- message queues
The <mqueue.h> header defines the mqd_t type, which is used for message queue descriptors. This will not be an array type. A message queue descriptor may be implemented using a file descriptor, in which case applications can open up to at least OPEN_MAX file and message queues.
The <mqueue.h> header defines the sigevent structure (as described in <signal.h>, see signal.h(3HEAD)) and the mq_attr structure, which is used in getting and setting the attributes of a message queue. Attributes are initially set when the message queue is created. A mq_attr structure has the following members:
long mq_flags message queue flags long mq_maxmsg maximum number of messages long mq_msgsize maximum message size long mq_curmsgs number of messages currently queued
Inclusion of the <mqueue.h> header may make visible symbols defined in the headers <fcntl.h>, <signal.h>, <sys/types.h>, and <time.h>.
See attributes(5) for descriptions of the following attributes: