Re: [asio-users] Waiting for the data while async_write

[Benjamin R. <be...@bl...>]

Hi Michael

If I were you I would avoid busy-waiting (running a while( !gotPacket) 
loop to wait) because it tends to keep one entire core busy until it is 
released.

If you need to wait for something, depending on what it is, use 
std::mutex and similar primitives. Of course, the ideal case would be if 
you could have everything wrapped inside asynchronous calls, such that 
no waiting is even necessary and you can just use one thread. The idea 
of ASIO is that everything 'fires' an event when it's ready, so you 
never have a thread just waiting.

Maybe you could have a flag that is atomically set to true if one of the 
asynchronous calls fires, and if the second one fires (whichever one it 
is), the work gets done. Like that, everything is asynchronous.

Cheers,
Benjamin

On 23.10.2017 18:26, Michael IV wrote:
> Hi again! I need an advice. I have a situation where the data can be 
> unavailable when asyn_write is getting called. What's the best 
> practice to wait for the data in such a case?
> Here is the case:
>
> void Connection::Send()
> {
> //we write syncrhoniously
> MyData packet;
> bool gotPacket = task->data_queue.try_dequeue(packet);
> if (!gotPacket)
> {
> // >>  ???? // Should I run a while(!gotPacket) here?
> }
>                //fill buffers with data here...
> auto self(shared_from_this());
> asio::async_write(mSocket, buffers,
> [this, self](const asio::error_code error, size_t bytes_transfered)
> {
> if (error)
> {
> std::cout << "Async write interrupted with error:" << error.message() 
> << std::endl;
> return;
> }
> assert(bytes_transfered);
>                        //chain:
>                        Send();
> }
> );
> }
>
> So should I run a while( !gotPacket) loop to wait for the data to be 
> available? Or I can somehow skip this async_write without losing
> the chaining? Thanks in advance.
>
>
>
>
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