/*

 * Copyright (c) 2017, 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.

 *

 */

#ifndef SHARE_VM_RUNTIME_THREADSMR_HPP

#define SHARE_VM_RUNTIME_THREADSMR_HPP

#include "memory/allocation.hpp"

#include "runtime/timer.hpp"

// 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.

// A fast list of JavaThreads.

//

class ThreadsList : public CHeapObj<mtThread> {

  friend class ScanHazardPtrGatherProtectedThreadsClosure;

  friend class Threads;

  const uint _length;

  ThreadsList* _next_list;

  JavaThread *const *const _threads;

  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; }

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;

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

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

};

// Linked list of ThreadsLists to support nested ThreadsListHandles.

class NestedThreadsList : public CHeapObj<mtThread> {

  ThreadsList*const _t_list;

  NestedThreadsList* _next;

public:

  NestedThreadsList(ThreadsList* t_list) : _t_list(t_list) {

    assert(Threads_lock->owned_by_self(),

           "must own Threads_lock for saved t_list to be valid.");

  }

  ThreadsList* t_list() { return _t_list; }

  NestedThreadsList* next() { return _next; }

  void set_next(NestedThreadsList* value) { _next = value; }

};

// 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:

  bool _target_needs_release;  // needs release only when set()

  Thread * _target;

public:

  ThreadsListSetter() : _target_needs_release(false), _target(Thread::current()) {

  }

  ~ThreadsListSetter();

  ThreadsList* list();

  void set();

  bool target_needs_release() { return _target_needs_release; }

};

// This stack allocated ThreadsListHandle keeps all JavaThreads in the

// ThreadsList from being deleted until it is safe.

//

class ThreadsListHandle : public StackObj {

  ThreadsList * _list;

  Thread *const _self;

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

public:

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

  ~ThreadsListHandle();

  ThreadsList *list() const {

    return _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;

  }

};

#endif // SHARE_VM_RUNTIME_THREADSMR_HPP