/*

 * Copyright (c) 2017, 2019, 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.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 *

 */

#include "precompiled.hpp"

#include "logging/logStream.hpp"

#include "memory/allocation.inline.hpp"

#include "runtime/jniHandles.inline.hpp"

#include "runtime/thread.inline.hpp"

#include "runtime/threadSMR.inline.hpp"

#include "runtime/vmOperations.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"

// The '_cnt', '_max' and '_times" fields are enabled via

// -XX:+EnableThreadSMRStatistics:

// # of parallel threads in _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::_delete_lock_wait_cnt = 0;

// Max # of parallel threads in _delete_lock->wait().

// Impl note: See _delete_lock_wait_cnt note.

uint                  ThreadsSMRSupport::_delete_lock_wait_max = 0;

// Flag to indicate when an _delete_lock->notify() is needed.

// Impl note: See _delete_lock_wait_cnt note.

volatile uint         ThreadsSMRSupport::_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::_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::_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::_deleted_thread_times = 0;

// The bootstrap list is empty and cannot be freed.

ThreadsList ThreadsSMRSupport::_bootstrap_list = ThreadsList(0);

// This is the VM's current "threads list" and it contains all of

// the JavaThreads the VM considers to be alive at this moment in

// time. The other ThreadsList objects in the VM contain past

// snapshots of the "threads list". _java_thread_list is initially

// set to _bootstrap_list so that we can detect when we have a very

// early use of a ThreadsListHandle.

ThreadsList* volatile ThreadsSMRSupport::_java_thread_list = &_bootstrap_list;

// # 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

// _deleted_thread_cnt field.

uint64_t              ThreadsSMRSupport::_java_thread_list_alloc_cnt = 1;

// # of ThreadsLists freed over VM lifetime.

// Impl note: See _java_thread_list_alloc_cnt note.

uint64_t              ThreadsSMRSupport::_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::_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::_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::_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::_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::_tlh_times = 0;

ThreadsList*          ThreadsSMRSupport::_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::_to_delete_list_cnt = 0;

// Max # of parallel ThreadsLists on the to-delete list.

// Impl note: See _to_delete_list_cnt note.

uint                  ThreadsSMRSupport::_to_delete_list_max = 0;

// 'inline' functions first so the definitions are before first use:

inline void ThreadsSMRSupport::add_deleted_thread_times(uint add_value) {

  Atomic::add(add_value, &_deleted_thread_times);

}

inline void ThreadsSMRSupport::inc_deleted_thread_cnt() {

  Atomic::inc(&_deleted_thread_cnt);

}

inline void ThreadsSMRSupport::inc_java_thread_list_alloc_cnt() {

  _java_thread_list_alloc_cnt++;

}

inline bool ThreadsSMRSupport::is_bootstrap_list(ThreadsList* list) {

  return list == &_bootstrap_list;

}

inline void ThreadsSMRSupport::update_deleted_thread_time_max(uint new_value) {

  while (true) {

    uint cur_value = _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, &_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_java_thread_list_max(uint new_value) {

  if (new_value > _java_thread_list_max) {

    _java_thread_list_max = new_value;

  }

}

inline ThreadsList* ThreadsSMRSupport::xchg_java_thread_list(ThreadsList* new_list) {

  return (ThreadsList*)Atomic::xchg(new_list, &_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) {

        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 _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);

  }

};

// 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) {

      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);

    }

  }

};

// 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) {

      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 _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;

      }

    }

  }

};

// 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.