Changes: Added to documents _exit() should be used instead of exit() with every other booster than exec-booster

RevBy: Pertti Kellomaki

doc/libmeegotouchboost.dox

@@ -166,8 +166,26 @@ Check that applauncherd package is installed and applancherd daemon is
 running. You can now run your application as usual as
 /usr/bin/application_binary, or use the mboosted launching by running:
 
+
+
 \code
 invoker --type=m /usr/bin/application_binary
 \endcode
+\_exit() should be used instead of exit() with every other booster than exec-booster 
+
+The basic difference between exit() and _exit() is that the former performs clean-up related to user-mode constructs in the library,
+and calls user-supplied cleanup-functions, whereas the latter performs only the kernel cleanup for the process.
+
+The function _exit() terminates the calling process "immediately". Any open file descriptors belonging to the process are closed; any children
+of the process are inherited by process.
+
+The exit() function causes normal process termination and the value of status is returned to the parent.
+a child process should strictly use _exit() instead of a simple exit() or a normal return from main(). 
+
+The user level initializations of the libraries are done once when the launcher daemon loads the libraries. 
+The launched applications are child processes of the launcher, and every time exit() is called, the corresponding cleanup actions are executed.
+The root problem is that the cleanup actions get done multiple times, and libraries may not be designed to tolerate this. 
+By calling _exit() in the applications, the problem is avoided. 
+
 */