1 (***********************************************************************)
5 (* Damien Doligez, projet Para, INRIA Rocquencourt *)
7 (* Copyright 1996 Institut National de Recherche en Informatique et *)
8 (* en Automatique. All rights reserved. This file is distributed *)
9 (* under the terms of the GNU Library General Public License, with *)
10 (* the special exception on linking described in file ../LICENSE. *)
12 (***********************************************************************)
14 (* $Id: gc.mli 9131 2008-11-18 10:24:43Z doligez $ *)
16 (** Memory management control and statistics; finalised values. *)
19 { minor_words : float;
20 (** Number of words allocated in the minor heap since
21 the program was started. This number is accurate in
22 byte-code programs, but only an approximation in programs
23 compiled to native code. *)
25 promoted_words : float;
26 (** Number of words allocated in the minor heap that
27 survived a minor collection and were moved to the major heap
28 since the program was started. *)
31 (** Number of words allocated in the major heap, including
32 the promoted words, since the program was started. *)
34 minor_collections : int;
35 (** Number of minor collections since the program was started. *)
37 major_collections : int;
38 (** Number of major collection cycles completed since the program
42 (** Total size of the major heap, in words. *)
45 (** Number of contiguous pieces of memory that make up the major heap. *)
48 (** Number of words of live data in the major heap, including the header
52 (** Number of live blocks in the major heap. *)
55 (** Number of words in the free list. *)
58 (** Number of blocks in the free list. *)
61 (** Size (in words) of the largest block in the free list. *)
64 (** Number of wasted words due to fragmentation. These are
65 1-words free blocks placed between two live blocks. They
66 are not available for allocation. *)
69 (** Number of heap compactions since the program was started. *)
72 (** Maximum size reached by the major heap, in words. *)
74 (** The memory management counters are returned in a [stat] record.
76 The total amount of memory allocated by the program since it was started
77 is (in words) [minor_words + major_words - promoted_words]. Multiply by
78 the word size (4 on a 32-bit machine, 8 on a 64-bit machine) to get
83 { mutable minor_heap_size : int;
84 (** The size (in words) of the minor heap. Changing
85 this parameter will trigger a minor collection. Default: 32k. *)
87 mutable major_heap_increment : int;
88 (** The minimum number of words to add to the
89 major heap when increasing it. Default: 124k. *)
91 mutable space_overhead : int;
92 (** The major GC speed is computed from this parameter.
93 This is the memory that will be "wasted" because the GC does not
94 immediatly collect unreachable blocks. It is expressed as a
95 percentage of the memory used for live data.
96 The GC will work more (use more CPU time and collect
97 blocks more eagerly) if [space_overhead] is smaller.
100 mutable verbose : int;
101 (** This value controls the GC messages on standard error output.
102 It is a sum of some of the following flags, to print messages
103 on the corresponding events:
104 - [0x001] Start of major GC cycle.
105 - [0x002] Minor collection and major GC slice.
106 - [0x004] Growing and shrinking of the heap.
107 - [0x008] Resizing of stacks and memory manager tables.
108 - [0x010] Heap compaction.
109 - [0x020] Change of GC parameters.
110 - [0x040] Computation of major GC slice size.
111 - [0x080] Calling of finalisation functions.
112 - [0x100] Bytecode executable search at start-up.
113 - [0x200] Computation of compaction triggering condition.
116 mutable max_overhead : int;
117 (** Heap compaction is triggered when the estimated amount
118 of "wasted" memory is more than [max_overhead] percent of the
119 amount of live data. If [max_overhead] is set to 0, heap
120 compaction is triggered at the end of each major GC cycle
121 (this setting is intended for testing purposes only).
122 If [max_overhead >= 1000000], compaction is never triggered.
125 mutable stack_limit : int;
126 (** The maximum size of the stack (in words). This is only
127 relevant to the byte-code runtime, as the native code runtime
128 uses the operating system's stack. Default: 256k. *)
130 mutable allocation_policy : int;
131 (** The policy used for allocating in the heap. Possible
132 values are 0 and 1. 0 is the next-fit policy, which is
133 quite fast but can result in fragmentation. 1 is the
134 first-fit policy, which can be slower in some cases but
135 can be better for programs with fragmentation problems.
138 (** The GC parameters are given as a [control] record. Note that
139 these parameters can also be initialised by setting the
140 OCAMLRUNPARAM environment variable. See the documentation of
143 external stat : unit -> stat = "caml_gc_stat"
144 (** Return the current values of the memory management counters in a
145 [stat] record. This function examines every heap block to get the
148 external quick_stat : unit -> stat = "caml_gc_quick_stat"
149 (** Same as [stat] except that [live_words], [live_blocks], [free_words],
150 [free_blocks], [largest_free], and [fragments] are set to 0. This
151 function is much faster than [stat] because it does not need to go
154 external counters : unit -> float * float * float = "caml_gc_counters"
155 (** Return [(minor_words, promoted_words, major_words)]. This function
156 is as fast at [quick_stat]. *)
158 external get : unit -> control = "caml_gc_get"
159 (** Return the current values of the GC parameters in a [control] record. *)
161 external set : control -> unit = "caml_gc_set"
162 (** [set r] changes the GC parameters according to the [control] record [r].
