292 lines
9.7 KiB
C
292 lines
9.7 KiB
C
/**************************************************************************/
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/* */
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/* OCaml */
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/* */
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/* Xavier Leroy, projet Cristal, INRIA Rocquencourt */
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/* */
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/* Copyright 2001 Institut National de Recherche en Informatique et */
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/* en Automatique. */
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/* */
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/* All rights reserved. This file is distributed under the terms of */
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/* the GNU Lesser General Public License version 2.1, with the */
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/* special exception on linking described in the file LICENSE. */
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/* */
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/**************************************************************************/
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#define CAML_INTERNALS
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/* Registration of global memory roots */
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#include "caml/memory.h"
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#include "caml/misc.h"
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#include "caml/mlvalues.h"
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#include "caml/roots.h"
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#include "caml/globroots.h"
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/* The sets of global memory roots are represented as skip lists
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(see William Pugh, "Skip lists: a probabilistic alternative to
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balanced binary trees", Comm. ACM 33(6), 1990). */
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struct global_root {
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value * root; /* the address of the root */
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struct global_root * forward[1]; /* variable-length array */
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};
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#define NUM_LEVELS 17
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struct global_root_list {
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value * root; /* dummy value for layout compatibility */
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struct global_root * forward[NUM_LEVELS]; /* forward chaining */
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int level; /* max used level */
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};
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/* Generate a random level for a new node: 0 with probability 3/4,
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1 with probability 3/16, 2 with probability 3/64, etc.
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We use a simple linear congruential PRNG (see Knuth vol 2) instead
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of random(), because we need exactly 32 bits of pseudo-random data
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(i.e. 2 * (NUM_LEVELS - 1)). Moreover, the congruential PRNG
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is faster and guaranteed to be deterministic (to reproduce bugs). */
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static uint32_t random_seed = 0;
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static int random_level(void)
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{
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uint32_t r;
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int level = 0;
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/* Linear congruence with modulus = 2^32, multiplier = 69069
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(Knuth vol 2 p. 106, line 15 of table 1), additive = 25173. */
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r = random_seed = random_seed * 69069 + 25173;
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/* Knuth (vol 2 p. 13) shows that the least significant bits are
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"less random" than the most significant bits with a modulus of 2^m,
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so consume most significant bits first */
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while ((r & 0xC0000000U) == 0xC0000000U) { level++; r = r << 2; }
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CAMLassert(level < NUM_LEVELS);
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return level;
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}
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/* Insertion in a global root list */
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static void caml_insert_global_root(struct global_root_list * rootlist,
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value * r)
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{
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struct global_root * update[NUM_LEVELS];
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struct global_root * e, * f;
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int i, new_level;
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CAMLassert(0 <= rootlist->level && rootlist->level < NUM_LEVELS);
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/* Init "cursor" to list head */
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e = (struct global_root *) rootlist;
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/* Find place to insert new node */
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for (i = rootlist->level; i >= 0; i--) {
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while (1) {
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f = e->forward[i];
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if (f == NULL || f->root >= r) break;
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e = f;
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}
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update[i] = e;
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}
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e = e->forward[0];
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/* If already present, don't do anything */
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if (e != NULL && e->root == r) return;
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/* Insert additional element, updating list level if necessary */
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new_level = random_level();
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if (new_level > rootlist->level) {
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for (i = rootlist->level + 1; i <= new_level; i++)
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update[i] = (struct global_root *) rootlist;
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rootlist->level = new_level;
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}
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e = caml_stat_alloc(sizeof(struct global_root) +
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new_level * sizeof(struct global_root *));
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e->root = r;
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for (i = 0; i <= new_level; i++) {
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e->forward[i] = update[i]->forward[i];
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update[i]->forward[i] = e;
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}
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}
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/* Deletion in a global root list */
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static void caml_delete_global_root(struct global_root_list * rootlist,
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value * r)
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{
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struct global_root * update[NUM_LEVELS];
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struct global_root * e, * f;
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int i;
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CAMLassert(0 <= rootlist->level && rootlist->level < NUM_LEVELS);
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/* Init "cursor" to list head */
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e = (struct global_root *) rootlist;
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/* Find element in list */
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for (i = rootlist->level; i >= 0; i--) {
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while (1) {
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f = e->forward[i];
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if (f == NULL || f->root >= r) break;
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e = f;
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}
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update[i] = e;
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}
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e = e->forward[0];
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/* If not found, nothing to do */
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if (e == NULL || e->root != r) return;
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/* Rebuild list without node */
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for (i = 0; i <= rootlist->level; i++) {
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if (update[i]->forward[i] == e)
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update[i]->forward[i] = e->forward[i];
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}
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/* Reclaim list element */
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caml_stat_free(e);
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/* Down-correct list level */
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while (rootlist->level > 0 &&
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rootlist->forward[rootlist->level] == NULL)
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rootlist->level--;
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}
