CODEWITHSUNDEEP
boostboost-asio
Nishant Sharma
Nishant Sharma

Reputation: 371

Creating a thread for running io_service

Consider the chat example at : http://www.boost.org/doc/libs/1_45_0/doc/html/boost_asio/examples.html

Look the client file : http://www.boost.org/doc/libs/1_45_0/doc/html/boost_asio/example/chat/chat_client.cpp

Here, seems like the point at which boost thread which runs the io_service is important..

chat_client c(io_service, iterator);

boost::thread t(boost::bind(&boost::asio::io_service::run, &io_service));

If I create the thread before I create an object of chat_client, then the io_service.stopped() returns true if printed in the while loop below that.

I do not understand why it is so?

Upvotes: 1

Views: 1590

Answers (1)

rafix07
rafix07

Reputation: 20918

What is io_service::run() doing ?

The run() function blocks until all work has finished and there are no more handlers to be dispatched, or until the io_service has been stopped.

when you call async function like (async_read,async_write, ...) you need to pass handlers to these functions. Handlers are called when async operation will be done. In io_service::run() async operations are being processed.

Before calling io_service::run at least one async operation must be waiting for executing. If you call io_service::run when there are no async operations planned, this method returns immediately. So

  1. call first async operation
  2. call io_service::run in thread to process async operations
  3. when first async operation will be ended, you have to plan another async operation to execute so that io_service::run works (this method runs as long as there are async operations)

Look at constructor of chat_client

    socket_.async_connect(endpoint,
    boost::bind(&chat_client::handle_connect, this,
      boost::asio::placeholders::error, ++endpoint_iterator));

async_connect method is invoked - this is first async operation to be executed.

io_service::stopped() returns true when io_service::run ends working because there are no async operations to be processed.

A normal exit from the run() function implies that the io_service object is stopped (the stopped() function returns true).

Upvotes: 2

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