163 The normal usage is: [Gc.set { (Gc.get()) with Gc.verbose = 0x00d }] *)
165 external minor : unit -> unit = "caml_gc_minor"
166 (** Trigger a minor collection. *)
168 external major_slice : int -> int = "caml_gc_major_slice";;
169 (** Do a minor collection and a slice of major collection. The argument
170 is the size of the slice, 0 to use the automatically-computed
171 slice size. In all cases, the result is the computed slice size. *)
173 external major : unit -> unit = "caml_gc_major"
174 (** Do a minor collection and finish the current major collection cycle. *)
176 external full_major : unit -> unit = "caml_gc_full_major"
177 (** Do a minor collection, finish the current major collection cycle,
178 and perform a complete new cycle. This will collect all currently
179 unreachable blocks. *)
181 external compact : unit -> unit = "caml_gc_compaction"
182 (** Perform a full major collection and compact the heap. Note that heap
183 compaction is a lengthy operation. *)
185 val print_stat : out_channel -> unit
186 (** Print the current values of the memory management counters (in
187 human-readable form) into the channel argument. *)
189 val allocated_bytes : unit -> float
190 (** Return the total number of bytes allocated since the program was
191 started. It is returned as a [float] to avoid overflow problems
192 with [int] on 32-bit machines. *)
194 val finalise : ('a -> unit) -> 'a -> unit
195 (** [finalise f v] registers [f] as a finalisation function for [v].
196 [v] must be heap-allocated. [f] will be called with [v] as
197 argument at some point between the first time [v] becomes unreachable
198 and the time [v] is collected by the GC. Several functions can
199 be registered for the same value, or even several instances of the
200 same function. Each instance will be called once (or never,
201 if the program terminates before [v] becomes unreachable).
203 The GC will call the finalisation functions in the order of
204 deallocation. When several values become unreachable at the
205 same time (i.e. during the same GC cycle), the finalisation
206 functions will be called in the reverse order of the corresponding
207 calls to [finalise]. If [finalise] is called in the same order
208 as the values are allocated, that means each value is finalised
209 before the values it depends upon. Of course, this becomes
210 false if additional dependencies are introduced by assignments.
212 Anything reachable from the closure of finalisation functions
213 is considered reachable, so the following code will not work
215 - [ let v = ... in Gc.finalise (fun x -> ...) v ]
217 Instead you should write:
218 - [ let f = fun x -> ... ;; let v = ... in Gc.finalise f v ]
221 The [f] function can use all features of O'Caml, including
222 assignments that make the value reachable again. It can also
223 loop forever (in this case, the other
224 finalisation functions will be called during the execution of f).
225 It can call [finalise] on [v] or other values to register other
226 functions or even itself. It can raise an exception; in this case
227 the exception will interrupt whatever the program was doing when
228 the function was called.
231 [finalise] will raise [Invalid_argument] if [v] is not
232 heap-allocated. Some examples of values that are not
233 heap-allocated are integers, constant constructors, booleans,
234 the empty array, the empty list, the unit value. The exact list
235 of what is heap-allocated or not is implementation-dependent.
236 Some constant values can be heap-allocated but never deallocated
237 during the lifetime of the program, for example a list of integer
238 constants; this is also implementation-dependent.
239 You should also be aware that compiler optimisations may duplicate
240 some immutable values, for example floating-point numbers when
241 stored into arrays, so they can be finalised and collected while
242 another copy is still in use by the program.
245 The results of calling {!String.make}, {!String.create},
246 {!Array.make}, and {!Pervasives.ref} are guaranteed to be
247 heap-allocated and non-constant except when the length argument is [0].
250 val finalise_release : unit -> unit;;
251 (** A finalisation function may call [finalise_release] to tell the
252 GC that it can launch the next finalisation function without waiting
253 for the current one to return. *)
256 (** An alarm is a piece of data that calls a user function at the end of
257 each major GC cycle. The following functions are provided to create
258 and delete alarms. *)
260 val create_alarm : (unit -> unit) -> alarm
261 (** [create_alarm f] will arrange for [f] to be called at the end of each
262 major GC cycle, starting with the current cycle or the next one.
263 A value of type [alarm] is returned that you can
264 use to call [delete_alarm]. *)
266 val delete_alarm : alarm -> unit
267 (** [delete_alarm a] will stop the calls to the function associated
268 to [a]. Calling [delete_alarm a] again has no effect. *)