Summary: a random hanging bug when receiving multicast datagrams on 2.6.x kernels. Keywards: hang, networking, kernel, multicast, recv, multicast loopback, poll hang, select hang Kernel version: 2.6.x Full description of the problem: ----------------------------------------------- * This simple program demonstrates a bug in Linux kernel 2.6.x releases (and * possibly 2.4 kernels also). I have tested this code on several 2.6 kernels * (RHEL 4.4, 4.5, 5.0 releases) all suffering the same bug. On Sun Solaris 10, * however, it always behave correctly. * * This bug also affects select/poll's behavior as demonstrated in CASE2. * * How to reproduce the bug... * * Please make sure the multicast group address and the port number are not * currently in use on your test system. I use group address 239.255.1.1 and * port number 12345 here. Here are commands you can use to verify: * netstat -gn * netstat -an | grep 12345 * If you don't see port 12345 and group address 239.255.1.1 listed, that is * good. * * Test scenarios: * 1. Run one copy of this program, if you see it's running and receiving its * own messages, control-C out of it (because that is how it should behave). * And try again. If you try that a few times, you will see that this program * will hang on recv() function! That is an incorrect behavior. This program * should always receive its own messages. * * 2. Follow scenario #1 until you get it hanging, open another window, and run * a second copy of this program. You will see both copies start running and * can receive each other's messages. That's a correct behavior -- the first * datagram from the second copy takes the first copy of the process out of * hanging state. Test program source file is attached. If you can't find the attached C++ source file, please send email to my personal email account at [email protected] and I'll send the testing code from there. -------------------------------------------------------- NOTICE: If received in error, please destroy and notify sender. Sender does not intend to waive confidentiality or privilege. Use of this email is prohibited when received in error.
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simplemcast.cc
Description: simplemcast.cc
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