tsv(n)tsv(n)______________________________________________________________________________NAMEtsv - Part of the Tcl threading extension allowing script level manipu‐
lation of data shared between threads.
SYNOPSIS
package require Tcl 8.4
package require Thread ?2.7?
tsv::names ?pattern?
tsv::object varname element
tsv::set varname element ?value?
tsv::get varname element ?namedvar?
tsv::unset varname ?element?
tsv::exists varname element
tsv::pop varname element
tsv::move varname oldname newname
tsv::incr varname element ?count?
tsv::append varname element value ?value ...?
tsv::lock varname arg ?arg ...?
tsv::lappend varname element value ?value ...?
tsv::linsert varname element index value ?value ...?
tsv::lreplace varname element first last ?value ...?
tsv::llength varname element
tsv::lindex varname element ?index?
tsv::lrange varname element from to
tsv::lsearch varname element ?options? pattern
tsv::lset varname element index ?index ...? value
tsv::lpop varname element ?index?
tsv::lpush varname element ?index?
tsv::array set varname list
tsv::array get varname ?pattern?
tsv::array names varname ?pattern?
tsv::array size varname
tsv::array reset varname list
tsv::array bind varname handle
tsv::array unbind varname
tsv::array isbound varname
tsv::keyldel varname keylist key
tsv::keylget varname keylist key ?retvar?
tsv::keylkeys varname keylist ?key?
tsv::keylset varname keylist key value ?key value..?
_________________________________________________________________DESCRIPTION
This section describes commands implementing thread shared variables.
A thread shared variable is very similar to a Tcl array but in contrast
to a Tcl array it is created in shared memory and can be accessed from
many threads at the same time. Important feature of thread shared vari‐
able is that each access to the variable is internaly protected by a
mutex so script programmer does not have to take care about locking the
variable himself.
Thread shared variables are not bound to any thread explicitly. That
means that when a thread which created any of thread shared variables
exits, the variable and associated memory is not unset/reclaimed. User
has to explicitly unset the variable to reclaim the memory consumed by
the variable.
ELEMENT COMMANDS
tsv::names ?pattern?
Returns names of shared variables matching optional ?pattern?
or all known variables if pattern is ommited.
tsv::object varname element
Creates object accessor command for the element in the shared
variable varname. Using this command, one can apply most of the
other shared variable commands as method functions of the ele‐
ment object command. The object command is automatically deleted
when the element which this command is pointing to is unset.
% tsv::set foo bar "A shared string"
% set string [tsv::object foo bar]
% $string append " appended"
=> A shared string appended
tsv::set varname element ?value?
Sets the value of the element in the shared variable varname to
value and returns the value to caller. The value may be ommited,
in which case the command will return the current value of the
element. If the element cannot be found, error is triggered.
tsv::get varname element ?namedvar?
Retrieves the value of the element from the shared variable var‐
name. If the optional argument namedvar is given, the value is
stored in the named variable. Return value of the command
depends of the existence of the optional argument namedvar. If
the argument is ommited and the requested element cannot be
found in the shared array, the command triggers error. If, how‐
ever, the optional argument is given on the command line, the
command returns true (1) if the element is found or false (0) if
the element is not found.
tsv::unset varname ?element?
Unsets the element from the shared variable varname. If the
optional element is not given, it deletes the variable.
tsv::exists varname element
Checks wether the element exists in the shared variable varname
and returns true (1) if it does or false (0) if it doesn't.
tsv::pop varname element
Returns value of the element in the shared variable varname and
unsets the element, all in one atomic operation.
tsv::move varname oldname newname
Renames the element oldname to the newname in the shared vari‐
able varname. This effectively performs an get/unset/set
sequence of operations but all in one atomic step.
tsv::incr varname element ?count?
Similar to standard Tcl incr command but increments the value of
the element in shared variaboe varname instead of the Tcl vari‐
able.
tsv::append varname element value ?value ...?
Similar to standard Tcl append command but appends one or more
values to the element in shared variable varname instead of the
Tcl variable.
tsv::lock varname arg ?arg ...?
This command concatenates passed arguments and evaluates the
resulting script under the internal mutex protection. During the
script evaluation, the entire shared variable is locked. For
shared variable commands within the script, internal locking is
disabled so no deadlock can occur. It is also allowed to unset
the shared variable from within the script. The shared variable
is automatically created if it did not exists at the time of the
first lock operation.
% tsv::lock foo {
tsv::lappend foo bar 1
tsv::lappend foo bar 2
puts stderr [tsv::set foo bar]
tsv::unset foo
}
LIST COMMANDS
Those command are similar to the equivalently named Tcl command. The
difference is that they operate on elements of shared arrays.
tsv::lappend varname element value ?value ...?
Similar to standard Tcl lappend command but appends one or more
values to the element in shared variable varname instead of the
Tcl variable.
tsv::linsert varname element index value ?value ...?
Similar to standard Tcl linsert command but inserts one or more
values at the index list position in the element in the shared
variable varname instead of the Tcl variable.
tsv::lreplace varname element first last ?value ...?
Similar to standard Tcl lreplace command but replaces one or
more values between the first and last position in the element
of the shared variable varname instead of the Tcl variable.
tsv::llength varname element
Similar to standard Tcl llength command but returns length of
the element in the shared variable varname instead of the Tcl
variable.
tsv::lindex varname element ?index?
