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>
33 * \brief IPC signals implementation.
35 * Signals are a low-level IPC primitive. A process receives a signal
36 * when some external event has happened. Like interrupt requests,
37 * signals do not carry any additional information. If processing a
38 * specific event requires additional data, the process must obtain it
39 * through some other mechanism.
41 * Despite the name, one shouldn't confuse these signals with POSIX
42 * signals. POSIX signals are usually executed synchronously, like
43 * software interrupts.
45 * Signals are very low overhead. Using them exclusively to wait
46 * for multiple asynchronous events results in very simple dispatch
47 * logic with low processor and resource usage.
49 * The "event" module is a higher-level interface that can optionally
50 * deliver signals to processes. Messages provide even higher-level
51 * IPC services built on signals. Semaphore arbitration is also
52 * implemented using signals.
54 * In this implementation, each process has a limited set of signal
55 * bits (usually 32) and can wait for multiple signals at the same
56 * time using sig_wait(). Signals can also be polled using sig_check(),
57 * but a process spinning on its signals usually defeats their purpose
58 * of providing a multitasking-friendly infrastructure for event-driven
61 * Signals are like flags: they are either active or inactive. After an
62 * external event has delivered a particular signal, it remains raised until
63 * the process acknowledges it using either sig_wait() or sig_check().
64 * Counting signals is not a reliable way to count how many times a
65 * particular event has occurred, because the same signal may be
66 * delivered twice before the process can notice.
68 * Signals can be delivered synchronously via sig_send() or asynchronously via
71 * In the synchronous case the process is awakened if it was waiting for any
72 * signal and immediately dispatched for execution via a direct context switch,
73 * if its priority is greater than the running process.
76 * - Synchronous-signal delivery:
78 * [P1]____sig_send()____proc_wakeup()____[P2]
81 * In the asynchronous case, the process is scheduled for execution as a
82 * consequence of the delivery, but it will be dispatched by the scheduler as
83 * usual, according to the scheduling policy.
86 * - Asynchronous-signal delivery:
88 * [P1]____sig_post()____[P1]____proc_schedule()____[P2]
91 * In this way, any execution context, including an interrupt handler, can
92 * deliver a signal to a process. However, synchronous signal delivery from a
93 * non-sleepable context (like an interrupt handler) is forbidden in order to
94 * avoid potential deadlock conditions. Instead, sig_post() can be used from
95 * any context, expecially from interrupt context or when the preemption is
98 * Multiple independent signals may be delivered at once with a single
99 * invocation of sig_send() or sig_post(), although this is rarely useful.
101 * \section signal_allocation Signal Allocation
103 * There's no hardcoded mapping of specific events to signal bits.
104 * The meaning of a particular signal bit is defined by an agreement
105 * between the delivering entity and the receiving process.
106 * For instance, a terminal driver may be designed to deliver
107 * a signal bit called SIG_INT when it reads the CTRL-C sequence
108 * from the keyboard, and a process may react to it by quitting.
110 * \section sig_single SIG_SINGLE
112 * The SIG_SINGLE bit is reserved as a convenient shortcut in those
113 * simple scenarios where a process needs to wait on just one event
114 * synchronously. By using SIG_SINGLE, there's no need to allocate
115 * a specific signal from the free pool. The constraints for safely
116 * accessing SIG_SINGLE are:
117 * - The process MUST sig_wait() exclusively on SIG_SINGLE
118 * - SIG_SIGNAL MUST NOT be left pending after use (sig_wait() will reset
120 * - Do not sleep between starting the asynchronous task that will fire
121 * SIG_SINGLE, and the call to sig_wait().
122 * - Do not call system functions that may implicitly sleep, such as
123 * timer_delayTicks().
125 * \author Bernie Innocenti <bernie@codewiz.org>
130 #include "cfg/cfg_timer.h"
131 #include <cfg/debug.h>
132 #include <cfg/depend.h>
135 #include <kern/proc.h>
136 #include <kern/proc_p.h>
139 #if CONFIG_KERN_SIGNALS
141 // Check config dependencies
142 CONFIG_DEPEND(CONFIG_KERN_SIGNALS, CONFIG_KERN);
145 * Check if any of the signals in \a sigs has occurred and clear them.
