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52. POSIX Message Queues > Relationship Between Descriptors and Message Queues

Relationship Between Descriptors and Message Queues

The relationship between a message queue descriptor and an open message queue is analogous to the relationship between a file descriptor and an open file (Figure 5-2, in Relationship Between File Descriptors and Open Files). A message queue descriptor is a per-process handle that refers to an entry in the system-wide table of open message queue descriptions, and this entry in turn refers to a message queue object. This relationship is illustrated in Figure 52-1.

Note

On Linux, POSIX message queues are implemented as i-nodes in a virtual file system, and message queue descriptors and open message queue descriptions are implemented as file descriptors and open file descriptions, respectively. However, these are implementation details that are not required by SUSv3 and don’t hold true on some other UNIX implementations. Nevertheless, we return to this point in Linux-Specific Features, because Linux provides some nonstandard features that are made possible by this implementation.


  

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