Message queues

The number of message queues is limited by the -n option to mqueue or mq. The default is 1024, and the maximum is 32768; you can query the current value with sysconf( _SC_MQ_OPEN_MAX ).

The default maximum number of entries in a queue, and the default maximum size of a queue entry depend on whether you're using the traditional (mqueue) or alternate (mq) implementation of message queues:

Attribute Traditional Alternate
Number of entries 1024 64
Message size 4096 256

For more information, see mqueue and mq in the Utilities Reference, and mq_open() in the QNX Neutrino C Library Reference.

Note: In the traditional implementation, each call to mq_open() uses one file descriptor; in the alternate implementation, each call to mq_open() uses two.