Module Gc

module Gc: sig .. end
Memory management control and statistics; finalised values.

module Stat: sig .. end
type stat = Stat.t 

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.

module Control: sig .. end
type control = Control.t 

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 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.Control.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 : Pervasives.out_channel -> 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 add_finalizer : 'a Heap_block.t -> ('a Heap_block.t -> unit) -> unit
add_finalizer b f ensures that f runs after b becomes unreachable. The OCaml runtime only supports finalizers on heap blocks, hence add_finalizer requires b : _ Heap_block.t. The runtime essentially maintains a set of finalizer pairs:

'a Heap_block.t * ('a Heap_block.t -> unit)

Each call to add_finalizer adds a new pair to the set. It is allowed for many pairs to have the same heap block, the same function, or both. Each pair is a distinct element of the set.

After a garbage collection determines that a heap block b is unreachable, it removes from the set of finalizers all finalizer pairs (b, f) whose block is b, and then and runs f b for all such pairs. Thus, a finalizer registered with add_finalizer will run at most once.

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 add_finalizer. If add_finalizer 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.

In a finalizer pair (b, f), it is a mistake for the closure of f to reference (directly or indirectly) b -- f should only access b via its argument. Referring to b in any other way will cause b to be kept alive forever, since f itself is a root of garbage collection, and can itself only be collected after the pair (b, f) is removed from the set of finalizers.

The f function can use all features of O'Caml, including assignments that make the value reachable again. It can also loop forever (in this case, the other finalisation functions will be called during the execution of f). It can call add_finalizer 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.

add_finalizer_exn b f is like add_finalizer, but will raise if b is not a heap block.

val add_finalizer_exn : 'a -> ('a -> unit) -> unit
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.
type 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 tune : ?logger:(string -> unit) ->
?minor_heap_size:int ->
?major_heap_increment:int ->
?space_overhead:int ->
?verbose:int ->
?max_overhead:int ->
?stack_limit:int -> ?allocation_policy:int -> unit -> unit
Adjust the specified GC parameters.