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unload(n)                                   Tcl Built-In Commands                                  unload(n)



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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 refer-ence reference
       ence 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 proce-dure procedure
       dure is determined by packageName and whether or not the target interpreter is a safe one.  For  nor-mal normal
       mal 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 proce-dure's procedure's
       dure'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 dur-ing during
       ing 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 tar-get target
       get 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 file-Name fileName
       Name 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  pack-age. package.
       age.   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  sys-tem system
       tem  (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  inter-preters interpreters
       preters 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 ver-sion) version)
       sion) without having to shut down the overall Tcl process.

SEE ALSO
       info sharedlibextension, load(n), safe(n)

KEYWORDS
       binary code, unloading, safe interpreter, shared library



Tcl                                                  8.5                                           unload(n)