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Re: [MIT-Scheme-devel] multi-threading problem: Unassigned variable: roo

From: Alex Shinn
Subject: Re: [MIT-Scheme-devel] multi-threading problem: Unassigned variable: root-continuation-default
Date: Fri, 27 Apr 2012 11:29:16 +0900

On Fri, Apr 27, 2012 at 9:47 AM, Matt Birkholz
<address@hidden> wrote:
>> From: Taylor R Campbell <address@hidden>
>> Date: Thu, 26 Apr 2012 22:01:29 +0000
>>    Date: Thu, 26 Apr 2012 13:29:33 -0700
>>    From: Matt Birkholz <address@hidden>
>>    > From: "Micah Brodsky" <address@hidden>
>>    > Date: Thu, 26 Apr 2012 11:10:47 -0400
>>    > While you're at it, do be careful about using sockets from multiple
>>    > threads simultaneously. They're not really thread-safe like native
>>    > OS sockets are. [...]
>>    Ummm... one should be careful when using ANY resource from multiple
>>    threads... so Scheme's ports/sockets each come with a mutex... so I
>>    can only wonder what you're on about...  How "really thread-safe" are
>>    "native OS sockets"?
>> The mutex in a port is advisory, not mandatory.  MIT Scheme uses it
>> only to grant ownership of the `console port' to a single thread.
>> Concurrent use of a port in two different threads can corrupt its
>> internal state.  Concurrent use of a file descriptor (or `native OS
>> socket', or `channel') from two different threads can't corrupt its in
>> internal state.
> You seem to think "native OS sockets" are channels, but Micah is
> talking about a Scheme port -- more comparable to a libc "stream", no?
> Do the latest libcs ensure putc and getchar are thread-safe?  (I hope
> not: what a waste!)

Yes, they do.  You need putc_unlocked, getchar_unlocked, etc.
to skip the mutex, which makes sense to be safe by default.


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