Download Expipe User Guide

Getting Started
Writing Program (WRPROG)
OPEN OUTPUT PIPE1 PIPE2.
PERFORM WRIT1 nn TIMES.
CLOSE
PIPE1 PIPE2.
WRIT1.
WRITE
REC1.
<––––(1)
WRITE
REC2.
<––––(2)
Reading Program (RPROG)
OPEN INPUT PIPE1 PIPE2.
PERFORM READ1 UNTIL cond_1.
:
PERFORM READ2 UNTIL cond_2.
:
READ1.
READ PIPE1 AT END para-1.
<––––(3)
READ PIPE2 AT END para-2.
<––––(4)
READ2.
In this example, the reading program RPROG has a cycle to access the pipe PIPE2,
which is quite different from that of the writing program WPROG. That is, RPROG starts
reading PIPE2 after it finishes reading PIPE1; whereas, WPROG writes to PIPE1 and
PIPE2 concurrently. Therefore, it is possible for the FIFO buffer for PIPE2 to become
full before control is passed to the READ statement (4), which results in both WPROG
and RPROG becoming deadlocked.
In order to avoid a deadlock situation, the writing program (WPROG) must be modified
so that it can have the cycle to access PIPE1 and PIPE2 similar to that of the reading
program (RPROG). The modified writing program is shown in the following example.
Modified Writing Program (WPROG)
OPEN OUTPUT PIPE1 PIPE2.
PERFORM WRIT1 nn TIMES.
CLOSE
PIPE1.
PERFORM WRIT2 nn TIMES.
CLOSE
PIPE2.
WRIT1.
WRITE
REC1.
WRIT2.
WRITE
REC2.
7846 7024–000
<––––(1)
<––––(2)
2–5