On Sat, 11 Sep 1999 21:26:47 -0700, John Gardiner Myers
<jgmyers@netscape.com> said:
> Alan Cox wrote:
>> POSIX real time signal queues are effectively completion ports.
> You must not have understood the post you were replying to. POSIX real
> time signal queues are inferior to completion ports in many ways.
> * As far as I know, there is no way to allocate a POSIX real time signal
> number in a thread safe manner. There is no equivalent to the socket()
> system call--one must just pick a number and hope that no other thread
> in the same process just picked the same number.
As far as I know, completion ports still have the demultiplexing done in
a single place, so in that model you still have to have extra explicit
application/library cooperation to let libraries share queues.
> * Chuck Lever informs me that the signal queue might overflow, leading
> to lost completion notifications. There is no reasonable way for an
> application to recover from such a condition.
There is. The existing kernel supports sending a separate, higher
priority event to notify the application of overflow, and poll is a
sufficient recovery mechanism. You don't expect overflow to be a
common, performance-critical case.
> * POSIX aio lacks a mechanism to request read polls.
Who is talking about POSIX aio? That is a totally different API. For
the purposes in question --- networking IO --- leave POSIX aio well
alone, Unix O_NONBLOCK plus completion events is a perfectly adequate
API. The async IO API is not necessary or desirable.
> * POSIX aio lacks asynchronous versions of writev() and sendfile().
> (Though the lack of an aio_writev() is made less important by
> TCP_CORK.)
See the previous point: you'd be crazy to want aio_writev on a socket.
--Stephen
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