Linux-kernel mailing list archive 1999-37,: Re: POSIX aio vs completion ports

# Re: POSIX aio vs completion ports

Alan Cox (alan@lxorguk.ukuu.org.uk)
Sun, 12 Sep 1999 15:37:35 +0100 (BST)

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> You must not have understood the post you were replying to. POSIX real
> time signal queues are inferior to completion ports in many ways.

Oh I do understand.

> * 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.

So you write a library routine for it. Now that is hard. Its a non kernel
issue.

> * 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.

Incorrect. On an overflow you get a signal without rt information that tells
you there was a queue overlfow

> * POSIX aio lacks a mechanism to request read polls. With completion
> ports, one may request an asynchronous read of 0 bytes--the completion
> is delivered when there is data to be read. Implementations of POSIX
> aio cause an aio_read() of 0 bytes to complete immediately, a useless
> semantic.

You get a real time signal when there is now data to read, indicating the
file handle.

> * POSIX aio lacks asynchronous versions of writev() and sendfile().
> (Though the lack of an aio_writev() is made less important by TCP_CORK.)

Which you can do with another thread.

Alan

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