PHP as FastCGI and exit() function

Question

How exactly is exit() function working when in fastcgi mode? does it finish whole instance of php process in fastcgi pool or just ends current request and return process to te pool?

if the second answer - what causes logs of this kind:

[warn] FastCGI: (dynamic) server "/php.fcgi" (pid 25113) terminated by calling exit with status '0'

??