Java example source code file (parCardTableModRefBS.cpp)
The parCardTableModRefBS.cpp Java example source code/*
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* This code is free software; you can redistribute it and/or modify it
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* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
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* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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#include "precompiled.hpp"
#include "memory/allocation.inline.hpp"
#include "memory/cardTableModRefBS.hpp"
#include "memory/cardTableRS.hpp"
#include "memory/sharedHeap.hpp"
#include "memory/space.inline.hpp"
#include "memory/universe.hpp"
#include "oops/oop.inline.hpp"
#include "runtime/java.hpp"
#include "runtime/mutexLocker.hpp"
#include "runtime/virtualspace.hpp"
#include "runtime/vmThread.hpp"
void CardTableModRefBS::non_clean_card_iterate_parallel_work(Space* sp, MemRegion mr,
OopsInGenClosure* cl,
CardTableRS* ct,
int n_threads) {
assert(n_threads > 0, "Error: expected n_threads > 0");
assert((n_threads == 1 && ParallelGCThreads == 0) ||
n_threads <= (int)ParallelGCThreads,
"# worker threads != # requested!");
assert(!Thread::current()->is_VM_thread() || (n_threads == 1), "There is only 1 VM thread");
assert(UseDynamicNumberOfGCThreads ||
!FLAG_IS_DEFAULT(ParallelGCThreads) ||
n_threads == (int)ParallelGCThreads,
"# worker threads != # requested!");
// Make sure the LNC array is valid for the space.
jbyte** lowest_non_clean;
uintptr_t lowest_non_clean_base_chunk_index;
size_t lowest_non_clean_chunk_size;
get_LNC_array_for_space(sp, lowest_non_clean,
lowest_non_clean_base_chunk_index,
lowest_non_clean_chunk_size);
uint n_strides = n_threads * ParGCStridesPerThread;
SequentialSubTasksDone* pst = sp->par_seq_tasks();
// Sets the condition for completion of the subtask (how many threads
// need to finish in order to be done).
pst->set_n_threads(n_threads);
pst->set_n_tasks(n_strides);
uint stride = 0;
while (!pst->is_task_claimed(/* reference */ stride)) {
process_stride(sp, mr, stride, n_strides, cl, ct,
lowest_non_clean,
lowest_non_clean_base_chunk_index,
lowest_non_clean_chunk_size);
}
if (pst->all_tasks_completed()) {
// Clear lowest_non_clean array for next time.
intptr_t first_chunk_index = addr_to_chunk_index(mr.start());
uintptr_t last_chunk_index = addr_to_chunk_index(mr.last());
for (uintptr_t ch = first_chunk_index; ch <= last_chunk_index; ch++) {
intptr_t ind = ch - lowest_non_clean_base_chunk_index;
assert(0 <= ind && ind < (intptr_t)lowest_non_clean_chunk_size,
"Bounds error");
lowest_non_clean[ind] = NULL;
}
}
}
void
CardTableModRefBS::
process_stride(Space* sp,
MemRegion used,
jint stride, int n_strides,
OopsInGenClosure* cl,
CardTableRS* ct,
jbyte** lowest_non_clean,
uintptr_t lowest_non_clean_base_chunk_index,
size_t lowest_non_clean_chunk_size) {
// We go from higher to lower addresses here; it wouldn't help that much
// because of the strided parallelism pattern used here.
// Find the first card address of the first chunk in the stride that is
// at least "bottom" of the used region.
jbyte* start_card = byte_for(used.start());
jbyte* end_card = byte_after(used.last());
uintptr_t start_chunk = addr_to_chunk_index(used.start());
uintptr_t start_chunk_stride_num = start_chunk % n_strides;
jbyte* chunk_card_start;
if ((uintptr_t)stride >= start_chunk_stride_num) {
chunk_card_start = (jbyte*)(start_card +
(stride - start_chunk_stride_num) *
ParGCCardsPerStrideChunk);
} else {
// Go ahead to the next chunk group boundary, then to the requested stride.
chunk_card_start = (jbyte*)(start_card +
(n_strides - start_chunk_stride_num + stride) *
ParGCCardsPerStrideChunk);
}
while (chunk_card_start < end_card) {
// Even though we go from lower to higher addresses below, the
// strided parallelism can interleave the actual processing of the
// dirty pages in various ways. For a specific chunk within this
// stride, we take care to avoid double scanning or missing a card
// by suitably initializing the "min_done" field in process_chunk_boundaries()
// below, together with the dirty region extension accomplished in
// DirtyCardToOopClosure::do_MemRegion().
jbyte* chunk_card_end = chunk_card_start + ParGCCardsPerStrideChunk;
// Invariant: chunk_mr should be fully contained within the "used" region.
