tsv -
Part of the Tcl threading extension allowing script-level manipulation
of data shared between threads in a simple, safe and protected fashion.
package require Thread ?2.5?
tsv::names ?pattern?
tsv::object array element
tsv::set array element value
tsv::get array element ?varname?
tsv::unset array ?element?
tsv::exists array ?element?
tsv::pop array element
tsv::move array old new
tsv::incr array element ?increment?
tsv::append array element value ?value ...?
tsv::lappend array element value ?value ...?
tsv::linsert array element index value ?value ...?
tsv::lreplace array element first last ?value ...?
tsv::llength array element
tsv::lindex array element index
tsv::lrange array element first last
tsv::lsearch array element ?mode? pattern
tsv::lpop array element ?index?
tsv::lpush array element value ?index?
tsv::lock arg ?arg ...?
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 thread-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
- Returns names of shared variables matching optional pattern or all known
variables if pattern is ommited. The tsv::names returns an empty list on
process start. All thread shared variables are created by explicit user action.
- tsv::object
- Creates object accessor command for the element in the given shared
array. 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
- Sets the value of the element in the shared array to
value and returns the value. The value may be ommited, and
the command will return the current value of the element. If the
element cannot be found, error is triggered.
- tsv::get
- Retrieves a value of the element located in the shared array.
The command triggers error if the element is not found. If the optional
varname is given, the value is stored in the named variable. In this case,
the command returns true (1) if element is found or false (0) if the
element is not found.
- tsv::unset
- Deletes the element in the shared array. If the element
is not given, it deletes the whole array.
- tsv::exists
- Checks wether the element exists in the shared array.
If the element is not given it tests the existence of the
array itself. Returns true (1) if the item exists,
false (0) if not.
- tsv::pop
- Returns value of the element in the shared array variable
and unsets the element in one atomic operation.
- tsv::move
- Renames the element old to new in the shared array.
This effectively performs an get/unset/set sequence of operations
but in one atomic step.
- tsv::incr
- Similar to standard Tcl incr but increments the value of the
element in shared array instead of the Tcl variable.
- tsv::append
- Similar to standard Tcl append but appends one or more values
to the element in the shared array instead of the Tcl variable.
- tsv::lappend
- Similar to standard Tcl lappend but appends one or more values
to the list element in the shared array instead of the Tcl variable.
- tsv::linsert
- Similar to standard Tcl linsert but inserts one or more values at the
index list position in the list element in the shared array
instead of the Tcl variable.
- tsv::lreplace
- Similar to standard Tcl lreplace but replaces one or more values
from the list element in the shared array instead of the Tcl variable.
- tsv::llength
- Similar to standard Tcl llength but returns length of the list
element in the shared array instead of the Tcl variable.
- tsv::lindex
- Similar to standard Tcl lindex but returns value at the index
list position from the list element in the shared array
instead of the Tcl variable.
- tsv::lrange
- Similar to standard Tcl lrange but returns values between first
and last list position from the list element in the shared array
instead of the Tcl variable.
- tsv::lsearch
- Similar to standard Tcl lsearch but searches the list element
in the shared array instead of the Tcl variable.
- tsv::lpop
- Splices out the value at the index list position from the list element
in the shared array. If index is not specified, it defaults to zero.
- tsv::lpush
- Inserts the value at the index list position in the list element
in the shared array. If index is not specified, it defaults to zero.
- tsv::lock
- This command concatenates passed arguments and evaluates the
resulting script under the internal mutex protection. During the
script evaluation, the entire shared array 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 {
# Atomically append two elements
tsv::lappend foo bar 1
tsv::lappend foo bar 2
puts stderr [tsv::array get foo]
tsv::unset foo
}
%
- tsv::array
- This command supports most of the options of the standard Tcl array
command like:
- tsv::array set
- Does the same as standard Tcl array set
- tsv::array get
- Does the same as standard Tcl array get
- tsv::array names
- Does the same as standard Tcl array names
- tsv::array size
- Does the same as standard Tcl array size
- tsv::array reset
- Does the same as standard Tcl array set but
it clears the array and sets new values atomically.
The current implementation of thread shared variables allows easy and
convenient access to data to be 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 in assuring that all
object data is properly locked and 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 3.+ highly scalable Web server from America Online.
Guide to the Tcl threading model
threads, synchronization, locking, thread shared data