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Subject: [Boost-users] boost::thread and boost::asio::io_service questions
From: Christopher Pisz (cpisz_at_[hidden])
Date: 2011-06-10 16:27:49

I am trying to understand both of these items and how they are executing in
our code, so I made a small demo to debug through.

1) Why can't I pass boost::io_service by reference in the call, boost::thread
workerThread(DoWork, 1, ioService); with a function signature of void DoWork
(const unsigned int threadNum, boost::asio::io_service * ioService) ? I
changed it to a pointer and it works, but I don't know why I can't do it by

2) If boost::thread is not copyable, how can I store a collection of "thread
handles" or boost::thread objects like the variable workerThread? I can't use
the std collections I would usually use...

3) When stepping through the code, the debugger jumps between the main thread,
the worker thread, and a call stack in the depths of boost code where one item
points to the line where the call to ioService->run() is. The first two make
sense. I don't understand the latter.

The call stack looks very much like one we get in production code and is all I
have to go on in trying to debug a problem. The challenge is trying to
determing who created the thread and find that line in source, because the
production code is keeps creating threads until the program crashes.

#include <iostream>

#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>
#include <boost/thread.hpp>

/// This function is the entry point for each worker thread
void DoWork(const unsigned int threadNum, boost::asio::io_service * ioService)
    std::cout << "Doing work in worker thread: " << threadNum << "\n";

    // Perform the work
    // Multiple threads may call io_service::run() to set up a pool
    // of threads from which completion handlers may be invoked.

/// This function gets called when the asynchronous operation completes
/// Guarantee - A completion handler will only get called from the same thread
that called boost::asio::io_service::run()
void OnCompletion(const boost::system::error_code & e, const unsigned *
    std::cout << "Completed item # " << *itemNum << " has completed. \n";

int main()
   boost::asio::io_service ioService;
   boost::asio::deadline_timer timer(ioService, boost::posix_time::seconds(5));
   const unsigned maxItems = 5;

   // Queue up some work
   for(unsigned int itemNum = 0; itemNum < maxItems; ++itemNum)
       // The work to do is an asynchronous wait
       timer.async_wait(boost::bind(OnCompletion, // Method to callback
                        boost::asio::placeholders::error, //
                        &itemNum)); // Arg 1 to pass

   // Create a thread to do the work
   boost::thread workerThread(DoWork, 1, &ioService);

   // Do other stuff in the main thread
   for(unsigned i = 0; i < 100; ++i)
       std::cout << "Doing other work in main thread\n";

   // Done
   return 0;

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