[Winpcap-users] Using threads.

[David Barnish]

Yes. I agree. Pcap_dispatch(), pcap_next_ex(), and the other read
functions eventually hit the PacketReadPacket() function. It is here
that they either wait for data or return immediately based on the read
timeout (and other) settings and the availability of packet data.


Thank you,
David Barnish
 
Senior Software Engineer R&D
Spanlink Communications


-----Original Message-----
From: winpcap-users-bounces at winpcap.org
[mailto:winpcap-users-bounces at winpcap.org] On Behalf Of Guy Harris
Sent: Wednesday, March 15, 2006 2:29 PM
To: winpcap-users at winpcap.org
Subject: Re: [Winpcap-users] Using threads.

David Barnish wrote:
> Whether the read call blocks or not depends on the read timeout value
> passed to the pcap_openxxx() function and the SetMinToCopy() value if
> used. If the pcap_openxxx() function was told to return immediately (a
> -1 is passed I believe for param 4), the pcap_dispatch() and
> pcap_next_ex() will return immediately whether there are any packets
to
> read or not.

...but that's independent of whether you use pcap_dispatch() or 
pcap_next_ex().

> The code that Ramiro included showed that a 1 millisecond
> read timeout is used. So, within his while loop, the code will wait at
> most 1 millisecond (give or take a few milliseconds) before it
returns.
> When it returns, it may have a packet of data, or it may return a null
> packet pointer if there were no packets to read. So, I still say that
he
> is spinning in his while loop and taking away CPU resources from other
> threads.

...and he'd be doing the same with pcap_dispatch(), which can return 
without ever having called the callback routine.

I.e., switching to pcap_dispatch() won't fix that problem; the code path

to and in the kernel is the same regardless of whether you use 
pcap_dispatch() or pcap_next_ex().

(Using pcap_loop() won't help, either; it just repeatedly calls the read

op.)
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