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




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 sys-
              tem 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 com-
       mand, 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 contain-
       ing 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 deter-
       mined by packageName and whether or not the  target  interpreter  is  a
       safe  one.  For normal interpreters the name of the initialization pro-
       cedure will have the form pkg_Unload, where pkg is the same as package-
       Name  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  func-
       tionality  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  tar-
       get  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 packa-
       geName 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 differ-
       ent platforms.  The default guess, which is used  on  most  UNIX  plat-
       forms,  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 -nocom-
              plain 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) with-
       out 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)

tcl 8.6.0 - Generated Sat Jan 12 16:21:12 CST 2013
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