Signal data structures

The kernel maintains per-process signal data structures to keep track of, signal disposition,blocked signals, and pending signal queues. The process task structure contains appropriate references to these data structures:

struct task_struct {

....
....
....
/* signal handlers */
 struct signal_struct *signal;
 struct sighand_struct *sighand;

 sigset_t blocked, real_blocked;
 sigset_t saved_sigmask; /* restored if set_restore_sigmask() was used */
 struct sigpending pending;

 unsigned long sas_ss_sp;
 size_t sas_ss_size;
 unsigned sas_ss_flags;
  ....
  ....
  ....
  ....

};

Signal descriptors

Recall from our earlier discussions in the first chapter that Linux supports multi-threaded applications through lightweight processes. All LWPs of a threaded application are part of a process group and share signal handlers; each LWP (thread) maintains its own pending, and blocked signal queues.

The signal pointer of the task structure refers to the instance of type signal_struct...