55 lines
2.2 KiB
C
55 lines
2.2 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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//
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// OBJC_LINTER
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// TODO: check license. This was forked from an internal header.
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/**
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* __WEAKNAME_ is a private macro used to generate a local variable name related
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* to the argument variable name. This generated local variable name is
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* intentionally stable across multiple invocations.
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*/
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#define __WEAKNAME_(variable) variable##_weak_
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/**
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* WEAKIFY defines a new local variable that is a weak reference to the argument
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* variable.
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*
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* This macro is generally used to capture a weak reference to be captured by an
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* Objective-C block to avoid unintentionally extending an object's lifetime or
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* avoid causing a retain cycle.
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*
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* The new local variable's name will be based on the name of the target
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* variable and is stable across multiple invocations of WEAKIFY. In general,
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* you should not need to invoke WEAKIFY multiple times on the same variable.
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*/
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#define WEAKIFY(variable) \
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__weak __typeof__(variable) __WEAKNAME_(variable) = (variable)
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/**
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* STRONGIFY defines a new shadow local variable with the same name as the
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* argument variable and initialize it with a resolved weak reference based on a
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* weak reference created previously using the WEAKIFY macro.
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*
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* @note:
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* This macro must be called within each block scope to prevent nested blocks
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* from capturing a strong reference from an outer block.
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*/
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#define STRONGIFY(variable) \
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_Pragma("clang diagnostic push") \
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_Pragma("clang diagnostic ignored \"-Wshadow\"") \
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__strong __typeof__(variable) variable = \
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__WEAKNAME_(variable) _Pragma("clang diagnostic pop")
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