Most processes "die" in the sense that they terminate the execution of the code they were supposed to run. When this occurs, the kernel must be notified so that it can release the resources owned by the process; this includes memory, open files, and any other odds and ends that we will encounter in this book, such as semaphores.
The usual way for a process to terminate is to invoke the
exit( ) library function, which releases the
resources allocated by the C library, executes each function registered
by the programmer, and ends up invoking a system call that evicts the
process from the system. The
library function may be inserted by the programmer
explicitly. Additionally, the C compiler always inserts an
exit( ) function call right after the last
statement of the
Alternatively, the kernel may force a whole thread group to die. This typically occurs when a process in the group has received a signal that it cannot handle or ignore (see Chapter 11) or when an unrecoverable CPU exception has been raised in Kernel Mode while the kernel was running on behalf of the process (see Chapter 4).
In Linux 2.6 there are two system calls that terminate a User Mode application:
system call, which terminates a full thread group,
that is, a whole multithreaded application. The main kernel
function that implements this system call is called
do_group_exit( ). This is the system call that should be invoked by the ...