Poly/ML August 2008

polyml@lists.polyml.org

8 participants
6 discussions

Re: Poly/ML 5.2 and signals on older Linux systems
by David.Matthews＠prolingua.co.uk 09 Sep '08

09 Sep '08

Rob Arthan wrote: > David, > However, while I agree that my "fix" is a hack because it's working around > what looks like a bug in the old glibc, I am a little concerned that your > signal handling design is not POSIX-conformant. The POSIX specification of > sigaction includes the following statement: > > "The result of the use of sigaction() and a sigwait() function concurrently > within a process on the same signal is unspecified." > > I take this to mean that if you change the disposition of a signal using > sigaction() while you are waiting for it with sigwait() then the result is > unspecified. So the Cygwin behaviour would be conformant. The documentation > on signal() doesn't say anything about sigwait(), but it does say: > > "Use of this function is unspecified in a multi-threaded process." > > I think the POSIX-compliant way of implementing the ML signal function would > be to service ML requests to change the disposition of a signal by waking up > the signal detection thread and having it call sigaction. Thanks for pointing this out. I've also had another look at the documentation for sigwait and discovered that the Cygwin behaviour might be acceptable, not because of the interaction with sigaction but because the behaviour of sigwait when a signal is not blocked is undefined. As a result of all this I've revisited the whole mechanism for signal handling. The difficulty is that the pthread mutex and condition variable functions are not safe when used in a signal handler but it turns out that POSIX sem_post is safe. I've reworked the code to use a signal handler rather than sigwait and this appears to work on all the platforms I've tried, with the inevitable tweaks for the peculiarities of semaphores on Mac OS X and Cygwin. The new version is in CVS so you can try it out if you wish. I still have to get to the bottom of the other bug. Regards, David Copied to the mailing list for information.

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InternalError: getSome raised while compiling
by tbourke＠cse.unsw.edu.au 28 Aug '08

28 Aug '08

I have a program that causes an InternalError in Poly/ML 5.2 on FreeBSD (but not MLton or SML/NJ). I haven't been able to test it under Linux. It can be reduced to these declarations: type int = Int.int; signature SIG = sig datatype t1 = T1 of int datatype t2 = T2 of { f : t1 } end; functor Fun () : SIG = struct datatype t1 = T1 of int datatype t2 = T2 of { f : t1 } end; structure Str1 = Fun () (*;*) structure Str2 : SIG = struct open Str1 end; fun g (Str2.T2 {f}) = (f=f); They compile if any of various changes are made: such as adding the semi-colon suggested above, removing the type int declaration, trying to shortcut Str2, removing the T1 label. Unfortunately, the corresponding changes are either difficult to make in the original program or do not seem to fix the problem. Sorry I haven't yet had time to look at Poly/ML myself. If a solution isn't readily suggested, I'll try to look harder over the weekend. Tim.

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Unicode in Poly/ML?
by Michael.Norrish＠nicta.com.au 21 Aug '08

21 Aug '08

It is possible to emit Unicode (UTF-8 encoded say) strings in a Poly/ML program by emitting the appropriate sequence of bytes: Poly/ML 5.2 Release > print "\u00e2\u0088\u0080\n"; ? val it = () : unit But as far as Poly is concerned, this is actually a sequence of four characters, not two (the universal quantifier and the newline). Are there any plans to implement some sort of sensible WideChar signature? (The existing WideChar signature in the Basis is not really a good base on which to build good support here.) Michael.

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Should -fno-strict-aliasing be in CXXFLAGS, too?
by lionel＠mamane.lu 18 Aug '08

18 Aug '08

Hi, Background: Achim Brucker and myself are packaging Poly/ML for Debian. I noticed that: 1) Compilation of file libpolyml/xwindows.cpp with gcc 4.2.3 gives several instances of: warning: dereferencing type-punned pointer will break strict-aliasing rules 2) libpolyml/Makefile.am has AM_CFLAGS = $(OSFLAG) -Wall -fno-strict-aliasing So I kinda guess that libpolyml/xwindows.cpp was supposed to be compiled with -fno-strict-aliasing, too, and you just forgot to put it in CXXFLAGS as well as CFLAGS? Or is the situation something else? -- Lionel

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Re: Assertion failure in gc.cpp
by David.Matthews＠prolingua.co.uk 14 Aug '08

14 Aug '08

Rob Arthan wrote: > I am working on porting ProofPower to Poly/ML 5.2. I get the following > assertion failure when I run one of the tests for my parser generator. I can > reproduce the problem deterministically, but the circumstances in which it > occurs are obscure: at first glance it seems to depend on whether I am > calling "use" directly or via a function of my own, but it doesn't fail if I > avoid compiling my function twice. It seems very dependent on exactly how > things are compiled. > > slrp-ml: gc.cpp:878: virtual POLYUNSIGNED > ProcessUpdate::ScanAddressAt(PolyWord*): Assertion > `obj->ContainsNormalLengthWord()' failed. > Rob, Thanks for sending the test program. I finally managed to get to the bottom of this. The problem turned out to be the way that the heap was restored after calling "export". It would only have shown up in certain circumstances and only in a garbage collection after the export. Generally, export is the last thing that is called in a session which may explain why it didn't show up earlier. I've fixed it in CVS and your test now runs successfully. Let me know if you get this again although this assertion could be triggered by any number of different faults connected with the GC. Regards, David.

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xwindows.xpp: deprecated conversion from string constant to 'char*'
by brucker＠spamfence.net 14 Aug '08

14 Aug '08

Hi, using a recent g++ version for compiling Poly/ML results in several warnings of the following form: xwindows.cpp: warning: deprecated conversion from string constant to 'char*' The warning is caused by implicit conversion from string constants (i.e., "foo") to non-constant char pointers. To this email, I attached a simple patch which should remove these warnings. The patch should be safe to apply as it either makes the casts explicit or changes some types from "char *" to "const char *". Please note that I could only test these modifications on my i386 box running Linux.... Achim

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Poly/ML August 2008