Date: Tue, 12 Mar 1996 10:17:39 PST From: "Marty Leisner" <leisner@sdsp.mc.xerox.com> To: Luigi Rizzo <luigi@labinfo.iet.unipi.it> Cc: msmith@atrad.adelaide.edu.au, questions@freebsd.org Subject: Re: non-blocking read ? Message-ID: <9603121817.AA08720@gnu.mc.xerox.com> In-Reply-To: Your message of "Tue, 12 Mar 1996 10:06:55 PST." <199603121806.TAA20924@labinfo.iet.unipi.it>
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In message <199603121806.TAA20924@labinfo.iet.unipi.it>, you write:
> result=read(handle, buf, size);
>
>The lseek might be non blocking -- no problem with that.
>The read is non-blocking because of the previous call to fcntl().
>
>But how much data will be available when I get the SIGIO (or select
>will return that I/O is possible) ? The amount I requested (assuming it
>is available), or the system idea of a block, or what ?
>
> Thanks
> Luigi
Reads on files have to block...the only think you can do
is set a timer to go off in about 10 Msec, and if the read
isn't done yet, the alarm will knock you out of the read with
an -EINTR.
I don't know if the kernel will continue on the read...
GNU libc says:
- Macro: int O_NONBLOCK
This prevents `open' from blocking for a "long time" to open the
file. This is only meaningful for some kinds of files, usually
devices such as serial ports; when it is not meaningful, it is
harmless and ignored. Often opening a port to a modem blocks
until the modem reports carrier detection; if `O_NONBLOCK' is
specified, `open' will return immediately without a carrier.
files but design "don't block"
marty
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