Interesting code execution inconsistent behavior
Paolo Fabio Zaino (28) 1882 posts |
While testing various aspects of executing code on RISC OS, I observed some inconsistencies in the code execution process it self, here are few examples: When someone tries to run code that will call Wimp_Initialise from a TaskWindow: *!RunImage (for a multitasking BASIC App fails with WindowManager in use error when it tries to initialize the task) *File_Run !RunImage (everything works fine and the multitask app is executed in the desktop correctly) *Run !RunImage (same issue as first case, execution fails with error WindowManager in use error) Also, it appears there are other differences when executing something using Run, I need to look at the RO Source code, but in certain tests showed some inconcistency when executing: *Run !Foo (where Foo is an App directory that will execute a multitasking app using !Run) vs *Filer_Run !Foo (Foo is same as above, but in this case everything always works fine) This is not necessarly a bug (althought if in modern OS world it would definitely be considered a bug), but I think it was worth mentioning it somewhere. Maybe it would be useful to add the info on the Wiki? |
Rick Murray (539) 13850 posts |
Not a bug nor inconsistent. Filer_Run will cause the run action to be performed on the given file by the Filer, whereas the other two will try to run the application directly within the TaskWindow environment, and as you noticed, Wimp tasks don’t work like that. Think of Filer_Run as a command that means “pretend I double-clicked on this file”. |
Paolo Fabio Zaino (28) 1882 posts |
Sure Rick, If you try to write a piece of code that checks if the desktop is active and so tries to execute “Wimp_Initialise” that will not end up well. But one can detect this and avoid quitting and run a multi-tasking code within the TaskWIndow and for example open Windows on the desktop. Now, if you do that, the pseudo Multi-task apps gets executed in a 3rd type of environment, so basically we have 3: 1) Pure CLI When you are in a TAskWIndow Limbo, which it’s very easy to enter, just write a desktop app that does not call Wimp_Initialise your code will be executed within the TaskWindow pageing, which is well… :D However, you can open windows and draw icons and, with some hacks, even control them. The other not available call is Wimp_Poll (this one makes sense given that the TASKwindow is a PMT hack on top of a CMT WIMP). Wimp_Poll will fail because it’s being executed in a PMT environment that however doesn’t support a `nice` like call, so kinda half backed. In other words, it’s definitely inconsistent, I am sorry to disagree on that, in some code tests I was able to do quite a bit of interesting things. However everything can be solved in multiple ways, one is the traditional “developer is responsible fo reverything”, so an App could Detect it’s being executed in a TAskWindow context and so, instead of initialising normally, it should just execute itself again via “Filer_Run” (or start itself as a task) and then the parent task just end. Tested that and works really well. |
Rick Murray (539) 13850 posts |
Only if you don’t understand what the commands are actually doing. Filer_Run is, as the clue in the name suggests, asking the Filer to run something. As such, it cannot be used outside of the desktop (see note 1 below). Run, Exec, BASIC -quit, etc etc are the underlying commands to actually do stuff, for certain types of file. 2 The two methods are related, but they are not the same thing.
Applications, that is to say anything liable to call Wimp_Initialise, are supposed to be self-contained and not be running in TaskWindows.
Basically, the TaskWindow is a Wimp app. It’s a Wimp app with many tentacles to do what it does, but it’s a Wimp app. You’re running inside a Wimp app. Which is why Initialise fails, Poll blows up, and you can (hairily!) create windows and icons and such. That you can sort-of maybe do some Wimp stuff in it is “undefined behaviour”.
:-) As for this part…
…that noise that you hear is the sound of a Gerph screaming.
We’ll have to disagree then, because as far as I’m concerned, wondering why you can’t run a multitasking program in a TaskWindow is about the same as wondering why you can’t hook into callbacks in BASIC. 3 The TaskWindow Is Not Intended For Multitasking Apps.
Oh, I’ll bet. RISC OS doesn’t have a habit of saying “nope”. It would rather try to be a good little Brownie, have a go, and then sit there bawling its eyes out when it all comes crashing down.
