< prev index next >
src/hotspot/share/runtime/threadSMR.cpp
Print this page
rev 48162 : 8191789: migrate more Thread-SMR stuff from thread.[ch]pp -> threadSMR.[ch]pp
Reviewed-by: stefank
rev 48163 : CR round 0: dcubed - move more code into sort order, add update_smr_tlh_stats(); stefank - refactor Threads::add() and Threads::remove() to allow more ThreadsSMRSupport functions to be private, move is_a_protected_JavaThread_with_lock() to threadSMR.inline.hpp
*** 21,72 ****
* questions.
*
*/
#include "precompiled.hpp"
#include "memory/allocation.inline.hpp"
#include "runtime/thread.inline.hpp"
! #include "runtime/threadSMR.hpp"
#include "services/threadService.hpp"
// 'entries + 1' so we always have at least one entry.
ThreadsList::ThreadsList(int entries) : _length(entries), _threads(NEW_C_HEAP_ARRAY(JavaThread*, entries + 1, mtThread)), _next_list(NULL) {
*(JavaThread**)(_threads + entries) = NULL; // Make sure the extra entry is NULL.
}
ThreadsList::~ThreadsList() {
FREE_C_HEAP_ARRAY(JavaThread*, _threads);
}
! ThreadsListSetter::~ThreadsListSetter() {
! if (_target_needs_release) {
! // The hazard ptr in the target needs to be released.
! Threads::release_stable_list(_target);
}
}
! void ThreadsListSetter::set() {
! assert(_target->get_threads_hazard_ptr() == NULL, "hazard ptr should not already be set");
! (void) Threads::acquire_stable_list(_target, /* is_ThreadsListSetter */ true);
! _target_needs_release = true;
}
! ThreadsListHandle::ThreadsListHandle(Thread *self) : _list(Threads::acquire_stable_list(self, /* is_ThreadsListSetter */ false)), _self(self) {
assert(self == Thread::current(), "sanity check");
if (EnableThreadSMRStatistics) {
_timer.start();
}
}
ThreadsListHandle::~ThreadsListHandle() {
! Threads::release_stable_list(_self);
if (EnableThreadSMRStatistics) {
_timer.stop();
uint millis = (uint)_timer.milliseconds();
! Threads::inc_smr_tlh_cnt();
! Threads::add_smr_tlh_times(millis);
! Threads::update_smr_tlh_time_max(millis);
}
}
// Convert an internal thread reference to a JavaThread found on the
// associated ThreadsList. This ThreadsListHandle "protects" the
--- 21,484 ----
* questions.
*
*/
#include "precompiled.hpp"
+ #include "logging/logStream.hpp"
#include "memory/allocation.inline.hpp"
#include "runtime/thread.inline.hpp"
! #include "runtime/threadSMR.inline.hpp"
#include "services/threadService.hpp"
+ #include "utilities/globalDefinitions.hpp"
+ #include "utilities/resourceHash.hpp"
+
+ Monitor* ThreadsSMRSupport::_smr_delete_lock =
+ new Monitor(Monitor::special, "smr_delete_lock",
+ false /* allow_vm_block */,
+ Monitor::_safepoint_check_never);
+ // The '_cnt', '_max' and '_times" fields are enabled via
+ // -XX:+EnableThreadSMRStatistics:
+
+ // # of parallel threads in _smr_delete_lock->wait().
+ // Impl note: Hard to imagine > 64K waiting threads so this could be 16-bit,
+ // but there is no nice 16-bit _FORMAT support.
+ uint ThreadsSMRSupport::_smr_delete_lock_wait_cnt = 0;
+
+ // Max # of parallel threads in _smr_delete_lock->wait().
+ // Impl note: See _smr_delete_lock_wait_cnt note.
+ uint ThreadsSMRSupport::_smr_delete_lock_wait_max = 0;
+
+ // Flag to indicate when an _smr_delete_lock->notify() is needed.
+ // Impl note: See _smr_delete_lock_wait_cnt note.
+ volatile uint ThreadsSMRSupport::_smr_delete_notify = 0;
+
+ // # of threads deleted over VM lifetime.
+ // Impl note: Atomically incremented over VM lifetime so use unsigned for more
+ // range. Unsigned 64-bit would be more future proof, but 64-bit atomic inc
+ // isn't available everywhere (or is it?).
+ volatile uint ThreadsSMRSupport::_smr_deleted_thread_cnt = 0;
+
+ // Max time in millis to delete a thread.
+ // Impl note: 16-bit might be too small on an overloaded machine. Use
+ // unsigned since this is a time value. Set via Atomic::cmpxchg() in a
+ // loop for correctness.
+ volatile uint ThreadsSMRSupport::_smr_deleted_thread_time_max = 0;
+
+ // Cumulative time in millis to delete threads.
+ // Impl note: Atomically added to over VM lifetime so use unsigned for more
+ // range. Unsigned 64-bit would be more future proof, but 64-bit atomic inc
+ // isn't available everywhere (or is it?).
+ volatile uint ThreadsSMRSupport::_smr_deleted_thread_times = 0;
+
+ ThreadsList* volatile ThreadsSMRSupport::_smr_java_thread_list = new ThreadsList(0);
+
+ // # of ThreadsLists allocated over VM lifetime.
+ // Impl note: We allocate a new ThreadsList for every thread create and
+ // every thread delete so we need a bigger type than the
+ // _smr_deleted_thread_cnt field.
+ uint64_t ThreadsSMRSupport::_smr_java_thread_list_alloc_cnt = 1;
+
+ // # of ThreadsLists freed over VM lifetime.
+ // Impl note: See _smr_java_thread_list_alloc_cnt note.
+ uint64_t ThreadsSMRSupport::_smr_java_thread_list_free_cnt = 0;
+
+ // Max size ThreadsList allocated.
+ // Impl note: Max # of threads alive at one time should fit in unsigned 32-bit.
+ uint ThreadsSMRSupport::_smr_java_thread_list_max = 0;
+
+ // Max # of nested ThreadsLists for a thread.
