- * Any execution context, including an interrupt handler, can deliver
- * a signal to a process using sig_signal(). Multiple independent signals
- * may be delivered at once with a single invocation of sig_signal(),
- * although this is rarely useful.
+ * Signals can be delivered synchronously via sig_send() or asynchronously via
+ * sig_post().
+ *
+ * In the synchronous case the process is awakened if it was waiting for any
+ * signal and immediately dispatched for execution via a direct context switch,
+ * if its priority is greater than the running process.
+ *
+ * <pre>
+ * - Synchronous-signal delivery:
+ *
+ * P1__ __P2
+ * \ /
+ * \__sig_send()____proc_wakeup()__/
+ * </pre>
+ *
+ * In the asynchronous case, the process is scheduled for execution as a
+ * consequence of the delivery, but it will be dispatched by the scheduler as
+ * usual, according to the scheduling policy.
+ *
+ * <pre>
+ * - Asynchronous-signal delivery:
+ *
+ * P1__ __P1__ __P2
+ * \ / \ /
+ * \__sig_post()__/ \__proc_schedule()__/
+ * </pre>
+ *
+ * In this way, any execution context, including an interrupt handler, can
+ * deliver a signal to a process. However, synchronous signal delivery from a
+ * non-sleepable context (like an interrupt handler) is forbidden in order to
+ * avoid potential deadlock conditions. Instead, sig_post() can be used from
+ * any context, expecially from interrupt context or when the preemption is
+ * disabled.
+ *
+ * Multiple independent signals may be delivered at once with a single
+ * invocation of sig_send() or sig_post(), although this is rarely useful.