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Plan execution language and executive

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Re: [plexil-support] Concurrency: How to resolve variable contention?

From: Dalal, M. (ARC-TI)[K. W. S. LLC] <mic...@na...> - 2025-04-28 18:15:46

Attachments: AssignmentPriority.ple image001.png

Hi Christopher,

Thanks for your interest in PLEXIL, and for providing an example plan. You ask a good question.

If you are using release 4.6 of PLEXIL (the releases/plexil-4.6 branch), which is its officially supported version, your plan will produce a runtime error because of the assignment conflict, and the way to deconflict the assignments is by adding a Priority clause to each assignment node. I’ve attached an example plan, which also prints the result.

Note that both assignments execute, at the same logical time (execution cycle) but in the prioritized order. The higher priority node (lower number) will execute *first*, which in this case means that the lower priority node (higher number) will be the final value. I realize this may be unintuitive!

If you are using Release 6 (the releases/plexil-6) or ‘develop’ branch, the situation is different – your original plan will execute and the assignments will occur in unspecified order. I can elaborate on this and explore options if needed.

Let us know if you have further questions.

Best,
Michael

K. Michael Dalal
Autonomous Systems and Robotics, Code TI
KBR Inc. at NASA Ames Research Center
Moffett Field, CA 94035
* Opinions expressed herein are my own *

On 4/25/25, 4:34 AM, "Christopher Gaudig via plexil-support" <ple...@li...<mailto:ple...@li...>> wrote:

Hi PLEXIL devs and users!

I was wondering how one could solve "variable contention" in cases where 2 or more concurrent blocks want so set a global "flag" variable to a value of 1 but I cannot guarantee that this writing to the variable will always happen at non-equal points in time.

Short simplified example:

MyConcurrence:
Concurrence
{
Integer flag = 0;

BlockA:
{
Wait 3.0, 1.0;
flag = 1;
}

BlockB:
{
Wait 3.0, 1.0;
flag = 1;
}
}

PlexilExec.cc handles these conflicts by using a VariableConflictSet and a comment mentions a "priority" there. Is there a way to give a higher priority to the assignment in BlockA ?

Thanks for your help!

Regards from Germany,
Christopher

[cid:image001.png@01DBB82E.C638CFE0]
Christopher Gaudig
Software Developer
Subsea Structures
T +4942120095703

[plexil-support] Concurrency: How to resolve variable contention?

From: Christopher G. <cg...@ro...> - 2025-04-25 11:33:53

Attachments: C2_signature_emailsignature_signet_8d318837-d133-4453-b371-a27ca558d1d2.png

Hi PLEXIL devs and users!

I was wondering how one could solve "variable contention" in cases where 2 or more concurrent blocks want so set a global "flag" variable to a value of 1 but I cannot guarantee that this writing to the variable will always happen at non-equal points in time.

Short simplified example:

MyConcurrence:
Concurrence
{
    Integer flag = 0;

    BlockA:
    {
        Wait 3.0, 1.0;
        flag = 1;
    }

    BlockB:
    {
        Wait 3.0, 1.0;
        flag = 1;
    }
}

PlexilExec.cc handles these conflicts by using a VariableConflictSet and a comment mentions a "priority" there. Is there a way to give a higher priority to the assignment in BlockA ?

Thanks for your help!

Regards from Germany,
Christopher


[cid:34a17f52-a99b-4448-a419-919a3ff7484a]
Christopher Gaudig
Software Developer
Subsea Structures
T +4942120095703

[plexil-support] Test message

From: Dalal, M. (ARC-TI)[K. W. S. LLC] <mic...@na...> - 2024-02-01 19:44:14

Test message – a brief reply would be helpful if you received this.

Thanks,
Mike

Re: [plexil-support] [EXTERNAL] [BULK] Installing PLEXIL on Raspberry Pi 4

From: Fry, C. R. {C. (ARC-TI)[K. W. S. LLC] <chu...@na...> - 2023-05-15 18:00:11

[BCC'd internal dev team]

Hi, sorry for the very delayed response.