+ // Impl note: Hard to imagine > 64K nested ThreadsLists so this could be
+ // 16-bit, but there is no nice 16-bit _FORMAT support.
+ uint ThreadsSMRSupport::_smr_nested_thread_list_max = 0;
+
+ // # of ThreadsListHandles deleted over VM lifetime.
+ // Impl note: Atomically incremented over VM lifetime so use unsigned for
+ // more range. There will be fewer ThreadsListHandles than threads so
+ // unsigned 32-bit should be fine.
+ volatile uint ThreadsSMRSupport::_smr_tlh_cnt = 0;
+
+ // Max time in millis to delete a ThreadsListHandle.
+ // Impl note: 16-bit might be too small on an overloaded machine. Use
+ // unsigned since this is a time value. Set via Atomic::cmpxchg() in a
+ // loop for correctness.
+ volatile uint ThreadsSMRSupport::_smr_tlh_time_max = 0;
+
+ // Cumulative time in millis to delete ThreadsListHandles.
+ // Impl note: Atomically added to over VM lifetime so use unsigned for more
+ // range. Unsigned 64-bit would be more future proof, but 64-bit atomic inc
+ // isn't available everywhere (or is it?).
+ volatile uint ThreadsSMRSupport::_smr_tlh_times = 0;
+
+ ThreadsList* ThreadsSMRSupport::_smr_to_delete_list = NULL;
+
+ // # of parallel ThreadsLists on the to-delete list.
+ // Impl note: Hard to imagine > 64K ThreadsLists needing to be deleted so
+ // this could be 16-bit, but there is no nice 16-bit _FORMAT support.
+ uint ThreadsSMRSupport::_smr_to_delete_list_cnt = 0;
+
+ // Max # of parallel ThreadsLists on the to-delete list.
+ // Impl note: See _smr_to_delete_list_cnt note.
+ uint ThreadsSMRSupport::_smr_to_delete_list_max = 0;
+
+
+ // 'inline' functions first so the definitions are before first use:
+
+ inline void ThreadsSMRSupport::add_smr_deleted_thread_times(uint add_value) {
+ Atomic::add(add_value, &_smr_deleted_thread_times);
+ }
+
+ inline void ThreadsSMRSupport::inc_smr_deleted_thread_cnt() {
+ Atomic::inc(&_smr_deleted_thread_cnt);
+ }
+
+ inline void ThreadsSMRSupport::inc_smr_java_thread_list_alloc_cnt() {
+ _smr_java_thread_list_alloc_cnt++;
+ }
+
+ inline void ThreadsSMRSupport::update_smr_deleted_thread_time_max(uint new_value) {
+ while (true) {
+ uint cur_value = _smr_deleted_thread_time_max;
+ if (new_value <= cur_value) {
+ // No need to update max value so we're done.
+ break;
+ }
+ if (Atomic::cmpxchg(new_value, &_smr_deleted_thread_time_max, cur_value) == cur_value) {
+ // Updated max value so we're done. Otherwise try it all again.
+ break;
+ }
+ }
+ }
+
+ inline void ThreadsSMRSupport::update_smr_java_thread_list_max(uint new_value) {
+ if (new_value > _smr_java_thread_list_max) {
+ _smr_java_thread_list_max = new_value;
+ }
+ }
+
+ inline ThreadsList* ThreadsSMRSupport::xchg_smr_java_thread_list(ThreadsList* new_list) {
+ return (ThreadsList*)Atomic::xchg(new_list, &_smr_java_thread_list);
+ }
+
+
+ // Hash table of pointers found by a scan. Used for collecting hazard
+ // pointers (ThreadsList references). Also used for collecting JavaThreads
+ // that are indirectly referenced by hazard ptrs. An instance of this
+ // class only contains one type of pointer.
+ //
+ class ThreadScanHashtable : public CHeapObj<mtThread> {
+ private:
+ static bool ptr_equals(void * const& s1, void * const& s2) {
+ return s1 == s2;
+ }
+
+ static unsigned int ptr_hash(void * const& s1) {
+ // 2654435761 = 2^32 * Phi (golden ratio)
+ return (unsigned int)(((uint32_t)(uintptr_t)s1) * 2654435761u);
+ }
+
+ int _table_size;
+ // ResourceHashtable SIZE is specified at compile time so our
+ // dynamic _table_size is unused for now; 1031 is the first prime
+ // after 1024.
+ typedef ResourceHashtable<void *, int, &ThreadScanHashtable::ptr_hash,
+ &ThreadScanHashtable::ptr_equals, 1031,
+ ResourceObj::C_HEAP, mtThread> PtrTable;
+ PtrTable * _ptrs;
+
+ public:
+ // ResourceHashtable is passed to various functions and populated in
+ // different places so we allocate it using C_HEAP to make it immune
+ // from any ResourceMarks that happen to be in the code paths.
+ ThreadScanHashtable(int table_size) : _table_size(table_size), _ptrs(new (ResourceObj::C_HEAP, mtThread) PtrTable()) {}
+
+ ~ThreadScanHashtable() { delete _ptrs; }
+
+ bool has_entry(void *pointer) {
+ int *val_ptr = _ptrs->get(pointer);
+ return val_ptr != NULL && *val_ptr == 1;
+ }
+
+ void add_entry(void *pointer) {
+ _ptrs->put(pointer, 1);
+ }
+ };
+
+ // Closure to gather JavaThreads indirectly referenced by hazard ptrs
+ // (ThreadsList references) into a hash table. This closure handles part 2
+ // of the dance - adding all the JavaThreads referenced by the hazard
+ // pointer (ThreadsList reference) to the hash table.
+ //
+ class AddThreadHazardPointerThreadClosure : public ThreadClosure {
+ private:
+ ThreadScanHashtable *_table;
+
+ public:
+ AddThreadHazardPointerThreadClosure(ThreadScanHashtable *table) : _table(table) {}
+
+ virtual void do_thread(Thread *thread) {
+ if (!_table->has_entry((void*)thread)) {
+ // The same JavaThread might be on more than one ThreadsList or
+ // more than one thread might be using the same ThreadsList. In
+ // either case, we only need a single entry for a JavaThread.
