November 2011 - mpi-forum - mailman3.cels.anl.gov

Re: [Mpi-forum] how to get MPI::Exception behavior from C bindings?
by Cownie, James H 02 Nov '11

02 Nov '11

> For example, if you have a call stack A->B->C->D->E, and E throws an exception, if the only matching "catch" statement > for that specific exception is way up in B, then it effectively bypasses the rest of E, D, and C, and jumps up to the > matching "catch" in B. But, critically, the runtime also executes destructors for any local variables that have them in the frames that are being unwound (E,D,C here), so it's not *just* a longjump... -- Jim James Cownie <james.h.cownie(a)intel.com> SSG/DPD/TCAR (Technical Computing, Analyzers and Runtimes) Tel: +44 117 9071438 -----Original Message----- From: mpi-forum-bounces(a)lists.mpi-forum.org [mailto:[email protected]] On Behalf Of Jeff Squyres Sent: Tuesday, November 01, 2011 11:46 PM To: Main MPI Forum mailing list Subject: Re: [Mpi-forum] how to get MPI::Exception behavior from C bindings? My $0.02: 1. Darius is right that you can write your own error handler function, register it with MPI_<foo>_CREATE_ERRHANDLER, and just throw an exception in your user-defined function that is caught in the same way that Jeff's sample madness code. This is the easiest conversion (it's essentially what we did for the first generation of the portable C++ bindings package in the mid-90's; the versions integrated into various MPI implementations these days are basically the same idea). You'll need to ensure that your MPI library is compiled to pass C++ exceptions through C code (you need to do this today, anyway, but it may no longer be the default if MPI implementations actually remove the C++ bindings. FWIW, OMPI doesn't enable this by default because there's a slight performance penalty at every function call, even in the we-never-threw-an-exception case). 2. If you keep this purely in C, it's a little messy. The benefit of exceptions is that they're kinda like longjumps. For example, if you have a call stack A->B->C->D->E, and E throws an exception, if the only matching "catch" statement for that specific exception is way up in B, then it effectively bypasses the rest of E, D, and C, and jumps up to the matching "catch" in B. So to convert this to C, you'll need to set ERRORS_RETURN and then check the return value from all MPI functions and all functions that call MPI functions. Eg: void A() { ... B(); ... } void B() { ... if (C() != MPI_SUCCESS) error(); ... } void C() { ... if ((ret = D()) != MPI_SUCCESS) return ret; ... } void D() { ... if ((ret = E()) != MPI_SUCCESS) return ret; ... } void E() { ... if ((ret = MPI_<whatever>()) != MPI_SUCCESS) return ret; ... } In Jeff's example below, if the MPI function is invoked directly in ((ThreadBase*)(self))->run(), then it's not quite as ugly as this, but the idea is the same. Of course, both 1) and 2) are somewhat of a losing game anyway since not many MPI implementations have well-defined semantics for what happens inside MPI after ERRORS_RETURN, anyway. :-) On Nov 1, 2011, at 6:29 PM, Darius Buntinas wrote: > > Create an error handler (function) that throws a C++ exception, then wherever the original code set the error handler to MPI:ERRORS_THROW_EXCEPTIONS, use your new error handler. > > I haven't looked up the standard here, but it might say that the error handler must return. If it does, then this would not be allowed, otherwise, this should work. > > -d > > > On Nov 1, 2011, at 4:18 PM, Jeff Hammond wrote: > >> Can someone explain how one can migrate (backwards) from the C++ to >> the C bindings if they currently use MPI::Exception in a try-catch >> block like this: >> >> =================================== >> try { >> ((ThreadBase*)(self))->run(); >> } >> catch (const MPI::Exception& e) { >> error("caught an MPI exception"); >> } >> =================================== >> >> This is taken from MADNESS, btw. >> >> I think it is only fair for those who want to kill the C++ bindings >> to provide a clear description of how this will not break existing >> codes that use C++ bindings. Clearly, many things, e.g. MPI::BYTE -> >> MPI_BYTE, are trivial, but I see error handling as being >> fundamentally nontrivial. >> >> Thanks, >> >> Jeff >> >> -- >> Jeff Hammond >> Argonne Leadership Computing Facility University of Chicago >> Computation Institute jhammond(a)alcf.anl.gov / (630) 252-5381 >> http://www.linkedin.com/in/jeffhammond >> https://wiki.alcf.anl.gov/index.php/User:Jhammond >> _______________________________________________ >> mpi-forum mailing list >> mpi-forum(a)lists.mpi-forum.org >> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi-forum > > > _______________________________________________ > mpi-forum mailing list > mpi-forum(a)lists.mpi-forum.org > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi-forum -- Jeff Squyres jsquyres(a)cisco.com For corporate legal information go to: http://www.cisco.com/web/about/doing_business/legal/cri/ _______________________________________________ mpi-forum mailing list mpi-forum(a)lists.mpi-forum.org http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi-forum --------------------------------------------------------------------- Intel Corporation (UK) Limited Registered No. 1134945 (England) Registered Office: Pipers Way, Swindon SN3 1RJ VAT No: 860 2173 47 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). 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Re: [Mpi-forum] how to get MPI::Exception behavior from C bindings?
by Jeff Squyres 01 Nov '11

