Linux (since 2.6.10) does have a WIFCONTINUED(status), which checks if status == 0xffff; could this be the source of it?
James > On 25 Apr 2016, at 14:07, David Matthews <david.matth...@prolingua.co.uk> > wrote: > > I've found something to suggest that the 255 value can come from an invalid > value being passed to "exit". I don't understand, though, what this value > says about the status of the process. Has it exited or not? It really seems > to be an incompatibility between the design of the ML basis library which > requires the exit status to match one of the cases and Linux which can > generate a value that doesn't. > > You can certainly handle the exception and use a value that makes sense. > From the Poly/ML side, though, I'd like to find out what this value actually > represents and include it in the datatype. It is possible that this is a bug > in the code but I can't see how it can arise. > > David > > On 25/04/2016 13:16, Michael Norrish wrote: >> I agree that it does seem to only happen on Linux. >> >> There's code doing waiting at line 303 of >> >> >> https://github.com/HOL-Theorem-Prover/HOL/blob/master/tools/Holmake/poly/ProcessMultiplexor.sml >> >> In the Poly sources, the fromStatus function is also called in doWait (a few >> lines further down in basis/Posix.sml) >> >> The HOL code does also call fromStatus, but after the call to waitpid_nh. >> As it happens, the status codes are coming from poly/ml executables being >> called via fork/exec. >> >> Could I just catch the Fail exn, and make the status a W_EXITSTATUS >> (Word8.fromInt 255)? (Not that I think the child poly should be failing...) >> >> Michael >> >>> On 25 Apr 2016, at 21:40, David Matthews <david.matth...@prolingua.co.uk> >>> wrote: >>> >>> Searching for Fail in the Posix code shows one situation where it could be >>> raised. Posix.Process.fromStatus converts a value of type >>> OS.Process.status into a value of type exit_status. exit_status is defined >>> as >>> datatype exit_status = >>> W_EXITED >>> | W_EXITSTATUS of Word8.word >>> | W_SIGNALED of signal >>> | W_STOPPED of signal >>> >>> The breaking out of the OS.Process.status is done in the run-time system >>> using the WIFEXITED, WIFSIGNALED and WIFSTOPPED macros. If none of these >>> applies then the Fail exception will be raised. >>> >>> I've run some tests on Debian Linux and it looks as though the value of 255 >>> fails to match any of these. That doesn't seem to happen on Mac OS. That >>> raises the question of where this value is coming from and how it should be >>> treated. Does this seem to fit with your code? Are you using >>> Posix.Process.fromStatus and where is the value coming from? >>> >>> David >>> >>> On 21/04/2016 12:34, Michael Norrish wrote: >>>> As can be seen in >>>> >>>> https://travis-ci.org/HOL-Theorem-Prover/HOL/jobs/124717527 >>>> >>>> our use of Posix waiting is occasionally causing a Fail exception to be >>>> raised from inside the Posix implementation (there's no Fail exception >>>> with that message in our source code, and our code *is* doing a wait at >>>> that point). >>>> >>>> I'm afraid this doesn't seem easy to reproduce. >>>> >>>> Michael >>>> >>>> >>>> ________________________________ >>>> >>>> The information in this e-mail may be confidential and subject to legal >>>> professional privilege and/or copyright. National ICT Australia Limited >>>> accepts no liability for any damage caused by this email or its >>>> attachments. >>>> _______________________________________________ >>>> polyml mailing list >>>> polyml@inf.ed.ac.uk >>>> http://lists.inf.ed.ac.uk/mailman/listinfo/polyml >>>> >> >> _______________________________________________ >> polyml mailing list >> polyml@inf.ed.ac.uk >> http://lists.inf.ed.ac.uk/mailman/listinfo/polyml >> > _______________________________________________ > polyml mailing list > polyml@inf.ed.ac.uk > http://lists.inf.ed.ac.uk/mailman/listinfo/polyml
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