+ _table->add_entry((void*)thread);
+ }
+ }
+ };
+
+ // Closure to gather JavaThreads indirectly referenced by hazard ptrs
+ // (ThreadsList references) into a hash table. This closure handles part 1
+ // of the dance - hazard ptr chain walking and dispatch to another
+ // closure.
+ //
+ class ScanHazardPtrGatherProtectedThreadsClosure : public ThreadClosure {
+ private:
+ ThreadScanHashtable *_table;
+ public:
+ ScanHazardPtrGatherProtectedThreadsClosure(ThreadScanHashtable *table) : _table(table) {}
+
+ virtual void do_thread(Thread *thread) {
+ assert_locked_or_safepoint(Threads_lock);
+
+ if (thread == NULL) return;
+
+ // This code races with ThreadsSMRSupport::acquire_stable_list() which
+ // is lock-free so we have to handle some special situations.
+ //
+ ThreadsList *current_list = NULL;
+ while (true) {
+ current_list = thread->get_threads_hazard_ptr();
+ // No hazard ptr so nothing more to do.
+ if (current_list == NULL) {
+ assert(thread->get_nested_threads_hazard_ptr() == NULL,
+ "cannot have a nested hazard ptr with a NULL regular hazard ptr");
+ return;
+ }
+
+ // If the hazard ptr is verified as stable (since it is not tagged),
+ // then it is safe to use.
+ if (!Thread::is_hazard_ptr_tagged(current_list)) break;
+
+ // The hazard ptr is tagged as not yet verified as being stable
+ // so we are racing with acquire_stable_list(). This exchange
+ // attempts to invalidate the hazard ptr. If we win the race,
+ // then we can ignore this unstable hazard ptr and the other
+ // thread will retry the attempt to publish a stable hazard ptr.
+ // If we lose the race, then we retry our attempt to look at the
+ // hazard ptr.
+ if (thread->cmpxchg_threads_hazard_ptr(NULL, current_list) == current_list) return;
+ }
+
+ // The current JavaThread has a hazard ptr (ThreadsList reference)
+ // which might be _smr_java_thread_list or it might be an older
+ // ThreadsList that has been removed but not freed. In either case,
+ // the hazard ptr is protecting all the JavaThreads on that
+ // ThreadsList.
+ AddThreadHazardPointerThreadClosure add_cl(_table);
+ current_list->threads_do(&add_cl);
+
+ // Any NestedThreadsLists are also protecting JavaThreads so
+ // gather those also; the ThreadsLists may be different.
+ for (NestedThreadsList* node = thread->get_nested_threads_hazard_ptr();
+ node != NULL; node = node->next()) {
+ node->t_list()->threads_do(&add_cl);
+ }
+ }
+ };
+
+ // Closure to gather hazard ptrs (ThreadsList references) into a hash table.
+ //
+ class ScanHazardPtrGatherThreadsListClosure : public ThreadClosure {
+ private:
+ ThreadScanHashtable *_table;
+ public:
+ ScanHazardPtrGatherThreadsListClosure(ThreadScanHashtable *table) : _table(table) {}
+
+ virtual void do_thread(Thread* thread) {
+ assert_locked_or_safepoint(Threads_lock);
+
+ if (thread == NULL) return;
+ ThreadsList *threads = thread->get_threads_hazard_ptr();
+ if (threads == NULL) {
+ assert(thread->get_nested_threads_hazard_ptr() == NULL,
+ "cannot have a nested hazard ptr with a NULL regular hazard ptr");
+ return;
+ }
+ // In this closure we always ignore the tag that might mark this
+ // hazard ptr as not yet verified. If we happen to catch an
+ // unverified hazard ptr that is subsequently discarded (not
+ // published), then the only side effect is that we might keep a
+ // to-be-deleted ThreadsList alive a little longer.
+ threads = Thread::untag_hazard_ptr(threads);
+ if (!_table->has_entry((void*)threads)) {
+ _table->add_entry((void*)threads);
+ }
+
+ // Any NestedThreadsLists are also protecting JavaThreads so
+ // gather those also; the ThreadsLists may be different.
+ for (NestedThreadsList* node = thread->get_nested_threads_hazard_ptr();
+ node != NULL; node = node->next()) {
+ threads = node->t_list();
+ if (!_table->has_entry((void*)threads)) {
+ _table->add_entry((void*)threads);
+ }
+ }
+ }
+ };
+
+ // Closure to print JavaThreads that have a hazard ptr (ThreadsList
+ // reference) that contains an indirect reference to a specific JavaThread.
+ //
+ class ScanHazardPtrPrintMatchingThreadsClosure : public ThreadClosure {
+ private:
+ JavaThread *_thread;
+ public:
+ ScanHazardPtrPrintMatchingThreadsClosure(JavaThread *thread) : _thread(thread) {}
+
+ virtual void do_thread(Thread *thread) {
+ assert_locked_or_safepoint(Threads_lock);
+
+ if (thread == NULL) return;
+ ThreadsList *current_list = thread->get_threads_hazard_ptr();
+ if (current_list == NULL) {
+ assert(thread->get_nested_threads_hazard_ptr() == NULL,
+ "cannot have a nested hazard ptr with a NULL regular hazard ptr");
+ return;
+ }
+ // If the hazard ptr is unverified, then ignore it.
+ if (Thread::is_hazard_ptr_tagged(current_list)) return;
+
+ // The current JavaThread has a hazard ptr (ThreadsList reference)
+ // which might be _smr_java_thread_list or it might be an older
+ // ThreadsList that has been removed but not freed. In either case,
+ // the hazard ptr is protecting all the JavaThreads on that
+ // ThreadsList, but we only care about matching a specific JavaThread.
