/*

 * 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 "memory/allocation.hpp"

#include "runtime/timer.hpp"

class JavaThread;

class Monitor;

class outputStream;

class Thread;

class ThreadClosure;

// Thread Safe Memory Reclamation (Thread-SMR) support.

//

// ThreadsListHandles are used to safely perform operations on one or more

// threads without the risk of the thread or threads exiting during the

// operation. It is no longer necessary to hold the Threads_lock to safely

// perform an operation on a target thread.

//

// There are several different ways to refer to java.lang.Thread objects

// so we have a few ways to get a protected JavaThread *:

//

// JNI jobject example:

//   jobject jthread = ...;

//   :

//   ThreadsListHandle tlh;

//   JavaThread* jt = NULL;

//   bool is_alive = tlh.cv_internal_thread_to_JavaThread(jthread, &jt, NULL);

//   if (is_alive) {

//     :  // do stuff with 'jt'...

//   }

//

// JVM/TI jthread example:

//   jthread thread = ...;

//   :

//   JavaThread* jt = NULL;

//   ThreadsListHandle tlh;

//   jvmtiError err = JvmtiExport::cv_external_thread_to_JavaThread(tlh.list(), thread, &jt, NULL);

//   if (err != JVMTI_ERROR_NONE) {

//     return err;

//   }

//   :  // do stuff with 'jt'...

//

// JVM/TI oop example (this one should be very rare):

//   oop thread_obj = ...;

//   :

//   JavaThread *jt = NULL;

//   ThreadsListHandle tlh;

//   jvmtiError err = JvmtiExport::cv_oop_to_JavaThread(tlh.list(), thread_obj, &jt);

//   if (err != JVMTI_ERROR_NONE) {

//     return err;

//   }

//   :  // do stuff with 'jt'...

//

// A JavaThread * that is included in the ThreadsList that is held by

// a ThreadsListHandle is protected as long as the ThreadsListHandle

// remains in scope. The target JavaThread * may have logically exited,

// but that target JavaThread * will not be deleted until it is no

// longer protected by a ThreadsListHandle.

// SMR Support for the Threads class.

//

class ThreadsSMRSupport : AllStatic {

  friend class SafeThreadsListPtr;  // for _nested_thread_list_max, delete_notify(), release_stable_list_wake_up() access

  // The coordination between ThreadsSMRSupport::release_stable_list() and

  // ThreadsSMRSupport::smr_delete() uses the delete_lock in order to

  // reduce the traffic on the Threads_lock.

  static Monitor* delete_lock() { return ThreadsSMRDelete_lock; }

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

  // -XX:+EnableThreadSMRStatistics (see thread.cpp for a

  // description about each field):

  static uint                  _delete_lock_wait_cnt;

  static uint                  _delete_lock_wait_max;

  // The delete_notify flag is used for proper double-check

  // locking in order to reduce the traffic on the system wide

  // Thread-SMR delete_lock.

  static volatile uint         _delete_notify;

  static volatile uint         _deleted_thread_cnt;

  static volatile uint         _deleted_thread_time_max;

  static volatile uint         _deleted_thread_times;

  static ThreadsList           _bootstrap_list;

  static ThreadsList* volatile _java_thread_list;

  static uint64_t              _java_thread_list_alloc_cnt;

  static uint64_t              _java_thread_list_free_cnt;

  static uint                  _java_thread_list_max;

  static uint                  _nested_thread_list_max;

  static volatile uint         _tlh_cnt;

  static volatile uint         _tlh_time_max;

  static volatile uint         _tlh_times;

  static ThreadsList*          _to_delete_list;

  static uint                  _to_delete_list_cnt;

  static uint                  _to_delete_list_max;

  static ThreadsList *acquire_stable_list_fast_path(Thread *self);

  static ThreadsList *acquire_stable_list_nested_path(Thread *self);

  static void add_deleted_thread_times(uint add_value);

  static void add_tlh_times(uint add_value);

  static void clear_delete_notify();

  static bool delete_notify();

  static void free_list(ThreadsList* threads);

  static void inc_deleted_thread_cnt();

  static void inc_java_thread_list_alloc_cnt();

  static void inc_tlh_cnt();

  static bool is_a_protected_JavaThread(JavaThread *thread);

  static void release_stable_list_wake_up(bool is_nested);

  static void set_delete_notify();

  static void threads_do(ThreadClosure *tc);

  static void threads_do(ThreadClosure *tc, ThreadsList *list);

  static void update_deleted_thread_time_max(uint new_value);

  static void update_java_thread_list_max(uint new_value);

  static void update_tlh_time_max(uint new_value);

  static void verify_hazard_ptr_scanned(Thread *self, ThreadsList *threads);

  static ThreadsList* xchg_java_thread_list(ThreadsList* new_list);

 public:

  static void add_thread(JavaThread *thread);

  static ThreadsList* get_java_thread_list();

  static bool is_a_protected_JavaThread_with_lock(JavaThread *thread);

  static bool is_bootstrap_list(ThreadsList* list);

  static void remove_thread(JavaThread *thread);

  static void smr_delete(JavaThread *thread);

  static void update_tlh_stats(uint millis);

  // Logging and printing support:

  static void log_statistics();

  static void print_info_elements_on(outputStream* st, ThreadsList* t_list);

  static void print_info_on(outputStream* st);

  static void print_info_on(const Thread* thread, outputStream* st);

};

// A fast list of JavaThreads.