IPC is a third-party module whose origins predate the Raspberry Pi and the 64-bit Arm architecture. It is no longer maintained by its creators. In recent years, we've seen an increasing number of build issues caused by IPC's quite dated C code and build system.

The multi-exec, robosim, and simulator examples depend on IPC. Several other examples can be built and executed without it. Unfortunately the top level Makefile doesn't have a convenience target to build the core components without IPC.

If you are willing to wade into the IPC build, the file plexil/src/third-party/ipc/src/formatters.h defines IPC_ALIGN for a variety of platforms. If you do come up with a working definition, please send us the diffs so we can incorporate them into the distribution.

I am sorry we are not able to offer more help with this issue. I've created an internal issue to find a replacement for IPC.

-- Chuck

Charles R. (Chuck) Fry - he/him/his
chu...@na...<mailto:chu...@na...>
Qualified Technical Services Inc. at Ames Research Center Code TI
Not speaking for QTS, KBR Wyle, Code TI, or NASA.

On 5/5/23, 8:49 PM, "Erich Geisert" <eri...@gm...<mailto:eri...@gm...>> wrote:

CAUTION: This email originated from outside of NASA. Please take care when clicking links or opening attachments. Use the "Report Message" button to report suspicious messages to the NASA SOC.

Hello,
I've been trying to install PLEXIL onto a new Raspberry Pi 4 model with 8gb ram, running the lastest Ubuntu, and I've run into an issue that I've been beating my head against for the past couple of days.

The issue in question is here:
make[5]: Entering directory '/home/user/plexil/src/third-party/ipc/src'
gcc -Wall -Wstrict-prototypes -Wnested-externs -Wmissing-prototypes -Wmissing-declarations -O2 -fPIC -I. -I/home/user/plexil/include -DREDHAT_52 -DREDHAT_6 -DREDHAT_71 -DTHREADED -c -fpic -o /home/user/plexil/src/third-party/ipc/sharedObj/Linux-6.2/datamsg.o datamsg.c
datamsg.c: In function ‘x_ipc_dataMsgCreate’:
datamsg.c:1162:40: error: ‘IPC_ALIGN’ undeclared (first use in this function)
1162 | dataMsg->alignment = (ALIGNMENT_TYPE)IPC_ALIGN;

I believe it has something to do with the compiler not linking files appropriately, but I do not know how to solve this issue. I've installed every library that I can think of. At this point. Has this issue ever come up in the past, and if so, how was it solved?

Thank you for reading this,
Erich Geisert

[plexil-support] Installing PLEXIL on Raspberry Pi 4

From: Erich G. <eri...@gm...> - 2023-05-06 03:49:03

Hello,
I've been trying to install PLEXIL onto a new Raspberry Pi 4 model with 8gb
ram, running the lastest Ubuntu, and I've run into an issue that I've been
beating my head against for the past couple of days.

The issue in question is here:
make[5]: Entering directory '/home/user/plexil/src/third-party/ipc/src'
gcc -Wall -Wstrict-prototypes -Wnested-externs -Wmissing-prototypes
-Wmissing-declarations -O2    -fPIC -I. -I/home/user/plexil/include
-DREDHAT_52 -DREDHAT_6 -DREDHAT_71 -DTHREADED  -c -fpic -o
/home/user/plexil/src/third-party/ipc/sharedObj/Linux-6.2/datamsg.o
datamsg.c
datamsg.c: In function ‘x_ipc_dataMsgCreate’:
datamsg.c:1162:40: error: ‘IPC_ALIGN’ undeclared (first use in this
function)
 1162 |   dataMsg->alignment = (ALIGNMENT_TYPE)IPC_ALIGN;

I believe it has something to do with the compiler not linking files
appropriately, but I do not know how to solve this issue. I've installed
every library that I can think of. At this point. Has this issue ever come
up in the past, and if so, how was it solved?

Thank you for reading this,
Erich Geisert

Re: [plexil-support] [EXTERNAL] Patches to use the library

From: Dalal, M. (ARC-TI)[K. W. S. LLC] <mic...@na...> - 2023-03-20 16:43:00

Hi Martin,

We appreciate your interest in and use of PLEXIL, and any contributions you are willing to make!