+ JavaThreadIterator jti(current_list);
+ for (JavaThread *p = jti.first(); p != NULL; p = jti.next()) {
+ if (p == _thread) {
+ log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_delete: thread1=" INTPTR_FORMAT " has a hazard pointer for thread2=" INTPTR_FORMAT, os::current_thread_id(), p2i(thread), p2i(_thread));
+ break;
+ }
+ }
+
+ // Any NestedThreadsLists are also protecting JavaThreads so
+ // check those also; the ThreadsLists may be different.
+ for (NestedThreadsList* node = thread->get_nested_threads_hazard_ptr();
+ node != NULL; node = node->next()) {
+ JavaThreadIterator jti(node->t_list());
+ for (JavaThread *p = jti.first(); p != NULL; p = jti.next()) {
+ if (p == _thread) {
+ log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_delete: thread1=" INTPTR_FORMAT " has a nested hazard pointer for thread2=" INTPTR_FORMAT, os::current_thread_id(), p2i(thread), p2i(_thread));
+ return;
+ }
+ }
+ }
+ }
+ };
+
// 'entries + 1' so we always have at least one entry.
ThreadsList::ThreadsList(int entries) : _length(entries), _threads(NEW_C_HEAP_ARRAY(JavaThread*, entries + 1, mtThread)), _next_list(NULL) {
*(JavaThread**)(_threads + entries) = NULL; // Make sure the extra entry is NULL.
}
ThreadsList::~ThreadsList() {
FREE_C_HEAP_ARRAY(JavaThread*, _threads);
}
! // Add a JavaThread to a ThreadsList. The returned ThreadsList is a
! // new copy of the specified ThreadsList with the specified JavaThread
! // appended to the end.
! ThreadsList *ThreadsList::add_thread(ThreadsList *list, JavaThread *java_thread) {
! const uint index = list->_length;
! const uint new_length = index + 1;
! const uint head_length = index;
! ThreadsList *const new_list = new ThreadsList(new_length);
!
! if (head_length > 0) {
! Copy::disjoint_words((HeapWord*)list->_threads, (HeapWord*)new_list->_threads, head_length);
}
+ *(JavaThread**)(new_list->_threads + index) = java_thread;
+
+ return new_list;
}
! int ThreadsList::find_index_of_JavaThread(JavaThread *target) {
! if (target == NULL) {
! return -1;
! }
! for (uint i = 0; i < length(); i++) {
! if (target == thread_at(i)) {
! return (int)i;
! }
! }
! return -1;
}
! JavaThread* ThreadsList::find_JavaThread_from_java_tid(jlong java_tid) const {
! for (uint i = 0; i < length(); i++) {
! JavaThread* thread = thread_at(i);
! oop tobj = thread->threadObj();
! // Ignore the thread if it hasn't run yet, has exited
! // or is starting to exit.
! if (tobj != NULL && !thread->is_exiting() &&
! java_tid == java_lang_Thread::thread_id(tobj)) {
! // found a match
! return thread;
! }
! }
! return NULL;
! }
!
! bool ThreadsList::includes(const JavaThread * const p) const {
! if (p == NULL) {
! return false;
! }
! for (uint i = 0; i < length(); i++) {
! if (thread_at(i) == p) {
! return true;
! }
! }
! return false;
! }
!
! // Remove a JavaThread from a ThreadsList. The returned ThreadsList is a
! // new copy of the specified ThreadsList with the specified JavaThread
! // removed.
! ThreadsList *ThreadsList::remove_thread(ThreadsList* list, JavaThread* java_thread) {
! assert(list->_length > 0, "sanity");
!
! uint i = (uint)list->find_index_of_JavaThread(java_thread);
! assert(i < list->_length, "did not find JavaThread on the list");
! const uint index = i;
! const uint new_length = list->_length - 1;
! const uint head_length = index;
! const uint tail_length = (new_length >= index) ? (new_length - index) : 0;
! ThreadsList *const new_list = new ThreadsList(new_length);
!
! if (head_length > 0) {
! Copy::disjoint_words((HeapWord*)list->_threads, (HeapWord*)new_list->_threads, head_length);
! }
! if (tail_length > 0) {
! Copy::disjoint_words((HeapWord*)list->_threads + index + 1, (HeapWord*)new_list->_threads + index, tail_length);
! }
!
! return new_list;
! }
!
! ThreadsListHandle::ThreadsListHandle(Thread *self) : _list(ThreadsSMRSupport::acquire_stable_list(self, /* is_ThreadsListSetter */ false)), _self(self) {
assert(self == Thread::current(), "sanity check");
if (EnableThreadSMRStatistics) {
_timer.start();
}
}
ThreadsListHandle::~ThreadsListHandle() {
! ThreadsSMRSupport::release_stable_list(_self);
if (EnableThreadSMRStatistics) {
_timer.stop();
uint millis = (uint)_timer.milliseconds();
! ThreadsSMRSupport::update_smr_tlh_stats(millis);
}
}
// Convert an internal thread reference to a JavaThread found on the
// associated ThreadsList. This ThreadsListHandle "protects" the
*** 117,121 ****
--- 529,1076 ----
// Return a live JavaThread that is "protected" by the
// ThreadsListHandle in the caller.
*jt_pp = java_thread;
return true;
}
+
+ ThreadsListSetter::~ThreadsListSetter() {
+ if (_target_needs_release) {
+ // The hazard ptr in the target needs to be released.
+ ThreadsSMRSupport::release_stable_list(_target);
+ }
+ }
+
+ void ThreadsListSetter::set() {
+ assert(_target->get_threads_hazard_ptr() == NULL, "hazard ptr should not already be set");
+ (void) ThreadsSMRSupport::acquire_stable_list(_target, /* is_ThreadsListSetter */ true);
+ _target_needs_release = true;
+ }
+
+ // Acquire a stable ThreadsList.
+ //
+ ThreadsList *ThreadsSMRSupport::acquire_stable_list(Thread *self, bool is_ThreadsListSetter) {
+ assert(self != NULL, "sanity check");
+ // acquire_stable_list_nested_path() will grab the Threads_lock
+ // so let's make sure the ThreadsListHandle is in a safe place.
+ // ThreadsListSetter cannot make this check on this code path.
