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Collects garbage


collectgarbage (opt, arg)


Note that this has changed considerably since Lua 5.0.

  • "stop": stops the garbage collector.
  • "restart": restarts the garbage collector.
  • "collect": performs a full garbage-collection cycle (this is the default if no option supplied)
  • "count": returns the total memory in use by Lua (in Kbytes).
  • "step": performs a garbage-collection step. The step "size" is controlled by arg (larger values mean more steps) in a non-specified way. If you want to control the step size you must experimentally tune the value of arg. Returns true if the step finished a collection cycle.
  • "setpause": sets arg/100 as the new value for the pause of the collector (see below).
  • "setstepmul": sets arg/100 as the new value for the step multiplier of the collector (see below).

Lua implements an incremental mark-and-sweep collector. It uses two numbers to control its garbage-collection cycles: the garbage-collector pause and the garbage-collector step multiplier.

The garbage-collector pause controls how long the collector waits before starting a new cycle. Larger values make the collector less aggressive. Values smaller than 1 mean the collector will not wait to start a new cycle. A value of 2 means that the collector waits for the total memory in use to double before starting a new cycle.

The step multiplier controls the relative speed of the collector relative to memory allocation. Larger values make the collector more aggressive but also increase the size of each incremental step. Values smaller than 1 make the collector too slow and may result in the collector never finishing a cycle. The default, 2, means that the collector runs at "twice" the speed of memory allocation.

Both "setpause" and "setstepmul" get percentage points as arguments (so an argument of 100 means a real value of 1). Both default to 200 when Lua starts up (and since they are divided by 100, effectively the default is 2 as described above).

collectgarbage ("collect") --> forces garbage collection

See Also ...

Lua functions

assert - Asserts that condition is not nil and not false
dofile - Executes a Lua file
error - Raises an error message
gcinfo - Returns amount of dynamic memory in use
getfenv - Returns the current environment table
getmetatable - Returns the metatable for the object
ipairs - Iterates over a numerically keyed table
load - Loads a chunk by calling a function repeatedly
loadfile - Loads a Lua file and parses it
loadlib - Loads a DLL (obsolete in Lua 5.1)
loadstring - Compiles a string of Lua code
module - Creates a Lua module
next - Returns next key / value pair in a table
pairs - Traverse all items in a table
pcall - Calls a function in protected mode
print - Prints its arguments
rawequal - Compares two values for equality without invoking metamethods
rawget - Gets the value of a table item without invoking metamethods
rawset - Sets the value of a table item without invoking metamethods
require - Loads a module
select - Returns items in a list
setfenv - Sets a function's environment
setmetatable - Sets the metatable for a table
tonumber - Converts a string (of the given base) to a number
tostring - Converts its argument to a string
type - Returns the type of a variable
unpack - Unpacks a table into individual items
xpcall - Calls a function with a custom error handler


Lua base functions
Lua bc (big number) functions
Lua bit manipulation functions
Lua coroutine functions
Lua debug functions
Lua io functions
Lua math functions
Lua os functions
Lua package functions
Lua PCRE regular expression functions
Lua script extensions
Lua string functions
Lua syntax
Lua table functions
Lua utilities
Scripting callbacks - plugins

(Help topic: lua=collectgarbage)

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