01 Nov '11

My $0.02: 1. Darius is right that you can write your own error handler function, register it with MPI_<foo>_CREATE_ERRHANDLER, and just throw an exception in your user-defined function that is caught in the same way that Jeff's sample madness code. This is the easiest conversion (it's essentially what we did for the first generation of the portable C++ bindings package in the mid-90's; the versions integrated into various MPI implementations these days are basically the same idea). You'll need to ensure that your MPI library is compiled to pass C++ exceptions through C code (you need to do this today, anyway, but it may no longer be the default if MPI implementations actually remove the C++ bindings. FWIW, OMPI doesn't enable this by default because there's a slight performance penalty at every function call, even in the we-never-threw-an-exception case). 2. If you keep this purely in C, it's a little messy. The benefit of exceptions is that they're kinda like longjumps. For example, if you have a call stack A->B->C->D->E, and E throws an exception, if the only matching "catch" statement for that specific exception is way up in B, then it effectively bypasses the rest of E, D, and C, and jumps up to the matching "catch" in B. So to convert this to C, you'll need to set ERRORS_RETURN and then check the return value from all MPI functions and all functions that call MPI functions. Eg: void A() { ... B(); ... } void B() { ... if (C() != MPI_SUCCESS) error(); ... } void C() { ... if ((ret = D()) != MPI_SUCCESS) return ret; ... } void D() { ... if ((ret = E()) != MPI_SUCCESS) return ret; ... } void E() { ... if ((ret = MPI_<whatever>()) != MPI_SUCCESS) return ret; ... } In Jeff's example below, if the MPI function is invoked directly in ((ThreadBase*)(self))->run(), then it's not quite as ugly as this, but the idea is the same. Of course, both 1) and 2) are somewhat of a losing game anyway since not many MPI implementations have well-defined semantics for what happens inside MPI after ERRORS_RETURN, anyway. :-) On Nov 1, 2011, at 6:29 PM, Darius Buntinas wrote: > > Create an error handler (function) that throws a C++ exception, then wherever the original code set the error handler to MPI:ERRORS_THROW_EXCEPTIONS, use your new error handler. > > I haven't looked up the standard here, but it might say that the error handler must return. If it does, then this would not be allowed, otherwise, this should work. > > -d > > > On Nov 1, 2011, at 4:18 PM, Jeff Hammond wrote: > >> Can someone explain how one can migrate (backwards) from the C++ to >> the C bindings if they currently use MPI::Exception in a try-catch >> block like this: >> >> =================================== >> try { >> ((ThreadBase*)(self))->run(); >> } >> catch (const MPI::Exception& e) { >> error("caught an MPI exception"); >> } >> =================================== >> >> This is taken from MADNESS, btw. >> >> I think it is only fair for those who want to kill the C++ bindings to >> provide a clear description of how this will not break existing codes >> that use C++ bindings. Clearly, many things, e.g. MPI::BYTE -> >> MPI_BYTE, are trivial, but I see error handling as being fundamentally >> nontrivial. >> >> Thanks, >> >> Jeff >> >> -- >> Jeff Hammond >> Argonne Leadership Computing Facility >> University of Chicago Computation Institute >> jhammond(a)alcf.anl.gov / (630) 252-5381 >> http://www.linkedin.com/in/jeffhammond >> https://wiki.alcf.anl.gov/index.php/User:Jhammond >> _______________________________________________ >> mpi-forum mailing list >> mpi-forum(a)lists.mpi-forum.org >> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi-forum > > > _______________________________________________ > mpi-forum mailing list > mpi-forum(a)lists.mpi-forum.org > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi-forum -- Jeff Squyres jsquyres(a)cisco.com For corporate legal information go to: http://www.cisco.com/web/about/doing_business/legal/cri/

