NAME¶
pkg_mkIndex - Build an index for automatic loading of packages
SYNOPSIS¶
pkg_mkIndex ?-direct? ?-lazy? ?-load pkgPat? ?-verbose? dir ?pattern pattern ...?
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.
- -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 isn't 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 won't 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