+ debug_only(if (!is_ThreadsListSetter && StrictSafepointChecks) self->check_for_valid_safepoint_state(/* potential_vm_operation */ false);)
+
+ if (self->get_threads_hazard_ptr() == NULL) {
+ // The typical case is first.
+ return acquire_stable_list_fast_path(self);
+ }
+
+ // The nested case is rare.
+ return acquire_stable_list_nested_path(self);
+ }
+
+ // Fast path (and lock free) way to acquire a stable ThreadsList.
+ //
+ ThreadsList *ThreadsSMRSupport::acquire_stable_list_fast_path(Thread *self) {
+ assert(self != NULL, "sanity check");
+ assert(self->get_threads_hazard_ptr() == NULL, "sanity check");
+ assert(self->get_nested_threads_hazard_ptr() == NULL,
+ "cannot have a nested hazard ptr with a NULL regular hazard ptr");
+
+ ThreadsList* threads;
+
+ // Stable recording of a hazard ptr for SMR. This code does not use
+ // locks so its use of the _smr_java_thread_list & _threads_hazard_ptr
+ // fields is racy relative to code that uses those fields with locks.
+ // OrderAccess and Atomic functions are used to deal with those races.
+ //
+ while (true) {
+ threads = get_smr_java_thread_list();
+
+ // Publish a tagged hazard ptr to denote that the hazard ptr is not
+ // yet verified as being stable. Due to the fence after the hazard
+ // ptr write, it will be sequentially consistent w.r.t. the
+ // sequentially consistent writes of the ThreadsList, even on
+ // non-multiple copy atomic machines where stores can be observed
+ // in different order from different observer threads.
+ ThreadsList* unverified_threads = Thread::tag_hazard_ptr(threads);
+ self->set_threads_hazard_ptr(unverified_threads);
+
+ // If _smr_java_thread_list has changed, we have lost a race with
+ // Threads::add() or Threads::remove() and have to try again.
+ if (get_smr_java_thread_list() != threads) {
+ continue;
+ }
+
+ // We try to remove the tag which will verify the hazard ptr as
+ // being stable. This exchange can race with a scanning thread
+ // which might invalidate the tagged hazard ptr to keep it from
+ // being followed to access JavaThread ptrs. If we lose the race,
+ // we simply retry. If we win the race, then the stable hazard
+ // ptr is officially published.
+ if (self->cmpxchg_threads_hazard_ptr(threads, unverified_threads) == unverified_threads) {
+ break;
+ }
+ }
+
+ // A stable hazard ptr has been published letting other threads know
+ // that the ThreadsList and the JavaThreads reachable from this list
+ // are protected and hence they should not be deleted until everyone
+ // agrees it is safe to do so.
+
+ return threads;
+ }
+
+ // Acquire a nested stable ThreadsList; this is rare so it uses
+ // Threads_lock.
+ //
+ ThreadsList *ThreadsSMRSupport::acquire_stable_list_nested_path(Thread *self) {
+ assert(self != NULL, "sanity check");
+ assert(self->get_threads_hazard_ptr() != NULL,
+ "cannot have a NULL regular hazard ptr when acquiring a nested hazard ptr");
+
+ // The thread already has a hazard ptr (ThreadsList ref) so we need
+ // to create a nested ThreadsListHandle with the current ThreadsList
+ // since it might be different than our current hazard ptr. The need
+ // for a nested ThreadsListHandle is rare so we do this while holding
+ // the Threads_lock so we don't race with the scanning code; the code
+ // is so much simpler this way.
+
+ NestedThreadsList* node;
+ {
+ // Only grab the Threads_lock if we don't already own it.
+ MutexLockerEx ml(Threads_lock->owned_by_self() ? NULL : Threads_lock);
+ node = new NestedThreadsList(get_smr_java_thread_list());
+ // We insert at the front of the list to match up with the delete
+ // in release_stable_list().
+ node->set_next(self->get_nested_threads_hazard_ptr());
+ self->set_nested_threads_hazard_ptr(node);
+ if (EnableThreadSMRStatistics) {
+ self->inc_nested_threads_hazard_ptr_cnt();
+ if (self->nested_threads_hazard_ptr_cnt() > _smr_nested_thread_list_max) {
+ _smr_nested_thread_list_max = self->nested_threads_hazard_ptr_cnt();
+ }
+ }
+ }
+ log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::acquire_stable_list: add NestedThreadsList node containing ThreadsList=" INTPTR_FORMAT, os::current_thread_id(), p2i(node->t_list()));
+
+ return node->t_list();
+ }
+
+ void ThreadsSMRSupport::add_thread(JavaThread *thread){
+ ThreadsList *new_list = ThreadsList::add_thread(ThreadsSMRSupport::get_smr_java_thread_list(), thread);
+ if (EnableThreadSMRStatistics) {
+ ThreadsSMRSupport::inc_smr_java_thread_list_alloc_cnt();
+ ThreadsSMRSupport::update_smr_java_thread_list_max(new_list->length());
+ }
+ // Initial _smr_java_thread_list will not generate a "Threads::add" mesg.
+ log_debug(thread, smr)("tid=" UINTX_FORMAT ": Threads::add: new ThreadsList=" INTPTR_FORMAT, os::current_thread_id(), p2i(new_list));
+
+ ThreadsList *old_list = ThreadsSMRSupport::xchg_smr_java_thread_list(new_list);
+ ThreadsSMRSupport::smr_free_list(old_list);
+ }
+
+ // set_smr_delete_notify() and clear_smr_delete_notify() are called
+ // under the protection of the smr_delete_lock, but we also use an
+ // Atomic operation to ensure the memory update is seen earlier than
+ // when the smr_delete_lock is dropped.
+ //
+ void ThreadsSMRSupport::clear_smr_delete_notify() {
+ Atomic::dec(&_smr_delete_notify);
+ }
+
+ // Return true if the specified JavaThread is protected by a hazard
+ // pointer (ThreadsList reference). Otherwise, returns false.
+ //
+ bool ThreadsSMRSupport::is_a_protected_JavaThread(JavaThread *thread) {
+ assert_locked_or_safepoint(Threads_lock);
+
+ // Hash table size should be first power of two higher than twice
+ // the length of the Threads list.
+ int hash_table_size = MIN2((int)get_smr_java_thread_list()->length(), 32) << 1;
+ hash_table_size--;
+ hash_table_size |= hash_table_size >> 1;
+ hash_table_size |= hash_table_size >> 2;
+ hash_table_size |= hash_table_size >> 4;
+ hash_table_size |= hash_table_size >> 8;
+ hash_table_size |= hash_table_size >> 16;
+ hash_table_size++;
+
+ // Gather a hash table of the JavaThreads indirectly referenced by
+ // hazard ptrs.
+ ThreadScanHashtable *scan_table = new ThreadScanHashtable(hash_table_size);
+ ScanHazardPtrGatherProtectedThreadsClosure scan_cl(scan_table);
+ Threads::threads_do(&scan_cl);
+
+ bool thread_is_protected = false;
+ if (scan_table->has_entry((void*)thread)) {
+ thread_is_protected = true;
+ }
+ delete scan_table;
+ return thread_is_protected;
+ }
+
+ // Release a stable ThreadsList.
+ //
+ void ThreadsSMRSupport::release_stable_list(Thread *self) {
+ assert(self != NULL, "sanity check");
+ // release_stable_list_nested_path() will grab the Threads_lock
+ // so let's make sure the ThreadsListHandle is in a safe place.
+ debug_only(if (StrictSafepointChecks) self->check_for_valid_safepoint_state(/* potential_vm_operation */ false);)
+
+ if (self->get_nested_threads_hazard_ptr() == NULL) {
+ // The typical case is first.
+ release_stable_list_fast_path(self);
+ return;
+ }
+
+ // The nested case is rare.
+ release_stable_list_nested_path(self);
+ }
+
+ // Fast path way to release a stable ThreadsList. The release portion
+ // is lock-free, but the wake up portion is not.
+ //
+ void ThreadsSMRSupport::release_stable_list_fast_path(Thread *self) {
+ assert(self != NULL, "sanity check");
+ assert(self->get_threads_hazard_ptr() != NULL, "sanity check");
+ assert(self->get_nested_threads_hazard_ptr() == NULL,
+ "cannot have a nested hazard ptr when releasing a regular hazard ptr");
+
+ // After releasing the hazard ptr, other threads may go ahead and
+ // free up some memory temporarily used by a ThreadsList snapshot.
+ self->set_threads_hazard_ptr(NULL);
+
+ // We use double-check locking to reduce traffic on the system
+ // wide smr_delete_lock.
+ if (ThreadsSMRSupport::smr_delete_notify()) {
+ // An exiting thread might be waiting in smr_delete(); we need to
+ // check with smr_delete_lock to be sure.
+ release_stable_list_wake_up((char *) "regular hazard ptr");
+ }
+ }
+
+ // Release a nested stable ThreadsList; this is rare so it uses
+ // Threads_lock.
+ //
+ void ThreadsSMRSupport::release_stable_list_nested_path(Thread *self) {
+ assert(self != NULL, "sanity check");
+ assert(self->get_nested_threads_hazard_ptr() != NULL, "sanity check");
+ assert(self->get_threads_hazard_ptr() != NULL,
+ "must have a regular hazard ptr to have nested hazard ptrs");
+
+ // We have a nested ThreadsListHandle so we have to release it first.
+ // The need for a nested ThreadsListHandle is rare so we do this while
+ // holding the Threads_lock so we don't race with the scanning code;
+ // the code is so much simpler this way.
+
+ NestedThreadsList *node;
+ {
+ // Only grab the Threads_lock if we don't already own it.
+ MutexLockerEx ml(Threads_lock->owned_by_self() ? NULL : Threads_lock);
+ // We remove from the front of the list to match up with the insert
+ // in acquire_stable_list().
+ node = self->get_nested_threads_hazard_ptr();
+ self->set_nested_threads_hazard_ptr(node->next());
+ if (EnableThreadSMRStatistics) {
+ self->dec_nested_threads_hazard_ptr_cnt();
+ }
+ }
+
+ // An exiting thread might be waiting in smr_delete(); we need to
+ // check with smr_delete_lock to be sure.
+ release_stable_list_wake_up((char *) "nested hazard ptr");
+
+ log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::release_stable_list: delete NestedThreadsList node containing ThreadsList=" INTPTR_FORMAT, os::current_thread_id(), p2i(node->t_list()));
+
+ delete node;
+ }
+
+ // Wake up portion of the release stable ThreadsList protocol;
+ // uses the smr_delete_lock().
+ //
+ void ThreadsSMRSupport::release_stable_list_wake_up(char *log_str) {
+ assert(log_str != NULL, "sanity check");
+
+ // Note: smr_delete_lock is held in smr_delete() for the entire
+ // hazard ptr search so that we do not lose this notify() if
+ // the exiting thread has to wait. That code path also holds
+ // Threads_lock (which was grabbed before smr_delete_lock) so that
+ // threads_do() can be called. This means the system can't start a
+ // safepoint which means this thread can't take too long to get to
+ // a safepoint because of being blocked on smr_delete_lock.
+ //
+ MonitorLockerEx ml(ThreadsSMRSupport::smr_delete_lock(), Monitor::_no_safepoint_check_flag);
+ if (ThreadsSMRSupport::smr_delete_notify()) {
+ // Notify any exiting JavaThreads that are waiting in smr_delete()
+ // that we've released a ThreadsList.
+ ml.notify_all();
+ log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::release_stable_list notified %s", os::current_thread_id(), log_str);
+ }
+ }
+
+ void ThreadsSMRSupport::remove_thread(JavaThread *thread) {
+ ThreadsList *new_list = ThreadsList::remove_thread(ThreadsSMRSupport::get_smr_java_thread_list(), thread);
+ if (EnableThreadSMRStatistics) {
+ ThreadsSMRSupport::inc_smr_java_thread_list_alloc_cnt();
+ // This list is smaller so no need to check for a "longest" update.