//

class ThreadsList : public CHeapObj<mtThread> {

  friend class SafeThreadsListPtr;  // for {dec,inc}_nested_handle_cnt() access

  friend class ThreadsSMRSupport;  // for _nested_handle_cnt, {add,remove}_thread(), {,set_}next_list() access

  const uint _length;

  ThreadsList* _next_list;

  JavaThread *const *const _threads;

  volatile intx _nested_handle_cnt;

  template <class T>

  void threads_do_dispatch(T *cl, JavaThread *const thread) const;

  ThreadsList *next_list() const        { return _next_list; }

  void set_next_list(ThreadsList *list) { _next_list = list; }

  void inc_nested_handle_cnt();

  void dec_nested_handle_cnt();

  static ThreadsList* add_thread(ThreadsList* list, JavaThread* java_thread);

  static ThreadsList* remove_thread(ThreadsList* list, JavaThread* java_thread);

public:

  ThreadsList(int entries);

  ~ThreadsList();

  template <class T>

  void threads_do(T *cl) const;

  uint length() const                       { return _length; }

  JavaThread *const thread_at(uint i) const { return _threads[i]; }

  JavaThread *const *threads() const        { return _threads; }

  // Returns -1 if target is not found.

  int find_index_of_JavaThread(JavaThread* target);

  JavaThread* find_JavaThread_from_java_tid(jlong java_tid) const;

  bool includes(const JavaThread * const p) const;

};

// An abstract safe ptr to a ThreadsList comprising either a stable hazard ptr

// for leaves, or a retained reference count for nested uses. The user of this

// API does not need to know which mechanism is providing the safety.

class SafeThreadsListPtr {

  friend class ThreadsListSetter;

  SafeThreadsListPtr* _previous;

  Thread*                 _thread;

  ThreadsList*            _list;

  bool                    _has_ref_count;

  bool                    _needs_release;

  void acquire_stable_list();

  void acquire_stable_list_fast_path();

  void acquire_stable_list_nested_path();

  void release_stable_list();

  void verify_hazard_ptr_scanned();

public:

  // Constructor that attaches the list onto a thread.

  SafeThreadsListPtr(Thread *thread, bool acquire) :

    _previous(NULL),

    _thread(thread),

    _list(NULL),

    _has_ref_count(false),

    _needs_release(false)

  {

    if (acquire) {

      acquire_stable_list();

    }

  }

  // Constructor that transfers ownership of the pointer.

  SafeThreadsListPtr(SafeThreadsListPtr& other) :

    _previous(other._previous),

    _thread(other._thread),

    _list(other._list),

    _has_ref_count(other._has_ref_count),

    _needs_release(other._needs_release)

  {

    other._needs_release = false;

  }

  ~SafeThreadsListPtr() {

    if (_needs_release) {

      release_stable_list();

    }

  }

  ThreadsList* list() const { return _list; }

  SafeThreadsListPtr* previous() const { return _previous; }

  void print_on(outputStream* st);

};

// A helper to optionally set the hazard ptr in ourself. This helper can

// be used by ourself or by another thread. If the hazard ptr is set(),

// then the destructor will release it.

//

class ThreadsListSetter : public StackObj {

private:

  SafeThreadsListPtr _list_ptr;

public:

  ThreadsListSetter() : _list_ptr(Thread::current(), /* acquire */ false) {}

  ThreadsList* list() { return _list_ptr.list(); }

  void set() { _list_ptr.acquire_stable_list(); }

  bool is_set() { return _list_ptr._needs_release; }

};

// This stack allocated ThreadsListHandle keeps all JavaThreads in the

// ThreadsList from being deleted until it is safe.

//

class ThreadsListHandle : public StackObj {

  SafeThreadsListPtr _list_ptr;

  elapsedTimer _timer;  // Enabled via -XX:+EnableThreadSMRStatistics.

public:

  ThreadsListHandle(Thread *self = Thread::current());

  ~ThreadsListHandle();

  ThreadsList *list() const {

    return _list_ptr.list();

  }

  template <class T>

  void threads_do(T *cl) const {

    return list()->threads_do(cl);

  }

  bool cv_internal_thread_to_JavaThread(jobject jthread, JavaThread ** jt_pp, oop * thread_oop_p);

  bool includes(JavaThread* p) {

    return list()->includes(p);

  }

  uint length() const {

    return list()->length();

  }

};

// This stack allocated JavaThreadIterator is used to walk the

// specified ThreadsList using the following style:

//

//   JavaThreadIterator jti(t_list);

//   for (JavaThread *jt = jti.first(); jt != NULL; jt = jti.next()) {

//     ...

//   }

//

class JavaThreadIterator : public StackObj {

  ThreadsList * _list;

  uint _index;

public:

  JavaThreadIterator(ThreadsList *list) : _list(list), _index(0) {

    assert(list != NULL, "ThreadsList must not be NULL.");

  }

  JavaThread *first() {

    _index = 0;

    return _list->thread_at(_index);

  }

  uint length() const {

    return _list->length();

  }

  ThreadsList *list() const {

    return _list;

  }

  JavaThread *next() {

    if (++_index >= length()) {

      return NULL;

    }

    return _list->thread_at(_index);

  }

};

// This stack allocated ThreadsListHandle and JavaThreadIterator combo

// is used to walk the ThreadsList in the included ThreadsListHandle

// using the following style:

//

//   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {

//     ...

//   }

//

class JavaThreadIteratorWithHandle : public StackObj {

  ThreadsListHandle _tlh;

  uint _index;

public:

  JavaThreadIteratorWithHandle() : _index(0) {}

  uint length() const {

    return _tlh.length();

  }

  ThreadsList *list() const {

    return _tlh.list();

  }

  JavaThread *next() {

    if (_index >= length()) {

      return NULL;

    }

    return _tlh.list()->thread_at(_index++);

  }

  void rewind() {

    _index = 0;

  }

};