Home My Page Projects Code Snippets Project Openings SML/NJ
 Summary Activity Forums Tracker Lists Tasks Docs Surveys News SCM Files

# SCM Repository

[smlnj] View of /sml/trunk/src/cm/Doc/03-usage.tex
 [smlnj] / sml / trunk / src / cm / Doc / 03-usage.tex

# View of /sml/trunk/src/cm/Doc/03-usage.tex

Tue Jun 5 19:10:21 2001 UTC (19 years ago) by blume
File size: 26293 byte(s)
index-file generation in CM; small changes to c-calls API

% -*- latex -*-

\section{Using CM}

\subsection{Structure CM}
\label{sec:api}

Functions that control CM's operation are accessible as members of a
structure named {\tt CM} which itself is exported from a library
called {\tt \$smlnj/cm.cm} (or, alternatively, {\tt \$smlnj/cm/cm.cm}).  This library is pre-registered for auto-loading
at the interactive top level.

Other libraries can exploit CM's functionality simply by putting a
{\tt \$smlnj/cm.cm} entry into their own description file. Section~\ref{sec:dynlink} shows one interesting use of this feature. Here is a description of all members: \subsubsection{Compiling} \label{sec:api:compiling} Two main activities when using CM are to compile ML source code and to build stable libraries: \begin{verbatim} val recomp : string -> bool val stabilize : bool -> string -> bool \end{verbatim} {\tt CM.recomp} takes the name of a program's root'' description file and compiles or recompiles all ML source files that are necessary to provide definitions for the root library's export list. ({\em Note:} The difference to {\tt CM.make} is that no linking takes place.) {\tt CM.stabilize} takes a boolean flag and then the name of a library and {\em stabilizes} this library. A library is stabilized by writing all information pertaining to it, including all of its library components (i.e., subgroups), into a single file. Sublibraries do not become part of the stabilized library; CM records stub entries for them. When a stabilized library is used in other programs, all members of the library are guaranteed to be up-to-date; no dependency analysis work and no recompilation work will be necessary. If the boolean flag is {\tt false}, then all sublibraries of the library must already be stable. If the flag is {\tt true}, then CM will recursively stabilize all libraries reachable from the given root. After a library has been stabilized it can be used even if none of its original sources---including the description file---are present. The boolean result of {\tt CM.recomp} and {\tt CM.stabilize} indicates success or failure of the operation ({\tt true} = success). \subsubsection{Linking and execution} In SML/NJ, linking means executing top-level code (i.e., module creation and initialization code) of each compilation unit. The resulting bindings can then be registered at the interactive top level. \begin{verbatim} val make : string -> bool val autoload : string -> bool \end{verbatim} {\tt CM.make} first acts like {\tt CM.recomp}. If the (re-)compilation is successful, then it proceeds by linking all modules that require linking. Provided there are no link-time errors, it finally introduces new bindings at top level. During the course of the same {\tt CM.make}, the code of each compilation module that is reachable from the root will be executed at most once. Code in units that are marked as {\it private} (see Section~\ref{sec:sharing}) will be executed exactly once. Code in other units will be executed only if the unit has been recompiled since it was executed last time or if it depends on another compilation unit whose code has been executed since. In effect, different invocations of {\tt CM.make} (and {\tt CM.autoload}) will share dynamic state created at link time as much as possible unless the compilation units in question have been explicitly marked private. {\tt CM.autoload} acts like {\tt CM.make}, only lazily''. See Section~\ref{sec:autoload} for more information. As before, the result of {\tt CM.make} indicates success or failure of the operation. The result of {\tt CM.autoload} indicates success or failure of the {\em registration}. (It does not know yet whether loading will actually succeed.) \subsubsection{Registers} \label{sec:registers} Several internal registers control the operation of CM. A register of type$T$is accessible via a variable of type$T${\tt controller}, i.e., a pair of {\tt get} and {\tt set} functions.\footnote{The type constructor {\tt controller} is defined as part of {\tt structure CM}.} Any invocation of the corresponding {\tt get} function reads the current value of the register. An invocation of the {\tt set} function replaces the current value with the argument given to {\tt set}. Controllers are members of {\tt CM.Control}, a sub-structure of structure {\tt CM}. \begin{verbatim} type 'a controller = { get: unit -> 'a, set: 'a -> unit } structure Control : sig val verbose : bool controller val debug : bool controller val keep_going : bool controller val parse_caching : int controller val warn_obsolete : bool controller val conserve_memory : bool controller val generate_index : bool controller end \end{verbatim} {\tt CM.Control.verbose} can be used to turn off CM's progress messages. The default is {\em true} and can be overriden at startup time by the environment