id,summary,reporter,owner,description,type,status,priority,component,version,resolution,keywords,cc,blockedby,blocking,reproduced,analyzed
609,Hang on reading UDP,Krieger,,"Sorry for inappropriately forming the report. Time constraints.

The symptoms:
When opening udp:// url with libavformat, and not having explicitly set fifo_size=0, there's a situation when av_read_frame never exits. When attaching with gdb, it shows the following bt (sorry for incompleteness).
I suspect that problem resides in libavformat/udp.c:565 of git HEAD 988f585fcb1cfb40fe4b706c32b31594b536bba0

We can't rely on select() to monitor new data arrival to socket that is recv()'ed by another thread (circular_buffer_task). Even if those socket calls are thread-safe, there's logical flaw.
We are probable to miss the moment of time when new data arrive, and kernel can notify our select() call. We repeatedly select() for 1 second intervals, but between them there's time for event to happen.
Although, this thinking does not answer on question 'why it hangs forever?'

{{{
(gdb) bt
#0  0x00007fe62b5def13 in select () from /lib64/libc.so.6
#1  0x00007fe62bbb7553 in udp_read (h=0x145a780, buf=<value optimized out>, size=<value optimized out>)
    at libavformat/udp.c:569
#2  0x00007fe62bb3598c in retry_transfer_wrapper (h=0x145a780, buf=0x146aaa0 ""G\037\377\020"", size=1472)
    at libavformat/avio.c:269
#3  ffurl_read (h=0x145a780, buf=0x146aaa0 ""G\037\377\020"", size=1472) at libavformat/avio.c:295
#4  0x00007fe62bb389c6 in fill_buffer (s=0x146b0c0, buf=0x7fffce573430 ""G\037\377\020"", size=188)
    at libavformat/aviobuf.c:568
#5  avio_read (s=0x146b0c0, buf=0x7fffce573430 ""G\037\377\020"", size=188) at libavformat/aviobuf.c:657
#6  0x00007fe62bb76d0b in read_packet (s=0x145a200, buf=0x7fffce573430 ""G\037\377\020"", 
    raw_packet_size=188) at libavformat/mpegts.c:1429
#7  0x00007fe62bb77866 in handle_packets (ts=0x146b180, nb_packets=0) at libavformat/mpegts.c:1485
#8  0x00007fe62bb7a01a in mpegts_read_packet (s=<value optimized out>, pkt=0x7fffce573610)
    at libavformat/mpegts.c:1706
#9  0x00007fe62bbbe66c in av_read_packet (s=0x145a200, pkt=0x7fffce573610) at libavformat/utils.c:744
#10 0x00007fe62bbc00da in read_frame_internal (s=0x145a200, pkt=0x7fffce573750)
    at libavformat/utils.c:1220
}}}
",defect,closed,normal,avformat,git-master,fixed,udp,,,,0,0