Similar to standard Tcl lindex command but returns the value at
the index list position of the element from the shared variable
varname instead of the Tcl variable.
tsv::lrange varname element from to
Similar to standard Tcl lrange command but returns values
between from and to list positions from the element in the
shared variable varname instead of the Tcl variable.
tsv::lsearch varname element ?options? pattern
Similar to standard Tcl lsearch command but searches the element
in the shared variable varname instead of the Tcl variable.
tsv::lset varname element index ?index ...? value
Similar to standard Tcl lset command but sets the element in the
shared variable varname instead of the Tcl variable.
tsv::lpop varname element ?index?
Similar to the standard Tcl lindex command but in addition to
returning, it also splices the value out of the element from the
shared variable varname in one atomic operation. In contrast to
the Tcl lindex command, this command returns no value to the
caller.
tsv::lpush varname element ?index?
This command performes the opposite of the tsv::lpop command.
As its counterpart, it returns no value to the caller.
ARRAY COMMANDS
This command supports most of the options of the standard Tcl array
command. In addition to those, it allows binding a shared variable to
some persisten storage databases. Currently the only persistent option
supported is the famous GNU Gdbm database. This option has to be
selected during the package compilation time. The implementation pro‐
vides hooks for defining other persistency layers, if needed.
tsv::array set varname list
Does the same as standard Tcl array set.
tsv::array get varname ?pattern?
Does the same as standard Tcl array get.
tsv::array names varname ?pattern?
Does the same as standard Tcl array names.
tsv::array size varname
Does the same as standard Tcl array size.
tsv::array reset varname list
Does the same as standard Tcl array set but it clears the var‐
name and sets new values from the list atomically.
tsv::array bind varname handle
Binds the varname to the persistent storage handle. The format
of the handle is <handler>:<address>. For the built-in GNU Gdbm
persistence layer, the format of the handle is "gdbm:<path>"
where <path> is the path to the Gdbm database file.
tsv::array unbind varname
Unbinds the shared array from its bound persistent storage.
tsv::array isbound varname
Returns true (1) if the shared varname is bound to some persis‐
tent storage or zero (0) if not.
KEYED LIST COMMANDS
Keyed list commands are borrowed from the TclX package. Keyed lists
provide a structured data type built upon standard Tcl lists. This is a
functionality similar to structs in the C programming language.
A keyed list is a list in which each element contains a key and value
pair. These element pairs are stored as lists themselves, where the key
is the first element of the list, and the value is the second. The key-
value pairs are referred to as fields. This is an example of a keyed
list:
{{NAME {Frank Zappa}} {JOB {musician and composer}}}
Fields may contain subfields; `.' is the separator character. Subfields
are actually fields where the value is another keyed list. Thus the
following list has the top level fields ID and NAME, and subfields
NAME.FIRST and NAME.LAST:
{ID 106} {NAME {{FIRST Frank} {LAST Zappa}}}
There is no limit to the recursive depth of subfields, allowing one to
build complex data structures. Keyed lists are constructed and accessed
via a number of commands. All keyed list management commands take the
name of the variable containing the keyed list as an argument (i.e.
passed by reference), rather than passing the list directly.
tsv::keyldel varname keylist key
Delete the field specified by key from the keyed list keylist in
the shared variable varname. This removes both the key and the
value from the keyed list.
tsv::keylget varname keylist key ?retvar?
Return the value associated with key from the keyed list keylist
in the shared variable varname. If the optional retvar is not
specified, then the value will be returned as the result of the
command. In this case, if key is not found in the list, an error
will result.
If retvar is specified and key is in the list, then the value is
returned in the variable retvar and the command returns 1 if the
key was present within the list. If key isn't in the list, the
command will return 0, and retvar will be left unchanged. If {}
is specified for retvar, the value is not returned, allowing the
Tcl programmer to determine if a key is present in a keyed list
without setting a variable as a side-effect.
tsv::keylkeys varname keylist ?key?
Return the a list of the keys in the keyed list keylist in the
shared variable varname. If key is specified, then it is the
name of a key field who's subfield keys are to be retrieved.
tsv::keylset varname keylist key value ?key value..?
Set the value associated with key, in the keyed list keylist to
value. If the keylist does not exists, it is created. If key is
not currently in the list, it will be added. If it already
exists, value replaces the existing value. Multiple keywords and
values may be specified, if desired.
DISCUSSION
The current implementation of thread shared variables allows for easy
and convenient access to data shared between different threads. Inter‐
nally, the data is stored in Tcl objects and all package commands oper‐
ate on internal data representation, thus minimizing shimmering and
improving performance. Special care has been taken to assure that all
object data is properly locked and deep-copied when moving objects
between threads.
Due to the internal design of the Tcl core, there is no provision of
full integration of shared variables within the Tcl syntax, unfortu‐
nately. All access to shared data must be performed with the supplied
package commands. Also, variable traces are not supported. But even
so, benefits of easy, simple and safe shared data manipulation out‐
weights imposed limitations.
CREDITS
Thread shared variables are inspired by the nsv interface found in
AOLserver, a highly scalable Web server from America Online.
SEE ALSO
thread, tpool, ttrace
KEYWORDS
locking, synchronization, thread shared data, threads
Tcl Threading 2.7 tsv(n)