147 * \return the signals that have occurred.
149 sigmask_t sig_check(sigmask_t sigs)
154 IRQ_SAVE_DISABLE(flags);
155 result = current_process->sig_recv & sigs;
156 current_process->sig_recv &= ~sigs;
164 * Sleep until any of the signals in \a sigs occurs.
165 * \return the signal(s) that have awoken the process.
167 sigmask_t sig_wait(sigmask_t sigs)
171 /* Sleeping with IRQs disabled or preemption forbidden is illegal */
172 IRQ_ASSERT_ENABLED();
173 ASSERT(proc_preemptAllowed());
176 * This is subtle: there's a race condition where a concurrent process
177 * or an interrupt may call sig_send()/sig_post() to set a bit in
178 * Process.sig_recv just after we have checked for it, but before we've
179 * set Process.sig_wait to let them know we want to be awaken.
181 * In this case, we'd deadlock with the signal bit already set and the
182 * process never being reinserted into the ready list.
186 /* Loop until we get at least one of the signals */
187 while (!(result = current_process->sig_recv & sigs))
190 * Tell "them" that we want to be awaken when any of these
193 current_process->sig_wait = sigs;
195 /* Go to sleep and proc_switch() to another process. */
198 * When we come back here, the wait mask must have been
199 * cleared by someone through sig_send()/sig_post(), and at
200 * least one of the signals we were expecting must have been
203 ASSERT(!current_process->sig_wait);
204 ASSERT(current_process->sig_recv & sigs);
207 /* Signals found: clear them and return */
208 current_process->sig_recv &= ~sigs;
214 #if CONFIG_TIMER_EVENTS
216 #include <drv/timer.h>
218 * Sleep until any of the signals in \a sigs or \a timeout ticks elapse.
219 * If the timeout elapse a SIG_TIMEOUT is added to the received signal(s).
220 * \return the signal(s) that have awoken the process.
221 * \note Caller must check return value to check which signal awoke the process.
223 sigmask_t sig_waitTimeout(sigmask_t sigs, ticks_t timeout)
229 ASSERT(!sig_check(SIG_TIMEOUT));
230 ASSERT(!(sigs & SIG_TIMEOUT));
231 /* IRQ are needed to run timer */
232 ASSERT(IRQ_ENABLED());
234 timer_set_event_signal(&t, proc_current(), SIG_TIMEOUT);
235 timer_setDelay(&t, timeout);
237 res = sig_wait(SIG_TIMEOUT | sigs);
239 IRQ_SAVE_DISABLE(flags);
240 /* Remove timer if sigs occur before timer signal */
241 if (!(res & SIG_TIMEOUT) && !sig_check(SIG_TIMEOUT))
247 #endif // CONFIG_TIMER_EVENTS
249 INLINE void __sig_signal(Process *proc, sigmask_t sigs, bool wakeup)
253 IRQ_SAVE_DISABLE(flags);
255 /* Set the signals */
256 proc->sig_recv |= sigs;
258 /* Check if process needs to be awoken */
259 if (proc->sig_recv & proc->sig_wait)
261 ASSERT(proc != current_process);
267 SCHED_ENQUEUE_HEAD(proc);
273 * Send the signals \a sigs to the process \a proc and immeditaly dispatch it
276 * The process will be awoken if it was waiting for any of them and immediately
277 * dispatched for execution.
279 * \note This function can't be called from IRQ context, use sig_post()
282 void sig_send(Process *proc, sigmask_t sigs)
284 ASSERT_USER_CONTEXT();
285 IRQ_ASSERT_ENABLED();
286 ASSERT(proc_preemptAllowed());
288 __sig_signal(proc, sigs, true);
292 * Send the signals \a sigs to the process \a proc.
293 * The process will be awoken if it was waiting for any of them.
295 * \note This call is interrupt safe.
297 void sig_post(Process *proc, sigmask_t sigs)
299 __sig_signal(proc, sigs, false);
302 #endif /* CONFIG_KERN_SIGNALS */