Re: [Boost-users] [iostreams] blocking read() confusion

From: Jeff Flinn (TriumphSprint2000_at_[hidden])
Date: 2006-05-23 11:19:03

Pedro Lamarão wrote:
> Dave Dribin escreveu:
>> According to the documentation I/O Streams defines blocking I/O as:
>>
>>    <http://www.boost.org/libs/iostreams/doc/concepts/blocking.html>
>>
>>> A Device is Blocking if a read request never produces fewer
>>> characters than requested except at end-of-stream, and if a write
>>> request never consumes fewer characters than requested under any
>>> circumstances.
>>
>> So, if I issue an iostream::read() with 10 characters, and only 5
>> come back, this is considered non-blocking.  To me, this is
>> inconsistent with at least Unix read() semantics.  As long as
>> iostream::read() blocks for at least 1 character, it should be
>> considered blocking, no?
>
> I think you're confusing nomenclature.
>
> "Blocking" means your process is kept out of the ready queue until the
> system call is "satisfied". In this context, "satisfied" means you get
> the data you asked for, or that became impossible, either because EOF
> was reached, or because an error happened.
>
> "Non-blocking" means your process is never kept out of the ready queue
> like this; to achieve that, the first "satisfaction" requirement is
> alleviated: a "non-blocking" call _may_ return less data than you
> asked for.
>
> "Blocking" in this context does not mean "spending some time in a
> function call (because it takes time to execute)", it means "being
> taken out of the ready queue (because an I/O device takes time to
> answer a request)".

Perhaps the OP is looking for the ASIO library's asynchronicity.

Jeff Flinn