[boost] [iostreams] cin wrapper

Subject: [boost] [iostreams] cin wrapper
From: Daniel Larimer (dlarimer_at_[hidden])
Date: 2012-07-06 13:09:29

I am attempting to 'wrap' std::cin such that all 'blocking' occurs in a dedicated 'cin' thread.  This is required because in a cooperatively scheduled thread, no fiber can call cin and block.

So I went about attempting a boost::iostreams::source:

class cin_source : public boost::iostreams::source {
streamsize read( char* s, streamsize n ) {
        if( n == 0 ) return n;
        auto r = std::cin.readsome(s,n);
        if( r <= 0 ) {
                // post read request to another thread.
                // cooperatively wait for it to finish... 
                return n;
        }
        return r;
}  
};

The problem I have is that this code causes read to be called with 'n == 0'; 

boost::iostreams::stream<cin_source>  my_cin;
char buf[100];
my_cin.read( buf, 100 );  

It doesn't matter how I attempt to read from the stream, n always equals 0.

What am I doing wrong?

Dan