+ }
+
+ // Final _smr_java_thread_list will not generate a "Threads::remove" mesg.
+ log_debug(thread, smr)("tid=" UINTX_FORMAT ": Threads::remove: new ThreadsList=" INTPTR_FORMAT, os::current_thread_id(), p2i(new_list));
+
+ ThreadsList *old_list = ThreadsSMRSupport::xchg_smr_java_thread_list(new_list);
+ ThreadsSMRSupport::smr_free_list(old_list);
+ }
+
+ // See note for clear_smr_delete_notify().
+ //
+ void ThreadsSMRSupport::set_smr_delete_notify() {
+ Atomic::inc(&_smr_delete_notify);
+ }
+
+ // Safely delete a JavaThread when it is no longer in use by a
+ // ThreadsListHandle.
+ //
+ void ThreadsSMRSupport::smr_delete(JavaThread *thread) {
+ assert(!Threads_lock->owned_by_self(), "sanity");
+
+ bool has_logged_once = false;
+ elapsedTimer timer;
+ if (EnableThreadSMRStatistics) {
+ timer.start();
+ }
+
+ while (true) {
+ {
+ // No safepoint check because this JavaThread is not on the
+ // Threads list.
+ MutexLockerEx ml(Threads_lock, Mutex::_no_safepoint_check_flag);
+ // Cannot use a MonitorLockerEx helper here because we have
+ // to drop the Threads_lock first if we wait.
+ ThreadsSMRSupport::smr_delete_lock()->lock_without_safepoint_check();
+ // Set the smr_delete_notify flag after we grab smr_delete_lock
+ // and before we scan hazard ptrs because we're doing
+ // double-check locking in release_stable_list().
+ ThreadsSMRSupport::set_smr_delete_notify();
+
+ if (!is_a_protected_JavaThread(thread)) {
+ // This is the common case.
+ ThreadsSMRSupport::clear_smr_delete_notify();
+ ThreadsSMRSupport::smr_delete_lock()->unlock();
+ break;
+ }
+ if (!has_logged_once) {
+ has_logged_once = true;
+ log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_delete: thread=" INTPTR_FORMAT " is not deleted.", os::current_thread_id(), p2i(thread));
+ if (log_is_enabled(Debug, os, thread)) {
+ ScanHazardPtrPrintMatchingThreadsClosure scan_cl(thread);
+ Threads::threads_do(&scan_cl);
+ }
+ }
+ } // We have to drop the Threads_lock to wait or delete the thread
+
+ if (EnableThreadSMRStatistics) {
+ _smr_delete_lock_wait_cnt++;
+ if (_smr_delete_lock_wait_cnt > _smr_delete_lock_wait_max) {
+ _smr_delete_lock_wait_max = _smr_delete_lock_wait_cnt;
+ }
+ }
+ // Wait for a release_stable_list() call before we check again. No
+ // safepoint check, no timeout, and not as suspend equivalent flag
+ // because this JavaThread is not on the Threads list.
+ ThreadsSMRSupport::smr_delete_lock()->wait(Mutex::_no_safepoint_check_flag, 0,
+ !Mutex::_as_suspend_equivalent_flag);
+ if (EnableThreadSMRStatistics) {
+ _smr_delete_lock_wait_cnt--;
+ }
+
+ ThreadsSMRSupport::clear_smr_delete_notify();
+ ThreadsSMRSupport::smr_delete_lock()->unlock();
+ // Retry the whole scenario.
+ }
+
+ if (ThreadLocalHandshakes) {
+ // The thread is about to be deleted so cancel any handshake.
+ thread->cancel_handshake();
+ }
+
+ delete thread;
+ if (EnableThreadSMRStatistics) {
+ timer.stop();
+ uint millis = (uint)timer.milliseconds();
+ ThreadsSMRSupport::inc_smr_deleted_thread_cnt();
+ ThreadsSMRSupport::add_smr_deleted_thread_times(millis);
+ ThreadsSMRSupport::update_smr_deleted_thread_time_max(millis);
+ }
+
+ log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_delete: thread=" INTPTR_FORMAT " is deleted.", os::current_thread_id(), p2i(thread));
+ }
+
+ bool ThreadsSMRSupport::smr_delete_notify() {
+ // Use load_acquire() in order to see any updates to _smr_delete_notify
+ // earlier than when smr_delete_lock is grabbed.
+ return (OrderAccess::load_acquire(&_smr_delete_notify) != 0);
+ }
+
+ // Safely free a ThreadsList after a Threads::add() or Threads::remove().
+ // The specified ThreadsList may not get deleted during this call if it
+ // is still in-use (referenced by a hazard ptr). Other ThreadsLists
+ // in the chain may get deleted by this call if they are no longer in-use.
+ void ThreadsSMRSupport::smr_free_list(ThreadsList* threads) {
+ assert_locked_or_safepoint(Threads_lock);
+
+ threads->set_next_list(_smr_to_delete_list);
+ _smr_to_delete_list = threads;
+ if (EnableThreadSMRStatistics) {
+ _smr_to_delete_list_cnt++;
+ if (_smr_to_delete_list_cnt > _smr_to_delete_list_max) {
+ _smr_to_delete_list_max = _smr_to_delete_list_cnt;
+ }
+ }
+
+ // Hash table size should be first power of two higher than twice the length of the ThreadsList
+ int hash_table_size = MIN2((int)get_smr_java_thread_list()->length(), 32) << 1;
+ hash_table_size--;
+ hash_table_size |= hash_table_size >> 1;
+ hash_table_size |= hash_table_size >> 2;
+ hash_table_size |= hash_table_size >> 4;
+ hash_table_size |= hash_table_size >> 8;
+ hash_table_size |= hash_table_size >> 16;
+ hash_table_size++;
+
+ // Gather a hash table of the current hazard ptrs:
+ ThreadScanHashtable *scan_table = new ThreadScanHashtable(hash_table_size);
+ ScanHazardPtrGatherThreadsListClosure scan_cl(scan_table);
+ Threads::threads_do(&scan_cl);
+
+ // Walk through the linked list of pending freeable ThreadsLists
+ // and free the ones that are not referenced from hazard ptrs.