Or be like everybody else and just crash. Because (say it with me) The TaskWindow Is Not Intended For Multitasking Apps. That people don’t check for this is not an omission on anybody’s part. It’s simply because (say it with me again) The TaskWindow Is Not Intended For Multitasking Apps. 1 You can certainly call Filer_Run from the command line, I find it is often useful to press F12 and Filer_Run something that the system knows (such as 2 It isn’t possible to completely escape file actions. If you tried to *Run a JPEG, you may well end up with a C backtrace. This is because a JPEG is not a known type that the system can handle, so it looks to see how to handle it. My backtrace is basically the system (in this case, I think it’s FileSwitch) starting up PrivateEye to handle the JPEG, and that subsequently crashing out because one can’t do that in the command line environment. 3 Unless you’re Steve, that is. |
Paolo Fabio Zaino (28) 1882 posts |
For anyone who’s actually testing their software thoroughly, this is how to avoid issues with this particular use case (using a BASIC example for brevity): SYS "TaskWindow_TaskInfo" TO TWCheck% IF TWCheck%=0 THEN SYS "Wimp_Initialise",300,&4B534154,"Your Task name" ELSE SYS"OS_GetEnv" TO xarg$ IF xarg$<>"" THEN IF LEFT$(xarg$,6)="BASIC " THEN xarg$=MID$(xarg$,7) IF LEFT$(xarg$,6)="-quit " OR LEFT$(xarg$,6)="-load " THEN xarg$=MID$(xarg$,7) IF LEFT$(xarg$,1)=CHR$34 THEN xarg$=MID$(xarg$,2,LENxarg$-3) OSCLI("Filer_Run "+xarg$) ENDIF END ENDIF REM rest of your code... This is also useful if one wants to make code that can run both in single AND multitasking.Obviously in such case, don’t try to run itself again via filer_Run. |
Charles Ferguson (8243) 427 posts |
I wouldn’t use TaskWindow_TaskInfo to check whether you’re within the desktop already. TaskWindow shouldn’t be considered special. Call Wimp_Initialise and if you get an error take appropriate action. Problems with the reinvocation you propose:
All in all, you’re better off just telling the user that multitasking applications cannot be run within a taskwindow, because dealing with all that just isn’t reasonable (or, in some cases, possible). Reporting a useful error message telling the user what to do, rather than crashing with a side effect, is a much better course of action than failing to handle these cases. 1 Actually it’s not – it’s a means by which you can ensure that SEAs work properly, but it has the effect of making execution of many programs at least a bit safer. |
Paolo Fabio Zaino (28) 1882 posts |
Sure, but that will require a bit more work, btw the BASIC example was just to express a concept (aka used as psudo code), not an actual complete implementation (I have mentioned: to be short, maybe only Oxford’s English is allowed here?).
This is true, but one can replace Filer_Run with Wimp_StartTask.
The problem you are referring to applies only to BBC BASIC (again I wasn’t specifically suggesting a definitive implementation that would have taken more space). In C it would not break anything, in Assembly the same, in Prolog and Forth same, c++ same. For the specifics of BBC BASIC, one can use a block to store a longer string, so if the need is to have a complete implementation instead of usign BASIC as a pseudo code then that could be a way to do it.
You can retrieve an app parameters-list if that’s what you refering to and pass them along.
Not the case when you are calling an executable directly, unless you’re using a macro or an alias, but that (unless the original developer set it) is a responsability of who creates the alias/macro etc.
true, replace it with Wimp_StartTask ;)
Play a bit more with string manipoulation and, instead of calling yourself back, call your !Run.
While this is true as a general statement, in most cases you’ll get the path resolved and NOT the <Obey$Dir>. form, while, if for whatever reasons, <Obey$Dir> is not defined and has been used, then obviously you won’t reach the executable either, so this last point seems irrelevant to me.
That is another good approach and you can decide what to do, or even leave it as the traditional form and let the Wimp give that error message “WindowManager in use” etc. which may be crytic for some user, but oh well. |
Charles Ferguson (8243) 427 posts |
Exept you cannot prior to Select 3 because it’s unsafe to use in a TaskWindow.
Pass them along how? As I stated Filer_Run cannot be given parameters to pass to the application.
