378 lines
10 KiB
C++
378 lines
10 KiB
C++
// natReference.cc - Native code for References
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/* Copyright (C) 2001, 2002, 2003, 2005, 2006 Free Software Foundation
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This file is part of libgcj.
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This software is copyrighted work licensed under the terms of the
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Libgcj License. Please consult the file "LIBGCJ_LICENSE" for
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details. */
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// Written by Tom Tromey <tromey@redhat.com>
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#include <config.h>
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#include <gcj/cni.h>
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#include <jvm.h>
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#include <java/lang/Throwable.h>
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#include <java/lang/ref/Reference.h>
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#include <java/lang/ref/SoftReference.h>
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#include <java/lang/ref/WeakReference.h>
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#include <java/lang/ref/PhantomReference.h>
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#include <java/lang/ref/ReferenceQueue.h>
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static void finalize_reference (jobject ref);
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static void finalize_referred_to_object (jobject obj);
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enum weight
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{
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SOFT = 0,
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WEAK = 1,
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FINALIZE = 2,
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PHANTOM = 3,
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// This is used to mark the head of a list.
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HEAD = 4,
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// This is used to mark a deleted item.
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DELETED = 5
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};
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// Objects of this type are used in the hash table to keep track of
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// the mapping between a finalizable object and the various References
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// which refer to it.
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struct object_list
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{
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// The reference object. This is NULL for FINALIZE weight.
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jobject reference;
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// The weight of this object.
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enum weight weight;
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// Next in list.
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object_list *next;
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};
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// Hash table used to hold mapping from object to References. The
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// object_list item in the hash holds the object itself in the
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// reference field; chained to it are all the references sorted in
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// order of weight (lowest first).
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static object_list *hash = NULL;
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// Number of slots used in HASH.
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static int hash_count = 0;
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// Number of slots total in HASH. Must be power of 2.
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static int hash_size = 0;
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#define DELETED_REFERENCE ((jobject) -1)
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static object_list *
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find_slot (jobject key)
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{
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jint hcode = _Jv_HashCode (key);
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/* step must be non-zero, and relatively prime with hash_size. */
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jint step = (hcode ^ (hcode >> 16)) | 1;
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int start_index = hcode & (hash_size - 1);
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int index = start_index;
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int deleted_index = -1;
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do
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{
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object_list *ptr = &hash[index];
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if (ptr->reference == key)
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return ptr;
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else if (ptr->reference == NULL)
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{
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if (deleted_index == -1)
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return ptr;
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else
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return &hash[deleted_index];
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}
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else if (ptr->weight == DELETED)
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{
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deleted_index = index;
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JvAssert (ptr->reference == DELETED_REFERENCE);
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}
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index = (index + step) & (hash_size - 1);
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}
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while (index != start_index);
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// Note that we can have INDEX == START_INDEX if the table has no
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// NULL entries but does have DELETED entries.
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JvAssert (deleted_index >= 0);
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return &hash[deleted_index];
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}
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static void
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rehash ()
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{
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if (hash == NULL)
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{
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hash_size = 1024;
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hash = (object_list *) _Jv_Malloc (hash_size * sizeof (object_list));
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memset (hash, 0, hash_size * sizeof (object_list));
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}
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else
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{
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object_list *old = hash;
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int i = hash_size;
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hash_size *= 2;
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hash = (object_list *) _Jv_Malloc (hash_size * sizeof (object_list));
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memset (hash, 0, hash_size * sizeof (object_list));
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while (--i >= 0)
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{
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if (old[i].reference == NULL || old[i].weight == DELETED)
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continue;
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object_list *newslot = find_slot (old[i].reference);
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*newslot = old[i];
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}
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_Jv_Free (old);
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}
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}
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// Remove a Reference.
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static void
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remove_from_hash (jobject obj)
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{
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java::lang::ref::Reference *ref
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= reinterpret_cast<java::lang::ref::Reference *> (obj);
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object_list *head = find_slot (ref->copy);
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// We might have found a new slot. We can just ignore that here.
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if (head->reference != ref->copy)
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return;
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object_list **link = &head->next;
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head = head->next;
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while (head && head->reference != ref)
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{
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link = &head->next;
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head = head->next;
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}
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// Remove the slot.
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if (head)
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{
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*link = head->next;
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_Jv_Free (head);
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}
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}
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// Return list head if object is in hash, NULL otherwise.
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object_list *
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in_hash (jobject obj)
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{
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// The hash table might not yet be initialized.
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if (hash == NULL)
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return NULL;
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object_list *head = find_slot (obj);
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if (head->reference != obj)
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return NULL;
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return head;
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}
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// FIXME what happens if an object's finalizer creates a Reference to
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// the object, and the object has never before been added to the hash?
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// Madness!
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// Add an item to the hash table. If the item is new, we also add a
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// finalizer item. We keep items in the hash table until they are
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// completely collected; this lets us know when an item is new, even
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// if it has been resurrected after its finalizer has been run.
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static void
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add_to_hash (java::lang::ref::Reference *the_reference)
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{
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JvSynchronize sync (java::lang::ref::Reference::lock);
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if (3 * hash_count >= 2 * hash_size)
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rehash ();
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// Use `copy' here because the `referent' field has been cleared.
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jobject referent = the_reference->copy;
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object_list *item = find_slot (referent);
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if (item->reference == NULL || item->reference == DELETED_REFERENCE)
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{
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// New item, so make an entry for the finalizer.
