Hi Maxim,
Don G wrote:
Personally, I don't think the multiplexing interface is appropriate or necessary.
Rather it's vital.
I agree that it is vital to use such a mechanism internally, but I see no reason (other than preference) to expose the grouping of connections to the user.
None of the calls should block.
But the sync ones _must_ block. All of the logical operations can be invoked sync/async. The non-blocking approach, from my definition<g>, is like this: - try the operation - get back a "would block" state - flag interest in change to "won't block" - wait for the state to arrive - repeat the operation (it won't block) I think this has a place for I/O, but not for connect/accept. These are binary steps whereas I/O can be viewed as a continuous march to completion.
Otherwise you won't be able to build single threaded applications with select/poll/epoll-based loops.
One can write in a single threaded style using what I am proposing, but it is not, IMHO, the way to go for optimal performance. What I am suggesting is that this style can be achieved by not basing the main loop on select/et.al.. Those API's will be used internally. Things like the Windows limit on connections/select and leverage of multiple CPU's would be details. This will not be the solution for _everyone_. But, I believe it will go a lot farther than you might think. []
* There should be an asynchronous design pattern which should be used by all Boost libraries which support asynchronous operations.
I agree completely on this one :)
I hope this won't happen. There are several I/O patterns in use out there.
But, honestly, how many do we need? I think all that we need is a way to achieve concurrent operations in C++. One technique would satisfy this. It would have advantage of allowing different libraries to communicate, as each would not be using an incompatible style.
* On a low level the network library should be close to what is known as Berkeley sockets to many programmers.
I think sockets should be hidden. They are not universally used, for example Mac OS9 doesn't and I just assume others exist. They don't have any magical powers; they are just a C abstraction.
Was not Mac OS Classic been buried long ago?
Hopefully :) It was offered as an existence proof. There is more to the world than Unix and Windows.
IMO, sockets are abstractions out of the scope of any language.
But they are realized as a C artifact. They were born as a C library. They are not sacred :)
Their interfaces can be implemented using any general purpose programming language, but still you'll have to call an underlying OS C API. That's a fact of life and I don't think this is bad - C is the most portable programming language ever.
Yes, C is portable. C++ is also. I will resist the C vs. C++ debate.
A C++ abstraction should replace them.
With this kind of attitude you might end up rewritting the whole world you've been living in <g>
Actually, I believe that is the point. Sometimes (often) these are just C++ facades over C libraries, but C++ offers a different idiom that many find attractive for various reasons. This is especially true when the C interface is as tedious as sockets. Whitness the level of interest in this topic. :)
Here is my two philosophy cents.
You propose another set of concepts over socket concepts just to send/receive a bunch of mere bytes. Geez, another glue layer over sockets that adds nothing but syntax sugar. Aren't we already tired of software bloated from glue layers over glue layers over...?
Not "just". It is to handle life-cycle safely, type safe control flow, non-portable aspects of sockets, to name a few.
You don't just send bytes, rather you execute protocols. Sockets have the right implementation level and complexity to build *efficient* protocols upon.
How hard should it be to write a protocol? How reusable should it be? Have you ever tried to use, say, OpenSSL? Everyone that wants to write a protocol today must grapple with these issues and all they have to begin with is a concrete API for sockets. But that is a bottom-only facility. Just try to expose SSL as a socket to your user! FWIW, openssl exposed their protocol implementation in a generic way so as not to tie one to sockets. That is, they created a C I/O mechanism (BIO's) that are unique to it. A C++ version could be written to use the net::stream I proposed and _be_ a net::stream implementation. Thanks to the BIO interface of OpenSSL, this could also be done using that library.
Protocol is the only glue layer you really always need, the layer that binds your application logic with network transport layer (sockets) providing the right C++ or whatever interface.
So, let's say we have an HTTP library. How do we wait for responses? Expose the socket(s) it uses? I think the async pattern we are talking about is the right answer. Best regards, Don __________________________________ Do you Yahoo!? Yahoo! Small Business - Try our new resources site! http://smallbusiness.yahoo.com/resources/