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re PR libgcj/10596 (Reference and String.intern don't work together)

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PR libgcj/10596:
	* include/jvm.h (_Jv_FinalizeString,
	_Jv_RegisterStringFinalizer): Declare.
	* java/lang/natString.cc (_Jv_FinalizeString): Renamed from
	unintern.
	(intern): Updated.
	(_Jv_NewStringUtf8Const): Likewise.
	* java/lang/ref/natReference.cc (finalize_referred_to_object):
	Add special case when finalizing a String.
	(in_hash): New function.
	(_Jv_RegisterStringFinalizer): Likewise.
	(maybe_add_finalize): Likewise.

From-SVN: r71915
This commit is contained in:
Tom Tromey 2003-09-29 21:13:55 +00:00 • committed by Tom Tromey
parent 51ac684e52
commit 2cd5614273
4 changed files with 116 additions and 26 deletions
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15
libjava/ChangeLog
View file

@ -1,3 +1,18 @@
2003-09-29 Tom Tromey <tromey@redhat.com>
PR libgcj/10596:
* include/jvm.h (_Jv_FinalizeString,
_Jv_RegisterStringFinalizer): Declare.
* java/lang/natString.cc (_Jv_FinalizeString): Renamed from
unintern.
(intern): Updated.
(_Jv_NewStringUtf8Const): Likewise.
* java/lang/ref/natReference.cc (finalize_referred_to_object):
Add special case when finalizing a String.
(in_hash): New function.
(_Jv_RegisterStringFinalizer): Likewise.
(maybe_add_finalize): Likewise.
2003-09-29 Michael Koch <konqueror@gmx.de>
* java/net/InetAddress.java:

6
libjava/include/jvm.h
View file

@ -290,6 +290,12 @@ void _Jv_GCRegisterDisappearingLink (jobject *objp);
implement soft references. */
jboolean _Jv_GCCanReclaimSoftReference (jobject obj);
/* Register a finalizer for a String object. This is only used by
the intern() implementation. */
void _Jv_RegisterStringFinalizer (jobject str);
/* This is called to actually finalize a possibly-intern()d String. */
void _Jv_FinalizeString (jobject str);
/* Return approximation of total size of heap. */
long _Jv_GCTotalMemory (void);
/* Return approximation of total free memory. */

59
libjava/java/lang/natString.cc
View file

@ -31,7 +31,6 @@ details. */
#include <gnu/gcj/runtime/StringBuffer.h>
#include <jvm.h>
static void unintern (jobject);
static jstring* strhash = NULL;
static int strhash_count = 0; /* Number of slots used in strhash. */
static int strhash_size = 0; /* Number of slots available in strhash.
@ -173,28 +172,38 @@ java::lang::String::intern()
jstring* ptr = _Jv_StringGetSlot(this);
if (*ptr != NULL && *ptr != DELETED_STRING)
{
// See description in unintern() to understand this.
// See description in _Jv_FinalizeString() to understand this.
*ptr = (jstring) MASK_PTR (*ptr);
return (jstring) UNMASK_PTR (*ptr);
}
jstring str = this->data == this ? this
: _Jv_NewString(JvGetStringChars(this), this->length());
jstring str = (this->data == this
? this
: _Jv_NewString(JvGetStringChars(this), this->length()));
SET_STRING_IS_INTERNED(str);
strhash_count++;
*ptr = str;
// When string is GC'd, clear the slot in the hash table.
_Jv_RegisterFinalizer ((void *) str, unintern);
_Jv_RegisterStringFinalizer (str);
return str;
}
/* Called by String fake finalizer. */
static void
unintern (jobject obj)
// The fake String finalizer. This is only used when the String has
// been intern()d. However, we must check this case, as it might be
// called by the Reference code for any String.
void
_Jv_FinalizeString (jobject obj)
{
JvSynchronize sync (&StringClass);
// We might not actually have intern()d any strings at all, if
// we're being called from Reference.
if (! strhash)
return;
jstring str = reinterpret_cast<jstring> (obj);
jstring* ptr = _Jv_StringGetSlot(str);
if (*ptr == NULL || *ptr == DELETED_STRING)
jstring *ptr = _Jv_StringGetSlot(str);
if (*ptr == NULL || *ptr == DELETED_STRING
|| (jobject) UNMASK_PTR (*ptr) != obj)
return;
// We assume the lowest bit of the pointer is free for our nefarious
@ -202,21 +211,21 @@ unintern (jobject obj)
// interning the String. If we subsequently re-intern the same
// String, then we set the bit. When finalizing, if the bit is set
// then we clear it and re-register the finalizer. We know this is
// a safe approach because both intern() and unintern() acquire
// the class lock; this bit can't be manipulated when the lock is
// not held. So if we are finalizing and the bit is clear then we
// know all references are gone and we can clear the entry in the
// hash table. The naive approach of simply clearing the pointer
// here fails in the case where a request to intern a new string
// with the same contents is made between the time the intern()d
// string is found to be unreachable and when the finalizer is
// actually run. In this case we could clear a pointer to a valid
// string, and future intern() calls for that particular value would
// spuriously fail.
// a safe approach because both intern() and _Jv_FinalizeString()
// acquire the class lock; this bit can't be manipulated when the
// lock is not held. So if we are finalizing and the bit is clear
// then we know all references are gone and we can clear the entry
// in the hash table. The naive approach of simply clearing the
// pointer here fails in the case where a request to intern a new
// string with the same contents is made between the time the
// intern()d string is found to be unreachable and when the
// finalizer is actually run. In this case we could clear a pointer
// to a valid string, and future intern() calls for that particular
// value would spuriously fail.
if (PTR_MASKED (*ptr))
{
*ptr = (jstring) UNMASK_PTR (*ptr);
_Jv_RegisterFinalizer ((void *) obj, unintern);
_Jv_RegisterStringFinalizer (obj);
}
else
{
@ -292,8 +301,10 @@ _Jv_NewStringUtf8Const (Utf8Const* str)
jstr->cachedHashCode = hash;
*ptr = jstr;
SET_STRING_IS_INTERNED(jstr);
// When string is GC'd, clear the slot in the hash table.
_Jv_RegisterFinalizer ((void *) jstr, unintern);
// When string is GC'd, clear the slot in the hash table. Note that
// we don't have to call _Jv_RegisterStringFinalizer here, as we
// know the new object cannot be referred to by a Reference.
_Jv_RegisterFinalizer ((void *) jstr, _Jv_FinalizeString);
return jstr;
}

