Avoid PID file overriden by additional ContextBroker instance

[fgalan]

Case 1

Let's start CB using a given PID file:

contextBroker -pidpath /tmp/pidfile1.pid -fg

PID file is correctly filled:

$ ps ax | grep context
 17907 pts/2    Sl+    0:00 contextBroker -pidpath /tmp/pidfile1.pid -fg
 17932 pts/1    S+     0:00 grep context

$ cat /tmp/pidfile1.pid ; echo
17907

Now, I try to start a second instance of CB, running again contextBroker -pidpath /tmp/pidfile1.pid -fg. Of course, it fails, as the port is already in use:

time=Tuesday 16 Jan 10:11:23 2018.743Z | lvl=FATAL | corr=N/A | trans=N/A | from=N/A | srv=N/A | subsrv=N/A | comp=Orion | op=rest.cpp[1744]:restStart | msg=Fatal Error (error starting REST interface)

However, PID file has lost its content, while the first instance is still running:

$ ps ax | grep context
 17907 pts/2    Sl+    0:00 contextBroker -pidpath /tmp/pidfile1.pid -fg
 17975 pts/1    S+     0:00 grep context

$ cat /tmp/pidfile1.pid ; echo
cat: /tmp/pidfile1.pid: No existe el fichero o el directorio

Case 2

Let's start CB using a given PID file:

contextBroker -pidpath /tmp/pidfile1.pid -fg

PID file is correctly filled:

$ ps ax | grep context
 17990 pts/2    Sl+    0:00 contextBroker -pidpath /tmp/pidfile1.pid -fg
 18018 pts/1    S+     0:00 grep context

$ cat /tmp/pidfile1.pid ; echo
17990

Now I run a second instance in a free port with ontextBroker -pidpath /tmp/pidfile1.pid -fg -port 1027 so the second instance runs. The situation is now:

fermin@neodeb:~$ ps ax | grep context
 17990 pts/2    Sl+    0:00 contextBroker -pidpath /tmp/pidfile1.pid -fg
 18026 pts/3    Sl+    0:00 contextBroker -pidpath /tmp/pidfile1.pid -fg -port 1027
 18055 pts/1    S+     0:00 grep context
fermin@neodeb:~$ cat /tmp/pidfile1.pid ; echo 
18026

i,e. the second instance has overriden the file and the reference to the first instance PID has lost.

Fix

Context Broker should check that PID file doesn't exist at the very begining (either before to check other error conditions as if the port is free). If exist, it has to exit with an error message without touching the PID file.

[fgalan]

Fixed by PR #3091