The Channel class / base.Channel methods |
Tests if some data can be read from the channel.
dataAvailable() RETURNING result BOOLEAN
The dataAvailable() method returns TRUE if some data can be read from the channel.
A consecutive call to a read method such as read() will not block.
The method opens up the possibility to read data asynchronously. One possible use for this method is to stop a data transfer to a remote site after receiving an error message from the remote site.
This function checks if at least one byte is available on the stream. A subsequent read will block if the read operation can not be completed. This should not happen: the methods read() and readLine() and their counterparts write() and writeLine() read and write complete lines (a line is a sequence of characters terminated by the line separator).This method is not typically used.
The local site sends a huge amount of data to the remote site using base.Channel.writeLine(). An error may occur during the processing of data by the remote side. The remote site writes an error message causing the local site to stop the data transmission.
-- this file: parent.4gl MAIN DEFINE i INT DEFINE c base.Channel LET c = base.Channel.create() CALL c.openPipe("fglrun child", "u") WHILE TRUE IF c.dataAvailable() THEN DISPLAY "message from child: ", c.readLine() EXIT WHILE END IF CALL c.writeLine("line " || i) END WHILE END MAIN
-- this file: child.4gl MAIN DEFINE c base.Channel DEFINE s STRING DEFINE n INT LET n = 0 LET c = base.Channel.create() CALL c.openFile("", "u") WHILE NOT c.isEof() LET s = c.readLine() LET n = n + 1 IF n == 3 THEN CALL c.writeLine("error: something happens") CALL readRemainingData(c) EXIT WHILE END IF END WHILE END MAIN FUNCTION readRemainingData(c) DEFINE c base.Channel DEFINE s STRING WHILE NOT c.isEof() LET s = c.readLine() END WHILE END FUNCTION