+ * In this implementation, each process has a limited set of signal
+ * bits (usually 32) and can wait for multiple signals at the same
+ * time using sig_wait(). Signals can also be polled using sig_check(),
+ * but a process spinning on its signals usually defeats their purpose
+ * of providing a multitasking-friendly infrastructure for event-driven
+ * applications.
+ *
+ * Signals are like flags: they are either active or inactive. After an
+ * external event has delivered a particular signal, it remains raised until
+ * the process acknowledges it using either sig_wait() or sig_check().
+ * Counting signals is not a reliable way to count how many times a
+ * particular event has occurred, because the same signal may be
+ * delivered twice before the process can notice.
+ *
+ * Any execution context, including an interrupt handler, can deliver
+ * a signal to a process using sig_signal(). Multiple distinct signals
+ * may be delivered at once with a single invocation of sig_signal(),
+ * although this is rarely useful.
+ *
+ * There's no hardcoded mapping of specific events to signal bits.
+ * The meaning of a particular signal bit is defined by an agreement
+ * between the delivering entity and the receiving process.
+ * For instance, a terminal driver may be written to deliver
+ * a signal bit called SIG_INT when it reads the CTRL-C sequence
+ * from the keyboard, and a process may react to it by quitting.
+ *
+ * The SIG_SINGLE bit is reserved for a special purpose (this is
+ * more a suggestion than a constraint). When a process wants
+ * wait for a single event on the fly, it needs not allocate a
+ * free signal from its pool. Instead, SIG_SINGLE can be used