You’re talking about a command on the command line being run in a taskwindow. So if a user typed in
Which, as I stated, cannot be used reliably within a TaskWindow.
That might be more reliable, but it’s nothing like what you suggested.
bw. While this is true as a general statement, in most cases you’ll get the path resolved and NOT the You’re assuming that the path is resolved by something. It’s not. If the user typed (actaully, in Pyromaniac I do perform canonicalisation at execution time, but I consider that to be a bug of laziness rather than a feature, as it goes against what RISC OS Classic will do – despite the fact that I think it’s a reasonable thing)
It’s always better to turn an error into something that tells the user what you couldn’t do, not what went wrong, in my opinion. But given the inability to solve all the above problems, I believe it’s better to report that it cannot be done in this case, rather than try to deal with the multitude of cases that cannot work, or are very difficult to handle. Expending such effort might help with the tiny number of people who do that, and would be the right thing to do if you could handle it right, but it’s so hard to do properly that if you’re handling it at all, an error is the best solution. |
Rick Murray (539) 13850 posts |
🍿 |
Paolo Fabio Zaino (28) 1882 posts |
@ Charles My friend, are you taking this as some sort of intellectual challenge? If so I’ll stop replying, I am not interested in such type of discussions. The reason why I have this feeling, is because of comments like this one:
Now, this is easy to solve, in your !Run use this: If "<Obey$Dir>" <> "" Then Set MyApp$Dir <Obey$Dir> If "<MyApp$Dir>" = "" Then Error You are trying to execute this App in an ambiguous way, blah blah ... <MyApp$Dir>.!RunImage %*0 What happens in this case can be one of the followings: Scenario 1 Scenario 2 Scenario 3 I hope you do not want me to list all possible scenarios, right? In general, given the frail nature of RISC OS, one should have that check anyway in a !Run file because things may go wrong also because the system has been put in an unstable state.
That was exactly my original point, the error returned is ambiguos. So one can either return a better error message or try to work around it. Not sure why we are having this endless discussion except you’re trying to debug all possible issues on a forum?
My understanding is that quite a lot of things are unsafe in a TaskWindow anyway, but again two options: return a meaningful non-ambiguous error message (for consistency) or try your luck and see if you can manage to make it work even in this case. Anyway thanks for the details… |
Dave Higton (1515) 3534 posts |
Paolo, I’m not sure if you know who Charles is. Let’s just say that his knowledge across all of RISC OS, from top to bottom, exceeds that of the rest of us here by some orders of magnitude. |
Paolo Fabio Zaino (28) 1882 posts |
@ Dave
Dave, I do very well, not sure why you’re mentioning this. The point here is: We should test before making assumptions. Chalers, allegedly, doesn’t use RISC OS 5 (or so he mentioned multiple times, not sure if it is still the case), however here is an example of tests outcome: Charles said “you can’t pass parameters through Filer_Run”, this is true only for OLD releases of RISC OS, while it DOESN’T seems to be true for RO 5. RO 5 seems to support the use of "" to wrap a command and its parameters for Filer_Open, while older releases of RO will return a “Bad String” error if you try that (how do I know? I test everything, literally everything). So, the following works fine in RO 5.28: Filer_Run "!MyApp test" And my app can retrieve test. While for older RO one can always use PipeFS to store parameters, but this would be a workaround. Also, before posting my comments, I indeed tested my findings on everything included RO 3.10, and in all honesty I have a perfectly working Launchpad that can be executed from a TaskWindow on all RO releases. There are obviously advantages on making apps executable from a TaskWindow, as an example one could create an editor that we can run from a local directory and it opens a file into a wimp based editor if the wimp is active, something like: *MyEdit @.test But again, just my 0.5c, nothing more. |
Steve Pampling (1551) 8172 posts |
Documentation is here in which we have: Notes This command can only be used within the desktop environment, or from within a Desktop boot file. |
Paolo Fabio Zaino (28) 1882 posts |
