NAME

       unload - Unload machine code

SYNOPSIS

       unload ?switches? fileName
       unload ?switches? fileName packageName
       unload ?switches? fileName packageName interp
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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.

SEE ALSO

       info sharedlibextension, load(3tcl), safe(3tcl)

KEYWORDS

       binary code, unloading, safe interpreter, shared library

Tcl                                                    8.5                                          unload(3tcl)