+ ThreadsList* current = _smr_to_delete_list;
+ ThreadsList* prev = NULL;
+ ThreadsList* next = NULL;
+ bool threads_is_freed = false;
+ while (current != NULL) {
+ next = current->next_list();
+ if (!scan_table->has_entry((void*)current)) {
+ // This ThreadsList is not referenced by a hazard ptr.
+ if (prev != NULL) {
+ prev->set_next_list(next);
+ }
+ if (_smr_to_delete_list == current) {
+ _smr_to_delete_list = next;
+ }
+
+ log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_free_list: threads=" INTPTR_FORMAT " is freed.", os::current_thread_id(), p2i(current));
+ if (current == threads) threads_is_freed = true;
+ delete current;
+ if (EnableThreadSMRStatistics) {
+ _smr_java_thread_list_free_cnt++;
+ _smr_to_delete_list_cnt--;
+ }
+ } else {
+ prev = current;
+ }
+ current = next;
+ }
+
+ if (!threads_is_freed) {
+ // Only report "is not freed" on the original call to
+ // smr_free_list() for this ThreadsList.
+ log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_free_list: threads=" INTPTR_FORMAT " is not freed.", os::current_thread_id(), p2i(threads));
+ }
+
+ delete scan_table;
+ }
+
+
+ // Debug, logging, and printing stuff at the end:
+
+ // Log Threads class SMR info.
+ void ThreadsSMRSupport::log_smr_statistics() {
+ LogTarget(Info, thread, smr) log;
+ if (log.is_enabled()) {
+ LogStream out(log);
+ print_smr_info_on(&out);
+ }
+ }
+
+ // Print Threads class SMR info.
+ void ThreadsSMRSupport::print_smr_info_on(outputStream* st) {
+ // Only grab the Threads_lock if we don't already own it
+ // and if we are not reporting an error.
+ MutexLockerEx ml((Threads_lock->owned_by_self() || VMError::is_error_reported()) ? NULL : Threads_lock);
+
+ st->print_cr("Threads class SMR info:");
+ st->print_cr("_smr_java_thread_list=" INTPTR_FORMAT ", length=%u, "
+ "elements={", p2i(_smr_java_thread_list),
+ _smr_java_thread_list->length());
+ print_smr_info_elements_on(st, _smr_java_thread_list);
+ st->print_cr("}");
+ if (_smr_to_delete_list != NULL) {
+ st->print_cr("_smr_to_delete_list=" INTPTR_FORMAT ", length=%u, "
+ "elements={", p2i(_smr_to_delete_list),
+ _smr_to_delete_list->length());
+ print_smr_info_elements_on(st, _smr_to_delete_list);
+ st->print_cr("}");
+ for (ThreadsList *t_list = _smr_to_delete_list->next_list();
+ t_list != NULL; t_list = t_list->next_list()) {
+ st->print("next-> " INTPTR_FORMAT ", length=%u, "
+ "elements={", p2i(t_list), t_list->length());
+ print_smr_info_elements_on(st, t_list);
+ st->print_cr("}");
+ }
+ }
+ if (!EnableThreadSMRStatistics) {
+ return;
+ }
+ st->print_cr("_smr_java_thread_list_alloc_cnt=" UINT64_FORMAT ","
+ "_smr_java_thread_list_free_cnt=" UINT64_FORMAT ","
+ "_smr_java_thread_list_max=%u, "
+ "_smr_nested_thread_list_max=%u",
+ _smr_java_thread_list_alloc_cnt,
+ _smr_java_thread_list_free_cnt,
+ _smr_java_thread_list_max,
+ _smr_nested_thread_list_max);
+ if (_smr_tlh_cnt > 0) {
+ st->print_cr("_smr_tlh_cnt=%u"
+ ", _smr_tlh_times=%u"
+ ", avg_smr_tlh_time=%0.2f"
+ ", _smr_tlh_time_max=%u",
+ _smr_tlh_cnt, _smr_tlh_times,
+ ((double) _smr_tlh_times / _smr_tlh_cnt),
+ _smr_tlh_time_max);
+ }
+ if (_smr_deleted_thread_cnt > 0) {
+ st->print_cr("_smr_deleted_thread_cnt=%u"
+ ", _smr_deleted_thread_times=%u"
+ ", avg_smr_deleted_thread_time=%0.2f"
+ ", _smr_deleted_thread_time_max=%u",
+ _smr_deleted_thread_cnt, _smr_deleted_thread_times,
+ ((double) _smr_deleted_thread_times / _smr_deleted_thread_cnt),
+ _smr_deleted_thread_time_max);
+ }
+ st->print_cr("_smr_delete_lock_wait_cnt=%u, _smr_delete_lock_wait_max=%u",
+ _smr_delete_lock_wait_cnt, _smr_delete_lock_wait_max);
+ st->print_cr("_smr_to_delete_list_cnt=%u, _smr_to_delete_list_max=%u",
+ _smr_to_delete_list_cnt, _smr_to_delete_list_max);
+ }
+
+ // Print ThreadsList elements (4 per line).
+ void ThreadsSMRSupport::print_smr_info_elements_on(outputStream* st,
+ ThreadsList* t_list) {
+ uint cnt = 0;
+ JavaThreadIterator jti(t_list);
+ for (JavaThread *jt = jti.first(); jt != NULL; jt = jti.next()) {
+ st->print(INTPTR_FORMAT, p2i(jt));
+ if (cnt < t_list->length() - 1) {
+ // Separate with comma or comma-space except for the last one.
+ if (((cnt + 1) % 4) == 0) {
+ // Four INTPTR_FORMAT fit on an 80 column line so end the
+ // current line with just a comma.
+ st->print_cr(",");
+ } else {
+ // Not the last one on the current line so use comma-space:
+ st->print(", ");
+ }
+ } else {
+ // Last one so just end the current line.
+ st->cr();
+ }
+ cnt++;
+ }
+ }
< prev index next >