Re: [Boost-users] Why can't I catch this exception in boost::thread?

From: af001 (fanzigui_at_[hidden])
Date: 2007-06-28 21:07:28

thanks

I get it, btw, I am using version 1.34.0

Andrew Holden wrote:
> 
> Af001 wrote:
>> Why can't I catch this exception in boost::thread?
>> 
>> 
>> #include <boost/thread/thread.hpp>
>> #include <iostream>
>> #include <exception>
>> 
>> void helloworld()
>> {
>>     std::cout << "Hello World!" << std::endl;
>> 	throw(std::string("err"));
>> }
>> 
>> int main()
>> {
>> 	try
>> 	{
>> 		boost::thread thrd(&helloworld);
>> 		thrd.join();
>> 	}
>> 	catch(...)
>> 	{
>> 		std::cout<<"err";
>> 	}
>> }
> 
> This is a limitation of exceptions in a multi-threaded environment.
> Exceptions must be caught in the same thread from which they are thrown.
> In your program, you created a new thread for helloworld().  Therefore,
> any exceptions thrown by helloworld will cause a runtime error, unless
> helloworld itself catches them.  You should be able to work around this
> my storing the exception in a global variable or something.  Perhaps:
> 
> #include <boost/thread/thread.hpp>
> #include <iostream>
> #include <exception>
> 
> volatile bool threaderror = false;
> std::string error;
> 
> void helloworld()
> {
> 	try
> 	{
> 		std::cout << "Hello World!" << std::endl;
> 		throw(std::string("err"));
> 	}
> 	catch (std::string &err)
> 	{
> 		threaderror = true;
> 		error = err;
> 	}
> }
> 
> int main()
> {
> 	try
> 	{
> 		boost::thread thrd(&helloworld);
> 		thrd.join();
> 		if (threaderror)
> 		{
> 			throw error;
> 		}
> 	}
> 	catch(...)
> 	{
> 		std::cout<<"err";
> 	}
> }
> 
> Notice how, in this version, helloworld() catches the exception itself
> and stores it in a global variable.  Main() then checks the variable and
> throws a copy of the original exception.
> 
> Does anyone have any ideas for a cleaner version of this?  It looks like
> boost.thread allows a functor for the initial function, so maybe you
> could convert helloworld() to a functor and declare those global
> variables I added as member variables, along with a member function to
> rethrow any exceptions caught.
> 
> Perhaps someone could create a generic version of this?  It could maybe
> take a MPL list of exception types that it should marshall across
> threads.  Is there a way to catch *any* exception in the thread and
> store it for a later rethrow?
> _______________________________________________
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> 
> 

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