pkgMkIndex(3tcl)
NAME
pkg_mkIndex - Build an index for automatic loading of packages
SYNOPSIS
pkg_mkIndex ?-direct? ?-lazy? ?-load pkgPat? ?-verbose? dir ?pattern pattern ...?
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DESCRIPTION
Pkg_mkIndex 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:
[1] 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.
[2] 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.
[3] 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.
[4] 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.
OPTIONS
The optional switches are:
-direct The generated index will implement direct loading of the
package upon package require. This is the default.
-lazy 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.
-load pkgPat 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.
-verbose 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
and auto_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.
DIRECT LOADING
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 argument.
COMPLEX CASES
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(3tcl)
KEYWORDS
auto-load, index, package, version
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