MemRegion chunk_mr = MemRegion(addr_for(chunk_card_start),
chunk_card_end >= end_card ?
used.end() : addr_for(chunk_card_end));
assert(chunk_mr.word_size() > 0, "[chunk_card_start > used_end)");
assert(used.contains(chunk_mr), "chunk_mr should be subset of used");
DirtyCardToOopClosure* dcto_cl = sp->new_dcto_cl(cl, precision(),
cl->gen_boundary());
ClearNoncleanCardWrapper clear_cl(dcto_cl, ct);
// Process the chunk.
process_chunk_boundaries(sp,
dcto_cl,
chunk_mr,
used,
lowest_non_clean,
lowest_non_clean_base_chunk_index,
lowest_non_clean_chunk_size);
// We want the LNC array updates above in process_chunk_boundaries
// to be visible before any of the card table value changes as a
// result of the dirty card iteration below.
OrderAccess::storestore();
// We do not call the non_clean_card_iterate_serial() version because
// we want to clear the cards: clear_cl here does the work of finding
// contiguous dirty ranges of cards to process and clear.
clear_cl.do_MemRegion(chunk_mr);
// Find the next chunk of the stride.
chunk_card_start += ParGCCardsPerStrideChunk * n_strides;
}
}
// If you want a talkative process_chunk_boundaries,
// then #define NOISY(x) x
#ifdef NOISY
#error "Encountered a global preprocessor flag, NOISY, which might clash with local definition to follow"
#else
#define NOISY(x)
#endif
void
CardTableModRefBS::
process_chunk_boundaries(Space* sp,
DirtyCardToOopClosure* dcto_cl,
MemRegion chunk_mr,
MemRegion used,
jbyte** lowest_non_clean,
uintptr_t lowest_non_clean_base_chunk_index,
size_t lowest_non_clean_chunk_size)
{
// We must worry about non-array objects that cross chunk boundaries,
// because such objects are both precisely and imprecisely marked:
// .. if the head of such an object is dirty, the entire object
// needs to be scanned, under the interpretation that this
// was an imprecise mark
// .. if the head of such an object is not dirty, we can assume
// precise marking and it's efficient to scan just the dirty
// cards.
// In either case, each scanned reference must be scanned precisely
// once so as to avoid cloning of a young referent. For efficiency,
// our closures depend on this property and do not protect against
// double scans.
uintptr_t cur_chunk_index = addr_to_chunk_index(chunk_mr.start());
cur_chunk_index = cur_chunk_index - lowest_non_clean_base_chunk_index;
NOISY(tty->print_cr("===========================================================================");)
NOISY(tty->print_cr(" process_chunk_boundary: Called with [" PTR_FORMAT "," PTR_FORMAT ")",
chunk_mr.start(), chunk_mr.end());)
// First, set "our" lowest_non_clean entry, which would be
// used by the thread scanning an adjoining left chunk with
// a non-array object straddling the mutual boundary.
// Find the object that spans our boundary, if one exists.
// first_block is the block possibly straddling our left boundary.
HeapWord* first_block = sp->block_start(chunk_mr.start());
assert((chunk_mr.start() != used.start()) || (first_block == chunk_mr.start()),
"First chunk should always have a co-initial block");
// Does the block straddle the chunk's left boundary, and is it
// a non-array object?
if (first_block < chunk_mr.start() // first block straddles left bdry
&& sp->block_is_obj(first_block) // first block is an object
&& !(oop(first_block)->is_objArray() // first block is not an array (arrays are precisely dirtied)
|| oop(first_block)->is_typeArray())) {
// Find our least non-clean card, so that a left neighbour
// does not scan an object straddling the mutual boundary
// too far to the right, and attempt to scan a portion of
// that object twice.
