7812 // under contention.
7813 bool CMSCollector::simulate_overflow() {
7814 if (_overflow_counter-- <= 0) { // just being defensive
7815 _overflow_counter = CMSMarkStackOverflowInterval;
7816 return true;
7817 } else {
7818 return false;
7819 }
7820 }
7821
7822 bool CMSCollector::par_simulate_overflow() {
7823 return simulate_overflow();
7824 }
7825 #endif
7826
7827 // Single-threaded
7828 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7829 assert(stack->isEmpty(), "Expected precondition");
7830 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7831 size_t i = num;
7832 oop cur = _overflow_list;
7833 const markOop proto = markOopDesc::prototype();
7834 NOT_PRODUCT(ssize_t n = 0;)
7835 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7836 next = oop(cur->mark());
7837 cur->set_mark(proto); // until proven otherwise
7838 assert(cur->is_oop(), "Should be an oop");
7839 bool res = stack->push(cur);
7840 assert(res, "Bit off more than can chew?");
7841 NOT_PRODUCT(n++;)
7842 }
7843 _overflow_list = cur;
7844 #ifndef PRODUCT
7845 assert(_num_par_pushes >= n, "Too many pops?");
7846 _num_par_pushes -=n;
7847 #endif
7848 return !stack->isEmpty();
7849 }
7850
7851 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
7852 // (MT-safe) Get a prefix of at most "num" from the list.
7853 // The overflow list is chained through the mark word of
7854 // each object in the list. We fetch the entire list,
7855 // break off a prefix of the right size and return the
7856 // remainder. If other threads try to take objects from
7857 // the overflow list at that time, they will wait for
7858 // some time to see if data becomes available. If (and
7859 // only if) another thread places one or more object(s)
7860 // on the global list before we have returned the suffix
7861 // to the global list, we will walk down our local list
7862 // to find its end and append the global list to
7863 // our suffix before returning it. This suffix walk can
7918 oop cur = prefix;
7919 // Walk down the first "num" objects, unless we reach the end.
7920 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
7921 if (cur->mark() == NULL) {
7922 // We have "num" or fewer elements in the list, so there
7923 // is nothing to return to the global list.
7924 // Write back the NULL in lieu of the BUSY we wrote
7925 // above, if it is still the same value.
7926 if (_overflow_list == BUSY) {
7927 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
7928 }
7929 } else {
7930 // Chop off the suffix and return it to the global list.
7931 assert(cur->mark() != BUSY, "Error");
7932 oop suffix_head = cur->mark(); // suffix will be put back on global list
7933 cur->set_mark(NULL); // break off suffix
7934 // It's possible that the list is still in the empty(busy) state
7935 // we left it in a short while ago; in that case we may be
7936 // able to place back the suffix without incurring the cost
7937 // of a walk down the list.
7938 oop observed_overflow_list = _overflow_list;
7939 oop cur_overflow_list = observed_overflow_list;
7940 bool attached = false;
7941 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7942 observed_overflow_list =
7943 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7944 if (cur_overflow_list == observed_overflow_list) {
7945 attached = true;
7946 break;
7947 } else cur_overflow_list = observed_overflow_list;
7948 }
7949 if (!attached) {
7950 // Too bad, someone else sneaked in (at least) an element; we'll need
7951 // to do a splice. Find tail of suffix so we can prepend suffix to global
7952 // list.
7953 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
7954 oop suffix_tail = cur;
7955 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
7956 "Tautology");
7957 observed_overflow_list = _overflow_list;
7958 do {
7959 cur_overflow_list = observed_overflow_list;
7960 if (cur_overflow_list != BUSY) {
7961 // Do the splice ...
7962 suffix_tail->set_mark(markOop(cur_overflow_list));
7963 } else { // cur_overflow_list == BUSY
7964 suffix_tail->set_mark(NULL);
7965 }
7966 // ... and try to place spliced list back on overflow_list ...
7967 observed_overflow_list =
7968 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7969 } while (cur_overflow_list != observed_overflow_list);
7970 // ... until we have succeeded in doing so.