variable {\tt CM\_VERBOSE}. In the case of a compile-time error {\tt CM.Contol.keep\_going} instructs the {\tt CM.recomp} phase to continue working on parts of the dependency graph that are not related to the error. (This does not work for outright syntax errors because a correct parse is needed before CM can construct the dependency graph.) The default is {\em false}, meaning quit on first error'', and can be overriden at startup by the environment variable {\tt CM\_KEEP\_GOING}. {\tt CM.Control.parse\_caching} sets a limit on how many parse trees are cached in main memory. In certain cases CM must parse source files in order to be able to calculate the dependency graph. Later, the same files may need to be compiled, in which case an existing parse tree saves the time to parse the file again. Keeping parse trees can be expensive in terms of memory usage. Moreover, CM makes special efforts to avoid re-parsing files in the first place unless they have actually been modified. Therefore, it may not make much sense to set this value very high. The default is {\em 100} and can be overriden at startup time by the environment variable {\tt CM\_PARSE\_CACHING}. This version of CM uses an ML-inspired syntax for expressions in its conditional compilation subsystem (see Section~\ref{sec:preproc}). However, for the time being it will accept most of the original C-inspired expressions but produces a warning for each occurrence of an old-style operator. {\tt CM.Control.warn\_obsolete} can be used to turn these warnings off. The default is {\em true}, meaning warnings are issued'', and can be overriden at startup time by the environment variable {\tt CM\_WARN\_OBSOLETE}. {\tt CM.Control.debug} can be used to turn on debug mode. This currently has the effect of dumping a trace of the master-slave protocol for parallel and distributed compilation (see Section~\ref{sec:parmake}) to TextIO.stdOut. The default is {\em false} and can be overriden at startup time by the environment variable {\tt CM\_DEBUG}. Using {\tt CM.Control.conserve\_memory}, CM can be told to be slightly more conservative with its use of main memory at the expense of occasionally incurring additional input from stable library files. This does not save very much and, therefore, is normally turned off. The default ({\em false}) can be overridden at startup by the environment variable {\tt CM\_CONSERVE\_MEMORY}. {\tt CM.Control.generate\_index} is used to control the generation of human-readable {\em index files} (see section~\ref{sec:indexfiles}). The default setting is {\em false} and can be overridden at startup by the environment variable {\tt CM\_GENERATE\_INDEX}. \subsubsection{Path anchors} \label{sec:api:anchors} Structure {\tt CM} also provides functions to explicitly manipulate the path anchor configuration. These functions are members of structure {\tt CM.Anchor}. \begin{verbatim} structure Anchor : sig val anchor : string -> string option controller val reset : unit -> unit end \end{verbatim} {\tt CM.Anchor.anchor} returns a pair of {\tt get} and {\tt set} functions that can be used to query and modify the status of the named anchor. Note that the {\tt get}-{\tt set}-pair operates over type {\tt string option}; a value of {\tt NONE} means that the anchor is currently not bound (or, in the case of {\tt set}, that it is being cancelled). The (optional) string given to {\tt set} must be a directory name in native syntax ({\em without} trailing arc separator, e.g., {\bf /} in Unix). If it is specified as a relative path name, then it will be expanded by prepending the name of the current working directory. {\tt CM.Anchor.reset} erases the entire existing path configuration. After a call of this function has completed, all root environment locations are marked as being undefined''. \subsubsection{Setting CM variables} CM variables are used by the conditional compilation system (see Section~\ref{sec:cmvars}). Some of these variables are predefined, but the user can add new ones and alter or remove those that already exist. \begin{verbatim} val symval : string -> int option controller \end{verbatim} Function {\tt CM.symval} returns a {\tt get}-{\tt set}-pair for the symbol whose name string was specified as the argument. Note that the {\tt get}-{\tt set}-pair operates over type {\tt int option}; a value of {\tt NONE} means that the variable is not defined. \noindent Examples: \begin{verbatim} #get (CM.symval "X") (); (* query value of X *) #set (CM.symval "Y") (SOME 1); (* set Y to 1 *) #set (CM.symval "Z") NONE; (* remove definition for Z *) \end{verbatim} Some care is necessary as {\tt CM.symval} does not check whether the syntax of the argument string is valid. (However, the worst thing that could happen is that a variable defined via {\tt CM.symval} is not accessible\footnote{from within CM's description files} because there is no legal syntax to name it.) \subsubsection{Library registry} \label{sec:libreg} To be able to share associated data structures such as symbol tables and dependency graphs, CM maintains an internal registry of all stable libraries that it has encountered during an ongoing interactive session. The {\tt CM.Library} sub-structure of structure {\tt CM} provides access to this registry. \begin{verbatim} structure Library : sig type lib val known : unit -> lib list val descr : lib -> string val osstring : lib -> string val dismiss : lib -> unit val unshare : lib -> unit end \end{verbatim} {\tt CM.Library.known}, when called, produces a list of currently known stable libraries. Each such library is represented by an element of the abstract data type {\tt CM.Library.lib}. {\tt CM.Library.descr} extracts a string describing the location of the CM description file associated with the given library. The syntax of this string is almost the same as that being used by CM's master-slave protocol (see section~\ref{sec:pathencode}). {\tt CM.Library.osstring} produces a string denoting the given library's description file using the underlying operating system's native pathname syntax. In other words, the result of a call of {\tt CM.Library.osstring} is suitable as an argument to {\tt TextIO.openIn}. {\tt CM.Library.dismiss} is used to remove a stable library from CM's internal registry. Although removing a library from the registry may recover considerable amounts of main memory, doing so also eliminates any chance of sharing the associated data structures with later references to the same library. Therefore, it is not always in the interest of memory-conscious users to use this feature. While dependency graphs and symbol tables need to be reloaded when a previously dismissed library is referenced again, the sharing of link-time state created by this library is {\em not} affected. (Link-time state is independently maintained in a separate data structure. See the discussion of {\tt CM.unshare} below.) {\tt CM.Library.unshare} is used to remove a stable library from CM's internal registry, and---at the same time---to inhibit future sharing with its existing link-time state. Any future references to this library will see newly created state (which will then be properly shared again). ({\bf Warning:} {\it This feature is not the preferred way of creating unshared state; use functors for that. However, it can come in handy when two different (and perhaps incompatible) versions of the same library are supposed to coexist---especially if one of the two versions is used by SML/NJ itself. Normally, only programmers working on SML/NJ's compiler are expected to be using this facility.}) \subsubsection{Internal state} For CM to work correctly, it must maintain an up-to-date picture of the state of the surrounding world (as far as that state affects CM's operation). Most of the time, this happens automatically and should be transparent to the user. However, occasionally it may become necessary to intervene expliticly. Access to CM's internal state is facilitated by members of the {\tt CM.State} structure. \begin{verbatim} structure State : sig val pending : unit -> string list val synchronize : unit -> unit val reset : unit -> unit end \end{verbatim} {\tt CM.State.pending} produces a list of strings, each string naming one of the symbols that are currently registered (i.e., virtually bound'') but not yet resolved by the autoloading mechanism. {\tt CM.State.synchronize} updates tables internal to CM to reflect changes in the file system. In particular, this will be necessary when the association of file names to file IDs'' (in Unix: inode numbers) changes during an ongoing session. In practice, the need for this tends to be rare. {\tt CM.State.reset} completely erases all internal state in CM. To do this is not very advisable since it will also break the association with pre-loaded libraries. It may be a useful tool for determining the amount of space taken up by the internal state, though. \subsubsection{Compile servers} On Unix-like systems, CM supports parallel compilation. For computers connected using a LAN, this can be extended to distributed compilation using a network file system and the operating system's rsh'' facility. For a detailed discussion, see Section~\ref{sec:parmake}. Sub-structure {\tt CM.Server} provides access to and manipulation of compile servers. Each attached server is represented by a value of type {\tt CM.Server.server}. \begin{verbatim} structure Server : sig type server val start : { name: string, cmd: string * string list, pathtrans: (string -> string) option, pref: int } -> server option val stop : server -> unit val kill : server -> unit val name : server -> string end \end{verbatim} CM is put into parallel'' mode by attaching at least one compile server. Compile servers are attached using invocations of {\tt CM.Server.start}. The function takes the name of the server (as an arbitrary string) ({\tt name}), the Unix command used to start the server in a form suitable as an argument to {\tt Unix.execute} ({\tt cmd}), an optional path transformation function'' for converting local path names to remote pathnames ({\tt pathtrans}), and a numeric preference'' value that is used to choose servers at times when more than one is idle ({\tt pref}). The optional result is the handle representing the successfully attached server. An existing server can be shut down and detached using {\tt CM.Server.stop} or {\tt CM.Server.kill}. The argument in either case must be the result of an earlier call of {\tt CM.Server.start}. Function {\tt CM.Server.stop} uses CM's master-slave protocol to instruct the server to shut down gracefully. Only if this fails it may become necessary to use {\tt CM.Server.kill}, which will send a Unix TERM signal to destroy the server. Given a server handle, function {\tt CM.Server.name} returns the string that was originally given to the call of\linebreak {\tt CM.Server.start} used to created the server. \subsubsection{Plug-ins} As an alternative to {\tt CM.make} or {\tt CM.autoload}, where the main purpose is to subsequently be able to access the library from interactively entered code, one can instruct CM to load libraries for effect''. \begin{verbatim} val load_plugin : string -> bool \end{verbatim} Function {\tt CM.load\_plugin} acts exactly like {\tt CM.make} except that even in the case of success no new symbols will be bound in the interactive top-level environment. That means that link-time side-effects will be visible, but none of the exported definitions become available. This mechanism can be used for plug-in'' modules: a core library provides hooks where additional functionality can be registered later via side-effects; extensions to this core are implemented as additional libraries which, when loaded, register themselves with those hooks. By using {\tt CM.load\_plugin} instead of {\tt CM.make}, one can avoid polluting the interactive top-level environment with spurious exports of the extension module. CM itself uses plug-in modules in its member-class subsystem (see section~\ref{sec:moretools}). This makes it possible to add new classes and tools very easily without having to reconfigure or recompile CM, not to mention modify its source code. \subsubsection{Support for stand-alone programs} \label{sec:mlbuild:support} CM can be used to build stand-alone programs. In fact SML/NJ itself---including CM---is an example of this. (The interactive system cannot rely on an existing compilation manager when starting up.) A stand-alone program is constructed by the runtime system from existing binfiles or members of existing stable libraries. CM must prepare those binfiles or libraries together with a list that describes them to the runtime system. \begin{verbatim} val mk_standalone : bool option -> { project: string, wrapper: string, target: string } -> string list option \end{verbatim} Here, {\tt project} and {\tt wrapper} name description files and {\tt target} is the name of a heap image---with or without the usual implicit heap image suffix; see the description of {\tt SMLofNJ.exportFn} from the (SML/NJ-specific extension of the) Basis Library~\cite{reppy99:basis}. A call of {\tt mk\_standalone} triggers the following three-stage procedure: \begin{enumerate} \item Depending on the optional boolean argument, {\tt project} is subjected to the equivalent of either {\tt CM.recomp} or {\tt CM.stabilize}. {\tt NONE} means {\tt CM.recomp}, and {\tt (SOME$r$)} means {\tt CM.stabilize$r$}. There are tree ways of how to continue from here: \begin{enumerate} \item If recompilation of {\tt project} failed, then a result of {\tt NONE} will be returned immediately. \item If everything was up-to-date (i.e, if no ML source had to be compiled and all these sources were older than the existing {\tt target}), then a result of {\tt SOME []} will be returned. \item Otherwise execution proceeds to the next stage. \end{enumerate} \item The {\em wrapper library} named by {\tt wrapper} is being recompiled (using the equivalent of {\tt CM.recomp}). If this fails, {\tt NONE} is returned. Otherwise execution proceeds to the next stage. \item {CM.mk\_standalone} constructs a topologically sorted list$l$of strings that, when written to a file, can be passed to the runtime system in order to perform stand-alone linkage of the program given by {\tt wrapper}. The final result is {\tt SOME$l$}. \end{enumerate} The idea is that {\tt project} names the library that actually implements the main program while {\tt wrapper} names an auxiliary wrapper library responsible for issuing a call of {\tt SMLofNJ.exportFn} (generating {\tt target}) on behalf of {\tt project}. The programmer should normally never have a need to invoke {\tt CM.mk\_standalone} directly. Instead, this function is used by an auxiliary script called {\tt ml-build} (see Section~\ref{sec:mlbuild}). \subsubsection{Finding all sources} \label{sec:makedepend:support} The {\tt CM.sources} function can be used to find the names of all source files that a given library depends on. It returns the names of all files involved with the exception of skeleton files and binfiles (see Section~\ref{sec:files}). Stable libraries are represented by their library file; their description file or consitutent members are {\em not} listed. Normally, the function reports actual file names as used for accessing the file system. For (stable) library files this behavior can be inconvenient because these names depend on architecture and operating system. For this reason, {\tt CM.sources} accepts an optional pair of strings that then will be used in place of the architecture- and OS-specific part of these names. \begin{verbatim} val sources : { arch: string, os: string } option -> string -> { file: string, class: string, derived: bool } list option \end{verbatim} In case there was some error analyzing the specified library or group, {\tt CM.sources} returns {\tt NONE}. Otherwise the result is a list of records, each carrying a file name, the corresponding class, and information about whether or not the source was created by some tool. Examples: \begin{description} \item[generating make'' dependencies:] To generate dependency information usable by Unix' {\tt make} command, one would be interested in all files that were not derived by some tool application. Moreover, one would probably like to use shell variables instead of concrete architecture- and OS-names: \begin{verbatim} Option.map (List.filter (not o #derived)) (CM.sources (SOME { arch = "$ARCH", os = "$OPSYS" }) "foo.cm"); \end{verbatim} A call of {\tt CM.sources} similar to the one shown here is used by the auxiliary script {\tt ml-makedepend} (see Section~\ref{sec:makedepend}). \item[finding all {\tt noweb} sources:] To find all {\tt noweb} sources (see Section~\ref{sec:builtin-tools:noweb}), e.g., to be able to run the document preparation program {\tt noweave} on them, one can simply look for entries of the {\tt noweb} class. Here, one would probably want to include derived sources: \begin{verbatim} Option.map (List.filter (fn x => #class x = "noweb")) (CM.sources NONE "foo.cm"); \end{verbatim} \end{description} \subsection{The autoloader} \label{sec:autoload} From the user's point of view, a call of {\tt CM.autoload} acts very much like the corresponding call of {\tt CM.make} because the same bindings that {\tt CM.make} would introduce into the top-level enviroment are also introduced by {\tt CM.autoload}. However, most work will be deferred until some code that is entered later refers to one or more of these bindings. Only then will CM go and perform just the minimal work necessary to provide the actual definitions. The autoloader plays a central role for the interactive system. Unlike in earlier versions, it cannot be turned off since it provides many of the standard pre-defined top-level bindings. The autoloader is a convenient mechanism for virtually loading'' an entire library without incurring an undue increase in memory consumption for library modules that are not actually being used. \subsection{Sharing of state} \label{sec:sharing} Whenever it is legal to do so, CM lets multiple invocations of {\tt CM.make} or {\tt CM.autoload} share dynamic state created by link-time effects. Of course, sharing is not possible (and hence not legal'') if the compilation unit in question has recently been recompiled or depends on another compilation unit whose code has recently been re-executed. The programmer can explicitly mark certain ML files as {\em shared}, in which case CM will issue a warning whenever the unit's code has to be re-executed. State created by compilation units marked as {\em private} is never shared across multiple calls to {\tt CM.make} or {\tt CM.autoload}. To understand this behavior it is useful to introduce the notion of a {\em traversal}. A traversal is the process of traversing the dependency graph on behalf of {\tt CM.make} or {\tt CM.autoload}. Several traversals can be executed interleaved with each other because a {\tt CM.autoload} traversal normally stays suspended and is performed incrementally driven by input from the interactive top level loop. As far as sharing is concerned, the rule is that during one traversal each compilation unit will be executed at most once. This means that the same program'' will not see multiple instantiations of the same compilation unit (where program'' refers to the code managed by one call of {\tt CM.make} or {\tt CM.autoload}). Each compilation unit will be linked at most once during a traversal and private state will not be confused with private state of other traversals that might be active at the same time. % Need a good example here. \subsubsection{Sharing annotations} ML source files in CM description files can be specified as being {\em private} or {\em shared}. This is done by adding a {\em tool parameter} specification for the file in the library- or group description file (see Section~\ref{sec:classes}). To mark an ML file as {\em private}, follow the file name with the word {\tt private} in parentheses. For {\em shared} ML files, replace {\tt private} with {\tt shared}. An ML source file that is not annotated will typically be treated as {\em shared} unless it statically depends on some other {\em private} source. It is an error, checked by CM, for a {\em shared} source to depend on a {\em private} source. \subsubsection{Sharing with the interactive system} The SML/NJ interactive system, which includes the compiler, is itself created by linking modules from various libraries. Some of these libraries can also be used in user programs. Examples are the Standard ML Basis Library {\tt \$/basis.cm}, the SML/NJ library {\tt
\$/smlnj-lib.cm}, and the ML-Yacc library {\tt \$/ml-yacc-lib.cm}.

If a module from a library is used by both the interactive system and
a user program running under control of the interactive system, then
CM will let them share code and dynamic state.  Moreover, the affected
portion of the library will never have to be relinked''.