go/src/pkg/runtime/mfinal.c

// Copyright 2010 The Go Authors.  All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

#include "runtime.h"
#include "malloc.h"

// Finalizer hash table.  Direct hash, linear scan, at most 3/4 full.
// Table size is power of 3 so that hash can be key % max.
// Key[i] == (void*)-1 denotes free but formerly occupied entry
// (doesn't stop the linear scan).
// Key and val are separate tables because the garbage collector
// must be instructed to ignore the pointers in key but follow the
// pointers in val.
typedef struct Fintab Fintab;
struct Fintab
{
	void **key;
	void **val;
	int32 nkey;	// number of non-nil entries in key
	int32 ndead;	// number of dead (-1) entries in key
	int32 max;	// size of key, val allocations
};

static void
addfintab(Fintab *t, void *k, void *v)
{
	int32 i, j;
	
	i = (uintptr)k % (uintptr)t->max;
	for(j=0; j<t->max; j++) {
		if(t->key[i] == nil) {
			t->nkey++;
			goto ret;
		}
		if(t->key[i] == (void*)-1) {
			t->ndead--;
			goto ret;
		}
		if(++i == t->max)
			i = 0;
	}

	// cannot happen - table is known to be non-full
	throw("finalizer table inconsistent");

ret:
	t->key[i] = k;
	t->val[i] = v;
}

static void*
lookfintab(Fintab *t, void *k, bool del)
{
	int32 i, j;
	void *v;
	
	if(t->max == 0)
		return nil;
	i = (uintptr)k % (uintptr)t->max;
	for(j=0; j<t->max; j++) {
		if(t->key[i] == nil)
			return nil;
		if(t->key[i] == k) {
			v = t->val[i];
			if(del) {
				t->key[i] = (void*)-1;
				t->val[i] = nil;
				t->ndead++;
			}
			return v;
		}
		if(++i == t->max)
			i = 0;
	}

	// cannot happen - table is known to be non-full
	throw("finalizer table inconsistent");
	return nil;
}

static Fintab fintab;

// add finalizer; caller is responsible for making sure not already in table
void
addfinalizer(void *p, void *f)
{
	Fintab newtab;
	int32 i;

	if(fintab.nkey >= fintab.max/2+fintab.max/4) {
		// keep table at most 3/4 full:
		// allocate new table and rehash.
		
		runtime_memclr((byte*)&newtab, sizeof newtab);
		newtab.max = fintab.max;
		if(newtab.max == 0)
			newtab.max = 3*3*3;
		else if(fintab.ndead < fintab.nkey/2) {
			// grow table if not many dead values.
			// otherwise just rehash into table of same size.
			newtab.max *= 3;
		}
		
		newtab.key = mallocgc(newtab.max*sizeof newtab.key[0], RefNoPointers, 0);
		newtab.val = mallocgc(newtab.max*sizeof newtab.val[0], 0, 0);
		
		for(i=0; i<fintab.max; i++) {
			void *k;
			
			k = fintab.key[i];
			if(k != nil && k != (void*)-1)
				addfintab(&newtab, k, fintab.val[i]);
		}
		free(fintab.key);
		free(fintab.val);
		fintab = newtab;
	}
	
	addfintab(&fintab, p, f);		
}

void*
getfinalizer(void *p, bool del)
{
	return lookfintab(&fintab, p, del);
}