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From: gwyn@brl-smoke.ARPA (Doug Gwyn )
Newsgroups: net.unix-wizards
Subject: Re: Checking for waiting characters
Message-ID: <737@brl-smoke.ARPA>
Date: Fri, 9-May-86 20:01:59 EDT
Article-I.D.: brl-smok.737
Posted: Fri May  9 20:01:59 1986
Date-Received: Sun, 25-May-86 06:29:38 EDT
References: <470@brl-smoke.ARPA> <1293@ptsfa.UUCP> <1364@ihuxy.UUCP>
Reply-To: gwyn@brl.ARPA
Organization: Ballistic Research Lab (BRL)
Lines: 17

In article <1364@ihuxy.UUCP> ejbjr@ihuxy.UUCP (Branagon) writes:
>> In article <470@brl-smoke.ARPA> KEN%NJITCCCC.BITNET@wiscvm.wisc.edu (Kenneth Ng) writes:
>> >On Unix System V version 2 on an AT&T 3b5, has anyone been able to
>> >successfully test if characters are pending?  I've got an application
>> >that needs to time out after a certain amount of time if no characters
>> >come through.
>
>The easiest way I've found to do this is to set an alarm, and use a signal
>trapping function (see alarm(2) and signal(2)).  The alarm can be set once
>at the beginning, or reset after each character.  I'm not sure if alarm()
>is sysV specific or not.

No, alarm() has been in all UNIXes since 6th Edition.
However, the alarm signal can mangle I/O involving "slow"
devices (typically terminal ports), so it is not suitable
for some applications like this.  Other approaches such
as using MIN,TIME are preferable.