Let me suggest an alternate approach for submitting your patches. Fork the PLEXIL repository, put the patch on a branch in the forked repo, and then submit a GitHub pull request from the fork’s branch to the target branch on the server that you based the patch on, e.g. releases/plexil-4.6.

This may be easier than creating patch files, and is a more standard workflow for GitHub. Indeed we need to establish and document a process for external contributions.

Best,
Mike

K. Michael Dalal
Lead, OceanWATERS (github.com/nasa/ow_simulator)
Autonomous Systems and Robotics, Code TI
KBR Inc. at NASA Ames Research Center
* Opinions expressed herein are only my own *

On 3/20/23, 9:11 AM, "Fry, Charles R. {Chuck} (ARC-TI)[KBR Wyle Services, LLC] via plexil-support" <ple...@li...<mailto:ple...@li...>> wrote:

Hello Martin. The PLEXIL team intended that users could write their own applications using the interfaces in the app-framework library. We realize this is not as well documented as it should be.

PLEXIL is intended to be compliant with C++ and POSIX standards, and is developed and maintained on multiple Linux distributions. Which Linux distro were you using, and on what hardware?

We would be interested in reviewing and possibly incorporating your changes. Could you please send them to us as patch files?

Thank you very much!

-- Chuck

Charles R. (Chuck) Fry - he/him/his
chu...@na...<mailto:chu...@na...>
Qualified Technical Services Inc. at Ames Research Center Code TI
Not speaking for QTS, KBR Wyle, Code TI, or NASA.

On 3/20/23, 4:24 AM, "Martin Fritsche" <mfr...@ro...<mailto:mfr...@ro...>> wrote:

Hi,
I tried to use Plexil as a library and link it to my own application (not using UniversalExec). This seems not to be the usual way, but I managed to do it with reading some code of UniversalExec and the library.
Still, I had to make a few patches to minimize crashing and remove some warnings. Are you interested in those? They are based on Plexil 4.6d0 and at least are functional with Linux (other OSs probably are a problem for one of them). If you are interested, what is the best way to make them available to you? I couldn’t find instructions for contributing.

Best,
Martin

Martin Fritsche
Software Engineer
Subsea Solutions
Creation Center

Phone +49-421-200957-09
Mobile +49-151-2645-2573
mfr...@ro...<mailto:mfr...@ro...>

ROSEN Creation Center GmbH
Branch Office Bremen
Arberger Hafendamm 22
28309 Bremen · GERMANY
www.rosen-group.com<https://gcc02.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.rosen-group.com%2F&data=05%7C01%7Cmichael.dalal%40nasa.gov%7C1c466ad93af2460522d508db295dc22a%7C7005d45845be48ae8140d43da96dd17b%7C0%7C0%7C638149254909249259%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=pSBCU7FPqpjJM5ErY5B2CdEgykka458D1x6V1zbbaD8%3D&reserved=0>
[Image removed by sender.]

This e-mail may contain confidential and/or privileged information. If you are not the intended recipient (or have received this e-mail in error) please notify the sender immediately and destroy this e-mail. Any unauthorized copying, disclosure or distribution of the material in this e-mail is strictly forbidden. This e-mail address is provided for business correspondence only. It is not to be used for promotional or bulk mail, or given or sold to a third party for any purpose.

Re: [plexil-support] [EXTERNAL] Patches to use the library

From: Fry, C. R. {C. (ARC-TI)[K. W. S. LLC] <chu...@na...> - 2023-03-20 16:11:17

Hello Martin. The PLEXIL team intended that users could write their own applications using the interfaces in the app-framework library. We realize this is not as well documented as it should be.

PLEXIL is intended to be compliant with C++ and POSIX standards, and is developed and maintained on multiple Linux distributions. Which Linux distro were you using, and on what hardware?

We would be interested in reviewing and possibly incorporating your changes. Could you please send them to us as patch files?

Thank you very much!

