1unload(n)                    Tcl Built-In Commands                   unload(n)
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NAME

8       unload - Unload machine code
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SYNOPSIS

11       unload ?switches? fileName
12       unload ?switches? fileName packageName
13       unload ?switches? fileName packageName interp
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DESCRIPTION

17       This  command  tries  to unload shared libraries previously loaded with
18       load from the application's address space.  fileName is the name of the
19       file  containing the library file to be unload;  it must be the same as
20       the filename provided to load for loading the library.  The packageName
21       argument  is  the  name  of  the package (as determined by or passed to
22       load), and is used to compute the name of the unload procedure; if  not
23       supplied, it is computed from fileName in the same manner as load.  The
24       interp argument is the path name  of  the  interpreter  from  which  to
25       unload the package (see the interp manual entry for details); if interp
26       is omitted, it defaults to the interpreter in which the unload  command
27       was invoked.
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29       If  the  initial arguments to unload start with - then they are treated
30       as switches.  The following switches are currently supported:
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32       -nocomplain
33              Suppresses all error messages. If this switch is  given,  unload
34              will never report an error.
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36       -keeplibrary
37              This  switch will prevent unload from issuing the operating sys‐
38              tem call that will unload the library from the process.
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40       --     Marks the end of switches.  The argument following this one will
41              be treated as a fileName even if it starts with a -.
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43   UNLOAD OPERATION
44       When a file containing a shared library is loaded through the load com‐
45       mand, Tcl associates two reference counts  to  the  library  file.  The
46       first  counter  shows  how  many times the library has been loaded into
47       normal (trusted) interpreters while the second describes how many times
48       the  library has been loaded into safe interpreters. As a file contain‐
49       ing a shared library can be loaded only once by  Tcl  (with  the  first
50       load  call on the file), these counters track how many interpreters use
51       the library.  Each subsequent call  to  load  after  the  first  simply
52       increments the proper reference count.
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54       unload  works  in  the opposite direction. As a first step, unload will
55       check whether the library is unloadable: an unloadable library  exports
56       a  special unload procedure. The name of the unload procedure is deter‐
57       mined by packageName and whether or not the  target  interpreter  is  a
58       safe  one.  For normal interpreters the name of the initialization pro‐
59       cedure will have the form pkg_Unload, where pkg is the same as package‐
60       Name  except  that  the first letter is converted to upper case and all
61       other letters are converted to lower case.  For example, if packageName
62       is  foo or FOo, the initialization procedure's name will be Foo_Unload.
63       If the target interpreter is a safe interpreter, then the name  of  the
64       initialization procedure will be pkg_SafeUnload instead of pkg_Unload.
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66       If  unload determines that a library is not unloadable (or unload func‐
67       tionality has been disabled  during  compilation),  an  error  will  be
68       returned.   If  the  library  is  unloadable, then unload will call the
69       unload procedure. If the unload procedure returns TCL_OK,  unload  will
70       proceed  and decrease the proper reference count (depending on the tar‐
71       get interpreter type). When both reference counts have reached  0,  the
72       library will be detached from the process.
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74   UNLOAD HOOK PROTOTYPE
75       The unload procedure must match the following prototype:
76              typedef int Tcl_PackageUnloadProc(Tcl_Interp *interp, int flags);
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78       The  interp  argument identifies the interpreter from which the library
79       is to  be  unloaded.   The  unload  procedure  must  return  TCL_OK  or
80       TCL_ERROR to indicate whether or not it completed successfully;  in the
81       event of an error it should set the interpreter's result to point to an
82       error  message.  In this case, the result of the unload command will be
83       the result returned by the unload procedure.
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85       The flags argument can be either TCL_UNLOAD_DETACH_FROM_INTERPRETER  or
86       TCL_UNLOAD_DETACH_FROM_PROCESS.   In   case  the  library  will  remain
87       attached to the  process  after  the  unload  procedure  returns  (i.e.
88       because    the    library    is    used    by    other   interpreters),
89       TCL_UNLOAD_DETACH_FROM_INTERPRETER will be  defined.  However,  if  the
90       library  is used only by the target interpreter and the library will be
91       detached from the application as soon as the unload procedure  returns,
92       the flags argument will be set to TCL_UNLOAD_DETACH_FROM_PROCESS.
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94   NOTES
95       The  unload  command cannot unload libraries that are statically linked
96       with the application.  If fileName is an empty string, then the  packa‐
97       geName argument must be specified.
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99       If packageName is omitted or specified as an empty string, Tcl tries to
100       guess the name of the package.  This may be done differently on differ‐
101       ent  platforms.   The  default  guess, which is used on most UNIX plat‐
102       forms, is to take the last element of fileName,  strip  off  the  first
103       three  characters if they are lib, and use any following alphabetic and
104       underline characters as the module  name.   For  example,  the  command
105       unload  libxyz4.2.so  uses  the  module name xyz and the command unload
106       bin/last.so {} uses the module name last.
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PORTABILITY ISSUES

109       Unix
110              Not all unix operating systems support library unloading.  Under
111              such an operating system unload returns an error (unless -nocom‐
112              plain has been specified).
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BUGS

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

125       If  an  unloadable  module in the file foobar.dll had been loaded using
126       the load command like this (on Windows):
127              load c:/some/dir/foobar.dll
128       then it would be unloaded like this:
129              unload c:/some/dir/foobar.dll
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131       This allows a C code module to be installed temporarily  into  a  long-
132       running  Tcl  program  and  then removed again (either because it is no
133       longer needed or because it is being updated with a new version)  with‐
134       out having to shut down the overall Tcl process.
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SEE ALSO

137       info sharedlibextension, load(n), safe(n)
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KEYWORDS

140       binary code, unloading, safe interpreter, shared library
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144Tcl                                   8.5                            unload(n)
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