LinkReadyQ[link] tests whether there is an expression ready to read from the specified MathLink connection.
link must be an active LinkObject, as returned by functions like LinkLaunch or Links.
If LinkReadyQ[link] returns True, then LinkRead[link] will not block under any normal circumstances.
If LinkReadyQ[link] returns False, then LinkRead[link] will block, and will not return until something becomes available to read on link.
LinkReadyQ[link] tests whether there is any data to read; it cannot determine whether the data represents a complete expression.
LinkReadyQ corresponds to the MathLink library function MLReady().
See The Mathematica Book: Section 2.12.6.
See also: LinkRead, LinkWrite, LinkInterrupt.