RTEMS C User's Guide
rtems_status_code rtems_message_queue_receive( rtems_id id, void *buffer, size_t *size, uint32_t option_set, rtems_interval timeout );
RTEMS_SUCCESSFUL - message received successfully
RTEMS_INVALID_ID - invalid queue id
buffer is NULL
count is NULL
RTEMS_UNSATISFIED - queue is empty
RTEMS_TIMEOUT - timed out waiting for message
RTEMS_OBJECT_WAS_DELETED - queue deleted while waiting
This directive receives a message from the message
queue specified in id. The
RTEMS_NO_WAIT options of the
options parameter allow the calling task to specify whether to
wait for a message to become available or return immediately.
For either option, if there is at least one message in the
queue, then it is copied to buffer, size is set to return the
length of the message in bytes, and this directive returns
immediately with a successful return code.
If the calling task chooses to return immediately and
the queue is empty, then a status code indicating this condition
is returned. If the calling task chooses to wait at the message
queue and the queue is empty, then the calling task is placed on
the message wait queue and blocked. If the queue was created
RTEMS_PRIORITY option specified, then
the calling task is inserted into the wait queue according to
its priority. But, if the queue was created with the
RTEMS_FIFO option specified, then the
calling task is placed at the rear of the wait queue.
A task choosing to wait at the queue can optionally
specify a timeout value in the timeout parameter. The timeout
parameter specifies the maximum interval to wait before the
calling task desires to be unblocked. If it is set to
RTEMS_NO_TIMEOUT, then the calling task will wait forever.
The following message receive option constants are defined by RTEMS:
RTEMS_WAIT- task will wait for a message (default)
RTEMS_NO_WAIT- task should not wait
Receiving a message from a global message queue which
does not reside on the local node will generate a request to the
remote node to obtain a message from the specified message
queue. If no message is available and
RTEMS_WAIT was specified, then
the task must be blocked until a message is posted. A proxy is
allocated on the remote node to represent the task until the
message is posted.
A clock tick is required to support the timeout functionality of this directive.
RTEMS C User's Guide
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