173 lines
7.1 KiB
Plaintext
173 lines
7.1 KiB
Plaintext
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'\"
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'\" Copyright (c) 2003 George Petasis <petasis@iit.demokritos.gr>.
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'\"
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'\" See the file "license.terms" for information on usage and redistribution
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'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
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'\"
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.TH unload n 8.5 Tcl "Tcl Built-In Commands"
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.so man.macros
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.BS
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'\" Note: do not modify the .SH NAME line immediately below!
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.SH NAME
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unload \- Unload machine code
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.SH SYNOPSIS
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\fBunload \fR?\fIswitches\fR? \fIfileName\fR
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.br
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\fBunload \fR?\fIswitches\fR? \fIfileName prefix\fR
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.br
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\fBunload \fR?\fIswitches\fR? \fIfileName prefix interp\fR
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.BE
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.SH DESCRIPTION
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.PP
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This command tries to unload shared libraries previously loaded
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with \fBload\fR from the application's address space. \fIfileName\fR
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is the name of the file containing the library file to be unload; it
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must be the same as the filename provided to \fBload\fR for
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loading the library.
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The \fIprefix\fR argument is the prefix (as
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determined by or passed to \fBload\fR), and is used to
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compute the name of the unload procedure; if not supplied, it is
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computed from \fIfileName\fR in the same manner as \fBload\fR.
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The \fIinterp\fR argument is the path name of the interpreter from
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which to unload the package (see the \fBinterp\fR manual entry for
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details); if \fIinterp\fR is omitted, it defaults to the
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interpreter in which the \fBunload\fR command was invoked.
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.PP
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If the initial arguments to \fBunload\fR start with \fB\-\fR then
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they are treated as switches. The following switches are
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currently supported:
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.TP
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\fB\-nocomplain\fR
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.
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Suppresses all error messages. If this switch is given, \fBunload\fR will
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never report an error.
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.TP
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\fB\-keeplibrary\fR
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.
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This switch will prevent \fBunload\fR from issuing the operating system call
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that will unload the library from the process.
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.TP
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\fB\-\|\-\fR
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.
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Marks the end of switches. The argument following this one will
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be treated as a \fIfileName\fR even if it starts with a \fB\-\fR.
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.SS "UNLOAD OPERATION"
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.PP
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When a file containing a shared library is loaded through the
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\fBload\fR command, Tcl associates two reference counts to the library
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file. The first counter shows how many times the library has been
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loaded into normal (trusted) interpreters while the second describes how many
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times the library has been loaded into safe interpreters. As a file containing
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a shared library can be loaded only once by Tcl (with the first \fBload\fR
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call on the file), these counters track how many interpreters use the library.
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Each subsequent call to \fBload\fR after the first simply increments the
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proper reference count.
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.PP
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\fBunload\fR works in the opposite direction. As a first step, \fBunload\fR
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will check whether the library is unloadable: an unloadable library exports
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a special unload procedure. The name of the unload procedure is determined by
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\fIprefix\fR and whether or not the target interpreter
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is a safe one. For normal interpreters the name of the initialization
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procedure will have the form \fIpfx\fB_Unload\fR, where \fIpfx\fR
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is the same as \fIprefix\fR except that the first letter is
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converted to upper case and all other letters
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are converted to lower case. For example, if \fIprefix\fR is
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\fBfoo\fR or \fBFOo\fR, the initialization procedure's name will
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be \fBFoo_Unload\fR.
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If the target interpreter is a safe interpreter, then the name
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of the initialization procedure will be \fIpkg\fB_SafeUnload\fR
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instead of \fIpkg\fB_Unload\fR.
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.PP
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If \fBunload\fR determines that a library is not unloadable (or unload
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functionality has been disabled during compilation), an error will be returned.
