----- Original Message ----- From: "Jerry" To: Sent: Monday, June 07, 2010 2:22 AM Subject: Re: [Boost-users] [thread] Is Boost suitable for this application?

Francisco Javier Porras Gálvez writes:

...

Hi, all.

I don't know anything about Boost, neither OpenMP, pthread nor Windows API thread library. So, before begin learning one of these, I'd like to explain to you how I want my application to work.

It deals with running two parallel loops, one in LabView, and the other in C++. It doesn't matter if you don't know anything about LabView, this explanation is easy enough to understand. Attached you can see a picture which shows the desired execution behaviour. I want to know whether my application would be possible to achieve using Boost, or using another API. In another general C++ forum, I was suggested to use Boost.

First, the execution begins in LabView. Here, I call a dll function written in C++. This is the "initialization" function. Its aim is to create another thread that will execute the main loop in C++. Then, this "initialization" function ends, because it has to return the control execution to LabView, but the new thread which has just been created must continue executing in its own loop.

Now we have two loops in parallel: LabView and C++. In LabView's loop, we call periodically another dll function that has to send and retrieve data from the independent thread in C++. This function, like the other, has to end executing to pass control to LabView again, after it has done its purpose.

This will be the behaviour until we call from LabView another dll function to stop the independent thread (not shown in the picture). After this, the LabView program ends.

Is it possible to use Boost for this? If so, could you post a brief example about how you'd make it?

Thanks in advance,Francisco

I did something almost exactly like this about 10 years ago with LabView 7. I made a DLL that created a thread that started a socket listner so that other computers could connect to the embedded Labview to get control data.

Now, Labview allows you to create sockets, but the protocol library for the socket data was already in C++ and I tried to create the socket in Labview and pass it into the DLL but I had quite a bit of trouble. It didn't work correctly in Labview 7. I raised a ticket with NI and they basically couldn't help me because none of their help desk knew anything about making your own DLL. Hopefully the support is better now.

So anyway, I created a DLL that started a thread and created a socket listner. Then periodically I would call another function in the DLL to deposit control data that the socket listener could send to requestors. I had it start a separate thread because I was using a blocking socket listener.

It all works fine. And from Labview's point of view it doesn't matter what library you use to create the socket because all that is hidden in the DLL. I used Visual Studio's C runtime beginthread function and that worked because the embedded Labview system was running on Windows, but of course it isn't portable (neither is pthread or Windows API threads). Boost Threads is portable and would work fine.

Do you know what OS your Labview app will be running on?

Jerry

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Hi, Jerry. Thanks for your support! I hadn't any idea about what a socket was, but after "googling" a little and read about in NI pages, I have it clearer now. LabView uses a tool called DataSocket to share data between different applications or/and the internet. Moreover, I "discovered" that LabView includes a set of C++ libraries in what is called "Measurement Studio". One of this libraries implements also "DataSocket", and in NI forums they state is possible to share data between two applications in C++ and LabView using this DataSocket tool. So, I think this is the right direction. Your clue was really useful. Thanks, Francisco

----- Original Message ----- From: "Jerry" To: Sent: Monday, June 07, 2010 4:51 AM Subject: Re: [Boost-users] [thread] Is Boost suitable for this application?

Francisco Javier Porras Gálvez writes:

...

Hi, Jerry.

Thanks for your support!

I hadn't any idea about what a socket was, but after "googling" a little and read about in NI pages, I have it clearer now.

LabView uses a tool called DataSocket to share data between different applications or/and the internet. Moreover, I "discovered" that LabView includes a set of C++ libraries in what is called "Measurement Studio". One of this libraries implements also "DataSocket", and in NI forums they state is possible to share data between two applications in C++ and LabView using this DataSocket tool.

So, I think this is the right direction. Your clue was really useful.

Thanks, Francisco

Sorry for the confusion: Actually I wasn't suggesting that you use a socket to communicate between two applications. Although if you want to be able to run the C++ stuff on a different machine or retrive the data from more than one application then this is a good move. If all you want is Labview to talk to another thread in the same application then use a DLL with a separate thread. There is no reason to make a socket if you can use a DLL instead unless you need to be able to connect to the DLL from more than one app or from an app on a different machine.

