2010-06-20T01:50:47Z

2010-06-18T21:29:40Z

Akhassin:

Man page: http://aolserver.com/docs/tcl/ns_ictl.html

----

'''NAME'''

: ns_ictl - Manipulate and introspect Tcl interpreter internals

'''SYNOPSIS'''

: '''ns_ictl''' ''option ?arg arg ...?''

'''DESCRIPTION'''

: This command provides access to the internal facilities to control and configure multi-threaded Tcl interpreters in the context of AOLserver virtual servers. It is normally used in startup initialization scripts to define how new interpreters are initialized when created and to support cleanup and re-initalization between transactions (e.g., HTTP connections).
*'''ns_ictl addmodule''' ''module''
: Add a module to the list of modules to be initialized at startup and returns the new list as the result. This command is not normally required as each module specified in the AOLserver modules config section for the corresponding server (e.g., ''ns/server/server1/modules'') is automatically added to the list. To be clear, this command simply appens the ''module'' to the list, it doesn't perform any loading of modules.
*'''ns_ictl cancel''' ''thread''
: Send an asynchronous interrupt request to the specified thread, cancelling any script currently executing on any AOLserver created interpreter (note the interrupt is not virtual-server specific). This command utilizes the facilities of '''Tcl_AsyncMark''' to mark as ready a callback registered with '''Tcl_AsyncCreate'''. The callback places an error message in the interpreter result and returns '''TCL_ERROR''' to unwind the call stack. The underlying Tcl facility has limitations, e.g., the interrupt will only be noticed when Tcl checks via '''Tcl_AsyncReady''' calls between commands and the interrupt can be caught with a '''catch''' command. See the man page for '''Tcl_AsyncCreate''' for details.
*'''ns_ictl cleanup'''
: This command invokes any callbacks registered during a transaction via the C-level '''Ns_TclRegisterDefer''' routine. Unlike callbacks registered with the '''ns_ictl trace deallocate''' command or '''Ns_TclRegisterTrace''' routine, these callbacks are executed only once and there is no Tcl-level access to the underlying '''Ns_TclRegisterDefer''' routine. Currently the only thing that uses this is the C code that releases database handles. This command is invoked by [[ns_cleanup]] Tcl procedure.
*'''ns_ictl epoch'''
: This command returns the unique id for the current duplication script for the virtual server. The id starts as 0 when the virtual server is created and is incremented each time a new script is saved via the '''ns_ictl save''' command.
*'''ns_ictl get'''
: Return the current duplication script for the virtual server. This command is useful to view the duplication script created by the initialization script at startup.
*'''ns_ictl getmodules'''
: Return the list of modules to be initialized at startup. This list corresponds to the names of modules specified in the virtual server modules config section, e.g., ''ns/server/server1/modules'' unless additional modules are added via the '''ns_ictl addmodule''' command.
*'''ns_ictl gettraces''' ''which''
: Return the list of traces which will be invoked at the specified time. The ''which'' argument can be one of ''create, delete, allocate, deallocate, getconn'', or ''freeconn''. The traces are returned in the order in which they will be executed. Script level traces are returns as strings to evaluate and C-level traces are returned with strings which specify the address of the underlying C procedure and argument.
*'''ns_ictl once''' ''key script''
: Evaluate given script once in the virtual server. The given key is a string name which uniquely identifies the corresponding script. This command is useful in a Tcl package which includes one-time initialization routines, e.g., calls to '''ns_register_proc''' or initialization of shared variables using '''nsv_set''' (see '''EXAMPLES''' below).
*'''ns_ictl oncleanup''' ''script''
: This command is equivalent to '''ns_ictl trace deallocate''' ''script''.
*'''ns_ictl oncreate''' ''script''
: This command is equivalent to '''ns_ictl trace create''' ''script''.
*'''ns_ictl ondelete''' ''script''
: This command is equivalent to '''ns_ictl trace delete''' ''script''.
*'''ns_ictl oninit''' ''script''
: This command is equivalent to '''ns_ictl trace allocate''' ''script''.
*'''ns_ictl package''' ''?-exact? package ?version?''
: This command is used to require a package in the calling interpreter and, if successfully loaded, it will require the exact same version in all other interpreters for the virtual server. If version consistency is not important, you can achieve the same effect with '''ns_ictl trace allocate''' {package require ''package''}. In addition, allocate too frequent for most packages. Package state is retained between thread allocations in a given interpreter, so at startup, doing ns_ictl oninit {package require ''package''} should be sufficient and will also work in AOLserver 4.0. This option can be useful, however, if you want to alter the state of already created interpreters at runtime.
*'''ns_ictl runtraces''' which''
: This command runs the requested traces. The ''which'' argument must be one of '''create''', '''delete''', '''allocate''', '''deallocate''', '''getconn''', or '''freeconn'''. Direct calls to this command are not normally necessary as the underlying C code will invoke the callbacks at the required times. Exceptions include calling '''ns_ictl runtraces''' or testing purposes or to mimic the normal cleanup and initialization work performed on between transactions in a long running thread (see '''EXAMPLES''' below).
*'''ns_ictl save''' ''script''
: Save the given script as the duplication script, incrementing the virtual server epoch number. This command is normally called by the bootstrap script after constructing the script to duplicate the procedures defined by sourcing the various module initialization script files. It's also used by [[ns_eval]] to dynamically update the interpreter 'template'.
*'''ns_ictl threads'''
: Return a list of all threads with interpreters for the virtual server. The ids return are small strings which represent the underlying thread ids and can be passed to the '''ns_ictl cancel''' command to send an asynchronous cancel request.
*'''ns_ictl trace create''' ''script''
: Register ''script'' to be called when an interpreter is first created. This is useful to create procedures, require packages, or initialize other state to be used during the lifetime of the interpreter.
*'''ns_ictl trace delete''' ''script''
: Register ''script'' to be called before an interpreter is destroyed. This is useful to free any resources which may have been allocated for the interpreter during the lifetime of the interpreter.
*'''ns_ictl trace allocate''' ''script''
: Register ''script'' to be called each time an interpreter is allocated for use by the '''Ns_TclAllocateInterp''' routine. This is useful for reinitializing resources which may be used during a single transaction in the interpreter.
*'''ns_ictl trace deallocate''' ''script''
: Register ''script'' to be called each time an interpreter is returned after a transaction with the '''Ns_TclDeAllocateInterp''' routine. This is useful for garbage collection, i.e., freeing any resources which may be used during a single transaction in the interpreter.
*'''ns_ictl trace getconn''' ''script''
: Register ''script'' to be called each time an interpreter is returned and associated with an HTTP connection with the '''Ns_GetConnInterp''' routine. This could be useful to define variables relative to the HTTP request.
*'''ns_ictl trace freeconn''' ''script''
: Register ''script'' to be called each time an HTTP connection is closed. This could be used to log information about the request, e.g., timing statistics. Note that the interpreter may still be actively evaluating a script after the connection is closed, i.e., this is not equivalent to '''ns_ictl trace deallocate''' for connection-related interpreters.
*'''ns_ictl update'''
: This command can be used to atomically compare the epoch of the current duplication script with the epoch of the interpreter, evaluating the script and updating the epoch in the interpreter if they do not match. This command is generally registered as a callback with '''ns_ictl trace allocate''' by the initialization code.

