPE_FRAMEWORK_LEGACY_CALCULATOR_SUPPORT_H_
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#define MEDIAPIPE_FRAMEWORK_LEGACY_CALCULATOR_SUPPORT_H_
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#include "mediapipe/framework/calculator_context.h"
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#include "mediapipe/framework/calculator_contract.h"
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namespace mediapipe {
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class LegacyCalculatorSupport {
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public:
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// Scoped is a RAII helper for setting the current CC in the current scope,
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// and unsetting it automatically (restoring the previous value) when
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// leaving the scope.
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//
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// This allows the current CC to be accessed at any point deeper in the
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// call stack of the current thread, until the scope is left. Creating
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// another Scoped instance deeper in the call stack applies to calls branching
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// from that point, and the previous value is restored when execution leaves
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// that scope, as one would expect.
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//
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// This is only meant to be used where backwards compatibility reasons prevent
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// passing the CC directly. Specifically, it can be used to access
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// CalculatorContext and CalculatorContract from legacy calculator code.
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template <class C>
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class Scoped {
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public:
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// The constructor saves the current value of current_ in an instance
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// member, which is then restored by the destructor.
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explicit Scoped(C* cc) {
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saved_ = current_;
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current_ = cc;
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}
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~Scoped() { current_ = saved_; }
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// The current C* for this thread.
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static C* current() { return current_; }
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private:
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// The value to restore after exiting this scope.
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C* saved_;
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// This needs NOLINT because, when included in Objective-C++ files,
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// clang-tidy suggests using an Objective-C naming convention, which is
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// inappropriate. (b/116015736) No category specifier because of b/71698089.
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//
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// ABSL_CONST_INIT triggers b/155992786 with some versions of Clang on Apple
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// platforms.
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#ifndef __APPLE__
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ABSL_CONST_INIT
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#endif // !__APPLE__
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static thread_local C* current_; // NOLINT
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};
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};
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#if !defined(_MSC_VER)
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// We only declare this variable for two specializations of the template because
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// it is only meant to be used for these two types.
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// Note that, since these variables are members of specific template
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// _specializations_, they are not themselves templates, and therefore their
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// definitions must be in the .cc file. However, a declaration still needs to be
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// included in the header, or some compilers will assume they have no
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// definition.
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template <>
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thread_local CalculatorContext*
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LegacyCalculatorSupport::Scoped<CalculatorContext>::current_;
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template <>
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thread_local CalculatorContract*
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LegacyCalculatorSupport::Scoped<CalculatorContract>::current_;
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#endif
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} // namespace mediapipe
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#endif // MEDIAPIPE_FRAMEWORK_LEGACY_CALCULATOR_SUPPORT_H_
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