4 * Copyright 2004 Develer S.r.l. (http://www.develer.com/)
5 * Copyright 1999, 2000, 2001 Bernardo Innocenti <bernie@develer.com>
6 * This file is part of DevLib - See devlib/README for information.
9 * \brief IPC signals implementation.
11 * Signals are a low-level IPC primitive. A process receives a signal
12 * when some external event has happened. Like interrupt requests,
13 * signals do not carry any additional information. If processing a
14 * specific event requires additional data, the process must obtain it
15 * through some other mechanism.
17 * Despite the name, one shouldn't confuse these signals with POSIX
18 * signals. POSIX signals are usually executed synchronously, like
19 * software interrupts.
21 * In this implementation, each process has a limited set of signal
22 * bits (usually 32) and can wait for multiple signals at the same
23 * time using sig_wait(). Signals can also be polled using sig_check(),
24 * but a process spinning on its signals usually defeats their purpose
25 * of providing a multitasking-friendly infrastructure for event-driven
28 * Signals are like flags: they are either active or inactive. After an
29 * external event has delivered a particular signal, it remains raised until
30 * the process acknowledges it using either sig_wait() or sig_check().
31 * Counting signals is not a reliable way to count how many times a
32 * particular event has occurred, because the same signal may be
33 * delivered twice before the process can notice.
35 * Any execution context, including an interrupt handler, can deliver
36 * a signal to a process using sig_signal(). Multiple distinct signals
37 * may be delivered at once with a single invocation of sig_signal(),
38 * although this is rarely useful.
40 * There's no hardcoded mapping of specific events to signal bits.
41 * The meaning of a particular signal bit is defined by an agreement
42 * between the delivering entity and the receiving process.
43 * For instance, a terminal driver may be written to deliver
44 * a signal bit called SIG_INT when it reads the CTRL-C sequence
45 * from the keyboard, and a process may react to it by quitting.
47 * The SIG_SINGLE bit is reserved for a special purpose (this is
48 * more a suggestion than a constraint). When a process wants
49 * wait for a single event on the fly, it needs not allocate a
50 * free signal from its pool. Instead, SIG_SINGLE can be used
52 * The "event" module is a higher-level interface that can optionally
53 * deliver signals to processes. Messages provide even higher-level
54 * IPC services built on signals. Semaphore arbitration is also
55 * implemented using signals.
57 * Signals are very low overhead. Using them exclusively to wait
58 * for multiple asynchronous events results in very simple dispatch
59 * logic with low processor and resource usage.
64 * \author Bernardo Innocenti <bernie@develer.com>
69 * Revision 1.5 2004/08/04 21:50:33 bernie
70 * Add extensive documentation.
72 * Revision 1.4 2004/07/30 14:30:27 rasky
73 * Resa la sig_signal interrupt safe (con il nuovo scheduler IRQ-safe)
74 * Rimossa event_doIntr (ora inutile) e semplificata la logica delle macro con funzioni inline
76 * Revision 1.3 2004/07/30 14:24:16 rasky
77 * Task switching con salvataggio perfetto stato di interrupt (SR)
78 * Kernel monitor per dump informazioni su stack dei processi
80 * Revision 1.2 2004/06/03 11:27:09 bernie
81 * Add dual-license information.
83 * Revision 1.1 2004/05/23 17:27:00 bernie
84 * Import kern/ subdirectory.
94 #if CONFIG_KERN_SIGNALS
97 * Check if any of the signals in \a sigs has occurred and clear them.
98 * Return the signals that have occurred.
100 sigset_t sig_check(sigset_t sigs)
105 DISABLE_IRQSAVE(flags);
106 result = CurrentProcess->sig_recv & sigs;
107 CurrentProcess->sig_recv &= ~sigs;
108 ENABLE_IRQRESTORE(flags);
114 * Sleep until any of the signals in \a sigs occurs.
115 * Return the signal(s) that have awaked the process.
117 sigset_t sig_wait(sigset_t sigs)
122 DISABLE_IRQSAVE(flags);
124 /* Loop until we get at least one of the signals */
125 while (!(result = CurrentProcess->sig_recv & sigs))
127 /* go to sleep and proc_schedule() another process */
128 CurrentProcess->sig_wait = sigs;
132 /* Signals found: clear them and return */
133 CurrentProcess->sig_recv &= ~sigs;
134 ENABLE_IRQRESTORE(flags);
140 * Send the signals \a sigs to the process \a proc.
141 * The process will be awaken if it was waiting for any of them.
143 * \note This call is interrupt safe.
145 void sig_signal(Process *proc, sigset_t sigs)
148 DISABLE_IRQSAVE(flags);
150 /* Set the signals */
151 proc->sig_recv |= sigs;
153 /* Check if process needs to be awaken */
154 if (proc->sig_recv & proc->sig_wait)
156 /* Wake up process and enqueue in ready list */
161 ENABLE_IRQRESTORE(flags);
164 #endif /* CONFIG_KERN_SIGNALS */