7971 }
7972 }
7973
7974 // Push the prefix elements on work_q
7975 assert(prefix != NULL, "control point invariant");
7976 const markOop proto = markOopDesc::prototype();
7977 oop next;
7980 next = oop(cur->mark());
7981 cur->set_mark(proto); // until proven otherwise
7982 assert(cur->is_oop(), "Should be an oop");
7983 bool res = work_q->push(cur);
7984 assert(res, "Bit off more than we can chew?");
7985 NOT_PRODUCT(n++;)
7986 }
7987 #ifndef PRODUCT
7988 assert(_num_par_pushes >= n, "Too many pops?");
7989 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
7990 #endif
7991 return true;
7992 }
7993
7994 // Single-threaded
7995 void CMSCollector::push_on_overflow_list(oop p) {
7996 NOT_PRODUCT(_num_par_pushes++;)
7997 assert(p->is_oop(), "Not an oop");
7998 preserve_mark_if_necessary(p);
7999 p->set_mark((markOop)_overflow_list);
8000 _overflow_list = p;
8001 }
8002
8003 // Multi-threaded; use CAS to prepend to overflow list
8004 void CMSCollector::par_push_on_overflow_list(oop p) {
8005 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8006 assert(p->is_oop(), "Not an oop");
8007 par_preserve_mark_if_necessary(p);
8008 oop observed_overflow_list = _overflow_list;
8009 oop cur_overflow_list;
8010 do {
8011 cur_overflow_list = observed_overflow_list;
8012 if (cur_overflow_list != BUSY) {
8013 p->set_mark(markOop(cur_overflow_list));
8014 } else {
8015 p->set_mark(NULL);
8016 }
8017 observed_overflow_list =
8018 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8019 } while (cur_overflow_list != observed_overflow_list);
8020 }
8021 #undef BUSY
8022
8023 // Single threaded
8024 // General Note on GrowableArray: pushes may silently fail
8025 // because we are (temporarily) out of C-heap for expanding
8026 // the stack. The problem is quite ubiquitous and affects
8027 // a lot of code in the JVM. The prudent thing for GrowableArray
8028 // to do (for now) is to exit with an error. However, that may
|
7812 // under contention.
7813 bool CMSCollector::simulate_overflow() {
7814 if (_overflow_counter-- <= 0) { // just being defensive
7815 _overflow_counter = CMSMarkStackOverflowInterval;
7816 return true;
7817 } else {
7818 return false;
7819 }
7820 }
7821
7822 bool CMSCollector::par_simulate_overflow() {
7823 return simulate_overflow();
7824 }
7825 #endif
7826
7827 // Single-threaded
7828 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7829 assert(stack->isEmpty(), "Expected precondition");
7830 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7831 size_t i = num;
7832 oop cur = oop(_overflow_list);
7833 const markOop proto = markOopDesc::prototype();
7834 NOT_PRODUCT(ssize_t n = 0;)
7835 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7836 next = oop(cur->mark());
7837 cur->set_mark(proto); // until proven otherwise
7838 assert(cur->is_oop(), "Should be an oop");
7839 bool res = stack->push(cur);
7840 assert(res, "Bit off more than can chew?");
7841 NOT_PRODUCT(n++;)
7842 }
7843 _overflow_list = (oopDesc*)cur;
7844 #ifndef PRODUCT
7845 assert(_num_par_pushes >= n, "Too many pops?");
7846 _num_par_pushes -=n;
7847 #endif
7848 return !stack->isEmpty();
7849 }
7850
7851 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
7852 // (MT-safe) Get a prefix of at most "num" from the list.
7853 // The overflow list is chained through the mark word of
7854 // each object in the list. We fetch the entire list,
7855 // break off a prefix of the right size and return the
7856 // remainder. If other threads try to take objects from
7857 // the overflow list at that time, they will wait for
7858 // some time to see if data becomes available. If (and
7859 // only if) another thread places one or more object(s)
7860 // on the global list before we have returned the suffix
7861 // to the global list, we will walk down our local list
7862 // to find its end and append the global list to
7863 // our suffix before returning it. This suffix walk can
7918 oop cur = prefix;
7919 // Walk down the first "num" objects, unless we reach the end.
7920 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
7921 if (cur->mark() == NULL) {
7922 // We have "num" or fewer elements in the list, so there
7923 // is nothing to return to the global list.
