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.