The asynchronous specifier determines whether asynchronous I/O occurs for a data transfer statement. It takes the following form:
ASYNCHRONOUS=i-expr
i-expr
Is a scalar character initialization expression that evaluates to 'YES' for asynchronous I/O or 'NO' for synchronous I/O. The value 'YES' should not appear unless the data transfer statement specifies a file unit number for io-unit. The default value is 'NO'.
Trailing blanks in the expression are ignored.
Asynchronous I/O is permitted only for external files opened with an OPEN statement that specifies ASYNCHRONOUS='YES'.
When an asynchronous I/O statement is executed, the following are defined to be the pending I/O storage sequence for the data transfer operation: