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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#include <boost/optional.hpp>
#include <cstddef>
namespace mongo {
/**
* Provides access to the current stack bounds and remaining
* available stack space.
*
* To use one, create it on the stack, like this:
*
* // Construct a new locator
* const StackLocator locator;
*
* // Get the start of the stack
* auto b = locator.begin();
*
* // Get the end of the stack
* auto e = locator.end();
*
* // Get the remaining space after 'locator' on the stack.
* auto avail = locator.available();
*/
class StackLocator {
public:
/**
* Constructs a new StackLocator. The locator must have automatic
* storage duration or the behavior is undefined.
*/
StackLocator();
/**
* Returns the address of the beginning of the stack, or nullptr
* if this cannot be done. Beginning here means those addresses
* that represent values of automatic duration found earlier in
* the call chain. Returns nullptr if the beginning of the stack
* could not be found.
*/
void* begin() const {
return _begin;
}
/**
* Returns the address of the end of the stack, or nullptr if
* this cannot be done. End here means those addresses that
* represent values of automatic duration allocated deeper in the
* call chain. Returns nullptr if the end of the stack could not
* be found.
*/
void* end() const {
return _end;
}
/**
* Returns the apparent size of the stack. Returns a disengaged
* optional if the size of the stack could not be determined.
*/
boost::optional<size_t> size() const;
/**
* Returns the remaining stack available after the location of
* this StackLocator. Obviously, the StackLocator must have been
* constructed on the stack. Calling 'available' on a heap
* allocated StackAllocator will have undefined behavior. Returns
* a disengaged optional if the remaining stack cannot be
* determined.
*/
boost::optional<std::size_t> available() const;
private:
void* _begin = nullptr;
void* _end = nullptr;
};
} // namespace mongo
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