jbyte* first_dirty_card = NULL;
jbyte* last_card_of_first_obj =
byte_for(first_block + sp->block_size(first_block) - 1);
jbyte* first_card_of_cur_chunk = byte_for(chunk_mr.start());
jbyte* last_card_of_cur_chunk = byte_for(chunk_mr.last());
jbyte* last_card_to_check =
(jbyte*) MIN2((intptr_t) last_card_of_cur_chunk,
(intptr_t) last_card_of_first_obj);
// Note that this does not need to go beyond our last card
// if our first object completely straddles this chunk.
for (jbyte* cur = first_card_of_cur_chunk;
cur <= last_card_to_check; cur++) {
jbyte val = *cur;
if (card_will_be_scanned(val)) {
first_dirty_card = cur; break;
} else {
assert(!card_may_have_been_dirty(val), "Error");
}
}
if (first_dirty_card != NULL) {
NOISY(tty->print_cr(" LNC: Found a dirty card at " PTR_FORMAT " in current chunk",
first_dirty_card);)
assert(0 <= cur_chunk_index && cur_chunk_index < lowest_non_clean_chunk_size,
"Bounds error.");
assert(lowest_non_clean[cur_chunk_index] == NULL,
"Write exactly once : value should be stable hereafter for this round");
lowest_non_clean[cur_chunk_index] = first_dirty_card;
} NOISY(else {
tty->print_cr(" LNC: Found no dirty card in current chunk; leaving LNC entry NULL");
// In the future, we could have this thread look for a non-NULL value to copy from its
// right neighbour (up to the end of the first object).
if (last_card_of_cur_chunk < last_card_of_first_obj) {
tty->print_cr(" LNC: BEWARE!!! first obj straddles past right end of chunk:\n"
" might be efficient to get value from right neighbour?");
}
})
} else {
// In this case we can help our neighbour by just asking them
// to stop at our first card (even though it may not be dirty).
NOISY(tty->print_cr(" LNC: first block is not a non-array object; setting LNC to first card of current chunk");)
assert(lowest_non_clean[cur_chunk_index] == NULL, "Write once : value should be stable hereafter");
jbyte* first_card_of_cur_chunk = byte_for(chunk_mr.start());
lowest_non_clean[cur_chunk_index] = first_card_of_cur_chunk;
}
NOISY(tty->print_cr(" process_chunk_boundary: lowest_non_clean[" INTPTR_FORMAT "] = " PTR_FORMAT
" which corresponds to the heap address " PTR_FORMAT,
cur_chunk_index, lowest_non_clean[cur_chunk_index],
(lowest_non_clean[cur_chunk_index] != NULL)
? addr_for(lowest_non_clean[cur_chunk_index])
: NULL);)
NOISY(tty->print_cr("---------------------------------------------------------------------------");)
// Next, set our own max_to_do, which will strictly/exclusively bound
// the highest address that we will scan past the right end of our chunk.
HeapWord* max_to_do = NULL;
if (chunk_mr.end() < used.end()) {
// This is not the last chunk in the used region.
// What is our last block? We check the first block of
// the next (right) chunk rather than strictly check our last block
// because it's potentially more efficient to do so.
HeapWord* const last_block = sp->block_start(chunk_mr.end());
assert(last_block <= chunk_mr.end(), "In case this property changes.");
if ((last_block == chunk_mr.end()) // our last block does not straddle boundary
|| !sp->block_is_obj(last_block) // last_block isn't an object
|| oop(last_block)->is_objArray() // last_block is an array (precisely marked)
|| oop(last_block)->is_typeArray()) {
max_to_do = chunk_mr.end();
NOISY(tty->print_cr(" process_chunk_boundary: Last block on this card is not a non-array object;\n"
" max_to_do left at " PTR_FORMAT, max_to_do);)
} else {
assert(last_block < chunk_mr.end(), "Tautology");
// It is a non-array object that straddles the right boundary of this chunk.
