4 * This file is part of BeRTOS.
6 * Bertos is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or
9 * (at your option) any later version.
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, write to the Free Software
18 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
20 * As a special exception, you may use this file as part of a free software
21 * library without restriction. Specifically, if other files instantiate
22 * templates or use macros or inline functions from this file, or you compile
23 * this file and link it with other files to produce an executable, this
24 * file does not by itself cause the resulting executable to be covered by
25 * the GNU General Public License. This exception does not however
26 * invalidate any other reasons why the executable file might be covered by
27 * the GNU General Public License.
29 * Copyright 2004, 2008 Develer S.r.l. (http://www.develer.com/)
30 * Copyright 1999, 2000, 2001 Bernie Innocenti <bernie@codewiz.org>
34 * \brief IPC signals implementation.
36 * Signals are a low-level IPC primitive. A process receives a signal
37 * when some external event has happened. Like interrupt requests,
38 * signals do not carry any additional information. If processing a
39 * specific event requires additional data, the process must obtain it
40 * through some other mechanism.
42 * Despite the name, one shouldn't confuse these signals with POSIX
43 * signals. POSIX signals are usually executed synchronously, like
44 * software interrupts.
46 * Signals are very low overhead. Using them exclusively to wait
47 * for multiple asynchronous events results in very simple dispatch
48 * logic with low processor and resource usage.
50 * The "event" module is a higher-level interface that can optionally
51 * deliver signals to processes. Messages provide even higher-level
52 * IPC services built on signals. Semaphore arbitration is also
53 * implemented using signals.
55 * In this implementation, each process has a limited set of signal
56 * bits (usually 32) and can wait for multiple signals at the same
57 * time using sig_wait(). Signals can also be polled using sig_check(),
58 * but a process spinning on its signals usually defeats their purpose
59 * of providing a multitasking-friendly infrastructure for event-driven
62 * Signals are like flags: they are either active or inactive. After an
63 * external event has delivered a particular signal, it remains raised until
64 * the process acknowledges it using either sig_wait() or sig_check().
65 * Counting signals is not a reliable way to count how many times a
66 * particular event has occurred, because the same signal may be
67 * delivered twice before the process can notice.
69 * Any execution context, including an interrupt handler, can deliver
70 * a signal to a process using sig_signal(). Multiple independent signals
71 * may be delivered at once with a single invocation of sig_signal(),
72 * although this is rarely useful.
74 * \section signal_allocation Signal Allocation
76 * There's no hardcoded mapping of specific events to signal bits.
77 * The meaning of a particular signal bit is defined by an agreement
78 * between the delivering entity and the receiving process.
79 * For instance, a terminal driver may be designed to deliver
80 * a signal bit called SIG_INT when it reads the CTRL-C sequence
81 * from the keyboard, and a process may react to it by quitting.
83 * \section sig_single SIG_SINGLE
85 * The SIG_SINGLE bit is reserved as a convenient shortcut in those
86 * simple scenarios where a process needs to wait on just one event
87 * synchronously. By using SIG_SINGLE, there's no need to allocate
88 * a specific signal from the free pool. The constraints for safely
89 * accessing SIG_SINGLE are:
90 * - The process MUST sig_wait() exclusively on SIG_SINGLE
91 * - SIG_SIGNAL MUST NOT be left pending after use (sig_wait() will reset
93 * - Do not sleep between starting the asynchronous task that will fire
94 * SIG_SINGLE, and the call to sig_wait().
95 * - Do not call system functions that may implicitly sleep, such as
96 * timer_delayTickes().
100 * \author Bernie Innocenti <bernie@codewiz.org>
105 #include <cfg/debug.h>
106 #include <drv/timer.h>
107 #include <kern/proc.h>
108 #include <kern/proc_p.h>
111 #if CONFIG_KERN_SIGNALS
114 * Check if any of the signals in \a sigs has occurred and clear them.
115 * \return the signals that have occurred.
117 sigmask_t sig_check(sigmask_t sigs)
122 IRQ_SAVE_DISABLE(flags);
123 result = CurrentProcess->sig_recv & sigs;
124 CurrentProcess->sig_recv &= ~sigs;
132 * Sleep until any of the signals in \a sigs occurs.
133 * \return the signal(s) that have awoken the process.
135 sigmask_t sig_wait(sigmask_t sigs)
141 * This is subtle: there's a race condition where a concurrent
142 * process or an interrupt calls sig_signal() to set a bit in
143 * out sig_recv just after we have checked for it, but before
144 * we've set sig_wait to tell them we want to be awaken.
146 * In this case, we'd deadlock with the signal bit already
147 * set and the process never being reinserted into the ready
150 IRQ_SAVE_DISABLE(flags);
152 /* Loop until we get at least one of the signals */
153 while (!(result = CurrentProcess->sig_recv & sigs))
156 * Tell "them" that we want to be awaken when any of these
159 CurrentProcess->sig_wait = sigs;
162 * Go to sleep and proc_schedule() another process.
164 * We re-enable IRQs because proc_schedule() does not
165 * guarantee to save and restore the interrupt mask.
169 IRQ_SAVE_DISABLE(flags);
172 * When we come back here, the wait mask must have been
173 * cleared by someone through sig_signal(), and at least
174 * one of the signals we were expecting must have been
177 ASSERT(!CurrentProcess->sig_wait);
178 ASSERT(CurrentProcess->sig_recv & sigs);
181 /* Signals found: clear them and return */
182 CurrentProcess->sig_recv &= ~sigs;
189 * Sleep until any of the signals in \a sigs or \a timeout ticks elapse.
190 * If the timeout elapse a SIG_TIMEOUT is added to the received signal(s).
191 * \return the signal(s) that have awoken the process.
192 * \note Caller must check return value to check which signal awoke the process.
194 sigmask_t sig_waitTimeout(sigmask_t sigs, ticks_t timeout)
200 ASSERT(!sig_check(SIG_TIMEOUT));
201 ASSERT(!(sigs & SIG_TIMEOUT));
202 /* IRQ are needed to run timer */
203 ASSERT(IRQ_ENABLED());
205 timer_set_event_signal(&t, proc_current(), SIG_TIMEOUT);
206 timer_setDelay(&t, timeout);
208 res = sig_wait(SIG_TIMEOUT | sigs);
210 IRQ_SAVE_DISABLE(flags);
211 /* Remove timer if sigs occur before timer signal */
212 if (!(res & SIG_TIMEOUT) && !sig_check(SIG_TIMEOUT))
220 * Send the signals \a sigs to the process \a proc.
221 * The process will be awoken if it was waiting for any of them.
223 * \note This call is interrupt safe.
225 void sig_signal(Process *proc, sigmask_t sigs)
229 /* See comment in sig_wait() for why this protection is necessary */
230 IRQ_SAVE_DISABLE(flags);
232 /* Set the signals */
233 proc->sig_recv |= sigs;
235 /* Check if process needs to be awoken */
236 if (proc->sig_recv & proc->sig_wait)
238 /* Wake up process and enqueue in ready list */
246 #endif /* CONFIG_KERN_SIGNALS */