hang in libcouchbase_wait() after get timeout

When one node is down and dropping packets, a store op trying to write to that node times out (OK) but libcouchbase_wait doesn't return (not OK).

[root@localhost cb-crank]# gcc -g -Wall -W -I$I/include -L$I/lib t.c -lcouchbase -o t
[root@localhost cb-crank]# export LD_LIBRARY_PATH=$I/lib
[root@localhost cb-crank]# ./t
Stored: hello (6)
Got: hellow (7) = world! (7)
[root@localhost cb-crank]# ./t hellow foo
Stored: hellow (7)
Got: hellow (7) = foo (4)
[root@localhost cb-crank]# ./t xyz
Got: hellow (7) = foo (4)
Failed during store 'xyz': Operation timed out

Setup: Start two nodes of Couchbase Server. In my test, they're on 10.4.2.13 and 10.4.2.14. Client (see attached code) is being run on host 10.4.2.14.

On one node (10.4.2.13), simulate a network problem with iptables:

iptables -I INPUT 1 -p tcp --sport 1000:60000 -j DROP
iptables -I INPUT 2 -p tcp --dport 1000:60000 -j DROP

Run the sample app a few times with different keys until you hit one that needs to access the down node. As seen in the output above, the storage callback is called with a timeout error, but the libcouchbase_wait() call never returns. Attach debugger to the client and view thread stacks:

1. gdb -p 21746
   GNU gdb (GDB) CentOS (7.0.1-42.el5.centos)
   Copyright (C) 2009 Free Software Foundation, Inc.
   License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
   This is free software: you are free to change and redistribute it.
   There is NO WARRANTY, to the extent permitted by law. Type "show copying"
   and "show warranty" for details.
   This GDB was configured as "x86_64-redhat-linux-gnu".
   For bug reporting instructions, please see:
   <http://www.gnu.org/software/gdb/bugs/>.
   Attaching to process 21746
   Reading symbols from /root/code/cb-crank/t...done.
   Reading symbols from /root/code/install/lib/libcouchbase.so.1...done.
   Loaded symbols for /root/code/install/lib/libcouchbase.so.1
   Reading symbols from /lib64/libc.so.6...(no debugging symbols found)...done.
   Loaded symbols for /lib64/libc.so.6
   Reading symbols from /root/code/install/lib/libvbucket.so.1...done.
   Loaded symbols for /root/code/install/lib/libvbucket.so.1
   Reading symbols from /lib64/libdl.so.2...(no debugging symbols found)...done.
   Loaded symbols for /lib64/libdl.so.2
   Reading symbols from /lib64/ld-linux-x86-64.so.2...(no debugging symbols found)...done.
   Loaded symbols for /lib64/ld-linux-x86-64.so.2
   Reading symbols from /lib64/libm.so.6...(no debugging symbols found)...done.
   Loaded symbols for /lib64/libm.so.6
   Reading symbols from /root/code/install/lib/libcouchbase_libevent.so.1...done.
   Loaded symbols for /root/code/install/lib/libcouchbase_libevent.so.1
   Reading symbols from /opt/couchbase/lib/libevent-2.0.so.5...(no debugging symbols found)...done.
   Loaded symbols for /opt/couchbase/lib/libevent-2.0.so.5
   Reading symbols from /lib64/librt.so.1...(no debugging symbols found)...done.
   Loaded symbols for /lib64/librt.so.1
   Reading symbols from /lib64/libpthread.so.0...(no debugging symbols found)...done.
   [Thread debugging using libthread_db enabled]
   Loaded symbols for /lib64/libpthread.so.0

warning: no loadable sections found in added symbol-file system-supplied DSO at 0x7fff822c0000
0x0000003407cd3603 in __epoll_wait_nocancel () from /lib64/libc.so.6
(gdb) where
#0 0x0000003407cd3603 in __epoll_wait_nocancel () from /lib64/libc.so.6
#1 0x00002b0211713c28 in ?? () from /opt/couchbase/lib/libevent-2.0.so.5
#2 0x00002b0211702a4c in event_base_loop () from /opt/couchbase/lib/libevent-2.0.so.5
#3 0x0000000000400d60 in main (argc=1, argv=0x7fff822027f0) at t.c:113
(gdb) thread apply all bt

Thread 1 (Thread 0x2b02114eeaf0 (LWP 21746)):
#0 0x0000003407cd3603 in __epoll_wait_nocancel () from /lib64/libc.so.6
#1 0x00002b0211713c28 in ?? () from /opt/couchbase/lib/libevent-2.0.so.5
#2 0x00002b0211702a4c in event_base_loop () from /opt/couchbase/lib/libevent-2.0.so.5
#3 0x0000000000400d60 in main (argc=1, argv=0x7fff822027f0) at t.c:113
(gdb) quit

Line t.c:113 is libcouchbase_wait().

Client compiled as:

gcc -g -Wall -W -I$I/include -L$I/lib t.c -lcouchbase -o t