// last_obj_card is the card corresponding to the start of the last object
// in the chunk. Note that the last object may not start in
// the chunk.
jbyte* const last_obj_card = byte_for(last_block);
const jbyte val = *last_obj_card;
if (!card_will_be_scanned(val)) {
assert(!card_may_have_been_dirty(val), "Error");
// The card containing the head is not dirty. Any marks on
// subsequent cards still in this chunk must have been made
// precisely; we can cap processing at the end of our chunk.
max_to_do = chunk_mr.end();
NOISY(tty->print_cr(" process_chunk_boundary: Head of last object on this card is not dirty;\n"
" max_to_do left at " PTR_FORMAT,
max_to_do);)
} else {
// The last object must be considered dirty, and extends onto the
// following chunk. Look for a dirty card in that chunk that will
// bound our processing.
jbyte* limit_card = NULL;
const size_t last_block_size = sp->block_size(last_block);
jbyte* const last_card_of_last_obj =
byte_for(last_block + last_block_size - 1);
jbyte* const first_card_of_next_chunk = byte_for(chunk_mr.end());
// This search potentially goes a long distance looking
// for the next card that will be scanned, terminating
// at the end of the last_block, if no earlier dirty card
// is found.
assert(byte_for(chunk_mr.end()) - byte_for(chunk_mr.start()) == ParGCCardsPerStrideChunk,
"last card of next chunk may be wrong");
for (jbyte* cur = first_card_of_next_chunk;
cur <= last_card_of_last_obj; cur++) {
const jbyte val = *cur;
if (card_will_be_scanned(val)) {
NOISY(tty->print_cr(" Found a non-clean card " PTR_FORMAT " with value 0x%x",
cur, (int)val);)
limit_card = cur; break;
} else {
assert(!card_may_have_been_dirty(val), "Error: card can't be skipped");
}
}
if (limit_card != NULL) {
max_to_do = addr_for(limit_card);
assert(limit_card != NULL && max_to_do != NULL, "Error");
NOISY(tty->print_cr(" process_chunk_boundary: Found a dirty card at " PTR_FORMAT
" max_to_do set at " PTR_FORMAT " which is before end of last block in chunk: "
PTR_FORMAT " + " PTR_FORMAT " = " PTR_FORMAT,
limit_card, max_to_do, last_block, last_block_size, (last_block+last_block_size));)
} else {
// The following is a pessimistic value, because it's possible
// that a dirty card on a subsequent chunk has been cleared by
// the time we get to look at it; we'll correct for that further below,
// using the LNC array which records the least non-clean card
// before cards were cleared in a particular chunk.
limit_card = last_card_of_last_obj;
max_to_do = last_block + last_block_size;
assert(limit_card != NULL && max_to_do != NULL, "Error");
NOISY(tty->print_cr(" process_chunk_boundary: Found no dirty card before end of last block in chunk\n"
" Setting limit_card to " PTR_FORMAT
" and max_to_do " PTR_FORMAT " + " PTR_FORMAT " = " PTR_FORMAT,
limit_card, last_block, last_block_size, max_to_do);)
}
assert(0 < cur_chunk_index+1 && cur_chunk_index+1 < lowest_non_clean_chunk_size,
"Bounds error.");
// It is possible that a dirty card for the last object may have been
// cleared before we had a chance to examine it. In that case, the value
// will have been logged in the LNC for that chunk.
// We need to examine as many chunks to the right as this object
// covers. However, we need to bound this checking to the largest
// entry in the LNC array: this is because the heap may expand
// after the LNC array has been created but before we reach this point,
// and the last block in our chunk may have been expanded to include
// the expansion delta (and possibly subsequently allocated from, so
// it wouldn't be sufficient to check whether that last block was
// or was not an object at this point).
