F.70 ctThrdQueueMlen

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Returns the length of the message at the beginning of a queue.

Short Name

ctThrdQueueMlen

TYPE

Threading function

DECLARATION

NINT ctThrdQueueMlen(NINT qid, LONG timeout)

DESCRIPTION

Returns the length of the message at the head (beginning) of the queue, waiting up to timeout milliseconds if the queue is empty. Ordinarily, this call would be followed by a call to ctThrdQueueRead with a zero timeout. If ctThrdLIFOWrite is used, ctThrdQueueMlen is of little value because the head of the queue can change before the message length primitive can be or'ed in a subsequent queue read.

RETURN

Value	Symbolic Constant	Explanation
0	NO_ERROR	Successful function.
90	NQUE_ERR	Invalid qid.
156	NTIM_ERR	block in use by another thread. Timeout error.
514	CQUE_ERR	Queue could not be closed.
636	TSYF_ERR	block get failed.

See Appendix A "c-tree Plus Error Codes" of the c-tree Plus Programmer's Reference Guide for a complete listing of valid c-tree Plus error values.

EXAMPLE

See ctmtap.c for ctThrdQueueMlen examples.

LIMITATIONS

Can only be used with a ctThrd library.

SEE ALSO

ctThrdQueueClose, ctThrdQueueCount, ctThrdLIFOWrite, ctThrdQueueOpen, ctThrdQueueRead, and ctThrdQueueWrite.