12-19-2010
Quote:
Originally Posted by
Loic Domaigne
Hi,
The answer from fpmurphy is short, but up to the point. Let me explain a little bit; In a multi-threaded process, a signal handler process-wide, that is global to all threads. However, when the signal is delivered, the system library / kernel picks up a particular thread that shall run the handler. This might be any thread in the process.
In your particular example, you wish that the handler runs in the context of thread1, so that the recvfrom() gets interrupted. But, unless you force it too, the handler may run in the context of the main thread. In that case, nothing will happen. This is likely what you are experiencing.
The way to force the handler to run in the context of thread1 (or equivalently, we say the signal to be delivered to thread1) is using pthread_sigmask() as mentioned by fpmurphy. Please refer to example in the link provided above, to see how it works. Incidentally, this example was my first contribution to the SUSv3 standard; so if you have questions please feel free to ask
And finally, I would suggest to resort other strategies than alarm() & co. to implement a timeout on the receive operation if you're multi-threaded.
Cheers, Loïc.
Thanks, I will try it today.
9 More Discussions You Might Find Interesting
1. Post Here to Contact Site Administrators and Moderators
I am unable to open the mimesender thread. I get the following message when clicking on https://www.unix.com/showthread.php?p=33233#post33233 : (2 Replies)
Discussion started by: dangral
2 Replies
2. IP Networking
Hi
I want a UDP client receiving program. Here is the scenario. The client has to listen to the UDP server and has to acknowledge back on receiving data from the server. Can anyone help me out.
regards,
Nirmala (1 Reply)
Discussion started by: Nirmala
1 Replies
3. Programming
Hi,
Am very new to socket programming.
When we use UDP sockets to communicate between two processess,
will both the client/server socket be able to send/recv ?
meaning can sendto()/ recvfrom() be used on both server and client?
It could be useful even if anybody provide some link on socket... (1 Reply)
Discussion started by: rvan
1 Replies
4. UNIX for Advanced & Expert Users
HI
I want to create a UDP concurrent server
can any one give the code for UDP concurrent server (8 Replies)
Discussion started by: chanikya
8 Replies
5. Forum Support Area for Unregistered Users & Account Problems
Hello,
I'd like to post a aix thread but I'm unable to.
Please let me know why this is happening.
Thanks.... (1 Reply)
Discussion started by: sullivjp
1 Replies
6. Programming
Hi,
I have a situation where i need to communicate a linux client with a windows server, I am using a UDP socket communication channel. I am able to send packets from my linux clients to the windows server but unable to receive any data packet from the server. Do i need to make any setting in... (0 Replies)
Discussion started by: John20
0 Replies
7. IP Networking
Hifriends
I have a doubt .
how to create a multi-chat server using UDP which can run on MAC systems..
Thank u in advance (3 Replies)
Discussion started by: babbu25
3 Replies
8. Forum Support Area for Unregistered Users & Account Problems
I am unable to post reply to a thread. Whenever I will reply to any post I get the message every time :
The message you have entered is too short. Please lengthen your message to at least 5 characters.
Even though length of the message is more than required.
for example I tried to post
... (3 Replies)
Discussion started by: Unregistered
3 Replies
9. Forum Support Area for Unregistered Users & Account Problems
Hi.
I registered, but when trying to post, I get ...
"Sorry, you do not have enough Bits to post a new thread"
Google & Forum search showed some hits, but no solution.
Please advide.
Thanks! (1 Reply)
Discussion started by: gehe
1 Replies
LEARN ABOUT NETBSD
pcap_breakloop
PCAP_BREAKLOOP(3) Library Functions Manual PCAP_BREAKLOOP(3)
NAME
pcap_breakloop - force a pcap_dispatch() or pcap_loop() call to return
SYNOPSIS
#include <pcap/pcap.h>
void pcap_breakloop(pcap_t *);
DESCRIPTION
pcap_breakloop() sets a flag that will force pcap_dispatch() or pcap_loop() to return rather than looping; they will return the number of
packets that have been processed so far, or -2 if no packets have been processed so far.
This routine is safe to use inside a signal handler on UNIX or a console control handler on Windows, as it merely sets a flag that is
checked within the loop.
The flag is checked in loops reading packets from the OS - a signal by itself will not necessarily terminate those loops - as well as in
loops processing a set of packets returned by the OS. Note that if you are catching signals on UNIX systems that support restarting system
calls after a signal, and calling pcap_breakloop() in the signal handler, you must specify, when catching those signals, that system calls
should NOT be restarted by that signal. Otherwise, if the signal interrupted a call reading packets in a live capture, when your signal
handler returns after calling pcap_breakloop(), the call will be restarted, and the loop will not terminate until more packets arrive and
the call completes.
Note also that, in a multi-threaded application, if one thread is blocked in pcap_dispatch(), pcap_loop(), pcap_next(), or pcap_next_ex(),
a call to pcap_breakloop() in a different thread will not unblock that thread; you will need to use whatever mechanism the OS provides for
breaking a thread out of blocking calls in order to unblock the thread, such as thread cancellation in systems that support POSIX threads.
Note that pcap_next() and pcap_next_ex() will, on some platforms, loop reading packets from the OS; that loop will not necessarily be ter-
minated by a signal, so pcap_breakloop() should be used to terminate packet processing even if pcap_next() or pcap_next_ex() is being used.
pcap_breakloop() does not guarantee that no further packets will be processed by pcap_dispatch() or pcap_loop() after it is called; at most
one more packet might be processed.
If -2 is returned from pcap_dispatch() or pcap_loop(), the flag is cleared, so a subsequent call will resume reading packets. If a posi-
tive number is returned, the flag is not cleared, so a subsequent call will return -2 and clear the flag.
SEE ALSO
pcap(3), pcap_loop(3), pcap_next_ex(3)
5 April 2008 PCAP_BREAKLOOP(3)