tk_rpl_rdv

Reply Rendezvous

[C Language Interface]

ER ercd = tk_rpl_rdv ( RNO rdvno, VP msg, INT rmsgsz ) ;
[Parameters]

RNO	rdvno	Rendezvous number


VP	msg	Reply message packet address


INT	rmsgsz	Reply message size (in bytes)
[Return Parameters]

ER	ercd	Error code
[Error Codes]

E_OK	Normal completion


E_PAR		Parameter error (rmsgsz < 0, rmsgsz > maxrmsz, or value in msg cannot be used)


E_OBJ	Invalid object state (rdvno is invalid)


E_CTX		Context error (issued from task-independent portion (implementation-dependent error))
[Description]

Returns a reply to the calling task in the rendezvous, ending the rendezvous.

The task issuing this system call (here “Task X”) must be engaged in a rendezvous, i.e., this system call can be issued only after executing tk_acp_por. In the discussion that follows, the rendezvous calling task is “Task Y”, and the rendezvous number passed in a return parameter by tk_acp_por is rdvno. When tk_rpl_rdv is executed in this situation, the rendezvous state between Task X and Task Y is released, and the state of Task Y goes from WAIT for rendezvous completion back to READY state. When a rendezvous is ended by tk_rpl_rdv, accepting Task X can send a reply message to calling Task Y. The contents of the message specified by the accepting task are copied to the memory space specified in msg passed by Task Y to tk_cal_por. The size of the reply message rmsgsz is passed as a return parameter of tk_cal_por.

Error code E_PAR is returned if rmsgsz is larger than maxrmsz specified with tk_cre_por. When this error is detected, the rendezvous is not ended and the task that called tk_cal_por remains in WAIT state for rendezvous completion.

Even when tk_fwd_por and tk_rpl_rdv are issued from the task in dispatch-disabled or interrupt-disabled state, these system calls must behave normally. This capability can be used to perform processing that is inseparable from tk_fwd_por or tk_rpl_rdv.

[Additional Notes]

If a task calling a rendezvous aborts for some reason before completion of the rendezvous (before tk_rpl_rdv is executed), the accepting task has no direct way of knowing of the abort. In such a case, error code E_OBJ is returned to the rendezvous accepting task when it executes tk_rpl_rdv.

After a rendezvous is established, tasks are in principle detached from the rendezvous port and have no need to reference information about each other. However, since the value of maxrmsz, used when checking the length of the reply message sent using tk_rpl_rdv, is dependent on the rendezvous port, the task in rendezvous must record this information somewhere. One possible implementation would be to put this information in the TCB of the calling task after it goes to WAIT state, or in another area that can be referenced from the TCB, such as a stack area.

[Rationale for the Specification]

The parameter rdvno is passed to tk_rpl_rdv and tk_fwd_por as information for distinguishing one established rendezvous from another, but the rendezvous port ID (porid) used when establishing a rendezvous is not specified. This is based on the design principle that tasks are no longer related to rendezvous ports after a rendezvous has been established.

Error code E_OBJ rather than E_PAR is returned for an invalid rdvno. This is because rdvno itself is an object indicating the task that called the rendezvous.

[Porting Guideline]

Note that rmsgsz is of INT type and the range of values that can be specified may vary depending on the system. For example, in 16-bit environments, the size of the message that can be received at a time may be limited to 32767 (approximately 32KB).

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