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/* Iterate over a global root list */
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static void caml_iterate_global_roots(scanning_action f,
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struct global_root_list * rootlist)
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{
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struct global_root * gr;
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for (gr = rootlist->forward[0]; gr != NULL; gr = gr->forward[0]) {
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f(*(gr->root), gr->root);
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}
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}
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/* Empty a global root list */
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static void caml_empty_global_roots(struct global_root_list * rootlist)
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{
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struct global_root * gr, * next;
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int i;
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CAMLassert(0 <= rootlist->level && rootlist->level < NUM_LEVELS);
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for (gr = rootlist->forward[0]; gr != NULL; /**/) {
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next = gr->forward[0];
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caml_stat_free(gr);
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gr = next;
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}
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for (i = 0; i <= rootlist->level; i++) rootlist->forward[i] = NULL;
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rootlist->level = 0;
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}
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/* The three global root lists */
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struct global_root_list caml_global_roots = { NULL, { NULL, }, 0 };
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/* mutable roots, don't know whether old or young */
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struct global_root_list caml_global_roots_young = { NULL, { NULL, }, 0 };
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/* generational roots pointing to minor or major heap */
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struct global_root_list caml_global_roots_old = { NULL, { NULL, }, 0 };
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/* generational roots pointing to major heap */
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/* Register a global C root of the mutable kind */
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CAMLexport void caml_register_global_root(value *r)
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{
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CAMLassert (((intnat) r & 3) == 0); /* compact.c demands this (for now) */
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caml_insert_global_root(&caml_global_roots, r);
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}
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/* Un-register a global C root of the mutable kind */
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CAMLexport void caml_remove_global_root(value *r)
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{
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caml_delete_global_root(&caml_global_roots, r);
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}
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/* Register a global C root of the generational kind */
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CAMLexport void caml_register_generational_global_root(value *r)
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{
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value v = *r;
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CAMLassert (((intnat) r & 3) == 0); /* compact.c demands this (for now) */
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if (Is_block(v)) {
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if (Is_young(v))
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caml_insert_global_root(&caml_global_roots_young, r);
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else if (Is_in_heap(v))
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caml_insert_global_root(&caml_global_roots_old, r);
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}
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}
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/* Un-register a global C root of the generational kind */
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CAMLexport void caml_remove_generational_global_root(value *r)
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{
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value v = *r;
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if (Is_block(v)) {
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if (Is_in_heap_or_young(v))
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caml_delete_global_root(&caml_global_roots_young, r);
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if (Is_in_heap(v))
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caml_delete_global_root(&caml_global_roots_old, r);
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}
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}
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/* Modify the value of a global C root of the generational kind */
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CAMLexport void caml_modify_generational_global_root(value *r, value newval)
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{
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value oldval = *r;
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/* It is OK to have a root in roots_young that suddenly points to
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the old generation -- the next minor GC will take care of that.
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What needs corrective action is a root in roots_old that suddenly
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points to the young generation. */
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if (Is_block(newval) && Is_young(newval) &&
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Is_block(oldval) && Is_in_heap(oldval)) {
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caml_delete_global_root(&caml_global_roots_old, r);
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caml_insert_global_root(&caml_global_roots_young, r);
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}
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/* PR#4704 */
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else if (!Is_block(oldval) && Is_block(newval)) {
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/* The previous value in the root was unboxed but now it is boxed.
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The root won't appear in any of the root lists thus far (by virtue
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of the operation of [caml_register_generational_global_root]), so we
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need to make sure it gets in, or else it will never be scanned. */
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if (Is_young(newval))
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caml_insert_global_root(&caml_global_roots_young, r);
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else if (Is_in_heap(newval))
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caml_insert_global_root(&caml_global_roots_old, r);
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}
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else if (Is_block(oldval) && !Is_block(newval)) {
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/* The previous value in the root was boxed but now it is unboxed, so
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the root should be removed. If [oldval] is young, this will happen
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anyway at the next minor collection, but it is safer to delete it
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here. */
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if (Is_in_heap_or_young(oldval))
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caml_delete_global_root(&caml_global_roots_young, r);
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if (Is_in_heap(oldval))
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caml_delete_global_root(&caml_global_roots_old, r);
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}
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/* end PR#4704 */
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*r = newval;
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}
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/* Scan all global roots */
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void caml_scan_global_roots(scanning_action f)
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{
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caml_iterate_global_roots(f, &caml_global_roots);
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caml_iterate_global_roots(f, &caml_global_roots_young);
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caml_iterate_global_roots(f, &caml_global_roots_old);
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}
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/* Scan global roots for a minor collection */
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void caml_scan_global_young_roots(scanning_action f)
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{
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struct global_root * gr;
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caml_iterate_global_roots(f, &caml_global_roots);
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caml_iterate_global_roots(f, &caml_global_roots_young);
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/* Move young roots to old roots */
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for (gr = caml_global_roots_young.forward[0];
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gr != NULL; gr = gr->forward[0]) {
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caml_insert_global_root(&caml_global_roots_old, gr->root);
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}
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caml_empty_global_roots(&caml_global_roots_young);
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}
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