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Re: [Mpi-forum] how to get MPI::Exception behavior from C bindings?
by Darius Buntinas 01 Nov '11

01 Nov '11

Create an error handler (function) that throws a C++ exception, then wherever the original code set the error handler to MPI:ERRORS_THROW_EXCEPTIONS, use your new error handler. I haven't looked up the standard here, but it might say that the error handler must return. If it does, then this would not be allowed, otherwise, this should work. -d On Nov 1, 2011, at 4:18 PM, Jeff Hammond wrote: > Can someone explain how one can migrate (backwards) from the C++ to > the C bindings if they currently use MPI::Exception in a try-catch > block like this: > > =================================== > try { > ((ThreadBase*)(self))->run(); > } > catch (const MPI::Exception& e) { > error("caught an MPI exception"); > } > =================================== > > This is taken from MADNESS, btw. > > I think it is only fair for those who want to kill the C++ bindings to > provide a clear description of how this will not break existing codes > that use C++ bindings. Clearly, many things, e.g. MPI::BYTE -> > MPI_BYTE, are trivial, but I see error handling as being fundamentally > nontrivial. > > Thanks, > > Jeff > > -- > Jeff Hammond > Argonne Leadership Computing Facility > University of Chicago Computation Institute > jhammond(a)alcf.anl.gov / (630) 252-5381 > http://www.linkedin.com/in/jeffhammond > https://wiki.alcf.anl.gov/index.php/User:Jhammond > _______________________________________________ > mpi-forum mailing list > mpi-forum(a)lists.mpi-forum.org > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi-forum

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Re: [Mpi-forum] MPI_Comm_create_group Meeting
by Marc Snir 01 Nov '11

01 Nov '11

please ignore -- wrong address On Nov 1, 2011, at 5:01 PM, Marc Snir wrote: > can skip > On Nov 1, 2011, at 2:33 PM, James Dinan wrote: > >> Hi All, >> >> I would like to form a group to review the MPI_Comm_create_group() proposal (#286) for a formal reading at the next Forum meeting. If you are interested in joining the discussion, could you please fill in your availability for a one hour conference call next week: >> >> http://www.doodle.com/9tganzq2hqiqy7kt >> >> We have a couple issues to discuss: >> >> 1.) The name of the function: MPI_Comm_create_group, MPI_Group_comm_create, MPI_Comm_create_from_group, ... >> >> 2.) The tag argument: Should we use a tag or a "color" to establish a safe communication conduit on the parent communicator. As discussed at the Forum, using a tag could conflict with the use of MPI_ANY_TAG on the parent communicator. A color would avoid this issue, however it could complicate tag matching. >> >> 3.) Changes to the text. >> >> Thanks, >> ~Jim. >> >> PS- I've attached a copy of the current text with comments from the formal reading at the last Forum meeting (in Acrobat: Comments -> Comments View -> Show Comments List for the full list). >> <ticket_286_oct_2011_with_notes.pdf>_______________________________________________ >> mpi-forum mailing list >> mpi-forum(a)lists.mpi-forum.org >> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi-forum > > > _______________________________________________ > mpi-forum mailing list > mpi-forum(a)lists.mpi-forum.org > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi-forum

