tsv - Part of the Tcl threading extension allowing script level
manipulation of data shared between threads.
package require Tcl 8.4
package require Thread ?2.8?
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::handlers
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..?
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
variable 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.
- 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 element 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
varname. 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, however, 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
variable 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
variable.
- 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
}
- tsv::handlers
- Returns the names of all persistent storage handlers enabled at compile
time. See ARRAY COMMANDS for details.
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.
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 persistent
options supported are the famous GNU Gdbm and LMDB. These options have to be
selected during the package compilation time. The implementation provides
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
varname 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>, where
<handler> is "gdbm" for GNU Gdbm and "lmdb" for
LMDB and <address> is the path to the 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 persistent
storage or zero (0) if not.
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.
The current implementation of thread shared variables allows for
easy and convenient access to data shared between different threads.
Internally, the data is stored in Tcl objects and all package commands
operate 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,
unfortunately. 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 outweights
imposed limitations.
Thread shared variables are inspired by the nsv interface found in
AOLserver, a highly scalable Web server from America Online.
locking, synchronization, thread shared data, threads