Language Reference

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WAIT

Purpose

The WAIT statement may be used to wait for an asynchronous data transfer to complete or it may be used to detect the completion status of an asynchronous data transfer statement.

Format

>>-WAIT--(--wait_list--)---------------------------------------><
 
 

wait_list

is a list that must contain one ID= specifier and at most one of each of the other valid specifiers. The valid specifiers are:

ID= integer_expr

indicates the data transfer with which this WAIT statement is identified. The integer_expr is a scalar of type INTEGER(4) or default integer. To initiate an asynchronous data transfer, the ID= specifier is used on a READ or WRITE statement.

IOSTAT= ios

is an input/output status specifier that specifies the status of the input/output operation. ios is a scalar variable of type INTEGER(4) or default integer. When the input/output statement containing this specifier finishes execution, ios is defined with:

• A zero value if no error condition occurs;
• A positive value if an error occurs;
• A negative value if an end-of-file condition is encountered and no error occurs.

The ios defined for the IOSTAT= specifier of the asynchronous data transfer statement need not be identical to the ios defined for the IOSTAT= specifier of the matching WAIT statement.

ERR= stmt_label

is an error specifier that specifies the statement label of an executable statement in the same scoping unit to which control is to transfer in case of an error. Coding the ERR= specifier suppresses error messages.

The stmt_label defined for the ERR= specifier of the asynchronous data transfer statement need not be identical to the stmt_label defined for the ERR= specifier of the matching WAIT statement.

END= stmt_label

is an end-of-file specifier that specifies a statement label at which the program is to continue if an endfile record is encountered and no error occurs. If an external file is positioned after the endfile record, the IOSTAT= specifier, if present, is assigned a negative value, and the NUM= specifier, if present, is assigned an integer value. Coding the END= specifier suppresses the error message for end-of-file. This specifier can be specified for a unit connected for either sequential or direct access.

The stmt_label defined for the END= specifier of the asynchronous data transfer statement need not be identical to the stmt_label defined for the END= specifier of the matching WAIT statement.

DONE= logical_variable

specifies whether or not the asynchronous I/O statement is complete. If the DONE= specifier is present, the logical_variable is set to true if the asynchronous I/O is complete and is set to false if it is not complete. If the returned value is false, then one or more WAIT statements must be executed until either the DONE= specifier is not present, or its returned value is true. A WAIT statement without the DONE= specifier, or a WAIT statement that sets the logical_variable value to true, is the matching WAIT statement to the data transfer statement identified by the same ID= value.

Rules

The matching WAIT statement must be in the same scoping unit as the corresponding asynchronous data transfer statement. Within the instance of that scoping unit, the program must not execute a RETURN, END, or STOP statement before the matching WAIT statement is executed.

Related Information

Executing Data Transfer Statements Asynchronously

"AIX Implementation Details of XL Fortran Input/Output" in the User's Guide

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