* signals. POSIX signals are usually executed synchronously, like
* software interrupts.
*
+ * Signals are very low overhead. Using them exclusively to wait
+ * for multiple asynchronous events results in very simple dispatch
+ * logic with low processor and resource usage.
+ *
+ * The "event" module is a higher-level interface that can optionally
+ * deliver signals to processes. Messages provide even higher-level
+ * IPC services built on signals. Semaphore arbitration is also
+ * implemented using signals.
+ *
* 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(),
* 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
+ * 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.
*
+ * \section signal_allocation Signal Allocation
+ *
* 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
+ * For instance, a terminal driver may be designed 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
- *
- * The "event" module is a higher-level interface that can optionally
- * deliver signals to processes. Messages provide even higher-level
- * IPC services built on signals. Semaphore arbitration is also
- * implemented using signals.
- *
- * Signals are very low overhead. Using them exclusively to wait
- * for multiple asynchronous events results in very simple dispatch
- * logic with low processor and resource usage.
- *
+ * \section sig_single SIG_SINGLE
+ *
+ * The SIG_SINGLE bit is reserved as a convenient shortcut in those
+ * simple scenarios where a process needs to wait on just one event
+ * synchronously. By using SIG_SINGLE, there's no need to allocate
+ * a specific signal from the free pool. The constraints for safely
+ * accessing SIG_SINGLE are:
+ * - The process MUST sig_wait() exclusively on SIG_SINGLE
+ * - SIG_SIGNAL MUST NOT be left pending after use (sig_wait() will reset
+ * it automatically)
+ * - Do not sleep between starting the asynchronous task that will fire
+ * SIG_SINGLE, and the call to sig_wait().
+ * - Do not call system functions that may implicitly sleep, such as
+ * timer_delayTickes().
*
* \version $Id$
*
/**
* Sleep until any of the signals in \a sigs occurs.
- * \return the signal(s) that have awaked the process.
+ * \return the signal(s) that have awoken the process.
*/
sigmask_t sig_wait(sigmask_t sigs)
{
/**
* Sleep until any of the signals in \a sigs or \a timeout ticks elapse.
* If the timeout elapse a SIG_TIMEOUT is added to the received signal(s).
- * \return the signal(s) that have awaked the process.
- * \note Caller must check return value to check which signal has awaked the process.
+ * \return the signal(s) that have awoken the process.
+ * \note Caller must check return value to check which signal awoke the process.
*/
sigmask_t sig_waitTimeout(sigmask_t sigs, ticks_t timeout)
{
ASSERT(!sig_check(SIG_TIMEOUT));
ASSERT(!(sigs & SIG_TIMEOUT));
- /* IRQ are needed to run timer */
- ASSERT(IRQ_ENABLED);
+ /* IRQ are needed to run timer */
+ ASSERT(IRQ_ENABLED());
timer_set_event_signal(&t, proc_current(), SIG_TIMEOUT);
timer_setDelay(&t, timeout);
if (!(res & SIG_TIMEOUT) && !sig_check(SIG_TIMEOUT))
timer_abort(&t);
IRQ_RESTORE(flags);
+ return res;
}
/**
* Send the signals \a sigs to the process \a proc.
- * The process will be awaken if it was waiting for any of them.
+ * The process will be awoken if it was waiting for any of them.
*
* \note This call is interrupt safe.
*/
/* Set the signals */
proc->sig_recv |= sigs;
- /* Check if process needs to be awaken */
+ /* Check if process needs to be awoken */
if (proc->sig_recv & proc->sig_wait)
{
/* Wake up process and enqueue in ready list */