RTEMS C User's Guide
The rtems_signal_send directive allows both
tasks and ISRs to send signals to a target task. The target task and
a set of signals are specified to the
rtems_signal_send directive. The sending
of a signal to a task has no effect on the execution state of
that task. If the task is not the currently running task, then
the signals are left pending and processed by the task's ASR the
next time the task is dispatched to run. The ASR is executed
immediately before the task is dispatched. If the currently
running task sends a signal to itself or is sent a signal from
an ISR, its ASR is immediately dispatched to run provided signal
processing is enabled.
If an ASR with signals enabled is preempted by another task or an ISR and a new signal set is sent, then a new copy of the ASR will be invoked, nesting the preempted ASR. Upon completion of processing the new signal set, control will return to the preempted ASR. In this situation, the ASR must be reentrant.
Like events, identical signals sent to a task are not queued. In other words, sending the same signal multiple times to a task (without any intermediate signal processing occurring for the task), has the same result as sending that signal to that task once.
RTEMS C User's Guide
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