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8246181: Avoid walking SymbolTable during -Xshare:dump
All symbols at dump are created as permanent. Store them in a global array to avoid working SymbolTable.

Reviewed-by: iklam, ccheung
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yminqi committed Jun 24, 2020
1 parent 1550fd8 commit 0e60e8ad856296c59064a7210cdace814093ecc8
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Showing 5 changed files with 47 additions and 42 deletions.
@@ -513,6 +513,13 @@ Symbol* SymbolTable::do_add_if_needed(const char* name, int len, uintx hash, boo
}

assert((sym == NULL) || sym->refcount() != 0, "found dead symbol");
#if INCLUDE_CDS
if (DumpSharedSpaces) {
if (sym != NULL) {
MetaspaceShared::add_symbol(sym);
}
}
#endif
return sym;
}

@@ -663,6 +663,33 @@ class CollectClassesClosure : public KlassClosure {
}
};

// Global object for holding symbols that created during class loading. See SymbolTable::new_symbol
static GrowableArray<Symbol*>* _global_symbol_objects = NULL;

static int compare_symbols_by_address(Symbol** a, Symbol** b) {
if (a[0] < b[0]) {
return -1;
} else if (a[0] == b[0]) {
ResourceMark rm;
log_warning(cds)("Duplicated symbol %s unexpected", (*a)->as_C_string());
return 0;
} else {
return 1;
}
}

void MetaspaceShared::add_symbol(Symbol* sym) {
MutexLocker ml(CDSAddSymbol_lock, Mutex::_no_safepoint_check_flag);
if (_global_symbol_objects == NULL) {
_global_symbol_objects = new (ResourceObj::C_HEAP, mtSymbol) GrowableArray<Symbol*>(2048, mtSymbol);
}
_global_symbol_objects->append(sym);
}

GrowableArray<Symbol*>* MetaspaceShared::collected_symbols() {
return _global_symbol_objects;
}

static void remove_unshareable_in_classes() {
for (int i = 0; i < _global_klass_objects->length(); i++) {
Klass* k = _global_klass_objects->at(i);
@@ -1238,34 +1265,6 @@ class VM_PopulateDumpSharedSpace: public VM_Operation {
bool allow_nested_vm_operations() const { return true; }
}; // class VM_PopulateDumpSharedSpace

class SortedSymbolClosure: public SymbolClosure {
GrowableArray<Symbol*> _symbols;
virtual void do_symbol(Symbol** sym) {
assert((*sym)->is_permanent(), "archived symbols must be permanent");
_symbols.append(*sym);
}
static int compare_symbols_by_address(Symbol** a, Symbol** b) {
if (a[0] < b[0]) {
return -1;
} else if (a[0] == b[0]) {
ResourceMark rm;
log_warning(cds)("Duplicated symbol %s unexpected", (*a)->as_C_string());
return 0;
} else {
return 1;
}
}

public:
SortedSymbolClosure() {
SymbolTable::symbols_do(this);
_symbols.sort(compare_symbols_by_address);
}
GrowableArray<Symbol*>* get_sorted_symbols() {
return &_symbols;
}
};

// ArchiveCompactor --
//
// This class is the central piece of shared archive compaction -- all metaspace data are
@@ -1277,7 +1276,6 @@ class ArchiveCompactor : AllStatic {
static const int MAX_TABLE_SIZE = 1000000;

static DumpAllocStats* _alloc_stats;
static SortedSymbolClosure* _ssc;

typedef KVHashtable<address, address, mtInternal> RelocationTable;
static RelocationTable* _new_loc_table;
@@ -1421,8 +1419,6 @@ class ArchiveCompactor : AllStatic {
public:
static void copy_and_compact() {
ResourceMark rm;
SortedSymbolClosure the_ssc; // StackObj
_ssc = &the_ssc;

