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diff --git a/doc/unload.n b/doc/unload.n new file mode 100644 index 0000000..f060cd6 --- /dev/null +++ b/doc/unload.n @@ -0,0 +1,162 @@ +'\" +'\" 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. +'\" +.so man.macros +.TH unload n 8.5 Tcl "Tcl Built-In Commands" +.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: +.CS +typedef int Tcl_PackageUnloadProc(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 +If an unloadable module in the file \fBfoobar.dll\fR had been loaded +using the \fBload\fR command like this (on Windows): +.CS +load c:/some/dir/foobar.dll +.CE +then it would be unloaded like this: +.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 |