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Re: [Mpi-forum] how to get MPI::Exception behavior from C bindings?
by Jeff Hammond 01 Nov '11

01 Nov '11

I didn't write that code so I'm not sure but I imagine one can figure it out from http://code.google.com/p/m-a-d-n-e-s-s/source/browse/local/trunk/src/lib/wo…. I confess that I know almost nothing about C++ exceptions. I just looked at MADNESS and tried to figure out how I could convert it (backwards) to using the C bindings. Jeff On Tue, Nov 1, 2011 at 5:09 PM, Bronis R. de Supinski <bronis(a)llnl.gov> wrote: > > What do they set as the error handler? It is not clear > to me that this code actually does anything... > > On Tue, 1 Nov 2011, Jeff Hammond wrote: > >> Can someone explain how one can migrate (backwards) from the C++ to >> the C bindings if they currently use MPI::Exception in a try-catch >> block like this: >> >> =================================== >> ï¿½ ï¿½ ï¿½ try { >> ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ((ThreadBase*)(self))->run(); >> ï¿½ ï¿½ ï¿½ } >> ï¿½ ï¿½ ï¿½ catch (const MPI::Exception& e) { >> ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ error("caught an MPI exception"); >> ï¿½ ï¿½ ï¿½ } >> =================================== >> >> This is taken from MADNESS, btw. >> >> I think it is only fair for those who want to kill the C++ bindings to >> provide a clear description of how this will not break existing codes >> that use C++ bindings. ï¿½Clearly, many things, e.g. MPI::BYTE -> >> MPI_BYTE, are trivial, but I see error handling as being fundamentally >> nontrivial. >> >> Thanks, >> >> Jeff >> >> -- >> Jeff Hammond >> Argonne Leadership Computing Facility >> University of Chicago Computation Institute >> jhammond(a)alcf.anl.gov / (630) 252-5381 >> http://www.linkedin.com/in/jeffhammond >> https://wiki.alcf.anl.gov/index.php/User:Jhammond >> _______________________________________________ >> mpi-forum mailing list >> mpi-forum(a)lists.mpi-forum.org >> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi-forum >> > _______________________________________________ > mpi-forum mailing list > mpi-forum(a)lists.mpi-forum.org > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi-forum > -- Jeff Hammond Argonne Leadership Computing Facility University of Chicago Computation Institute jhammond(a)alcf.anl.gov / (630) 252-5381 http://www.linkedin.com/in/jeffhammond https://wiki.alcf.anl.gov/index.php/User:Jhammond

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Re: [Mpi-forum] how to get MPI::Exception behavior from C bindings?
by Bronis R. de Supinski 01 Nov '11

01 Nov '11

What do they set as the error handler? It is not clear to me that this code actually does anything... On Tue, 1 Nov 2011, Jeff Hammond wrote: > Can someone explain how one can migrate (backwards) from the C++ to > the C bindings if they currently use MPI::Exception in a try-catch > block like this: > > =================================== > try { > ((ThreadBase*)(self))->run(); > } > catch (const MPI::Exception& e) { > error("caught an MPI exception"); > } > =================================== > > This is taken from MADNESS, btw. > > I think it is only fair for those who want to kill the C++ bindings to > provide a clear description of how this will not break existing codes > that use C++ bindings. Clearly, many things, e.g. MPI::BYTE -> > MPI_BYTE, are trivial, but I see error handling as being fundamentally > nontrivial. > > Thanks, > > Jeff > > -- > Jeff Hammond > Argonne Leadership Computing Facility > University of Chicago Computation Institute > jhammond(a)alcf.anl.gov / (630) 252-5381 > http://www.linkedin.com/in/jeffhammond > https://wiki.alcf.anl.gov/index.php/User:Jhammond > _______________________________________________ > mpi-forum mailing list > mpi-forum(a)lists.mpi-forum.org > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi-forum >

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Re: [Mpi-forum] MPI_Comm_create_group Meeting
by Marc Snir 01 Nov '11

01 Nov '11

can skip On Nov 1, 2011, at 2:33 PM, James Dinan wrote: > Hi All, > > I would like to form a group to review the MPI_Comm_create_group() proposal (#286) for a formal reading at the next Forum meeting. If you are interested in joining the discussion, could you please fill in your availability for a one hour conference call next week: > > http://www.doodle.com/9tganzq2hqiqy7kt > > We have a couple issues to discuss: > > 1.) The name of the function: MPI_Comm_create_group, MPI_Group_comm_create, MPI_Comm_create_from_group, ... > > 2.) The tag argument: Should we use a tag or a "color" to establish a safe communication conduit on the parent communicator. As discussed at the Forum, using a tag could conflict with the use of MPI_ANY_TAG on the parent communicator. A color would avoid this issue, however it could complicate tag matching. > > 3.) Changes to the text. > > Thanks, > ~Jim. > > PS- I've attached a copy of the current text with comments from the formal reading at the last Forum meeting (in Acrobat: Comments -> Comments View -> Show Comments List for the full list). > <ticket_286_oct_2011_with_notes.pdf>_______________________________________________ > mpi-forum mailing list > mpi-forum(a)lists.mpi-forum.org > http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi-forum

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how to get MPI::Exception behavior from C bindings?
by Jeff Hammond 01 Nov '11

01 Nov '11

Can someone explain how one can migrate (backwards) from the C++ to the C bindings if they currently use MPI::Exception in a try-catch block like this: =================================== try { ((ThreadBase*)(self))->run(); } catch (const MPI::Exception& e) { error("caught an MPI exception"); } =================================== This is taken from MADNESS, btw. I think it is only fair for those who want to kill the C++ bindings to provide a clear description of how this will not break existing codes that use C++ bindings. Clearly, many things, e.g. MPI::BYTE -> MPI_BYTE, are trivial, but I see error handling as being fundamentally nontrivial. Thanks, Jeff -- Jeff Hammond Argonne Leadership Computing Facility University of Chicago Computation Institute jhammond(a)alcf.anl.gov / (630) 252-5381 http://www.linkedin.com/in/jeffhammond https://wiki.alcf.anl.gov/index.php/User:Jhammond

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MPI_Comm_create_group Meeting
by James Dinan 01 Nov '11

01 Nov '11

Hi All, I would like to form a group to review the MPI_Comm_create_group() proposal (#286) for a formal reading at the next Forum meeting. If you are interested in joining the discussion, could you please fill in your availability for a one hour conference call next week: http://www.doodle.com/9tganzq2hqiqy7kt We have a couple issues to discuss: 1.) The name of the function: MPI_Comm_create_group, MPI_Group_comm_create, MPI_Comm_create_from_group, ... 2.) The tag argument: Should we use a tag or a "color" to establish a safe communication conduit on the parent communicator. As discussed at the Forum, using a tag could conflict with the use of MPI_ANY_TAG on the parent communicator. A color would avoid this issue, however it could complicate tag matching. 3.) Changes to the text. Thanks, ~Jim. PS- I've attached a copy of the current text with comments from the formal reading at the last Forum meeting (in Acrobat: Comments -> Comments View -> Show Comments List for the full list).

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