7924 // Write back the NULL in lieu of the BUSY we wrote
7925 // above, if it is still the same value.
7926 if (_overflow_list == BUSY) {
7927 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
7928 }
7929 } else {
7930 // Chop off the suffix and return it to the global list.
7931 assert(cur->mark() != BUSY, "Error");
7932 oop suffix_head = cur->mark(); // suffix will be put back on global list
7933 cur->set_mark(NULL); // break off suffix
7934 // It's possible that the list is still in the empty(busy) state
7935 // we left it in a short while ago; in that case we may be
7936 // able to place back the suffix without incurring the cost
7937 // of a walk down the list.
7938 oop observed_overflow_list = oop(_overflow_list);
7939 oop cur_overflow_list = observed_overflow_list;
7940 bool attached = false;
7941 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7942 observed_overflow_list =
7943 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7944 if (cur_overflow_list == observed_overflow_list) {
7945 attached = true;
7946 break;
7947 } else cur_overflow_list = observed_overflow_list;
7948 }
7949 if (!attached) {
7950 // Too bad, someone else sneaked in (at least) an element; we'll need
7951 // to do a splice. Find tail of suffix so we can prepend suffix to global
7952 // list.
7953 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
7954 oop suffix_tail = cur;
7955 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
7956 "Tautology");
7957 observed_overflow_list = oop(_overflow_list);
7958 do {
7959 cur_overflow_list = observed_overflow_list;
7960 if (cur_overflow_list != BUSY) {
7961 // Do the splice ...
7962 suffix_tail->set_mark(markOop(cur_overflow_list));
7963 } else { // cur_overflow_list == BUSY
7964 suffix_tail->set_mark(NULL);
7965 }
7966 // ... and try to place spliced list back on overflow_list ...
7967 observed_overflow_list =
7968 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7969 } while (cur_overflow_list != observed_overflow_list);
7970 // ... until we have succeeded in doing so.
7971 }
7972 }
7973
7974 // Push the prefix elements on work_q
7975 assert(prefix != NULL, "control point invariant");
7976 const markOop proto = markOopDesc::prototype();
7977 oop next;
7980 next = oop(cur->mark());
7981 cur->set_mark(proto); // until proven otherwise
7982 assert(cur->is_oop(), "Should be an oop");
7983 bool res = work_q->push(cur);
7984 assert(res, "Bit off more than we can chew?");
7985 NOT_PRODUCT(n++;)
7986 }
7987 #ifndef PRODUCT
7988 assert(_num_par_pushes >= n, "Too many pops?");
7989 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
7990 #endif
7991 return true;
7992 }
7993
7994 // Single-threaded
7995 void CMSCollector::push_on_overflow_list(oop p) {
7996 NOT_PRODUCT(_num_par_pushes++;)
7997 assert(p->is_oop(), "Not an oop");
7998 preserve_mark_if_necessary(p);
7999 p->set_mark((markOop)_overflow_list);
8000 _overflow_list = (oopDesc*)p;
8001 }
8002
8003 // Multi-threaded; use CAS to prepend to overflow list
8004 void CMSCollector::par_push_on_overflow_list(oop p) {
8005 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8006 assert(p->is_oop(), "Not an oop");
8007 par_preserve_mark_if_necessary(p);
8008 oop observed_overflow_list = oop(_overflow_list);
8009 oop cur_overflow_list;
8010 do {
8011 cur_overflow_list = observed_overflow_list;
8012 if (cur_overflow_list != BUSY) {
8013 p->set_mark(markOop(cur_overflow_list));
8014 } else {
8015 p->set_mark(NULL);
8016 }
8017 observed_overflow_list =
8018 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8019 } while (cur_overflow_list != observed_overflow_list);
8020 }
8021 #undef BUSY
8022
8023 // Single threaded
8024 // General Note on GrowableArray: pushes may silently fail
8025 // because we are (temporarily) out of C-heap for expanding
8026 // the stack. The problem is quite ubiquitous and affects
8027 // a lot of code in the JVM. The prudent thing for GrowableArray
8028 // to do (for now) is to exit with an error. However, that may
|