Import Tcl-core 8.6.6 (as of svn r86089)

doc/unload.n

@@ -0,0 +1,172 @@
+'\"
+'\" Copyright (c) 2003 George Petasis <petasis@iit.demokritos.gr>.
+'\"
+'\" See the file "license.terms" for information on usage and redistribution
+'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
+'\"
+.TH unload n 8.5 Tcl "Tcl Built-In Commands"
+.so man.macros
+.BS
+'\" Note:  do not modify the .SH NAME line immediately below!
+.SH NAME
+unload \- Unload machine code
+.SH SYNOPSIS
+\fBunload \fR?\fIswitches\fR? \fIfileName\fR
+.br
+\fBunload \fR?\fIswitches\fR? \fIfileName packageName\fR
+.br
+\fBunload \fR?\fIswitches\fR? \fIfileName packageName interp\fR
+.BE
+.SH DESCRIPTION
+.PP
+This command tries to unload shared libraries previously loaded
+with \fBload\fR from the application's address space.  \fIfileName\fR
+is the name of the file containing the library file to be unload;  it
+must be the same as the filename provided to \fBload\fR for
+loading the library.
+The \fIpackageName\fR argument is the name of the package (as
+determined by or passed to \fBload\fR), and is used to
+compute the name of the unload procedure; if not supplied, it is
+computed from \fIfileName\fR in the same manner as \fBload\fR.
+The \fIinterp\fR argument is the path name of the interpreter from
+which to unload the package (see the \fBinterp\fR manual entry for
+details); if \fIinterp\fR is omitted, it defaults to the
+interpreter in which the \fBunload\fR command was invoked.
+.PP
+If the initial arguments to \fBunload\fR start with \fB\-\fR then
+they are treated as switches.  The following switches are
+currently supported:
+.TP
+\fB\-nocomplain\fR
+.
+Suppresses all error messages. If this switch is given, \fBunload\fR will
+never report an error.
+.TP
+\fB\-keeplibrary\fR
+.
+This switch will prevent \fBunload\fR from issuing the operating system call
+that will unload the library from the process.
+.TP
+\fB\-\|\-\fR
+.
+Marks the end of switches.  The argument following this one will
+be treated as a \fIfileName\fR even if it starts with a \fB\-\fR.
+.SS "UNLOAD OPERATION"
+.PP
+When a file containing a shared library is loaded through the
+\fBload\fR 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 \fBload\fR
+call on the file), these counters track how many interpreters use the library.
+Each subsequent call to \fBload\fR after the first simply increments the
+proper reference count.
+.PP
+\fBunload\fR works in the opposite direction. As a first step, \fBunload\fR
+will check whether the library is unloadable: an unloadable library exports
+a special unload procedure. The name of the unload procedure is determined by
+\fIpackageName\fR and whether or not the target interpreter
+is a safe one.  For normal interpreters the name of the initialization
+procedure will have the form \fIpkg\fB_Unload\fR, where \fIpkg\fR
+is the same as \fIpackageName\fR except that the first letter is
+converted to upper case and all other letters
+are converted to lower case.  For example, if \fIpackageName\fR is
+\fBfoo\fR or \fBFOo\fR, the initialization procedure's name will
+be \fBFoo_Unload\fR.
+If the target interpreter is a safe interpreter, then the name
+of the initialization procedure will be \fIpkg\fB_SafeUnload\fR
+instead of \fIpkg\fB_Unload\fR.
+.PP
+If \fBunload\fR 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 \fBunload\fR will call the unload
+procedure. If the unload procedure returns \fBTCL_OK\fR, \fBunload\fR 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.
+.SS "UNLOAD HOOK PROTOTYPE"
+.PP
+The unload procedure must match the following prototype:
+.PP
+.CS
+typedef int \fBTcl_PackageUnloadProc\fR(
+        Tcl_Interp *\fIinterp\fR,
+        int \fIflags\fR);
+.CE
+.PP
+The \fIinterp\fR argument identifies the interpreter from which the
+library is to be unloaded.  The unload procedure must return
+\fBTCL_OK\fR or \fBTCL_ERROR\fR 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
+\fBunload\fR command will be the result returned by the unload procedure.
+.PP
+The \fIflags\fR argument can be either \fBTCL_UNLOAD_DETACH_FROM_INTERPRETER\fR
+or \fBTCL_UNLOAD_DETACH_FROM_PROCESS\fR. 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),
+\fBTCL_UNLOAD_DETACH_FROM_INTERPRETER\fR 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 \fIflags\fR argument will be set to \fBTCL_UNLOAD_DETACH_FROM_PROCESS\fR.
+.SS NOTES
+.PP
+The \fBunload\fR command cannot unload libraries that are statically
+linked with the application.
+If \fIfileName\fR is an empty string, then the \fIpackageName\fR argument must
+be specified.
+.PP
+If \fIpackageName\fR 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 \fIfileName\fR, strip off the first
+three characters if they are \fBlib\fR, and use any following
+alphabetic and underline characters as the module name.
+For example, the command \fBunload libxyz4.2.so\fR uses the module
+name \fBxyz\fR and the command \fBunload bin/last.so {}\fR uses the
+module name \fBlast\fR.
+.SH "PORTABILITY ISSUES"
+.TP
+\fBUnix\fR\0\0\0\0\0
+.
+Not all unix operating systems support library unloading. Under such
+an operating system \fBunload\fR returns an error (unless \fB\-nocomplain\fR
+has been specified).
+.SH BUGS
+.PP
+If the same file is \fBload\fRed by different \fIfileName\fRs, 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
+\fBunload\fR on such a library (as the library will be completely detached
+from the application while some interpreters will continue to use it).
+.SH EXAMPLE
+.PP
+If an unloadable module in the file \fBfoobar.dll\fR had been loaded
+using the \fBload\fR command like this (on Windows):
+.PP
+.CS
+load c:/some/dir/foobar.dll
+.CE
+.PP
+then it would be unloaded like this:
+.PP
+.CS
+\fBunload\fR c:/some/dir/foobar.dll
+.CE
+.PP
+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.
+.SH "SEE ALSO"
+info sharedlibextension, load(n), safe(n)
+.SH KEYWORDS
+binary code, unloading, safe interpreter, shared library
+.\" Local Variables:
+.\" mode: nroff
+.\" End: