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src/hotspot/share/runtime/threadSMR.cpp
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rev 49938 : Moving existing code into new locations for easier diffs after refactoring.
rev 49939 : imported patch 8191798.eosterlund.open.patch.00
rev 49940 : imported patch 8191798.dcubed.open.cr0.00
rev 49941 : Fix a couple of print bugs; the nested_threads_hazard_ptr_cnt field is enabled via -XX:+EnableThreadSMRStatistics option so fix some refactor bugs.
@@ -1,7 +1,7 @@
/*
- * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2017, 2018, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
@@ -30,10 +30,11 @@
#include "runtime/threadSMR.inline.hpp"
#include "runtime/vm_operations.hpp"
#include "services/threadService.hpp"
#include "utilities/copy.hpp"
#include "utilities/globalDefinitions.hpp"
+#include "utilities/ostream.hpp"
#include "utilities/resourceHash.hpp"
#include "utilities/vmError.hpp"
Monitor* ThreadsSMRSupport::_delete_lock =
new Monitor(Monitor::special, "Thread_SMR_delete_lock",
@@ -250,12 +251,10 @@
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.
@@ -276,17 +275,10 @@
// 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.
//
@@ -300,12 +292,10 @@
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
@@ -313,20 +303,10 @@
// 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.
@@ -341,12 +321,10 @@
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;
@@ -360,29 +338,222 @@
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));
+// Closure to determine if the specified JavaThread is found by
+// threads_do().
+//
+class VerifyHazardPtrThreadClosure : public ThreadClosure {
+ private:
+ bool _found;
+ Thread *_self;
+
+ public:
+ VerifyHazardPtrThreadClosure(Thread *self) : _found(false), _self(self) {}
+
+ bool found() const { return _found; }
+
+ virtual void do_thread(Thread *thread) {
+ if (thread == _self) {
+ _found = true;
+ }
+ }
+};
+
+
+// Acquire a stable ThreadsList.
+//
+void SafeThreadsListPtr::acquire_stable_list() {
+ assert(_thread != NULL, "sanity check");
+ _needs_release = true;
+ _previous = _thread->_threads_list_ptr;
+ _thread->_threads_list_ptr = this;
+
+ if (_thread->get_threads_hazard_ptr() == NULL) {
+ // The typical case is first.
+ acquire_stable_list_fast_path();
return;
}
+
+ // The nested case is rare.
+ acquire_stable_list_nested_path();
+}
+
+// Fast path way to acquire a stable ThreadsList.
+//
+void SafeThreadsListPtr::acquire_stable_list_fast_path() {
+ assert(_thread != NULL, "sanity check");
+ assert(_thread->get_threads_hazard_ptr() == NULL, "sanity check");
+
+ 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 = ThreadsSMRSupport::get_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);
+ _thread->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 (ThreadsSMRSupport::get_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 (_thread->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.
+
+ _list = threads;
+
+ verify_hazard_ptr_scanned();
+}
+
+// Acquire a nested stable ThreadsList; this is rare so it uses
+// reference counting.
+//
+void SafeThreadsListPtr::acquire_stable_list_nested_path() {
+ assert(_thread != NULL, "sanity check");
+ assert(_thread->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. To remedy
+ // the situation, the ThreadsList pointed to by the pre-existing
+ // stable hazard ptr is reference counted before the hazard ptr may
+ // be released and moved to a new ThreadsList. The old ThreadsList
+ // is remembered in the ThreadsListHandle.
+
+ ThreadsList* current_list = _previous->_list;
+ if (EnableThreadSMRStatistics) {
+ _thread->inc_nested_threads_hazard_ptr_cnt();
}
-};
+ current_list->inc_nested_handle_cnt();
+ _previous->_has_ref_count = true; // promote SafeThreadsListPtr to be reference counted
+ _thread->_threads_hazard_ptr = NULL; // clear the hazard ptr so we can go through the fast path below
+
+ if (EnableThreadSMRStatistics && _thread->nested_threads_hazard_ptr_cnt() > ThreadsSMRSupport::_nested_thread_list_max) {
+ ThreadsSMRSupport::_nested_thread_list_max = _thread->nested_threads_hazard_ptr_cnt();
+ }
+
+ acquire_stable_list_fast_path();
+
+ verify_hazard_ptr_scanned();
+
+ log_debug(thread, smr)("tid=" UINTX_FORMAT ": SafeThreadsListPtr::acquire_stable_list: add nested list pointer to ThreadsList=" INTPTR_FORMAT, os::current_thread_id(), p2i(_list));
+}
+
+// Release a stable ThreadsList.
