16.4. Directives

This section details the directives of the Signal Manager. A subsection is dedicated to each of this manager’s directives and lists the calling sequence, parameters, description, return values, and notes of the directive.

16.4.1. rtems_signal_catch()

Establishes an asynchronous signal routine (ASR) for the calling task.

CALLING SEQUENCE:

rtems_status_code rtems_signal_catch(
  rtems_asr_entry asr_handler,
  rtems_mode      mode_set
);

PARAMETERS:

asr_handler

This parameter is the handler to process an asynchronous signal set.

mode_set

This parameter is the task mode while an asynchronous signal set is processed by the handler. See rtems_task_mode().

DESCRIPTION:

This directive establishes an asynchronous signal routine (ASR) for the calling task. The asr_handler parameter specifies the entry point of the ASR. A task may have at most one handler installed at a time. The most recently installed handler is used. When asr_handler is NULL, the ASR for the calling task is invalidated and all pending signals are cleared. Any signals sent to a task with an invalid ASR are discarded. The mode_set parameter specifies the execution mode for the ASR. This execution mode supersedes the task’s execution mode while the ASR is executing.

RETURN VALUES:

RTEMS_SUCCESSFUL

The requested operation was successful.

RTEMS_NOT_IMPLEMENTED

The RTEMS_NO_PREEMPT was set in mode_set and the system configuration had no implementation for this mode.

RTEMS_NOT_IMPLEMENTED

The RTEMS_INTERRUPT_LEVEL() was set to a positive level in mode_set and the system configuration had no implementation for this mode.

NOTES:

It is strongly recommended to disable ASR processing during ASR processing by setting RTEMS_NO_ASR in mode_set, otherwise a recursion may happen during ASR processing. Uncontrolled recursion may lead to stack overflows.

Using the same mutex (in particular a recursive mutex) in normal task context and during ASR processing may result in undefined behaviour.

Asynchronous signal handlers can access thread-local storage (TLS). When thread-local storage is shared between normal task context and ASR processing, it may be protected by disabled interrupts.

CONSTRAINTS:

The following constraints apply to this directive:

  • The directive may be called from within task context.

  • The directive will not cause the calling task to be preempted.

16.4.2. rtems_signal_send()

Sends the signal set to the task.

CALLING SEQUENCE:

rtems_status_code rtems_signal_send(
  rtems_id         id,
  rtems_signal_set signal_set
);

PARAMETERS:

id

This parameter is the identifier of the target task to receive the signal set.

signal_set

This parameter is the signal set to send.

DESCRIPTION:

This directive sends the signal set, signal_set, to the target task identified by id.

If a caller sends a signal set to a task with an invalid ASR, then an error code is returned to the caller. If a caller sends a signal set to a task whose ASR is valid but disabled, then the signal set will be caught and left pending for the ASR to process when it is enabled. If a caller sends a signal set to a task with an ASR that is both valid and enabled, then the signal set is caught and the ASR will execute the next time the task is dispatched to run.

RETURN VALUES:

RTEMS_SUCCESSFUL

The requested operation was successful.

RTEMS_INVALID_NUMBER

The signal_set parameter was 0.

RTEMS_INVALID_ID

There was no task associated with the identifier specified by id.

RTEMS_NOT_DEFINED

The target task had no valid ASR installed.

NOTES:

Sending a signal set to a task has no effect on that task’s state. If a signal set is sent to a blocked task, then the task will remain blocked and the signals will be processed when the task becomes the running task.

Sending a signal set to a global task which does not reside on the local node will generate a request telling the remote node to send the signal set to the specified task.

CONSTRAINTS:

The following constraints apply to this directive:

  • The directive may be called from within interrupt context.

  • The directive may be called from within device driver initialization context.

  • The directive may be called from within task context.

  • When the directive operates on a local object, the directive will not cause the calling task to be preempted.

  • When the directive operates on a remote object, the directive sends a message to the remote node and waits for a reply. This will preempt the calling task.