HP Fortran Programmer Guide (766160-001, March 2014)

! when alarm is set by wake_up.f90, this program breaks out
! of the DO loop, prints message (which wake_up.f90 has
! written to), and exits.
COMMON /shared_data/ alarm, message
alarm = .FALSE.
! Wait for alarm to be set...
DO WHILE (alarm .EQ. .FALSE.)
! sleep(1) is an HP-UX system call that suspends a process
! for the number of seconds specified by the argument.
! The %VAL function tells Fortran that sleep expects its
! argument to be passed by value.
CALL sleep(%VAL(1))
END DO
! Message from wake.f90:
PRINT *, message
! The shared memory segment is destroyed when this program halts.
END
IMPORTANT In the example above, you must use +U77to access the correct sleep in the Fortran
library. If you use +U77, the line above:
CALL sleep (%VAL(1))
should instead read:
CALL sleep (1)
nl
PROGRAM main
! This program, wake_up.f90, should be run just after its
! companion, go_to_sleep.f90, starts to execute but in a
! separate process. The $HP$ SHARED_COMMON directive
! enables both programs to share the same memory.
! Directive puts the common block in shared memory.
$SHARED_COMMON KEY=’scb1’ /shared_common/
LOGICAL :: alarm
CHARACTER(LEN=8) :: message
! Declare a named common block for shared memory. It must
! be laid out n exactly the same way in both programs.
COMMON /shared_common/ alarm, message
! Write to message, sleep reads it.
message = "I'm up!"
! Set alarm to wake up sleep.
alarm = .TRUE.
! The shared memory segment will now be detached.
! However, because go_to_sleep is still running,
! the segment will still be present in memory until
! it stops executing, too.
END
Following are the command lines to compile each program:
$ f90 -o go_to_sleep go_to_sleep.f
$ f90 -o wake_up wake_up.f
Run the first program in any process by doing the following:
$ go_to_sleep
In another process, use the following command line to confirm that a shared memory segment has
been created for the program (the last in the list is the newly created one):
$ ipcs -m
IPC status from /dev/kmem as of Fri Mar 21 15:55:29 1997
T ID KEY MODE OWNER GROUP
Shared Memory:
m 0 0x4119c72b --rw-rw-rw- root root
m 1 0x4e180002 --rw-rw-rw- root root
m 2 0x41187bf4 --rw-rw-rw- root root
m 3 0x00000000 --rw------- root sys
m 7004 0x43186ea0 --rw-rw-rw- daemon daemon
m 6005 0x73636231 --rw-rw-rw- ed lang
Sharing data among programs 73