module BatGc:sig
..end
Memory management control and statistics; finalised values.
This module extends Stdlib's Gc module, go there for documentation on the rest of the functions and types.
typestat =
Stdlib.Gc.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.
| *) |
}
The memory management counters are returned in a 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.
typecontrol =
Stdlib.Gc.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
immediately 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 | *) |
|
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 | *) |
|
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.
| *) |
|
window_size : |
(* | The size of the window used by the major GC for smoothing out variations in its workload. This is an integer between 1 and 50. Default: 1.
| *) |
|
custom_major_ratio : |
(* | Target ratio of floating garbage to major heap size for
out-of-heap memory held by custom values located in the major
heap. The GC speed is adjusted to try to use this much memory
for dead values that are not yet collected. Expressed as a
percentage of major heap size. The default value keeps the
out-of-heap floating garbage about the same size as the
in-heap overhead.
Note: this only applies to values allocated with
| *) |
|
custom_minor_ratio : |
(* | Bound on floating garbage for out-of-heap memory held by
custom values in the minor heap. A minor GC is triggered when
this much memory is held by custom values located in the minor
heap. Expressed as a percentage of minor heap size.
Note: this only applies to values allocated with
| *) |
|
custom_minor_max_size : |
(* | Maximum amount of out-of-heap memory for each custom value
allocated in the minor heap. When a custom value is allocated
on the minor heap and holds more than this many bytes, only
this value is counted against
| *) |
}
The GC parameters are given as a 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
Return the current values of the memory management counters in a
stat
record. This function examines every heap block to get the
statistics.
val quick_stat : unit -> stat
Same as 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
Return (minor_words, promoted_words, major_words)
. This function
is as fast at quick_stat
.
val minor_words : unit -> float
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.
In native code this function does not allocate.
val get : unit -> control
Return the current values of the GC parameters in a 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
Trigger a minor collection.
val major_slice : int -> int
Do a minor collection and a slice of major collection. The argument is the size of the slice, 0 to use the automatically-computed slice size. In all cases, the result is the computed slice size.
val major : unit -> unit
Do a minor collection and finish the current major collection cycle.
val full_major : unit -> unit
Do a minor collection, finish the current major collection cycle, and perform a complete new cycle. This will collect all currently unreachable blocks.
val compact : unit -> unit
Perform a full major collection and compact the heap. Note that heap compaction is a lengthy operation.
val print_stat : 'a BatInnerIO.output -> unit
Print the current values of the memory management counters (in human-readable form) into the channel argument.
val allocated_bytes : unit -> float
Return the total number of bytes allocated since the program was
started. It is returned as a float
to avoid overflow problems
with int
on 32-bit machines.
val get_minor_free : unit -> int
Return the current size of the free space inside the minor heap.
val get_bucket : int -> int
get_bucket n
returns the current size of the n
-th future bucket
of the GC smoothing system. The unit is one millionth of a full GC.
Raise Invalid_argument
if n
is negative, return 0 if n is larger
than the smoothing window.
val get_credit : unit -> int
get_credit ()
returns the current size of the "work done in advance"
counter of the GC smoothing system. The unit is one millionth of a
full GC.
val huge_fallback_count : unit -> int
Return the number of times we tried to map huge pages and had to fall
back to small pages. This is always 0 if OCAMLRUNPARAM
contains H=1
.
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
Instead you should write:
let f = fun x -> ... ;; let v = ... in Gc.finalise f v
The 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 Pervasives.ref
are guaranteed to be
heap-allocated and non-constant except when the length argument is 0
.
val finalise_last : (unit -> unit) -> 'a -> unit
same as BatGc.finalise
except the value is not given as argument. So
you can't use the given value for the computation of the
finalisation function. The benefit is that the function is called
after the value is unreachable for the last time instead of the
first time. So contrary to BatGc.finalise
the value will never be
reachable again or used again. In particular every weak pointers
and ephemerons that contained this value as key or data is unset
before running the finalisation function. Moreover the
finalisation function attached with `GC.finalise` are always
called before the finalisation function attached with `GC.finalise_last`.
val finalise_release : unit -> unit
A finalisation function may call finalise_release
to tell the
GC that it can launch the next finalisation function without waiting
for the current one to return.
typealarm =
Stdlib.Gc.alarm
An alarm is a piece of data that calls a user function at the end of each major GC cycle. The following functions are provided to create and delete alarms.
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.
val eventlog_pause : unit -> unit
eventlog_pause ()
will pause the collection of traces in the
runtime.
Traces are collected if the program is linked to the instrumented runtime
and started with the environment variable OCAML_EVENTLOG_ENABLED.
Events are flushed to disk after pausing, and no new events will be
recorded until eventlog_resume
is called.
val eventlog_resume : unit -> unit
eventlog_resume ()
will resume the collection of traces in the
runtime.
Traces are collected if the program is linked to the instrumented runtime
and started with the environment variable OCAML_EVENTLOG_ENABLED.
This call can be used after calling eventlog_pause
, or if the program
was started with OCAML_EVENTLOG_ENABLED=p. (which pauses the collection of
traces before the first event.)
module Memprof:sig
..end
Memprof
is a sampling engine for allocated memory words.