Linux Manual Pages

Free Software * Books

Source Code

Free Media

Linux

unload

NAME
SYNOPSIS
DESCRIPTION
PORTABILITY ISSUES
BUGS
EXAMPLE
SEE ALSO
KEYWORDS

___________________________

NAME

unload − Unload machine code

SYNOPSIS

unload ?switches? fileName
unload ?switches? fileName packageName
unload ?switches? fileName packageName interp ___________________________

DESCRIPTION

This command tries to unload shared libraries previously loaded with load from the application’s address space. fileName is the name of the file containing the library file to be unload; it must be the same as the filename provided to load for loading the library. The packageName argument is the name of the package (as determined by or passed to load), and is used to compute the name of the unload procedure; if not supplied, it is computed from fileName in the same manner as load. The interp argument is the path name of the interpreter from which to unload the package (see the interp manual entry for details); if interp is omitted, it defaults to the interpreter in which the unload command was invoked.

If the initial arguments to unload start with − then they are treated as switches. The following switches are currently supported:
−nocomplain

Suppresses all error messages. If this switch is given, unload will never report an error.

−keeplibrary

This switch will prevent unload from issuing the operating system call that will unload the library from the process.

−−

Marks the end of switches. The argument following this one will be treated as a fileName even if it starts with a −.

UNLOAD OPERATION
When a file containing a shared library is loaded through the load command, Tcl associates two reference counts to the library file. The first counter shows how many times the library has been loaded into normal (trusted) interpreters while the second describes how many times the library has been loaded into safe interpreters. As a file containing a shared library can be loaded only once by Tcl (with the first load call on the file), these counters track how many interpreters use the library. Each subsequent call to load after the first simply increments the proper reference count.

unload works in the opposite direction. As a first step, unload will check whether the library is unloadable: an unloadable library exports a special unload procedure. The name of the unload procedure is determined by packageName and whether or not the target interpreter is a safe one. For normal interpreters the name of the initialization procedure will have the form pkg_Unload, where pkg is the same as packageName except that the first letter is converted to upper case and all other letters are converted to lower case. For example, if packageName is foo or FOo, the initialization procedure’s name will be Foo_Unload. If the target interpreter is a safe interpreter, then the name of the initialization procedure will be pkg_SafeUnload instead of pkg_Unload.

If unload determines that a library is not unloadable (or unload functionality has been disabled during compilation), an error will be returned. If the library is unloadable, then unload will call the unload procedure. If the unload procedure returns TCL_OK, unload will proceed and decrease the proper reference count (depending on the target interpreter type). When both reference counts have reached 0, the library will be detached from the process.

UNLOAD HOOK PROTOTYPE
The unload procedure must match the following prototype:

typedef int Tcl_PackageUnloadProc(
Tcl_Interp *interp,
int flags);

The interp argument identifies the interpreter from which the library is to be unloaded. The unload procedure must return TCL_OK or TCL_ERROR to indicate whether or not it completed successfully; in the event of an error it should set the interpreter’s result to point to an error message. In this case, the result of the unload command will be the result returned by the unload procedure.

The flags argument can be either TCL_UNLOAD_DETACH_FROM_INTERPRETER or TCL_UNLOAD_DETACH_FROM_PROCESS. In case the library will remain attached to the process after the unload procedure returns (i.e. because the library is used by other interpreters), TCL_UNLOAD_DETACH_FROM_INTERPRETER will be defined. However, if the library is used only by the target interpreter and the library will be detached from the application as soon as the unload procedure returns, the flags argument will be set to TCL_UNLOAD_DETACH_FROM_PROCESS.

NOTES
The unload command cannot unload libraries that are statically linked with the application. If fileName is an empty string, then the packageName argument must be specified.

If packageName is omitted or specified as an empty string, Tcl tries to guess the name of the package. This may be done differently on different platforms. The default guess, which is used on most UNIX platforms, is to take the last element of fileName, strip off the first three characters if they are lib, and use any following alphabetic and underline characters as the module name. For example, the command unload libxyz4.2.so uses the module name xyz and the command unload bin/last.so {} uses the module name last.

PORTABILITY ISSUES

Unix

Not all unix operating systems support library unloading. Under such an operating system unload returns an error (unless −nocomplain has been specified).

BUGS

If the same file is loaded by different fileNames, it will be loaded into the process’s address space multiple times. The behavior of this varies from system to system (some systems may detect the redundant loads, others may not). In case a library has been silently detached by the operating system (and as a result Tcl thinks the library is still loaded), it may be dangerous to use unload on such a library (as the library will be completely detached from the application while some interpreters will continue to use it).

EXAMPLE

If an unloadable module in the file foobar.dll had been loaded using the load command like this (on Windows):

load c:/some/dir/foobar.dll

then it would be unloaded like this:

unload c:/some/dir/foobar.dll

This allows a C code module to be installed temporarily into a long-running Tcl program and then removed again (either because it is no longer needed or because it is being updated with a new version) without having to shut down the overall Tcl process.

KEYWORDS

binary code, unloading, safe interpreter, shared library

Opportunity

Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.

Free Software

Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.

Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.

Free Books

The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.

Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.

Education

Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.

Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.