'''INTERPRETER ALLOCATION'''

: Tcl interpreter in AOLserver are available on demand with state specific to a virtual server. These interpreters are also expected to be reused for multiple transactions (e.g., HTTP connections, scheduled procedures, socket callbacks).
: To support reuse, AOLserver provides the C-level '''Ns_TclAllocateInterp''' routine to allocate an interpreter from a per-thread cache (creating and initializing a new interpreter if necessary) and the '''Ns_TclDeAllocateInterp''' routine to return an interpreter to the cache when no longer required. All interpreters in the per-thread cache are destroyed when a thread exists.
: In general, only C-level extension writers need to call the C-level API's directly; the various Tcl-level interfaces in AOLserver (e.g., '''ADP''' pages, '''ns_regiseter_proc''', '''ns_schedule_proc''', '''ns_thread''', etc.) allocate and reuse interpreters using the C-level API's automatically before invoking the cooresponding script or ADP page.

'''INTERPRETER TRACES'''

: To ensure a consistent state of interpreters when allocated and enable cleanup and reinitialization between transactions, each virtual server maintains a list of callbacks to be invoked at various points in the lifetime of an interpreter. These callbacks are generally installed when the server is initialized at startup and then called automatically by the '''Ns_TclAllocateInterp''' and '''Ns_TclDeAllocateInterp''' API's at the appropriate times and in consistent order. The '''Ns_TclRegisterTrace''' routine can be used to register C-level callbacks and the '''ns_ictl trace''' command can be used to register Tcl script callbacks. The '''ns_ictl gettraces''' command can be used to list all currently registered callbacks, both at the Tcl script and C level.
: Callbacks registered via the tracing facility are invoked in a specific order depending on the type. Initialization style callbacks including '''create''', '''allocate''', and '''getconn''' are invoked in FIFO order, with all script callbacks invoked after all C-level callbacks. This enables extension writers to utilize the facilities of previously initialized extensions. Correspondingly, cleanup style callbacks including '''freeconn''', '''deallocate''', and '''delete''' are invoked in LIFO order, with all scripts callbacks invoked before C-level callbacks. This helps avoid the possibility that a cleanup callback utilizes features of a previously cleaned up extension.
: In addition, the '''ns_ictl package''' command can be used to consistently manage the loading of a Tcl package in all interpreters for a virtual server. This feature is mostly a convenience routine built above the generic trace framework with additional checks to ensure version number consistency. Coupled with '''ns_ictl once''', the '''ns_ictl package''' command provides a clean framework to utilize Tcl packages in multi-threaded AOLserver (see '''EXAMPLES''').

'''VIRTUAL SERVER TCL INITIALIZATION'''

: AOLserver also supports a Tcl initialization framework for virtual servers based on callbacks registered by loadable modules and the sourcing of scripts files located in corresponding directories. Options to '''ns_ictl''' to support this framework include ''save'', ''get'', ''epoch'', and ''update'' and are used in conjunction with the generic tracing facility by the virtual server bootstrap script (normally ''bin/init.tcl''). The '''ns_eval''' command also relies on this framework to support dynamic update of the state of interpreters.
: This initialization framework pre-dates the Tcl package facilities and utilizes introspection of the state of a startup interpreter at the end of initialization to construct a single script which attempts to duplicate the state in subsequent interpreters. Steps taken during this initialization include:
*1. Load all modules in the server's module config section, e.g.,
: ''ns/server/server1/modules''. Modules with Tcl C-level extensions typically call the legacy '''Ns_TclInitInterps''' routine or the more general '''Ns_TclRegisterTrace''' routine with the ''NS_TCL_TRACE_CREATE'' flag in their module init routine to register a callback to invoke when new interpreters are created. The callback normally creates one or more new commands in the interpreter with '''Tcl_CreateObjCommand''' but may perform any per-interpreter initialization required, e.g., creating and saving private state with the '''Tcl_SetAssocData''' facility. In addition, as modules are loaded, the string name of the module is added to the list of known modules.
