Data Manipulation Language Statements › #LINEOUT—requests a transfer of data

#LINEOUT—requests a transfer of data

The #LINEOUT statement requests a transfer of data from the issuing program to the terminal, after appending line and device control characters appropriate to the physical terminal in use. #LINEOUT also establishes, modifies, and deletes page header lines.

A data transfer requested by the #LINEOUT statement can be synchronous or asynchronous; requests are asynchronous only when the NOWAIT option is specified:

• Synchronous—Following a synchronous request, control passes to the DC/UCF system. The system places the issuing task in an inactive state; when the #LINEOU request is completed, the task is redispatched according to its established priority. With 3270 terminals, a synchronous #LINEOUT request causes a processing delay immediately following the request while the system transfers the line to the page buffer. If the line of data fills the buffer, the system transfers the entire page of data to the terminal. Control does not return to the issuing program until the terminal operator has pressed the ENTER key. Thus, the program is made conversational.
• Asynchronous—Following an asynchronous request, control returns immediately to the issuing program. Thereafter, each time the program issues a line-mode I/O request, the system automatically checks to determine if the last asynchronous request has completed, and whether a new data transfer can be initiated.

  Asynchronous requests enable programs to buffer all required pages of output without suspending task execution during the actual data transmission. With an asynchronous request, the task can optionally terminate itself, freeing all its resources. The terminal operator can then review the buffered output, if desired.

The system processes I/O requests in the sequence received from the task; thus, if a program issues a synchronous #LINEOUT request after issuing one or more asynchronous requests, the system will complete all I/O requests before returning control to the issuing program.

The #LINEOUT request issued automatically by the system to empty partially-filled buffers on completion of a task is synchronous; therefore the terminal operator can view all screens and catch up with processing at that time.

If an application necessitates allowing the terminal operator to interrupt or terminate processing at some point in a task, a synchronous request must be issued to suspend processing while waiting for an operator response.

To transfer data immediately to a terminal, a write-direct-to-terminal #LINEOUT request (blast) can be issued. The system does not page multiple blast requests. The following #LINEOUT parameters are ignored during blast requests:

• HDR=
• OPTNS=(NOWAIT/NOBKPG/NEWPAGE)

(The NEWPAGE option is automatically forced during blast requests.)

Header lines can be defined for each new page of output to be transferred to a terminal. A maximum of three header lines can be established for each new page of output. The #LINEOUT statement specifies a header line and corresponding header-line number that can be used in subsequent new pages. The established header lines are sent to the terminal and written with each new page of output. The existing header lines may be overridden or deleted at any time during processing by issuing a #LINEOUT request specifying the appropriate line number and, for an override, the corresponding new header line.