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POSIX Message Queues

Why (continued)

POSIX MQs provide improvements on System V MQs:

• Queues identified by names (/name).

  ("open", "unlink")

• Reference counted
  
  
  • Kernel counts number of open references.
    
    
  • After mq_unlink(), queue is only deleted when reference count falls to zero (makes deletion decisions easier).
    
    
  • System V message queues are connectionless.
    
    
• API is more consistent with Unix model.

  ("open", "close", "unlink"; reference counting).

• Send/receive with timeout: mq_timedsend(2), mq_timedreceive(2).
  
  
• Asynchronous notification feature (more in moment).
  
  
• Message queue descriptor can be monitored with poll(2), select(2), or epoll.

  Linux specific!

(C) 2006, Michael Kerrisk