module Gc:Memory management control and statistics; finalised values.sig
..end
type
stat = {
|
minor_words : |
(* | Number of words allocated in the minor heap since the program was started. This number is accurate in byte-code programs, but only an approximation in programs compiled to native code. | *) |
|
promoted_words : |
(* | Number of words allocated in the minor heap that survived a minor collection and were moved to the major heap since the program was started. | *) |
|
major_words : |
(* | Number of words allocated in the major heap, including the promoted words, since the program was started. | *) |
|
minor_collections : |
(* | Number of minor collections since the program was started. | *) |
|
major_collections : |
(* | Number of major collection cycles completed since the program was started. | *) |
|
heap_words : |
(* | Total size of the major heap, in words. | *) |
|
heap_chunks : |
(* | Number of contiguous pieces of memory that make up the major heap. | *) |
|
live_words : |
(* | Number of words of live data in the major heap, including the header words. | *) |
|
live_blocks : |
(* | Number of live blocks in the major heap. | *) |
|
free_words : |
(* | Number of words in the free list. | *) |
|
free_blocks : |
(* | Number of blocks in the free list. | *) |
|
largest_free : |
(* | Size (in words) of the largest block in the free list. | *) |
|
fragments : |
(* | Number of wasted words due to fragmentation. These are 1-words free blocks placed between two live blocks. They are not available for allocation. | *) |
|
compactions : |
(* | Number of heap compactions since the program was started. | *) |
|
top_heap_words : |
(* | Maximum size reached by the major heap, in words. | *) |
|
stack_size : |
(* | Current size of the stack, in words. | *) |
stat
record.
The total amount of memory allocated by the program since it was started
is (in words) minor_words + major_words - promoted_words
. Multiply by
the word size (4 on a 32-bit machine, 8 on a 64-bit machine) to get
the number of bytes.
type
control = {
|
mutable minor_heap_size : |
(* | The size (in words) of the minor heap. Changing this parameter will trigger a minor collection. Default: 32k. | *) |
|
mutable major_heap_increment : |
(* | The minimum number of words to add to the major heap when increasing it. Default: 124k. | *) |
|
mutable space_overhead : |
(* | The major GC speed is computed from this parameter.
This is the memory that will be "wasted" because the GC does not
immediatly collect unreachable blocks. It is expressed as a
percentage of the memory used for live data.
The GC will work more (use more CPU time and collect
blocks more eagerly) if space_overhead is smaller.
Default: 80. | *) |
|
mutable verbose : |
(* | This value controls the GC messages on standard error output.
It is a sum of some of the following flags, to print messages
on the corresponding events:
| *) |
|
mutable max_overhead : |
(* | Heap compaction is triggered when the estimated amount
of "wasted" memory is more than max_overhead percent of the
amount of live data. If max_overhead is set to 0, heap
compaction is triggered at the end of each major GC cycle
(this setting is intended for testing purposes only).
If max_overhead >= 1000000 , compaction is never triggered.
If compaction is permanently disabled, it is strongly suggested
to set allocation_policy to 1.
Default: 500. | *) |
|
mutable stack_limit : |
(* | The maximum size of the stack (in words). This is only relevant to the byte-code runtime, as the native code runtime uses the operating system's stack. Default: 256k. | *) |
|
mutable allocation_policy : |
(* | The policy used for allocating in the heap. Possible values are 0 and 1. 0 is the next-fit policy, which is quite fast but can result in fragmentation. 1 is the first-fit policy, which can be slower in some cases but can be better for programs with fragmentation problems. Default: 0. | *) |
control
record. Note that
these parameters can also be initialised by setting the
OCAMLRUNPARAM environment variable. See the documentation of
ocamlrun
.val stat : unit -> stat
stat
record. This function examines every heap block to get the
statistics.val quick_stat : unit -> stat
stat
except that live_words
, live_blocks
, free_words
,
free_blocks
, largest_free
, and fragments
are set to 0. This
function is much faster than stat
because it does not need to go
through the heap.val counters : unit -> float * float * float
(minor_words, promoted_words, major_words)
. This function
is as fast as quick_stat
.val get : unit -> control
control
record.val set : control -> unit
set r
changes the GC parameters according to the control
record r
.
The normal usage is: Gc.set { (Gc.get()) with Gc.verbose = 0x00d }
val minor : unit -> unit
val major_slice : int -> int
val major : unit -> unit
val full_major : unit -> unit
val compact : unit -> unit
val print_stat : out_channel -> unit
val allocated_bytes : unit -> float
float
to avoid overflow problems
with int
on 32-bit machines.val finalise : ('a -> unit) -> 'a -> unit
finalise f v
registers f
as a finalisation function for v
.
v
must be heap-allocated. f
will be called with v
as
argument at some point between the first time v
becomes unreachable
and the time v
is collected by the GC. Several functions can
be registered for the same value, or even several instances of the
same function. Each instance will be called once (or never,
if the program terminates before v
becomes unreachable).
The GC will call the finalisation functions in the order of
deallocation. When several values become unreachable at the
same time (i.e. during the same GC cycle), the finalisation
functions will be called in the reverse order of the corresponding
calls to finalise
. If finalise
is called in the same order
as the values are allocated, that means each value is finalised
before the values it depends upon. Of course, this becomes
false if additional dependencies are introduced by assignments.
Anything reachable from the closure of finalisation functions is considered reachable, so the following code will not work as expected:
let v = ... in Gc.finalise (fun x -> ...) v
let f = fun x -> ... ;; let v = ... in Gc.finalise f v
f
function can use all features of OCaml, including
assignments that make the value reachable again. It can also
loop forever (in this case, the other
finalisation functions will not be called during the execution of f,
unless it calls finalise_release
).
It can call finalise
on v
or other values to register other
functions or even itself. It can raise an exception; in this case
the exception will interrupt whatever the program was doing when
the function was called.
finalise
will raise Invalid_argument
if v
is not
heap-allocated. Some examples of values that are not
heap-allocated are integers, constant constructors, booleans,
the empty array, the empty list, the unit value. The exact list
of what is heap-allocated or not is implementation-dependent.
Some constant values can be heap-allocated but never deallocated
during the lifetime of the program, for example a list of integer
constants; this is also implementation-dependent.
You should also be aware that compiler optimisations may duplicate
some immutable values, for example floating-point numbers when
stored into arrays, so they can be finalised and collected while
another copy is still in use by the program.
The results of calling String.make
, String.create
,
Array.make
, and ref
are guaranteed to be
heap-allocated and non-constant except when the length argument is 0
.
val finalise_release : unit -> unit
finalise_release
to tell the
GC that it can launch the next finalisation function without waiting
for the current one to return.type
alarm
val create_alarm : (unit -> unit) -> alarm
create_alarm f
will arrange for f
to be called at the end of each
major GC cycle, starting with the current cycle or the next one.
A value of type alarm
is returned that you can
use to call delete_alarm
.val delete_alarm : alarm -> unit
delete_alarm a
will stop the calls to the function associated
to a
. Calling delete_alarm a
again has no effect.