*2. After all C modules are loaded, AOLserver creates a new Tcl
: interpreter for the virtual server, executing any trace callbacks already registered via the loaded C modules (e.g., any '''Ns_TclInitInterps''' callbacks) and then sources the virtual server bootstrap script, normally ''bin/init.tcl''. This script creates a few utility procedures and then sources all ''private'' and ''public'' script files in directories which correspond to loaded modules in the order in which they were loaded. These directories are normally relative to the virtual server and to the AOLserver installation directory, e.g., initialization script files for the module ''mymod'' in the ''server1'' virtual server would be searched for in the ''servers/server1/modules/tcl/mymod/'' and ''modules/tcl/mymod/''. Any ''init.tcl'' file found in each directory is sourced first with all remaining files sourced in alphabetical order. In addition, any files in the ''public'' directory with identical names to files in the private directory are skipped as a means to enable overloading of specific functionality on a per-server basis. In practice, most modules only contain shared utility procedures defined in the ''public'' directories and the ''private'' directories are empty or non-existant. The script files normally contain a mix of commands to evaluate once for server configuration (e.g., a call to '''ns_register_proc''' to bind a Tcl procedure to an HTTP request URL) with '''proc''' and '''namespace''' commands to provide additional functionality in the interpreter.
*3. After all script files have been sourced, the bootstrap script
: code then uses a collection of recursive procedures to extract the definitions of all procedures defined in all namespaces. The definitions are used to construct a script which attempts to duplicate the state of the initialization interpreters. This scripts is then saved as the per-virtual server duplication script with the '''ns_ictl save''' command which also increments the ''epoch'' to 1. There are limits to this approach to determine the full state, e.g., it does not attempt to duplicate any global variables which may have been defined in the startup scripts. Typically, startup scripts will use '''nsv_set''' or other mechanisms to store such shared state.
*4. The bootstrap code then uses the '''ns_ictl trace allocate'''
: command to register a callback to the '''ns_ictl update''' command each time an interpreter is allocated for use. In practice, interpreters are created with the default ''epoch'' of 0 and the first call to '''ns_ictl update''' determines an out-of-date condition, evaluates the duplication script, and increments the interpreter's ''epoch'' to 1 to match the state created by the startup interp.
*5. Subsequent calls the '''ns_eval''', if any, will evaluate the
: given script and then re-generate and save the duplication script as was done at startup, incrementing the ''epoch'' once again. In this way, dynamic updates which are detected in other interpreters on their next call to '''ns_ictl update''' can be supported in a limited fashion.
: In practice, while generally successful, this duplication technique has inhibited the clean use of proper Tcl package extensions and encouraged the use of the '''ns_eval''' command which is generally not recommended for the non-deterministic manner in which it attempts to dynamically reconfigure a server. Also, commands required to configure the server once (e.g., calls to '''ns_register_proc''') are inter-mixed with '''proc''' commands designed to extend functionality in all interpreters, complicating configuration management.
: As an alternative, the example below illustrates a means to more explicitly manage configuration through a combination of direct calls to '''ns_ictl trace create''' and '''ns_ictl once'''. Unfortunately, the all encompassing nature of the legacy initialization approach makes it difficult to incrementally move to this cleaner approach because the duplication script construction code is unable to distinguish between state created with the newer, cleaner '''ns_ictl''' commands and state created as a side effect of one or more script files being sourced. As such, it is expected the legacy initialization framework will remain in place until AOLserver 5.x when it will be removed entirely in a non-backwards compatible move towards the cleaner API's.

