- pkg_mkIndex — Build an index for automatic loading of packages
PACKAGES AND THE AUTO-LOADER
HOW IT WORKS
pkg_mkIndex — Build an index for automatic loading of packages
?pattern pattern ...
is a utility procedure that is part of the standard Tcl library. It is used to create index files that allow packages to be loaded automatically when package require
commands are executed. To use pkg_mkIndex
, follow these steps:
- Create the package(s). Each package may consist of one or more Tcl script files or binary files. Binary files must be suitable for loading with the load command with a single argument; for example, if the file is test.so it must be possible to load this file with the command load test.so. Each script file must contain a package provide command to declare the package and version number, and each binary file must contain a call to Tcl_PkgProvide.
- Create the index by invoking pkg_mkIndex. The dir argument gives the name of a directory and each pattern argument is a glob-style pattern that selects script or binary files in dir. The default pattern is *.tcl and *.[info sharedlibextension].
Pkg_mkIndex will create a file pkgIndex.tcl in dir with package information about all the files given by the pattern arguments. It does this by loading each file into a slave interpreter and seeing what packages and new commands appear (this is why it is essential to have package provide commands or Tcl_PkgProvide calls in the files, as described above). If you have a package split among scripts and binary files, or if you have dependencies among files, you may have to use the -load option or adjust the order in which pkg_mkIndex processes the files. See COMPLEX CASES below.
- Install the package as a subdirectory of one of the directories given by the tcl_pkgPath variable. If $tcl_pkgPath contains more than one directory, machine-dependent packages (e.g., those that contain binary shared libraries) should normally be installed under the first directory and machine-independent packages (e.g., those that contain only Tcl scripts) should be installed under the second directory. The subdirectory should include the package's script and/or binary files as well as the pkgIndex.tcl file. As long as the package is installed as a subdirectory of a directory in $tcl_pkgPath it will automatically be found during package require commands.
If you install the package anywhere else, then you must ensure that the directory containing the package is in the auto_path global variable or an immediate subdirectory of one of the directories in auto_path. Auto_path contains a list of directories that are searched by both the auto-loader and the package loader; by default it includes $tcl_pkgPath. The package loader also checks all of the subdirectories of the directories in auto_path. You can add a directory to auto_path explicitly in your application, or you can add the directory to your TCLLIBPATH environment variable: if this environment variable is present, Tcl initializes auto_path from it during application startup.
- Once the above steps have been taken, all you need to do to use a package is to invoke package require. For example, if versions 2.1, 2.3, and 3.1 of package Test have been indexed by pkg_mkIndex, the command package require Test will make version 3.1 available and the command package require -exact Test 2.1 will make version 2.1 available. There may be many versions of a package in the various index files in auto_path, but only one will actually be loaded in a given interpreter, based on the first call to package require. Different versions of a package may be loaded in different interpreters.
The optional switches are:
- The generated index will implement direct loading of the package upon package require. This is the default.
- The generated index will manage to delay loading the package until the use of one of the commands provided by the package, instead of loading it immediately upon package require. This is not compatible with the use of auto_reset, and therefore its use is discouraged.
- The index process will pre-load any packages that exist in the current interpreter and match pkgPat into the slave interpreter used to generate the index. The pattern match uses string match rules, but without making case distinctions. See COMPLEX CASES below.
- Generate output during the indexing process. Output is via the tclLog procedure, which by default prints to stderr.
- End of the flags, in case dir begins with a dash.
Packages and the auto-loader
The package management facilities overlap somewhat with the auto-loader, in that both arrange for files to be loaded on-demand. However, package management is a higher-level mechanism that uses the auto-loader for the last step in the loading process. It is generally better to index a package with pkg_mkIndex
rather than auto_mkindex
because the package mechanism provides version control: several versions of a package can be made available in the index files, with different applications using different versions based on package require
commands. In contrast, auto_mkindex
does not understand versions so it can only handle a single version of each package. It is probably not a good idea to index a given package with both pkg_mkIndex
. If you use pkg_mkIndex
to index a package, its commands cannot be invoked until package require
has been used to select a version; in contrast, packages indexed with auto_mkindex
can be used immediately since there is no version control.
How it works Pkg_mkIndex
depends on the package unknown
command, the package ifneeded
command, and the auto-loader. The first time a package require
command is invoked, the package unknown
script is invoked. This is set by Tcl initialization to a script that evaluates all of the pkgIndex.tcl
files in the auto_path
. The pkgIndex.tcl
files contain package ifneeded
commands for each version of each available package; these commands invoke package provide
commands to announce the availability of the package, and they setup auto-loader information to load the files of the package. If the -lazy
flag was provided when the pkgIndex.tcl
was generated, a given file of a given version of a given package is not actually loaded until the first time one of its commands is invoked. Thus, after invoking package require
you may not see the package's commands in the interpreter, but you will be able to invoke the commands and they will be auto-loaded.
Some packages, for instance packages which use namespaces and export commands or those which require special initialization, might select that their package files be loaded immediately upon package require
instead of delaying the actual loading to the first use of one of the package's command. This is the default mode when generating the package index. It can be overridden by specifying the -lazy
Most complex cases of dependencies among scripts and binary files, and packages being split among scripts and binary files are handled OK. However, you may have to adjust the order in which files are processed by pkg_mkIndex
. These issues are described in detail below.
If each script or file contains one package, and packages are only contained in one file, then things are easy. You simply specify all files to be indexed in any order with some glob patterns.
In general, it is OK for scripts to have dependencies on other packages. If scripts contain package require commands, these are stubbed out in the interpreter used to process the scripts, so these do not cause problems. If scripts call into other packages in global code, these calls are handled by a stub unknown command. However, if scripts make variable references to other package's variables in global code, these will cause errors. That is also bad coding style.
If binary files have dependencies on other packages, things can become tricky because it is not possible to stub out C-level APIs such as Tcl_PkgRequire API when loading a binary file. For example, suppose the BLT package requires Tk, and expresses this with a call to Tcl_PkgRequire in its Blt_Init routine. To support this, you must run pkg_mkIndex in an interpreter that has Tk loaded. You can achieve this with the -load pkgPat option. If you specify this option, pkg_mkIndex will load any packages listed by info loaded and that match pkgPat into the interpreter used to process files. In most cases this will satisfy the Tcl_PkgRequire calls made by binary files.
If you are indexing two binary files and one depends on the other, you should specify the one that has dependencies last. This way the one without dependencies will get loaded and indexed, and then the package it provides will be available when the second file is processed. You may also need to load the first package into the temporary interpreter used to create the index by using the -load flag; it will not hurt to specify package patterns that are not yet loaded.
If you have a package that is split across scripts and a binary file, then you should avoid the -load flag. The problem is that if you load a package before computing the index it masks any other files that provide part of the same package. If you must use -load, then you must specify the scripts first; otherwise the package loaded from the binary file may mask the package defined by the scripts.
See also package
Copyright © 1996 Sun Microsystems, Inc.