+//
+void SafeThreadsListPtr::release_stable_list() {
+ assert(_thread != NULL, "sanity check");
+ assert(_thread->_threads_list_ptr == this, "sanity check");
+ _thread->_threads_list_ptr = _previous;
+
+ if (_has_ref_count) {
+ // If a SafeThreadsListPtr has been promoted to use reference counting
+ // due to nesting of ThreadsListHandles, then the reference count must be
+ // decremented, at which point it may be freed. The forgotten value of
+ // the list no longer matters at this point and should already be NULL.
+ assert(_thread->get_threads_hazard_ptr() == NULL, "sanity check");
+ if (EnableThreadSMRStatistics) {
+ _thread->dec_nested_threads_hazard_ptr_cnt();
+ }
+ _list->dec_nested_handle_cnt();
+
+ log_debug(thread, smr)("tid=" UINTX_FORMAT ": SafeThreadsListPtr::release_stable_list: delete nested list pointer to ThreadsList=" INTPTR_FORMAT, os::current_thread_id(), p2i(_list));
+ } else {
+ // The normal case: a leaf ThreadsListHandle. This merely requires setting
+ // the thread hazard ptr back to NULL.
+ assert(_thread->get_threads_hazard_ptr() != NULL, "sanity check");
+ _thread->set_threads_hazard_ptr(NULL);
+ }
+
+ // After releasing the hazard ptr, other threads may go ahead and
+ // free up some memory temporarily used by a ThreadsList snapshot.
+
+ // We use double-check locking to reduce traffic on the system
+ // wide Thread-SMR delete_lock.
+ if (ThreadsSMRSupport::delete_notify()) {
+ // An exiting thread might be waiting in smr_delete(); we need to
+ // check with delete_lock to be sure.
+ ThreadsSMRSupport::release_stable_list_wake_up(_has_ref_count);
+ }
+}
+
+// Verify that the stable hazard ptr used to safely keep threads
+// alive is scanned by threads_do() which is a key piece of honoring
+// the Thread-SMR protocol.
+void SafeThreadsListPtr::verify_hazard_ptr_scanned() {
+#ifdef ASSERT
+ assert(_list != NULL, "_list must not be NULL");
+
+ // The closure will attempt to verify that the calling thread can
+ // be found by threads_do() on the specified ThreadsList. If it
+ // is successful, then the specified ThreadsList was acquired as
+ // a stable hazard ptr by the calling thread in a way that honored
+ // the Thread-SMR protocol.
+ //
+ // If the calling thread cannot be found by threads_do() and if
+ // it is not the shutdown thread, then the calling thread is not
+ // honoring the Thread-SMR ptotocol. This means that the specified
+ // ThreadsList is not a stable hazard ptr and can be freed by
+ // another thread from the to-be-deleted list at any time.
+ //
+ // Note: The shutdown thread has removed itself from the Threads
+ // list and is safe to have a waiver from this check because
+ // VM_Exit::_shutdown_thread is not set until after the VMThread
+ // has started the final safepoint which holds the Threads_lock
+ // for the remainder of the VM's life.
+ //
+ VerifyHazardPtrThreadClosure cl(_thread);
+ ThreadsSMRSupport::threads_do(&cl, _list);
+ // If the calling thread is not honoring the Thread-SMR protocol,
+ // then we will either crash in threads_do() above because 'threads'
+ // was freed by another thread or we will fail the assert() below.
+ // In either case, we won't get past this point with a badly placed
+ // ThreadsListHandle.
+
+ assert(cl.found() || _thread == VM_Exit::shutdown_thread(), "Acquired a ThreadsList snapshot from a thread not recognized by the Thread-SMR protocol.");
+#endif
+}
// '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) {
+ThreadsList::ThreadsList(int entries) :
+ _length(entries),
+ _next_list(NULL),
+ _threads(NEW_C_HEAP_ARRAY(JavaThread*, entries + 1, mtThread)),
+ _nested_handle_cnt(0)
+{
*(JavaThread**)(_threads + entries) = NULL; // Make sure the extra entry is NULL.
}
ThreadsList::~ThreadsList() {
FREE_C_HEAP_ARRAY(JavaThread*, _threads);
@@ -403,10 +574,19 @@
*(JavaThread**)(new_list->_threads + index) = java_thread;
return new_list;
}
+void ThreadsList::dec_nested_handle_cnt() {
+ // The decrement needs to be MO_ACQ_REL. At the moment, the Atomic::dec
+ // backend on PPC does not yet conform to these requirements. Therefore
+ // the decrement is simulated with an Atomic::sub(1, &addr).
+ // Without this MO_ACQ_REL Atomic::dec simulation, the nested SMR mechanism
+ // is not generally safe to use.
+ Atomic::sub(1, &_nested_handle_cnt);
+}
+
int ThreadsList::find_index_of_JavaThread(JavaThread *target) {
if (target == NULL) {
return -1;
}
for (uint i = 0; i < length(); i++) {
@@ -430,10 +610,26 @@
}
}
return NULL;
}
+void ThreadsList::inc_nested_handle_cnt() {
+ // The increment needs to be MO_SEQ_CST. At the moment, the Atomic::inc
+ // backend on PPC does not yet conform to these requirements. Therefore
+ // the increment is simulated with a load phi; cas phi + 1; loop.
+ // Without this MO_SEQ_CST Atomic::inc simulation, the nested SMR mechanism
+ // is not generally safe to use.
+ intx sample = OrderAccess::load_acquire(&_nested_handle_cnt);
+ for (;;) {
+ if (Atomic::cmpxchg(sample + 1, &_nested_handle_cnt, sample) == sample) {
+ return;
+ } else {
+ sample = OrderAccess::load_acquire(&_nested_handle_cnt);
+ }
+ }
+}
+
bool ThreadsList::includes(const JavaThread * const p) const {
if (p == NULL) {
return false;
}
for (uint i = 0; i < length(); i++) {
@@ -466,19 +662,18 @@
}
return new_list;
}
-ThreadsListHandle::ThreadsListHandle(Thread *self) : _list(ThreadsSMRSupport::acquire_stable_list(self, /* is_ThreadsListSetter */ false)), _self(self) {
+ThreadsListHandle::ThreadsListHandle(Thread *self) : _list_ptr(self, /* acquire */ true) {
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_tlh_stats(millis);
}
@@ -534,214 +729,21 @@
// 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);
- }
-}
-
-// Closure to determine if the specified JavaThread is found by
-// threads_do().
-//
-class VerifyHazardPointerThreadClosure : public ThreadClosure {
- private:
- bool _found;
- Thread *_self;
-
- public:
- VerifyHazardPointerThreadClosure(Thread *self) : _found(false), _self(self) {}
-
- bool found() const { return _found; }
-
- virtual void do_thread(Thread *thread) {
- if (thread == _self) {
- _found = true;
- }
- }
-};
-
-// Apply the closure to all threads in the system, with a snapshot of
-// all JavaThreads provided by the list parameter.
-void ThreadsSMRSupport::threads_do(ThreadClosure *tc, ThreadsList *list) {
- list->threads_do(tc);
- Threads::non_java_threads_do(tc);
-}
-
-// Apply the closure to all threads in the system.
-void ThreadsSMRSupport::threads_do(ThreadClosure *tc) {
- threads_do(tc, _java_thread_list);
-}
-
-// Verify that the stable hazard pointer used to safely keep threads
-// alive is scanned by threads_do() which is a key piece of honoring
-// the Thread-SMR protocol.
-void ThreadsSMRSupport::verify_hazard_pointer_scanned(Thread *self, ThreadsList *threads) {
-#ifdef ASSERT
- assert(threads != NULL, "threads must not be NULL");
-
- // The closure will attempt to verify that the calling thread can
- // be found by threads_do() on the specified ThreadsList. If it
- // is successful, then the specified ThreadsList was acquired as
- // a stable hazard pointer by the calling thread in a way that
- // honored the Thread-SMR protocol.