The only reason I mentioned the socket stuff was as an example of something I needed to run a thread in a DLL to accomplish. I guess I ramble a bit too much :-)

Jerry

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Hi, Jerry. Hehehe, ok, don't worry. I think this "DataSocket" stuff it's going to be very useful for another application I have to deal with. So, in the end, it was very helpful:) So, your suggestion is to use the first aproach, isn't it? This application will run on Windows. In "Cplusplus" forums I was suggested to use Boost because Windows API threads aren't very friendly with synchronization. I don't know much about threads, but what I find more difficult to asume is the fact of creating a thread with a function, and then, after this function has ended, share data with the created thread using another function. Due to this, I can't use OpenMP, for example, because its thread behaviour follows the fork-join model. Anyway, I'll follow your advice and try to integrate your example in my code. Thanks for the attached code! Francisco

Some example code, makes use of boost thread, function and bind: 1st - a queue. It accepts "Jobs" which are of type boost::function More about creating jobs later #include #include #include #include <list> // cross-thread job queue. multiple threads can post jobs, one or many threads can execute jobs. class job_queue { public: typedef boost::function Job; private: boost::mutex mtx_; boost::condition cnd_; typedef std::list<Job> Jobs; Jobs jobs_; int stop_; public: // puts a job into the queue void post(Job job) { boost::mutex::scoped_lock lock(mtx_); jobs_.push_back(job); cnd_.notify_one(); } // pulls one job from the queue, returns false when stopped bool pull(Job* job) { boost::mutex::scoped_lock lock(mtx_); for(;;) { // handle spurious wake-ups while(!stop_ && jobs_.empty()) cnd_.wait(lock); if(!jobs_.empty() && 2 != stop_) { job->swap(jobs_.front()); // move efficiently, avoiding *job = jobs.front() jobs_.pop_front(); return true; } else if(stop_) { return false; } } } // make pull() return false void stop(bool cancel_jobs) { boost::mutex::scoped_lock lock(mtx_); stop_ = 1 + cancel_jobs; // 1 - complete jobs, 2 - cancel jobs cnd_.notify_all(); } job_queue() : stop_() {} ~job_queue() { this->stop(true); } }; //----------------------------------------------------------------------- 2nd, you need to create a thread. The thread accepts a pointer to an event_queue, and loops indefinitely, pulling jobs off the queue and executing them. #include #include #include <iostream> void loop(job_queue* queue) { std::cout << __PRETTY_FUNCTION__ << " thread id is: " << boost::this_thread::get_id() << std::endl; job_queue::Job job; // wait and execute jobs till stopped while(queue->pull(&job)) job(); // execute the job } //----------------------------------------------------------------------- boost::thread create_thread(job_queue* queue) { return boost::thread(boost::bind(loop, queue)); } //----------------------------------------------------------------------- Now you need to create jobs and post them to the queue. All jobs are functors. A functor is something which has the function operator "R operator()(A...)" - it must be of the form "void ()" for this queue to accept it. You can create your own functor (example below), or use boost::bind to create function objects for you. boost::bind can bind class member functions or free functions or even bind arguments to functors. See some example usage below: struct my_functor { void operator()() { std::cout << "Here I am, doing some work in " << __PRETTY_FUNCTION__ << " on thread " << boost::this_thread::get_id() << std::endl; } }; struct my_class { void some_function(int b) { std::cout << "Here I am, doing some work in " << __PRETTY_FUNCTION__ << " on thread " << boost::this_thread::get_id() << " and my input is " << b << std::endl; } }; void free_function_1() { std::cout << "Here I am, doing some work in " << __PRETTY_FUNCTION__ << " on thread " << boost::this_thread::get_id() << std::endl; } void free_function_2(char c) { std::cout << "Here I am, doing some work in " << __PRETTY_FUNCTION__ << " on thread " << boost::this_thread::get_id() << " and my input is " << c << std::endl; } int main() { std::cout << __PRETTY_FUNCTION__ << " thread id is: " << boost::this_thread::get_id() << std::endl; job_queue queue; boost::thread another_thread = create_thread(&queue); my_functor mf; my_class mc; queue.post(mf); // post a function object (functor) to the queue queue.post(boost::bind(&my_class::some_function, mc, 7)); // bind creates a functor - binding member function to class instance, and an argument queue.post(boost::bind(&free_function_1)); // bind creates a functor from a free function queue.post(boost::bind(&free_function_2, 'z')); // bind creates a functor from a free function and binds the argument // stop the queue and let it complete all jobs queue.stop(false); another_thread.join(); return 0; } //-----------------------------------------------------------------------