62
libjava/java/lang/ref/natReference.cc
View file

@ -159,6 +159,19 @@ remove_from_hash (jobject obj)
}
}
// Return list head if object is in hash, NULL otherwise.
object_list *
in_hash (jobject obj)
{
// The hash table might not yet be initialized.
if (hash == NULL)
return NULL;
object_list *head = find_slot (obj);
if (head->reference != obj)
return NULL;
return head;
}
// FIXME what happens if an object's finalizer creates a Reference to
// the object, and the object has never before been added to the hash?
// Madness!
@ -212,6 +225,29 @@ add_to_hash (java::lang::ref::Reference *the_reference)
*link = n;
}
// Add a FINALIZE entry if one doesn't exist.
static void
maybe_add_finalize (object_list *entry, jobject obj)
{
object_list **link = &entry->next;
object_list *iter = *link;
while (iter && iter->weight < FINALIZE)
{
link = &iter->next;
iter = *link;
}
// We want at most one FINALIZE entry in the queue.
if (iter && iter->weight == FINALIZE)
return;
object_list *n = (object_list *) _Jv_Malloc (sizeof (object_list));
n->reference = obj;
n->weight = FINALIZE;
n->next = *link;
*link = n;
}
// This is called when an object is ready to be finalized. This
// actually implements the appropriate Reference semantics.
static void
@ -236,16 +272,21 @@ finalize_referred_to_object (jobject obj)
enum weight w = head->weight;
if (w == FINALIZE)
{
// Update the list first, as _Jv_FinalizeString might end up
// looking at this data structure.
list->next = head->next;
_Jv_Free (head);
// If we have a Reference A to a Reference B, and B is
// finalized, then we have to take special care to make sure
// that B is properly deregistered. This is super gross. FIXME
// will it fail if B's finalizer resurrects B?
if (java::lang::ref::Reference::class$.isInstance (obj))
finalize_reference (obj);
else if (obj->getClass() == &java::lang::String::class$)
_Jv_FinalizeString (obj);
else
_Jv_FinalizeObject (obj);
list->next = head->next;
_Jv_Free (head);
}
else if (w != SOFT || _Jv_GCCanReclaimSoftReference (obj))
{
@ -286,6 +327,23 @@ finalize_reference (jobject ref)
_Jv_FinalizeObject (ref);
}
void
_Jv_RegisterStringFinalizer (jobject str)
{
// This function might be called before any other Reference method,
// so we must ensure the class is initialized.
_Jv_InitClass (&java::lang::ref::Reference::class$);
JvSynchronize sync (java::lang::ref::Reference::lock);
// If the object is in our hash table, then we might need to add a
// new FINALIZE entry. Otherwise, we just register an ordinary
// finalizer.
object_list *entry = in_hash (str);
if (entry)
maybe_add_finalize (entry, str);
else
_Jv_RegisterFinalizer ((void *) str, _Jv_FinalizeString);
}
void
::java::lang::ref::Reference::create (jobject ref)
{