- //
- // If the calling thread cannot be found by threads_do() and if
- // it is not the shutdown thread, then the calling thread is not
- // honoring the Thread-SMR ptotocol. This means that the specified
- // ThreadsList is not a stable hazard pointer and can be freed
- // by another thread from the to-be-deleted list at any time.
- //
- // Note: The shutdown thread has removed itself from the Threads
- // list and is safe to have a waiver from this check because
- // VM_Exit::_shutdown_thread is not set until after the VMThread
- // has started the final safepoint which holds the Threads_lock
- // for the remainder of the VM's life.
- //
- VerifyHazardPointerThreadClosure cl(self);
- threads_do(&cl, threads);
-
- // If the calling thread is not honoring the Thread-SMR protocol,
- // then we will either crash in threads_do() above because 'threads'
- // was freed by another thread or we will fail the assert() below.
- // In either case, we won't get past this point with a badly placed
- // ThreadsListHandle.
-
- assert(cl.found() || self == VM_Exit::shutdown_thread(), "Acquired a ThreadsList snapshot from a thread not recognized by the Thread-SMR protocol.");
-#endif
-}
-
-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 _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_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 _java_thread_list has changed, we have lost a race with
- // Threads::add() or Threads::remove() and have to try again.
- if (get_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.
-
- verify_hazard_pointer_scanned(self, threads);
-
- 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_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() > _nested_thread_list_max) {
- _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()));
-
- verify_hazard_pointer_scanned(self, node->t_list());
-
- return node->t_list();
-}
-
void ThreadsSMRSupport::add_thread(JavaThread *thread){
- ThreadsList *new_list = ThreadsList::add_thread(ThreadsSMRSupport::get_java_thread_list(), thread);
+ ThreadsList *new_list = ThreadsList::add_thread(get_java_thread_list(), thread);
if (EnableThreadSMRStatistics) {
- ThreadsSMRSupport::inc_java_thread_list_alloc_cnt();
- ThreadsSMRSupport::update_java_thread_list_max(new_list->length());
+ inc_java_thread_list_alloc_cnt();
+ update_java_thread_list_max(new_list->length());
}
// Initial _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_java_thread_list(new_list);
- ThreadsSMRSupport::free_list(old_list);
+ ThreadsList *old_list = xchg_java_thread_list(new_list);
+ free_list(old_list);
}
// set_delete_notify() and clear_delete_notify() are called
// under the protection of the delete_lock, but we also use an
// Atomic operation to ensure the memory update is seen earlier than
@@ -785,20 +787,22 @@
// Gather a hash table of the current hazard ptrs:
ThreadScanHashtable *scan_table = new ThreadScanHashtable(hash_table_size);
ScanHazardPtrGatherThreadsListClosure scan_cl(scan_table);
threads_do(&scan_cl);
+ OrderAccess::acquire(); // Must order reads of hazard ptr before reads of
+ // nested reference counters
// Walk through the linked list of pending freeable ThreadsLists
// and free the ones that are not referenced from hazard ptrs.
ThreadsList* current = _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)) {
+ if (!scan_table->has_entry((void*)current) && current->_nested_handle_cnt == 0) {
// This ThreadsList is not referenced by a hazard ptr.
if (prev != NULL) {
prev->set_next_list(next);
}
if (_to_delete_list == current) {
@@ -847,100 +851,40 @@
// 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_do(&scan_cl);
+ OrderAccess::acquire(); // Must order reads of hazard ptr before reads of
+ // nested reference counters
+
+ // Walk through the linked list of pending freeable ThreadsLists
+ // and include the ones that are currently in use by a nested
+ // ThreadsListHandle in the search set.
+ ThreadsList* current = _to_delete_list;
+ while (current != NULL) {
+ if (current->_nested_handle_cnt != 0) {
+ // 'current' is in use by a nested ThreadsListHandle so the hazard
+ // ptr is protecting all the JavaThreads on that ThreadsList.
+ AddThreadHazardPointerThreadClosure add_cl(scan_table);
+ current->threads_do(&add_cl);
+ }
+ current = current->next_list();
+ }
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 Thread-SMR delete_lock.
- if (ThreadsSMRSupport::delete_notify()) {
- // An exiting thread might be waiting in smr_delete(); we need to
- // check with 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 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 delete_lock().