'''EXAMPLES'''

: This example illustrates the use of '''ns_ictl package''' and '''ns_ictl once''' to load an AOLserver-aware Tcl package into a virtual server. The following code could be added to the virtual server bootstrap script, ''bin/init.tcl'', to load ''MyPkg'' in the virtual server:
:
<pre>

#
# Startup code in bin/init.tcl:
#
# Load MyPkg in all interps (including this one).
#
ns_ictl package require MyPkg

</pre>
: This call will result in the package being loaded into the startup interpreter in the ordinary Tcl fashion (see the '''package''' man page for details). Ordinary Tcl extension packages would need no modifications but packages which utilize AOLserver-specific features or require garbage collection between transactions could also use '''ns_ictl''' for finer grained control. For example, the ''init.tcl'' script specified by the '''package ifneeded''' command in the ''MyPkg'' package's ''pkgIndex.tcl'' file could contains:
:
<pre>

#
# Package code in lib/myPkg1.0/init.tcl:
#
#

package provide MyPkg 1.0

#
# Server init which will be executed the first time called,
# normally in the context of the startup interpreter as above.
#

ns_ictl once MyPkg {
# Register the run Tcl proc HTTP handler.
ns_register_proc /mypkg mkpkg::run
# Register a garbage collection callback.
ns_ictl trace deallocate mypkg::cleanup
}

#
# Code which will be invoked to initialize the package in
# all interpreters when required.
#
proc mypkg::run {} {
... handle /mypkg requests ...
}
proc mkpkg::cleanup {} {
... cleanup transaction resources for mypkg, e.g., db handles ...
}

</pre>
: Other examples:
% ns_ictl epoch
1

% ns_ictl getmodules
nsdb nslog nscp

'''SEE ALSO'''

: [[ns_cleanup]], [[ns_init]], [[ns_eval]], [[ns_markfordelete]]

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[[Category:Documentation]] - [[Category:Core Tcl API]]