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item->reference = referent;
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item->weight = HEAD;
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item->next = (object_list *) _Jv_Malloc (sizeof (object_list));
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item->next->reference = NULL;
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item->next->weight = FINALIZE;
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item->next->next = NULL;
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++hash_count;
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}
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object_list *n = (object_list *) _Jv_Malloc (sizeof (object_list));
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n->reference = the_reference;
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enum weight w = PHANTOM;
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if (java::lang::ref::SoftReference::class$.isInstance (the_reference))
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w = SOFT;
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else if (java::lang::ref::WeakReference::class$.isInstance (the_reference))
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w = WEAK;
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n->weight = w;
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object_list **link = &item->next;
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object_list *iter = *link;
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while (iter && iter->weight < n->weight)
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{
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link = &iter->next;
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iter = *link;
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}
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n->next = *link;
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*link = n;
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}
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// Add a FINALIZE entry if one doesn't exist.
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static void
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maybe_add_finalize (object_list *entry, jobject obj)
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{
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object_list **link = &entry->next;
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object_list *iter = *link;
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while (iter && iter->weight < FINALIZE)
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{
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link = &iter->next;
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iter = *link;
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}
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// We want at most one FINALIZE entry in the queue.
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if (iter && iter->weight == FINALIZE)
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return;
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object_list *n = (object_list *) _Jv_Malloc (sizeof (object_list));
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n->reference = obj;
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n->weight = FINALIZE;
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n->next = *link;
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*link = n;
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}
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// This is called when an object is ready to be finalized. This
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// actually implements the appropriate Reference semantics.
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static void
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finalize_referred_to_object (jobject obj)
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{
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JvSynchronize sync (java::lang::ref::Reference::lock);
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object_list *list = find_slot (obj);
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object_list *head = list->next;
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if (head == NULL)
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{
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// We have a truly dead object: the object's finalizer has been
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// run, all the object's references have been processed, and the
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// object is unreachable. There is, at long last, no way to
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// resurrect it.
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list->reference = DELETED_REFERENCE;
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list->weight = DELETED;
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--hash_count;
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return;
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}
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enum weight w = head->weight;
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if (w == FINALIZE)
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{
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// Update the list first, as _Jv_FinalizeString might end up
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// looking at this data structure.
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list->next = head->next;
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_Jv_Free (head);
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// If we have a Reference A to a Reference B, and B is
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// finalized, then we have to take special care to make sure
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// that B is properly deregistered. This is super gross. FIXME
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// will it fail if B's finalizer resurrects B?
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if (java::lang::ref::Reference::class$.isInstance (obj))
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finalize_reference (obj);
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else if (obj->getClass() == &java::lang::String::class$)
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_Jv_FinalizeString (obj);
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else
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_Jv_FinalizeObject (obj);
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}
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else if (w != SOFT || _Jv_GCCanReclaimSoftReference (obj))
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{
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// If we just decided to reclaim a soft reference, we might as
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// well do all the weak references at the same time.
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if (w == SOFT)
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w = WEAK;
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while (head && head->weight <= w)
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{
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java::lang::ref::Reference *ref
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= reinterpret_cast<java::lang::ref::Reference *> (head->reference);
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if (! ref->cleared)
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ref->enqueue ();
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object_list *next = head->next;
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_Jv_Free (head);
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head = next;
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}
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list->next = head;
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}
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// Re-register this finalizer. We always re-register because we
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// can't know until the next collection cycle whether or not the
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// object is truly unreachable.
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_Jv_RegisterFinalizer (obj, finalize_referred_to_object);
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}
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// This is called when a Reference object is finalized. If there is a
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// Reference pointing to this Reference then that case is handled by
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// finalize_referred_to_object.
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static void
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finalize_reference (jobject ref)
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{
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JvSynchronize sync (java::lang::ref::Reference::lock);
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remove_from_hash (ref);
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// The user might have a subclass of Reference with a finalizer.
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_Jv_FinalizeObject (ref);
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}
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void
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_Jv_RegisterStringFinalizer (jobject str)
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{
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// This function might be called before any other Reference method,
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// so we must ensure the class is initialized.
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_Jv_InitClass (&java::lang::ref::Reference::class$);
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JvSynchronize sync (java::lang::ref::Reference::lock);
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// If the object is in our hash table, then we might need to add a
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// new FINALIZE entry. Otherwise, we just register an ordinary
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// finalizer.
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object_list *entry = in_hash (str);
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if (entry)
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maybe_add_finalize (entry, str);
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else
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_Jv_RegisterFinalizer ((void *) str, _Jv_FinalizeString);
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}
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void
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::java::lang::ref::Reference::create (jobject ref)
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{
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// Nothing says you can't make a Reference with a NULL referent.
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// But there's nothing to do in such a case.
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referent = reinterpret_cast<gnu::gcj::RawData *> (ref);
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copy = referent;
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if (referent != NULL)
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{
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JvSynchronize sync (java::lang::ref::Reference::lock);
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// `this' is a new Reference object. We register a new
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// finalizer for pointed-to object and we arrange a special
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// finalizer for ourselves as well.
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_Jv_RegisterFinalizer (this, finalize_reference);
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_Jv_RegisterFinalizer (referent, finalize_referred_to_object);
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gnu::gcj::RawData **p = &referent;
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_Jv_GCRegisterDisappearingLink ((jobject *) p);
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add_to_hash (this);
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}
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}
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::java::lang::Object *
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::java::lang::ref::Reference::get()
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{
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JvSynchronize sync (lock);
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return referent;
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}
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