//
-void ThreadsSMRSupport::release_stable_list_wake_up(char *log_str) {
- assert(log_str != NULL, "sanity check");
+void ThreadsSMRSupport::release_stable_list_wake_up(bool is_nested) {
+ const char* log_str = is_nested ? "nested hazard ptr" : "regular hazard ptr";
// Note: 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 delete_lock) so that
@@ -1012,10 +956,17 @@
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_do(&scan_cl);
+ ThreadsList* current = _to_delete_list;
+ while (current != NULL) {
+ if (current->_nested_handle_cnt != 0 && current->includes(thread)) {
+ log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_delete: found nested hazard pointer to thread=" INTPTR_FORMAT, os::current_thread_id(), p2i(thread));
+ }
+ current = current->next_list();
+ }
}
}
} // We have to drop the Threads_lock to wait or delete the thread
if (EnableThreadSMRStatistics) {
@@ -1053,22 +1004,69 @@
}
log_debug(thread, smr)("tid=" UINTX_FORMAT ": ThreadsSMRSupport::smr_delete: thread=" INTPTR_FORMAT " is deleted.", os::current_thread_id(), p2i(thread));
}
+// Apply the closure to all threads in the system, with a snapshot of
+// all JavaThreads provided by the list parameter.
+void ThreadsSMRSupport::threads_do(ThreadClosure *tc, ThreadsList *list) {
+ list->threads_do(tc);
+ Threads::non_java_threads_do(tc);
+}
+
+// Apply the closure to all threads in the system.
+void ThreadsSMRSupport::threads_do(ThreadClosure *tc) {
+ threads_do(tc, _java_thread_list);
+}
+
// Debug, logging, and printing stuff at the end:
+// Print SMR info for a SafeThreadsListPtr to a given output stream.
+void SafeThreadsListPtr::print_on(outputStream* st) {
+ if (this == _thread->_threads_list_ptr) {
+ // The top level hazard ptr.
+ st->print(" _threads_hazard_ptr=" INTPTR_FORMAT, p2i(_list));
+ } else {
+ // Nested hazard ptrs.
+ st->print(", _nested_threads_hazard_ptr=" INTPTR_FORMAT, p2i(_list));
+ }
+}
+
// Log Threads class SMR info.
void ThreadsSMRSupport::log_statistics() {
LogTarget(Info, thread, smr) log;
if (log.is_enabled()) {
LogStream out(log);
print_info_on(&out);
}
}
+// Print SMR info for a thread to a given output stream.
+void ThreadsSMRSupport::print_info_on(const Thread* thread, outputStream* st) {
+ if (thread->_threads_hazard_ptr != NULL) {
+ st->print(" _threads_hazard_ptr=" INTPTR_FORMAT, p2i(thread->_threads_hazard_ptr));
+ }
+ if (EnableThreadSMRStatistics && thread->_threads_list_ptr != NULL) {
+ // The count is only interesting if we have a _threads_list_ptr.
+ st->print(", _nested_threads_hazard_ptr_cnt=%u", thread->_nested_threads_hazard_ptr_cnt);
+ }
+ if (SafepointSynchronize::is_at_safepoint() || Thread::current() == thread) {
+ // It is only safe to walk the list if we're at a safepoint or the
+ // calling thread is walking its own list.
+ SafeThreadsListPtr* current = thread->_threads_list_ptr;
+ if (current != NULL) {
+ // Skip the top nesting level as it is always printed above.
+ current = current->previous();
+ }
+ while (current != NULL) {
+ current->print_on(st);
+ current = current->previous();
+ }
+ }
+}
+
// Print Threads class SMR info.
void ThreadsSMRSupport::print_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);
@@ -1094,12 +1092,12 @@
}
}
if (!EnableThreadSMRStatistics) {
return;
}
- st->print_cr("_java_thread_list_alloc_cnt=" UINT64_FORMAT ","
- "_java_thread_list_free_cnt=" UINT64_FORMAT ","
+ st->print_cr("_java_thread_list_alloc_cnt=" UINT64_FORMAT ", "
+ "_java_thread_list_free_cnt=" UINT64_FORMAT ", "
"_java_thread_list_max=%u, "
"_nested_thread_list_max=%u",
_java_thread_list_alloc_cnt,
_java_thread_list_free_cnt,
_java_thread_list_max,
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