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If the library is unloadable, then \fBunload\fR will call the unload
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procedure. If the unload procedure returns \fBTCL_OK\fR, \fBunload\fR will proceed
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and decrease the proper reference count (depending on the target interpreter
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type). When both reference counts have reached 0, the library will be
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detached from the process.
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.SS "UNLOAD HOOK PROTOTYPE"
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.PP
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The unload procedure must match the following prototype:
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.PP
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.CS
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typedef int \fBTcl_PackageUnloadProc\fR(
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Tcl_Interp *\fIinterp\fR,
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int \fIflags\fR);
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.CE
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.PP
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The \fIinterp\fR argument identifies the interpreter from which the
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library is to be unloaded. The unload procedure must return
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\fBTCL_OK\fR or \fBTCL_ERROR\fR to indicate whether or not it completed
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successfully; in the event of an error it should set the interpreter's result
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to point to an error message. In this case, the result of the
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\fBunload\fR command will be the result returned by the unload procedure.
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.PP
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The \fIflags\fR argument can be either \fBTCL_UNLOAD_DETACH_FROM_INTERPRETER\fR
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or \fBTCL_UNLOAD_DETACH_FROM_PROCESS\fR. In case the library will remain
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attached to the process after the unload procedure returns (i.e. because
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the library is used by other interpreters),
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\fBTCL_UNLOAD_DETACH_FROM_INTERPRETER\fR will be defined. However, if the
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library is used only by the target interpreter and the library will be
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detached from the application as soon as the unload procedure returns,
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the \fIflags\fR argument will be set to \fBTCL_UNLOAD_DETACH_FROM_PROCESS\fR.
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.SS NOTES
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.PP
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The \fBunload\fR command cannot unload libraries that are statically
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linked with the application.
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If \fIfileName\fR is an empty string, then the \fIprefix\fR argument must
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be specified.
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.PP
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If \fIprefix\fR is omitted or specified as an empty string,
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Tcl tries to guess the prefix. This may be done differently on
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different platforms. The default guess, which is used on most
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UNIX platforms, is to take the last element of
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\fIfileName\fR, strip off the first three characters if they
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are \fBlib\fR, and use any following alphabetic and
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underline characters, converted to titlecase as the prefix.
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For example, the command \fBunload libxyz4.2.so\fR uses the prefix
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\fBXyz\fR and the command \fBunload bin/last.so {}\fR uses the
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prefix \fBLast\fR.
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.SH "PORTABILITY ISSUES"
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.TP
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\fBUnix\fR\0\0\0\0\0
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.
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Not all unix operating systems support library unloading. Under such
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an operating system \fBunload\fR returns an error (unless \fB\-nocomplain\fR
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has been specified).
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.SH BUGS
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.PP
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If the same file is \fBload\fRed by different \fIfileName\fRs, it will
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be loaded into the process's address space multiple times. The
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behavior of this varies from system to system (some systems may
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detect the redundant loads, others may not). In case a library has been
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silently detached by the operating system (and as a result Tcl thinks the
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library is still loaded), it may be dangerous to use
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\fBunload\fR on such a library (as the library will be completely detached
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from the application while some interpreters will continue to use it).
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.SH EXAMPLE
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.PP
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If an unloadable module in the file \fBfoobar.dll\fR had been loaded
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using the \fBload\fR command like this (on Windows):
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.PP
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.CS
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load c:/some/dir/foobar.dll
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.CE
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.PP
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then it would be unloaded like this:
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.PP
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.CS
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\fBunload\fR c:/some/dir/foobar.dll
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.CE
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.PP
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This allows a C code module to be installed temporarily into a
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long-running Tcl program and then removed again (either because it is
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no longer needed or because it is being updated with a new version)
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without having to shut down the overall Tcl process.
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.SH "SEE ALSO"
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info sharedlibextension, load(n), safe(n)
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.SH KEYWORDS
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binary code, unloading, safe interpreter, shared library
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.\" Local Variables:
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.\" mode: nroff
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.\" End:
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