Just looking through J3/18-007r1 ...

11.6.7 says

R1171 event-variable is scalar-variable

C1176 (R1171) An event-variable shall be of type EVENT_TYPE from
the intrinsic module ISO_FORTRAN- ENV (16.10.2).

Clear so far.

11.6.8 tells me

C1177 (R1172) The event-variable in an event-wait-stmt shall not
be coindexed.

and

The event-variable shall not depend on the value of stat-variable
or errmsg-variable.

So... does an event-variable have to be a coarray? It would make
sense, certainly, but I see nothing prescribing it. Or am I missing
something?

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Thomas Koenig schrieb am Freitag, 25. Februar 2022 um 08:19:06 UTC+1:

Just looking through J3/18-007r1 ...

11.6.7 says

R1171 event-variable is scalar-variable

C1176 (R1171) An event-variable shall be of type EVENT_TYPE from
the intrinsic module ISO_FORTRAN- ENV (16.10.2).

Clear so far.

11.6.8 tells me

C1177 (R1172) The event-variable in an event-wait-stmt shall not
be coindexed.

and

The event-variable shall not depend on the value of stat-variable
or errmsg-variable.

So... does an event-variable have to be a coarray? It would make
sense, certainly, but I see nothing prescribing it. Or am I missing something?

I don‘t use Events with my CAF codes and I usually don‘t refer to the standards text. Modern Fortran explained, p.395, says “An event variable must be a coarray or a component of a coarray;...”.
Using coarray components as event variables is also allowed and even the only way for using Events with distributed objects models (using OOP syntax to implement the distributed objects).
OpenCoarrays/gfortran does currently only support the use of ordinary coarrays as event variables (and gives a compile time message if you try another form), ifort does allow all three forms for use with event variables:

program event_example
! using a coarray
use iso_fortran_env
implicit none
type(event_type), codimension[*] :: ev
integer a[*]
integer b
if (this_image()==1) then
event wait(ev)
b = a[2]
write(*,*)'image1, b value:',b
else if (this_image()==2) then
write(*,*)'image2'
a = 77
event post(ev[1])
end if
end program event_example

program event_example
! using a component of a coarray
use iso_fortran_env
implicit none
type t
type(event_type) ev
end type t
type(t), codimension[*] :: t1
integer a[*]
integer b
if (this_image()==1) then
event wait(t1%ev)
b = a[2]
write(*,*)'image1, b value:',b
else if (this_image()==2) then
write(*,*)'image2'
a = 77
event post(t1[1]%ev)
end if
end program event_example

program event_example
! using a coarray component
use iso_fortran_env
implicit none
type t
type(event_type), codimension[:], allocatable :: ev
end type t
type(t) t1
integer a[*]
integer b
allocate (t1%ev[*])
if (this_image()==1) then
event wait(t1%ev)
b = a[2]
write(*,*)'image1, b value:',b
else if (this_image()==2) then
write(*,*)'image2'
a = 77
event post(t1%ev[1])
end if
end program event_example

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Thomas Koenig schrieb am Freitag, 25. Februar 2022 um 08:19:06 UTC+1:

Just looking through J3/18-007r1 ...

11.6.7 says

R1171 event-variable is scalar-variable

C1176 (R1171) An event-variable shall be of type EVENT_TYPE from
the intrinsic module ISO_FORTRAN- ENV (16.10.2).

Clear so far.

11.6.8 tells me

C1177 (R1172) The event-variable in an event-wait-stmt shall not
be coindexed.

and

The event-variable shall not depend on the value of stat-variable
or errmsg-variable.

So... does an event-variable have to be a coarray? It would make
sense, certainly, but I see nothing prescribing it. Or am I missing something?

The requirement that event variables be coarrays is in 16.10.2.10 (C1604).

Regards
Reinhold

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On Thursday, February 24, 2022 at 11:19:06 PM UTC-8, Thomas Koenig wrote:

(snip)

So... does an event-variable have to be a coarray? It would make
sense, certainly, but I see nothing prescribing it. Or am I missing something?

I would have thought EVENT variables would be used with
asynchronous I/O, and then would not be coarrays, but then I haven't
tried using asynchronous I/O in Fortran.

The underlying I/O model for many IBM OSs is asynchronous, based on
the ECB, event control block, which I believe is related to event variables in some high-level languages.

Programs can test the ECB for completion, and then when appropriate,
WAIT on one (or more). You can, for example, wait for only some of a
group of ECB to complete, such as only one, and then handle the completed
on as appropriate. That is, have many outstanding events, and handle them
as they complete.

But I don't see why that should be coarrays.

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rbader <Bader@lrz.de> schrieb:

Thomas Koenig schrieb am Freitag, 25. Februar 2022 um 08:19:06 UTC+1:

Just looking through J3/18-007r1 ...

11.6.7 says

R1171 event-variable is scalar-variable

C1176 (R1171) An event-variable shall be of type EVENT_TYPE from
the intrinsic module ISO_FORTRAN- ENV (16.10.2).

Clear so far.

11.6.8 tells me

C1177 (R1172) The event-variable in an event-wait-stmt shall not
be coindexed.

and

The event-variable shall not depend on the value of stat-variable
or errmsg-variable.

So... does an event-variable have to be a coarray? It would make
sense, certainly, but I see nothing prescribing it. Or am I missing
something?

The requirement that event variables be coarrays is in 16.10.2.10 (C1604).

Ah, in the section describing EVENT_TYPE. I only searched the standard
for event-variable, not for that.

Thanks!

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gah4 <gah4@u.washington.edu> schrieb:

On Thursday, February 24, 2022 at 11:19:06 PM UTC-8, Thomas Koenig wrote:

(snip)

So... does an event-variable have to be a coarray? It would make
sense, certainly, but I see nothing prescribing it. Or am I missing
something?

I would have thought EVENT variables would be used with
asynchronous I/O, and then would not be coarrays, but then I haven't
tried using asynchronous I/O in Fortran.

Asynchronous I/O is quite a different kettle of fish. For
asynchronous I/O, you open a file as asynchronous, you read or
write with ASYNCHRONOUS="YES", you do something else, and you wait
(either with an explicit WAIT statement or with a non-asynchronous
statement).

The underlying I/O model for many IBM OSs is asynchronous, based on
the ECB, event control block, which I believe is related to event variables in
some high-level languages.

For Fortran, an event is something different.

Programs can test the ECB for completion, and then when appropriate,
WAIT on one (or more). You can, for example, wait for only some of a
group of ECB to complete, such as only one, and then handle the completed
on as appropriate. That is, have many outstanding events, and handle them
as they complete.

That sounds similar to the Fortran model of asynchronous I/O (although
gfortran implements that using pthreads).

But I don't see why that should be coarrays.

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