我正在尝试使用此处概述的方法将 C++ 类包装在 matlab mex 包装器中。基本上，我有一个初始化 mex 文件，它返回一个 C++ 对象句柄：
handle = myclass_init()
然后我可以将它传递给另一个myclass_amethod使用句柄调用类方法的 mex 文件（例如），然后最终myclass_delete释放 C++ 对象：
retval = myclass_amethod(handle, parameter)
myclass_delete(handle)
为了便于使用，我将其封装在一个 MATLAB 类中：
classdef myclass < handle
properties(SetAccess=protected)
cpp_handle_
end
methods
% class constructor
function obj = myclass()
obj.cpp_handle_ = myclass_init();
end
% class destructor
function delete(obj)
myclass_delete(obj.cpp_handle_);
end
% class method
function amethod(parameter)
myclass_amethod(obj.cpp_handle_, parameter);
end
end
end
问题：这在并行代码中不起作用
这在非并行代码中运行良好。但是，一旦我从内部调用它parfor：
cls = myclass();
parfor i = 1:10
cls.amethod(i)
end
我得到一个段错误，因为类的副本是在parfor循环中（在每个工作人员中）制作的，但是由于每个工作人员都是一个单独的进程，所以 C++ 对象实例没有被复制，导致指针无效。
我最初尝试检测每个类方法何时在 parfor 循环中运行，并且在这些情况下也重新分配 C++ 对象。但是，由于无法检查对象是否已分配给当前工作人员，这会导致多次重新分配，然后仅删除一次（当工作人员退出时）导致内存泄漏（请参阅底部的附录详情提问）。
尝试的解决方案：复制构造函数并使用matlab.mixin.Copyable
在 C++ 中，处理这种情况的方法是复制构造函数（这样 C++ 对象只会在复制包装 MATLAB 类时重新分配一次）。快速搜索一下matlab.mixin.Copyable类类型，它似乎提供了所需的功能（即 MATLAB 句柄类的深层副本）。因此，我尝试了以下方法：
classdef myclass < matlab.mixin.Copyable
properties(SetAccess=protected)
cpp_handle_
end
methods
function obj = myclass(val)
if nargin < 1
% regular constructor
obj.cpp_handle_ = rand(1);
disp(['Initialized myclass with handle: ' num2str(obj.cpp_handle_)]);
else
% copy constructor
obj.cpp_handle_ = rand(1);
disp(['Copy initialized myclass with handle: ' num2str(obj.cpp_handle_)]);
end
end
% destructor
function delete(obj)
disp(['Deleted myclass with handle: ' num2str(obj.cpp_handle_)]);
end
% class method
function amethod(obj)
disp(['Class method called with handle: ' num2str(obj.cpp_handle_)]);
end
end
end
如上所述测试此类，即：
cls = myclass();
parfor i = 1:10
cls.amethod(i)
end
输出结果：
Initialized myclass with handle: 0.65548
Class method called with handle: 0.65548
Class method called with handle: 0.65548
Class method called with handle: 0.65548
Class method called with handle: 0.65548
Class method called with handle: 0.65548
Class method called with handle: 0.65548
Class method called with handle: 0.65548
Class method called with handle: 0.65548
Class method called with handle: 0.65548
Class method called with handle: 0.65548
Deleted myclass with handle: 0.65548
Deleted myclass with handle: 0.65548
Deleted myclass with handle: 0.65548
换句话说，似乎在为 parfor 生成工人时没有调用复制构造函数。是否有人对我做错了什么有任何指示，或者是否有某种方法可以在复制 MATLAB 包装类时实现重新初始化 C++ 对象句柄的期望行为？
替代方法：检测何时在工作人员上运行
仅供参考，这是我在工作人员中使用的重新分配的替代方法：
classdef myclass < handle
properties(SetAccess=protected)
cpp_handle_
end
methods
function obj = myclass(val)
obj.cpp_handle_ = rand(1);
disp(['Initialized myclass with handle: ' num2str(obj.cpp_handle_)]);
end
% destructor
function delete(obj)
disp(['Deleted myclass with handle: ' num2str(obj.cpp_handle_)]);
end
% class method
function amethod(obj)
obj.check_handle()
disp(['Class method called with handle: ' num2str(obj.cpp_handle_)]);
end
% reinitialize cpp handle if in a worker:
function check_handle(obj)
try
t = getCurrentTask();
% if 'getCurrentTask()' returns a task object, it means we
% are running in a worker, so reinitialize the class
if ~isempty(t)
obj.cpp_handle_ = rand(1);
disp(['cpp_handle_ reinitialized to ' num2str(obj.cpp_handle_)]);
end
catch e
% in case of getCurrentTask() being undefined, this
% probably simply means the PCT is not installed, so
% continue without throwing an error
if ~strcmp(e.identifier, 'MATLAB:UndefinedFunction')
rethrow(e);
end
end
end
end
end
和输出：
Initialized myclass with handle: 0.034446
cpp_handle_ reinitialized to 0.55625
Class method called with handle: 0.55625
cpp_handle_ reinitialized to 0.0048098
Class method called with handle: 0.0048098
cpp_handle_ reinitialized to 0.58711
Class method called with handle: 0.58711
cpp_handle_ reinitialized to 0.81725
Class method called with handle: 0.81725
cpp_handle_ reinitialized to 0.43991
cpp_handle_ reinitialized to 0.79006
cpp_handle_ reinitialized to 0.0015995
Class method called with handle: 0.0015995
cpp_handle_ reinitialized to 0.0042699
cpp_handle_ reinitialized to 0.51094
Class method called with handle: 0.51094
Class method called with handle: 0.0042699
Class method called with handle: 0.43991
cpp_handle_ reinitialized to 0.45428
Deleted myclass with handle: 0.0042699
Class method called with handle: 0.79006
Deleted myclass with handle: 0.43991
Deleted myclass with handle: 0.79006
Class method called with handle: 0.45428
从上面可以看出，当在 worker 中运行时，确实会发生重新分配。但是，无论 C++ 类被重新分配多少次，每个 worker 只调用一次析构函数，从而导致内存泄漏。
解决方案：使用loadobj
以下作品：
classdef myclass < handle
properties(SetAccess=protected, Transient=true)
cpp_handle_
end
methods(Static=true)
function obj = loadobj(a)
a.cpp_handle_ = rand(1);
disp(['Load initialized encoder with handle: ' num2str(a.cpp_handle_)]);
obj = a;
end
end
methods
function obj = myclass(val)
obj.cpp_handle_ = rand(1);
disp(['Initialized myclass with handle: ' num2str(obj.cpp_handle_)]);
end
% destructor
function delete(obj)
disp(['Deleted myclass with handle: ' num2str(obj.cpp_handle_)]);
end
% class method
function amethod(obj)
disp(['Class method called with handle: ' num2str(obj.cpp_handle_)]);
end
end
end