log_info(cds)("Scanning all metaspace objects ... ");
{
@@ -1458,9 +1454,11 @@ class ArchiveCompactor : AllStatic {
{
log_info(cds)("Fixing symbol identity hash ... ");
os::init_random(0x12345678);
GrowableArray<Symbol*>* symbols = _ssc->get_sorted_symbols();
for (int i=0; i<symbols->length(); i++) {
symbols->at(i)->update_identity_hash();
GrowableArray<Symbol*>* all_symbols = MetaspaceShared::collected_symbols();
all_symbols->sort(compare_symbols_by_address);
for (int i = 0; i < all_symbols->length(); i++) {
assert(all_symbols->at(i)->is_permanent(), "archived symbols must be permanent");
all_symbols->at(i)->update_identity_hash();
}
}
#ifdef ASSERT
@@ -1471,10 +1469,6 @@ class ArchiveCompactor : AllStatic {
iterate_roots(&checker);
}
#endif


// cleanup
_ssc = NULL;
}

// We must relocate the System::_well_known_klasses only after we have copied the
@@ -1510,8 +1504,8 @@ class ArchiveCompactor : AllStatic {
// (see Symbol::operator new(size_t, int)). So if we iterate the Symbols by
// ascending address order, we ensure that all Symbols are copied into deterministic
// locations in the archive.
GrowableArray<Symbol*>* symbols = _ssc->get_sorted_symbols();
for (int i=0; i<symbols->length(); i++) {
GrowableArray<Symbol*>* symbols = _global_symbol_objects;
for (int i = 0; i < symbols->length(); i++) {
it->push(symbols->adr_at(i));
}
if (_global_klass_objects != NULL) {
@@ -1541,7 +1535,6 @@ class ArchiveCompactor : AllStatic {
};

DumpAllocStats* ArchiveCompactor::_alloc_stats;
SortedSymbolClosure* ArchiveCompactor::_ssc;
ArchiveCompactor::RelocationTable* ArchiveCompactor::_new_loc_table;

void VM_PopulateDumpSharedSpace::dump_symbols() {
@@ -213,6 +213,8 @@ class MetaspaceShared : AllStatic {
TRAPS) NOT_CDS_RETURN_(0);

static GrowableArray<Klass*>* collected_klasses();
static GrowableArray<Symbol*>* collected_symbols();
static void add_symbol(Symbol* sym) NOT_CDS_RETURN;

static ReservedSpace* shared_rs() {
CDS_ONLY(return &_shared_rs);
@@ -151,6 +151,7 @@ Mutex* CDSClassFileStream_lock = NULL;
#endif
Mutex* DumpTimeTable_lock = NULL;
Mutex* CDSLambda_lock = NULL;
Mutex* CDSAddSymbol_lock = NULL;
#endif // INCLUDE_CDS

#if INCLUDE_JVMCI
@@ -344,8 +345,9 @@ void mutex_init() {
#if INCLUDE_JVMTI
def(CDSClassFileStream_lock , PaddedMutex , max_nonleaf, false, _safepoint_check_always);
#endif
def(DumpTimeTable_lock , PaddedMutex , leaf - 1, true, _safepoint_check_never);
def(DumpTimeTable_lock , PaddedMutex , leaf - 1, true, _safepoint_check_never);
def(CDSLambda_lock , PaddedMutex , leaf, true, _safepoint_check_never);
def(CDSAddSymbol_lock , PaddedMutex , leaf - 1, true, _safepoint_check_never);
#endif // INCLUDE_CDS

#if INCLUDE_JVMCI
@@ -130,6 +130,7 @@ extern Mutex* CDSClassFileStream_lock; // FileMapInfo::open_stream_for
#endif
extern Mutex* DumpTimeTable_lock; // SystemDictionaryShared::find_or_allocate_info_for
extern Mutex* CDSLambda_lock; // SystemDictionaryShared::get_shared_lambda_proxy_class
extern Mutex* CDSAddSymbol_lock; // SystemDictionaryShared::add_symbol
#endif // INCLUDE_CDS
#if INCLUDE_JFR
extern Mutex* JfrStacktrace_lock; // used to guard access to the JFR stacktrace table

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