X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=docs%2Fusers_guide%2Fusing.xml;h=20bb687b4f8b10dd0ff8048e783ad29ddde84f6b;hb=43e0bca04009902c16f8f764dcb9a78c8da277c9;hp=ce7ef7680b2f174ce1cd8f478a42289a1b9481b6;hpb=6867d7a5ba5bdde3f6216d932d9486405c9115b3;p=ghc-hetmet.git diff --git a/docs/users_guide/using.xml b/docs/users_guide/using.xml index ce7ef76..20bb687 100644 --- a/docs/users_guide/using.xml +++ b/docs/users_guide/using.xml @@ -46,26 +46,25 @@ ghc [argument...] Sometimes it is useful to make the connection between a source file and the command-line options it requires quite - tight. For instance, if a Haskell source file uses GHC - extensions, it will always need to be compiled with the - option. Rather than maintaining + tight. For instance, if a Haskell source file deliberately + uses name shadowing, it should be compiled with the + option. Rather than maintaining the list of per-file options in a Makefile, it is possible to do this directly in the source file using the OPTIONS_GHC pragma OPTIONS_GHC pragma: -{-# OPTIONS_GHC -fglasgow-exts #-} +{-# OPTIONS_GHC -fno-warn-name-shadowing #-} module X where ... - OPTIONS_GHC pragmas are only looked for at - the top of your source files, upto the first - (non-literate,non-empty) line not containing - OPTIONS_GHC. Multiple OPTIONS_GHC - pragmas are recognised. Do not put comments before, or on the same line - as, the OPTIONS_GHC pragma. + OPTIONS_GHC is a file-header pragma + (see ). + + Only dynamic flags can be used in an OPTIONS_GHC pragma + (see ). Note that your command shell does not get to the source file options, they are just included literally @@ -919,6 +918,23 @@ ghc -c Foo.hs + : + + + + warnings + pragmas + Causes a warning to be emitted when a + pragma that GHC doesn't recognise is used. As well as pragmas + that GHC itself uses, GHC also recognises pragmas known to be used + by other tools, e.g. OPTIONS_HUGS and + DERIVE. + + This option is on by default. + + + + : @@ -1765,15 +1781,58 @@ f "2" = 2 linkend="lang-parallel" /> we describe the language features that affect parallelism. - - Options for SMP parallelism + + Compile-time options for SMP parallelism In order to make use of multiple CPUs, your program must be linked with the option (see ). Then, to run a program on multiple - CPUs, use the RTS option: + linkend="options-linker" />). Additionally, the following + compiler options affect parallelism: + + + + + + Blackholing is the act of marking a thunk (lazy + computuation) as being under evaluation. It is useful for + three reasons: firstly it lets us detect certain kinds of + infinite loop (the NonTermination + exception), secondly it avoids certain kinds of space + leak, and thirdly it avoids repeating a computation in a + parallel program, because we can tell when a computation + is already in progress. + + + The option causes + each thunk to be blackholed as soon as evaluation begins. + The default is "lazy blackholing", whereby thunks are only + marked as being under evaluation when a thread is paused + for some reason. Lazy blackholing is typically more + efficient (by 1-2% or so), because most thunks don't + need to be blackholed. However, eager blackholing can + avoid more repeated computation in a parallel program, and + this often turns out to be important for parallelism. + + + + We recommend compiling any code that is intended to be run + in parallel with the + flag. + + + + + + + + RTS options for SMP parallelism + + To run a program on multiple CPUs, use the + RTS option: + +