uintptr_t last_chunk_index_to_check = addr_to_chunk_index(last_block + last_block_size - 1)
- lowest_non_clean_base_chunk_index;
const uintptr_t last_chunk_index = addr_to_chunk_index(used.last())
- lowest_non_clean_base_chunk_index;
if (last_chunk_index_to_check > last_chunk_index) {
assert(last_block + last_block_size > used.end(),
err_msg("Inconsistency detected: last_block [" PTR_FORMAT "," PTR_FORMAT "]"
" does not exceed used.end() = " PTR_FORMAT ","
" yet last_chunk_index_to_check " INTPTR_FORMAT
" exceeds last_chunk_index " INTPTR_FORMAT,
last_block, last_block + last_block_size,
used.end(),
last_chunk_index_to_check, last_chunk_index));
assert(sp->used_region().end() > used.end(),
err_msg("Expansion did not happen: "
"[" PTR_FORMAT "," PTR_FORMAT ") -> [" PTR_FORMAT "," PTR_FORMAT ")",
sp->used_region().start(), sp->used_region().end(), used.start(), used.end()));
NOISY(tty->print_cr(" process_chunk_boundary: heap expanded; explicitly bounding last_chunk");)
last_chunk_index_to_check = last_chunk_index;
}
for (uintptr_t lnc_index = cur_chunk_index + 1;
lnc_index <= last_chunk_index_to_check;
lnc_index++) {
jbyte* lnc_card = lowest_non_clean[lnc_index];
if (lnc_card != NULL) {
// we can stop at the first non-NULL entry we find
if (lnc_card <= limit_card) {
NOISY(tty->print_cr(" process_chunk_boundary: LNC card " PTR_FORMAT " is lower than limit_card " PTR_FORMAT,
" max_to_do will be lowered to " PTR_FORMAT " from " PTR_FORMAT,
lnc_card, limit_card, addr_for(lnc_card), max_to_do);)
limit_card = lnc_card;
max_to_do = addr_for(limit_card);
assert(limit_card != NULL && max_to_do != NULL, "Error");
}
// In any case, we break now
break;
} // else continue to look for a non-NULL entry if any
}
assert(limit_card != NULL && max_to_do != NULL, "Error");
}
assert(max_to_do != NULL, "OOPS 1 !");
}
assert(max_to_do != NULL, "OOPS 2!");
} else {
max_to_do = used.end();
NOISY(tty->print_cr(" process_chunk_boundary: Last chunk of this space;\n"
" max_to_do left at " PTR_FORMAT,
max_to_do);)
}
assert(max_to_do != NULL, "OOPS 3!");
// Now we can set the closure we're using so it doesn't to beyond
// max_to_do.
dcto_cl->set_min_done(max_to_do);
#ifndef PRODUCT
dcto_cl->set_last_bottom(max_to_do);
#endif
NOISY(tty->print_cr("===========================================================================\n");)
}
#undef NOISY
void
CardTableModRefBS::
get_LNC_array_for_space(Space* sp,
jbyte**& lowest_non_clean,
uintptr_t& lowest_non_clean_base_chunk_index,
size_t& lowest_non_clean_chunk_size) {
int i = find_covering_region_containing(sp->bottom());
MemRegion covered = _covered[i];
size_t n_chunks = chunks_to_cover(covered);
// Only the first thread to obtain the lock will resize the
// LNC array for the covered region. Any later expansion can't affect
// the used_at_save_marks region.
// (I observed a bug in which the first thread to execute this would
// resize, and then it would cause "expand_and_allocate" that would
// increase the number of chunks in the covered region. Then a second
// thread would come and execute this, see that the size didn't match,
// and free and allocate again. So the first thread would be using a
// freed "_lowest_non_clean" array.)
// Do a dirty read here. If we pass the conditional then take the rare
// event lock and do the read again in case some other thread had already
// succeeded and done the resize.
int cur_collection = Universe::heap()->total_collections();
if (_last_LNC_resizing_collection[i] != cur_collection) {
MutexLocker x(ParGCRareEvent_lock);
if (_last_LNC_resizing_collection[i] != cur_collection) {
if (_lowest_non_clean[i] == NULL ||
n_chunks != _lowest_non_clean_chunk_size[i]) {
// Should we delete the old?
if (_lowest_non_clean[i] != NULL) {
assert(n_chunks != _lowest_non_clean_chunk_size[i],
"logical consequence");
FREE_C_HEAP_ARRAY(CardPtr, _lowest_non_clean[i], mtGC);
_lowest_non_clean[i] = NULL;
}
// Now allocate a new one if necessary.
if (_lowest_non_clean[i] == NULL) {
_lowest_non_clean[i] = NEW_C_HEAP_ARRAY(CardPtr, n_chunks, mtGC);
_lowest_non_clean_chunk_size[i] = n_chunks;
_lowest_non_clean_base_chunk_index[i] = addr_to_chunk_index(covered.start());
for (int j = 0; j < (int)n_chunks; j++)
_lowest_non_clean[i][j] = NULL;
}
}
_last_LNC_resizing_collection[i] = cur_collection;
}
}
// In any case, now do the initialization.
lowest_non_clean = _lowest_non_clean[i];
lowest_non_clean_base_chunk_index = _lowest_non_clean_base_chunk_index[i];
lowest_non_clean_chunk_size = _lowest_non_clean_chunk_size[i];
}
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