-- Chuck

Charles R. (Chuck) Fry - he/him/his
chu...@na...<mailto:chu...@na...>
Qualified Technical Services Inc. at Ames Research Center Code TI
Not speaking for QTS, KBR Wyle, Code TI, or NASA.

On 3/20/23, 4:24 AM, "Martin Fritsche" <mfr...@ro...<mailto:mfr...@ro...>> wrote:

Best,
Martin

Martin Fritsche
Software Engineer
Subsea Solutions
Creation Center

Phone +49-421-200957-09
Mobile +49-151-2645-2573
mfr...@ro...<mailto:mfr...@ro...>

ROSEN Creation Center GmbH
Branch Office Bremen
Arberger Hafendamm 22
28309 Bremen · GERMANY
www.rosen-group.com<https://gcc02.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.rosen-group.com%2F&data=05%7C01%7CChuck.Fry%40nasa.gov%7C6d886cc1a1bd48fd29a708db2935ae4c%7C7005d45845be48ae8140d43da96dd17b%7C0%7C0%7C638149082817195651%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=guzZjIXNnkfYREai%2BpseBhDPwpV%2FuG%2BHRxdIA%2FZgZbE%3D&reserved=0>
[Image removed by sender.]

[plexil-support] Patches to use the library

From: Martin F. <mfr...@ro...> - 2023-03-20 11:24:17

Hi,
I tried to use Plexil as a library and link it to my own application (not using UniversalExec). This seems not to be the usual way, but I managed to do it with reading some code of UniversalExec and the library.
Still, I had to make a few patches to minimize crashing and remove some warnings. Are you interested in those? They are based on Plexil 4.6d0 and at least are functional with Linux (other OSs probably are a problem for one of them). If you are interested, what is the best way to make them available to you? I couldn't find instructions for contributing.

Best,
Martin

Martin Fritsche
Software Engineer
Subsea Solutions
Creation Center

Phone +49-421-200957-09
Mobile +49-151-2645-2573
mfr...@ro...<mailto:mfr...@ro...>

ROSEN Creation Center GmbH
Branch Office Bremen
Arberger Hafendamm 22
28309 Bremen * GERMANY
www.rosen-group.com<http://www.rosen-group.com>

[https://pictures.rosen-group.com/signatures/ROSEN_Logo_Transparent_160x48.png]



This e-mail may contain confidential and/or privileged information. If you are not the intended recipient (or have received this e-mail in error) please notify the sender immediately and destroy this e-mail. Any unauthorized copying, disclosure or distribution of the material in this e-mail is strictly forbidden. This e-mail address is provided for business correspondence only. It is not to be used for promotional or bulk mail, or given or sold to a third party for any purpose.

Re: [plexil-support] [EXTERNAL] plexil-support subscription notification

From: Dalal, M. (ARC-TI)[K. W. S. LLC] <mic...@na...> - 2021-05-20 01:02:13

Great, and my next experiment confirmed that the actual email address is:

  ple...@li...

Caroline was missing the 'lists'.

I also learned that anyone can add themselves to this list, as you saw my personal email get added.  Not sure this is good.

I also discovered that the 'plexil-discussion' list has been used sparsely and in only two years ever, 2008 and 2017.

Also, that every message ever sent to these lists is archived on Sourceforge.

I propose that we eliminate these lists.  The concept seems so 90s!  I think we just a technical support email whose membership is under our control.  I propose we use ple...@nx..., assuming that we can update this list, at least with SG's help.

On the other hand, if you're fine with the unlimited access plexil-support and/or a barely used plexil-discussion list, I can live with that. 

Mike


On 5/19/21, 5:46 PM, "Fry, Charles R. {Chuck} (ARC-TI)[KBR Wyle Services, LLC]" <chu...@na...> wrote:

    Look what just showed up in my inbox. -- Chuck

    On 5/19/21, 5:44 PM, "sit...@li..." <sit...@li...> wrote:

        Subscribed: km...@pa...

[plexil-support] Test

From: Dalal, M. (ARC-TI)[K. W. S. LLC] <mic...@na...> - 2021-05-20 00:48:09

Sorry for the broad distribution -- just a test!