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An OS-9/OS-9000 Message Based Interprocess Communication Facility implemented as a kernel extension.
A message port is a FIFO queue of structured objects. Each port is identified by a unique name and may be read or written by any task knowing this name subject to access permissions.
A name of up to eleven characters.
A unique identifier assigned by the system called a Message Port Id (MPID).
A queue length determining the maximum number of messages that can be held by the port at any time.
The user and group Id of its creator.
Access permissions for owner, group and others for send,m receive, link and deletion.
There is no limit to the size of a message other than available memory. However FAST message ports are limited to messages of 64KB or less.
Each message port can hold a number of messages equal to its queue length, as specified when the port was created. A queue length of up to 65535 messages can be specified when creating a message port.
The maximum number of message ports is a system configuration parameter and cannot be changed without re-starting the system. Up to 65535 message ports may be allowed for.
Each message system requires an initial memory allocation of 2+(4*MAX) bytes where MAX is the maximum number of message ports to be allowed for.
Each message port requires 48+(4*QLEN) bytes, where QLEN is the maximum queue length of the port.
Each message queue on a message port requires an amount of memory equal to the size of the application message plus 12 bytes of message header information.
For FAST message ports, an amount of memory equal to the maximum message size times the maximum number of queued messages is allocated on port creation.
The message passing system is compatible with OS-9000 and with version 2.1 or later OS-9/680X0.
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