Date: Tue, 11 Apr 2000 22:38:58 -0700 From: Arun Sharma <adsharma@sharmas.dhs.org> To: ming@yahoo-inc.com Cc: hackers@freebsd.org Subject: Re: Multithread safe gethostbyname() ? Message-ID: <200004120538.WAA17491@sharmas.dhs.org> In-Reply-To: <Pine.BSF.4.10.10004111813310.81762-100000@pious.yahoo.com> References: <Pine.BSF.4.10.10004111813310.81762-100000@pious.yahoo.com>
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In muc.lists.freebsd.hackers, you wrote:
>
> Is there a MT-safe implementation of gethostbyname() in FreeBSD (3.4/4.0)?
>
> On Solaris there is gethostbyname_r(). Calling gethostbyname() with in
> two threads cause both threads to block.
You seem to be talking about two different things:
1. A reentrant function - two different threads can be in the same function
simultaneously
2. A non blocking function.
Reading the code in /usr/src/lib/libc{,_r}, it appears to me that, the
FreeBSD implementation is not reentrant, and blocking. However,
gethostbyname calls poll(2), which causes a reschedule to another runnable
pthread, if any.
In your case, both the threads are waiting for a DNS server response,
so the thread scheduler doesn't have a thread to schedule.
I think it'd be very useful to have a non-blocking DNS lookup API (one
which exposes the underlying file descriptor) . Winsock has this. UNIX
netscape 4.x would freeze half as often if this was done right.
-Arun
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