From drsalists at gmail.com  Fri Mar  2 09:29:50 2012
From: drsalists at gmail.com (Dan Stromberg)
Date: Thu, 1 Mar 2012 15:29:50 -0800
Subject: [TUHS] "Slow system call" and EINTR
Message-ID: <CAGGBd_p12gWvRTz5soB_swFkT4QxL0upTKxLP2L_P=UKym2Z6w@mail.gmail.com>

I gather system calls can return EINTR only when they are "slow".  True?

What makes a system call "slow"?  Is it the ability to block for a while?
But I wouldn't think dup(2) would block, for example.

(I -=Love=- *ix!)
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From ramble1035 at dslextreme.com  Fri Mar  2 09:59:53 2012
From: ramble1035 at dslextreme.com (ramble1035 @dslextreme.com)
Date: Thu, 1 Mar 2012 15:59:53 -0800
Subject: [TUHS] "Slow system call" and EINTR
In-Reply-To: <CAGGBd_p12gWvRTz5soB_swFkT4QxL0upTKxLP2L_P=UKym2Z6w@mail.gmail.com>
References: <CAGGBd_p12gWvRTz5soB_swFkT4QxL0upTKxLP2L_P=UKym2Z6w@mail.gmail.com>
Message-ID: <CAFn3HkPJ7ccGZXrupAeFo5nK6Xab_Denuu2qW4qAwenixHdCrQ@mail.gmail.com>

On Thu, Mar 1, 2012 at 3:29 PM, Dan Stromberg <drsalists at gmail.com> wrote:
>
> I gather system calls can return EINTR only when they are "slow".  True?

For a unique definition of "slow"...  :)

> What makes a system call "slow"?  Is it the ability to block for a while?
> But I wouldn't think dup(2) would block, for example.

>From my experience, a slow vs fast call is only partially based on
time.  It's more based on obtaining and releasing resources.

A slow system call is one that might take a long time, and any
resource allocations requested during the system call processing can
be easily undone (returned).  TTY input, as an example.

Things like a disk request are *supposed* to be quick, but even if
they're not, they involve allocating buffers, queueing disk requests,
setting up possible interrupts or DMA, and other messy internal
details.  Aborting a pending disk request would be a substantial
amount of effort.  Thus, a disk request cannot be interrupted and it's
classified as "fast".  (or "not slow")

This presents a few difficulties when you consider something like NFS,
which acts like a disk request until it gets down to the network
layer, where things might well take a long time.  But interrupting and
aborting this is not easy, which is why some NFS requests, when hung,
stay hung even when you bang on Control-C for a while.

Really simple things like dup, which involves a simple copy, would
probably not block unless there were extreme issues with memory
allocation or something.

  -- Chris


From jfoust at threedee.com  Wed Mar 14 02:09:04 2012
From: jfoust at threedee.com (John Foust)
Date: Tue, 13 Mar 2012 11:09:04 -0500
Subject: [TUHS] ASR 37 teletype desired by LCM / Vulcan.com
In-Reply-To: <E5C6A964-1931-4EB9-9B62-303309FDDAA6@bsdimp.com>
References: <CAFCBnZvMuUvZNm72pvWkS30PH7o3eS8ii2WQ5XaZyviAxhwHOA@mail.gmail.com>
	<20120201121214.55c73577@cnb.csic.es>
	<4F2A907D.9000000@fastmail.us>
	<89159FF1-5521-4890-A5F0-30DC9E5B7EC9@bsdimp.com>
	<20120202173623.GQ30634@mercury.ccil.org>
	<alpine.BSF.2.00.1202030759350.66525@aneurin.horsfall.org>
	<52BD3851-95AF-4DFC-8728-9F2DB1E1614C@bsdimp.com>
	<CAGSRWbiJesxtoC38_FEZM7_jMa3cvx=SUjT+nUoGd5irxr_ajg@mail.gmail.com>
	<E5C6A964-1931-4EB9-9B62-303309FDDAA6@bsdimp.com>
Message-ID: <20120313170240.00A7C28E3D@minnie.tuhs.org>


I forward a request from the Greenkeys (teletype) mailing list. 

The ASR 37 did upper- and lower-case.

- John

From: Cynde Moya <CyndeM at vulcan.com>
To: greenkeys <GreenKeys at mailman.qth.net>
Date: Mon, 12 Mar 2012 22:01:51 +0000
Subject: [GreenKeys] Wanted : ASR 37
 
The Living Computer Museum is looking to purchase a working or restorable ASR 37 teletype. Do you have any leads? Thanks very much.
 
 
Cynde Moya
Librarian/Archivist, Vintage Computing
Vulcan Inc
206 342-2385
http://www.vulcan.com
http://www.LivingComputerMuseum.org
 