@ Steve Here is the source: https://gitlab.riscosopen.org/rool/Filer/-/blob/master/s/Commands#L320 Read it. Filer_Run seems to be using ReadArgs macro, to read all passed parameters. Given that on RO 5 ReadArgs seems to have been improved and can correctly determine that a string between double quotes is a single parameter, as a side effect of this, now Filer_Run seems to be able to accept a file path + (that file’s) parameters when they are specified between double quotes. If this is the case, then the documentation needs to be updated btw. I need to double check this, but I am not home and this is all I can do using a phone. [edit] |
Steve Pampling (1551) 8172 posts |
@ Steve I don’t need to read it. I do recall discussion about alterations/improvements to ReadArgs – maybe the current behaviour is an unintended consequence, maybe it was intended, and the documentation update was missed. |
Charles Ferguson (8243) 427 posts |
{quote} @ Charles My friend, are you taking this as some sort of intellectual challenge? If so I’ll stop replying, I am not interested in such type of discussions. {/quote} I’m sorry that you feel that way. You were describing some situations that you encountered unexpected (to you) behaviour and mechanisms to avoid them. I was pointing out that these situations generate unexpected (to most people) behaviour and that there is much more care needed to handle such cases than was suggested. When you are talking about unexpected behaviour in special circumstances, I don’t think it’s unreasonable to discuss the other unexpected behaviour that is caused by the solution. {quote} The reason why I have this feeling, is because of comments like this one: You’re assuming that the path is resolved by something. It’s not. If the user typed /!MyApp arguments then FileSwitch will try to run Run with the arguments supplied. If that file is an Obey file that contains Run <Obey$Dir>.!RunImage %*0 then your environment will contain <Obey$Dir>.!RunImage arguments. Nothing will have expanded the <Obey$Dir>.Now, this is easy to solve, in your !Run use this: If "<Obey$Dir>" <> "" Then Set MyApp$Dir <Obey$Dir> If "<MyApp$Dir>" = "" Then Error You are trying to execute this App in an ambiguous way, blah blah ... <MyApp$Dir>.!RunImage %*0 {/quote} WTF?! But… but… but… that’s not the way I understood it. I’m clearly wrong as your example demonstrates. FileSwitch must be expanding that when it runs it – which I didn’t think happened. I thought it retained the originally specified name, which was the reason I asserted that it was not getting expanded. In RISC OS Pyromaniac, I keep the expanded version and pass it on to the environment, but I thought that was my laziness and that I was doing it wrong. It looks like I’m right in how RISC OS Pyromaniac implements it due to lazinesss, and wrong in my understanding of the execution. Sorry about that. It’s not me being awkward, but my having a misunderstanding about the manner that particular operation worked. Oops.
Sorry, you stated that “this is how to avoid issues with this particular use case”… which generated its own set of issues (which, I’m sorry, I was wrong about one of them). If you’re giving a solution to a problem and that solution causes other problems – particularly if the problem you’re working around is an odd case – it’s worth being aware of those problems. Or to look at it another way, I was responding with “this is the set of issues you will encounter if you apply this solution”.
I don’t see how it can be true. In order to support Filer_Run the command must be passed first to DataOpen, and the DataOpen cannot be passed parameters. When the DataOpen bounces it could have remembered the additional parameters passed to the command through the yourref/myref and reintroduce them into the execution of the alias’d command, BUT then that would have produced a disparity in behaviour between when you executed a file with parameters and there is an application present to handle the DataOpen after the Filer_Run (no parameters passed) and the action when there is no application present, and the alias could be used. This could have been addressed in RISC OS 5, but I don’t see a mechanism by which you might do that which wouldn’t itself introduce the inconsistency for applications that do not support it (or potential crashes).
I believe that would be more of a bug, because of the inconsistent behaviour I describe above, than a feature. It would be unwise to rely on the inconsistent behaviour. |
Paolo Fabio Zaino (28) 1882 posts |
@ Charles
All good, by reading your last post I realised that I had wrong assumptions. I was 1000% sure that you knew that “trick”, so your previous comment got me confused and I had no idea why you were posting that. So, my fault too, sorry.
I agree, anyway I switched to use PipeFS to store parameters passed from the first run and that seems to work fine from RO 3.10 onwards. I’ll run more tests to ensure everything is stable and the OS doesn’t get in a funky state. |