Measuring memory usage presents techniques and tools for determining the memory requirements and/or actual memory usage of algorithms and programs.
The reason these are not on the Compact data storage page (where many of them are used) is that Tcl itself does not by default provide any way in which this can be measured, and hence one must instead rely on various platform-dependent tricks. There is of course the memory command, and the commands below try to make use of it when it is available, but in practice it usually isn't.
The growth procedure
Idea: Evaluate a couple of scripts (sequences of commands) and measure the size of the shell before, after, and in between every pair of them. To avoid errors caused by having made other measurements previously, the scripts are evaluated in a shell which constitutes a completely different process and which is terminated when all the scripts have been evaluated.
Syntax:
Returns: a list of measurements of the size of the subshell spawned. If there are N script arguments then the return value will be a list with N+1 elements.
Limitation: Makes use of the ps command, so it probably only works on UNIX.
Note: The code assumes that there is a file "memsizehelper.tcl" in the current directory. The first block of code below will create this file if it doesn't already exist.
if {![file exists memsizehelper.tcl]} then {
set F [open memsizehelper.tcl w]
puts $F {
fileevent stdin readable {
catch [join [gets stdin] \n]
if {[catch {
puts stdout [list mark [
lindex [split [lindex [split [memory info] \n] 3]] end]]
}]} then {puts stdout [list mark ?]}
}
vwait forever
}
close $F
}
proc growth args {
variable the_child [open |[list tclsh memsizehelper.tcl] r+]
fconfigure $the_child -blocking 0
lappend args exit
variable to_do $args
variable measurements [list]
fileevent $the_child readable {
if {[gets $the_child the_line] < 0} then {
close $the_child
set the_child {}
} elseif {![string match {mark *} $the_line]} then {
puts stdout $the_line
} else {
if {![regexp {^mark ([0-9]+)$} $the_line -> measured_size]} then {
# Change the [exec ps ...] below if it doesn't work in general
scan [lindex [split [exec ps --pid [
pid $the_child] --format vsize] \n] end] %d measured_size
set measured_size [expr {1024*$measured_size}]
}
lappend measurements $measured_size
puts $the_child [split [lindex $to_do 0] \n]
set to_do [lreplace $to_do 0 0]
flush $the_child
}
}
uplevel #0 [list set oldsize 0]
puts $the_child {}
flush $the_child
vwait the_child
return $measurements
}Example of use:
growth {set a [string repeat Abracadabra 2000]}returns something like
2097152 2142208
and the difference between these numbers is the amount of bytes that the child shell grew.
Trickier example (using Delta):
for {set N 100} {$N <= 3000} {incr N 100} {
set D [Delta [growth [format {
set a [string repeat Abracadabra %d]
} $N]]]
puts stderr [format {%5d %10d} $N $D]
}The output is
100 8192 200 8192 300 8192 400 8192 500 8192 600 20480 700 20480 800 20480 900 20480 1000 20480 1100 45056 1200 45056 1300 45056 1400 45056 1500 45056 1600 45056 1700 45056 1800 45056 1900 45056 2000 45056 2100 90112 2200 90112 2300 90112 2400 90112 2500 90112 2600 90112 2700 90112 2800 90112 2900 90112 3000 90112
and this illustrates a problem with this kind of measurements. If the number of parts of an object grows as (TeX notation:) $c_1 n$, then the amount of memory Tcl allocates tends to grow as $c_1 2^{\lceil c_2 + \log_2 n \rceil - c_2}$, for some $0<c_2<1$ (end TeX notation). This makes single-data-point measurements risky.
The Delta procedure
Takes a list of numbers as argument and returns the list of differences between adjacent numbers.
proc Delta list {
set res [list]
set prev [lindex $list 0]
foreach item [lrange $list 1 end] {
lappend res [expr {$item-$prev}]
set prev $item
}
set res
}For Windows, here's what I'm using:
proc usedmem x {
set q1 [join [regexp -inline Name.* [exec pslist -m $x 2>nul]]]
set words {}
while {[scan $q1 %s%n word length] == 2} {
lappend words $word
set q1 [string range $q1 $length end]
}
return [expr {[lindex $words$ 14] * 1024}]
} pslist is part of Sysinternals Process Utilities and can be downloaded here here .
-hans