Testing item vfs.dir.count under Windows, it was possible to cause Zabbix agent to hang or exit. The last lines in log are:
2236:20171117:153542.878 vfs_dir_count() pro=2 count=30
2236:20171117:153542.893 vfs_dir_count() 10=c:\/Z/zabbix-4.0.0alpha1=1 tmA/C/M=1510312786/1510312715/1510312712=? size=0=OK
2236:20171117:153542.910 vfs_dir_count() pro=2 count=31
2276:20171117:153542.925 WIN zbx_execute_threaded_metric() TIMEOUTED: WaitForSingleObject()
zabbix_agentd.exe : ERROR file:..\..\..\src\libs\zbxsys\mutexs.c,line:135 Something impossible has just happened.
To reproduce, one of the threaded metrics (vfs.dir.size, vfs.dir.count, vfs.fs.size) must be writing something into zabbix_agentd.log at the moment they time out. That is a very slim possibility, although the first two items are naturally long-running.
To reproduce artificially, void __zbx_zabbix_log(int level, const char *fmt, ...) can be slowed down with e.g. Sleep(1).
As per https://msdn.microsoft.com/en-us/library/windows/desktop/ms687032(v=vs.85).aspx , WAIT_ABANDONED is returned when child process failed to release mutex before termination. Zabbix agent chooses to terminate in response.
Zabbix agent should not terminate under unusual conditions that do not themselves prevent its further function.